Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/26/21
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1010 PM EDT Sun Jul 25 2021
.SYNOPSIS...
Isolated thunderstorms will diminish this evening,
allowing for a mostly clear sky with patchy fog for tonight. High
pressure will allow for dry and warm weather on Monday. The next
storm system will approach for Tuesday, with some scattered
afternoon showers and thunderstorms. Drier and less humid conditions
should return for Wednesday.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 1010 PM EDT...Showers and thunderstorms have dissipated
over the region, with any remaining isolated showers remaining
south and east of the region. With nocturnal cooling taking
over, all showers and storms over the region should be
completely done by the next hour or two. Any clouds should
also be dissipating or exiting as well as surface high pressure
to the west stretches towards the area.
Moist low levels remain in place and with a quickly cooling
boundary layer thanks to the fairly clear skies, it looks to be
a good setup for radiational valley fog overnight. The fog will
be most dense for areas that saw recent rainfall for the late
night hours, but should start to lift after sunrise Monday.
Overnight lows will generally be upper 50s to mid 60s, with the
coolest temps across the Adirondacks, Catskills and southern
Vermont.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Monday, high pressure builds overhead setting the stage for a
period of dry weather into Tuesday. Partly to mostly sunny skies
are expected with high temperatures warming into the upper 70s to
mid 80s. Haze/smoke from the wildfires out west should also be
evident from the Capital District northward throughout the day. Have
added in the haze wording into the forecast to account for this (per
latest HRRR smoke forecast guidance and upstream observations).
Clouds begin increasing late Monday night as a cold front approaches
from the Saint Lawrence River Valley. Overnight lows will be in the
upper 50s to low 60s once again.
Tuesday, a cold front will drop south through the forecast area,
mainly during the afternoon and evening hours. There is still
some timing differences between the model guidance but if the
passage is coincident with peak heating, could be an active
severe weather day. Model soundings indicate ample SBCAPE (>1500
J/kg), modest low level lapse rates and increasing PWATS. Given
the uncertainty of the timing, we are not in an severe weather
outlook from SPC quite yet and have therefore maintained just a
chance for thunder (with no enhanced wording) in the forecast.
With all that in mind, showers and thunderstorms are expected to
traverse the forecast area from north to south throughout
Tuesday afternoon/evening before exiting to the south late
Tuesday night.
Also dependent on the frontal passage will be afternoon high
temperatures with low 70s expected to the north, and upper 80s
to the south.
Drier, cooler air filters in Monday night, with lows dipping
into the low 50s up north to the low 60s down south.
Wednesday looks like another dry and mostly sunny summer day
with highs in the low to upper 70s.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
A persistent mid-to-upper level pattern will continue over the CONUS
through this period with strong ridging over the Rockies and plains
and northwest flow over the northeast. The main system to affect
our area during this period will be a short wave trough diving
southeast from Ontario across the northeast CONUS Thursday and
Thursday night. The GFS and ECMWF and ensembles are in good
agreement with this scenario, which would bring a good chance of
showers and thunderstorms to the area Thursday into Thursday night.
Enough warm air and higher dew points will likely be drawn
northeastward ahead of this system so that a severe threat and
localized convective heavy rain potential will exist on Thursday,
although obviously with this system still several days away
certainty on any details is low.
High pressure will build southeast behind the short wave trough on
Friday and Saturday, setting the stage for a period of dry,
comfortable weather. Temperatures will be a bit below normal with
highs in the 70s to near 80 and lows Friday night mostly in the 50s,
with some 40s possible over higher terrain and across the north
country.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Showers and thunderstorms are dissipating and moving away from
the region. With a thunderstorm exiting the Pittsfield area,
will continue a TEMPO for one hour at KPSF for any lingering
clouds/light rain with the exiting storm, but the threat for
precip looks to be ending quickly.
With a humid airmass in place at low levels, will expect
radiational fog to form tonight thanks to fairly clear skies and
light winds. All sites have a chance at seeing some fog, but
KGFL/KPSF have the best chance at a prolonged period of IFR fog
after midnight. Can`t rule out IFR fog at KALB and possibly
KPOU as well, but it looks to occur just for a short period
prior to daybreak for those sites.
Any fog/mist should dissipate shortly after sunrise, allowing
for VFR conditons to return to all sites. Light southwest winds
will become westerly at 5 to 10 kts. Few-sct diurnal cu around
5-6 kft will develop by afternoon, but it will remain VFR for
all sites through the day with no precipitation.
Outlook...
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: High Operational Impact. Likely SHRA...TSRA.
Tuesday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Wednesday: Low Operational Impact. Slight Chance of SHRA.
Wednesday Night: Low Operational Impact. Slight Chance of SHRA.
Thursday: Moderate Operational Impact. Likely SHRA...TSRA.
Thursday Night: Moderate Operational Impact. Chance of SHRA.
Friday: Low Operational Impact. NO SIG WX.
&&
.FIRE WEATHER...
Dry air has quickly filtered into the region, allowing
for a mostly sunny summer day. Skies will clear overnight as high
pressure builds into the region, resulting in a dry period of
weather Monday into Tuesday. Temperatures will be seasonable. The
next chance for rain and thunderstorms arrives on Tuesday with a
cold frontal passage.
RH values will increase to 90 to 100 percent tonight with
patchy fog forming. The RH values will decrease to 40 to 55
percent during Monday afternoon before recovering into the 85 to
95 percent range Monday night.
South to southwest winds at 10 to 20 mph are expected through
this evening. The winds will be west or southwest at 5 to 10
mph tonight into Monday.
&&
.HYDROLOGY...
Outside of an isolated shower or storm this
afternoon, dry weather is expected through Monday night which
will allow streams and rivers to lower closer to late July
normals.
The next chance of showers and thunderstorms will be Tuesday
afternoon and also on Thursday.
For details on specific area rivers and lakes, including
observed and forecast river stages and lake elevations, please
visit the Advanced Hydrologic Prediction Service /AHPS/ graphs
on our website.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.
&&
$$
SYNOPSIS...Frugis
NEAR TERM...Frugis
SHORT TERM...JLV
LONG TERM...MSE
AVIATION...Frugis
FIRE WEATHER...JLV/Wasula
HYDROLOGY...JLV/Wasula
Area Forecast Discussion
National Weather Service Burlington VT
1019 PM EDT Sun Jul 25 2021
.SYNOPSIS...
Any lingering showers or thunderstorms will be ending overnight
with with patchy fog developing. Monday will feature partly
sunny skies, seasonal temperatures and a few isolated showers
and thunderstorms in the afternoon. A cold front will bring more
numerous showers and thunderstorms Tuesday, followed by high
pressure and cooler temperatures on Wednesday.
&&
.NEAR TERM /THROUGH MONDAY NIGHT/...
As of 1019 PM EDT Sunday...Still hanging on to a couple
isolated showers and thunderstorms with a subtle short wave trof
skirting just north of the international border. They should be
winding down soon. Still looking at patchy fog, especially in
the river valleys of VT and where it rained. Visibility
restricted in fog/haze/smoke overnight.
Previous Discussion...Fairly quiet weather is expected this
evening and overnight. Convection has had a hard time developing
this afternoon due to the copious amount of dry air aloft. That
being said, have seen a few light returns on radar recently, so
still believe a light shower or two will be possible through
sunset. Precipitation chances are a little better along the
international border later tonight as a weak upper shortwave
skirts through southern Ontario/Quebec, though coverage will
remain limited by the aforementioned dry air. There will be a
little elevated instability, so a rumble of thunder or two will
also be possible. Moisture will be plentiful at low levels
however, and with clearing skies and light winds, patchy fog is
expected late tonight into early Monday, especially in the
favored valley locations. Lows tonight will be on the muggy
side, generally in the upper 50s to mid 60s.
For tomorrow, still expect a few showers and thunderstorms to pop up
in the afternoon. There`s little in the way of forcing outside of
daytime heating and shear is unimpressive. The dry air at mid-levels
will also remain, so coverage and intensity of any convection will
be minimal. Also of concern for tomorrow is the potential for hazy
conditions due to smoke drifting in from western wildfires. Smoke is
clearly visible on satellite and a fair number of observations in
Ontario north of the Great Lakes have been reporting visibility
restrictions due to smoke and/or haze most of the day. HRRR model
guidance indicates that this will drift over our region tomorrow, so
anticipate we`ll see haze through a good part of the day. Highs will
be in the upper 70s to mid 80s. Isolated showers/thunderstorms
continue to be possible in northern sections Monday night with a
cold front slowly approaching from the north. Otherwise, it should
be partly cloudy with patchy fog once again. Lows will be very
similar to what is expected tonight.
&&
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 346 PM EDT Sunday...Main challenge for this period continues to
revolve around the timing of a strong cold front. Its passage in the
latest data looks a bit later on a whole, which will increase the
chances of thunderstorms for central and southern areas. High
temperatures also have been pushed up into the low 80s over a wider
area of south central Vermont, with otherwise little change from the
previous forecast. The front will be marked by a sharp low-level
temperature change as winds turn northerly. Therefore, in spite of
daytime heating, surface temperatures should fall behind the front.
As an example, currently show temperatures falling from the mid-70s
to upper 60s along the western slopes of the central Greens from
noon through mid-afternoon. Still think showers and thunderstorms
should be likely across our region given the strong forcing, but
best chances of any stronger storms will be limited to the
aforementioned southern Vermont areas. Much cooler and drier air
Tuesday night will help temperatures fall into the upper 40s to low
50s in most areas with skies clearing out.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 346 PM EDT Sunday...A fall-like pattern will dominate during
this period as the jet stream sinks south of the area with a broad
upper-level trough over the Northeast promoting shots of
unseasonably cool and dry air. For those who prefer sun over clouds,
you are in luck, as the upper- level low migrates well to our north,
which will keep forcing for showers weak in our area aside from
transient low pressure systems. We do have better clarity on timing
of precipitation for this period, with both Wednesday and Friday
night through Saturday morning looking dry areawide. A wave of low
pressure passing to our north on Thursday is trending stronger among
model guidance, with good moisture transport ahead of its
accompanying cold front. For now have left out mention of thunder
with progged instability low in the vicinity of 100 J/kg, but will
have to keep an eye on temperature trends as greater heating could
lead to more favorable parameters for thunderstorms. Behind that
front we will see another shot of cool, dry air with breezy
northerly or northwesterly flow. We may see a rinse and repeat over
the weekend with another quick round of showers on Sunday in
response to another frontal system, but no significant pattern
change is evident in the global models.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Through 00Z Tuesday...Other than a thunderstorm at MPV this
hour...mainly VFR over the next 24 hours, though it does look
like the possibility of 5-6SM in HZ at times through the period
due to wildfire smoke coming down from Canada. Otherwise the
main concern will be local VLIFR/LIFR conditions in fog,
especially at KSLK, KMPV, and KEFK. Have also added IFR in BR at
KRUT where it rained recently. Start time of the fog a bit
uncertain due rain there and expected rain at KMPV but thinking
3-5Z. Fog will lift 12-13z with VFR to prevail at all terminals
through the remainder of the TAF period. South to southwest
winds remain 5 to 10 kt with brief gusts to around 15 kt through
22z, then becoming light overnight before increasing out of the
south- southwest after 13z Monday.
Outlook...
Monday Night: VFR. Slight chance SHRA.
Tuesday: Mainly VFR, with areas MVFR possible. Chance SHRA,
Slight chance TSRA.
Tuesday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Wednesday: VFR. NO SIG WX.
Wednesday Night: VFR. Chance SHRA.
Thursday: VFR. Chance SHRA.
Thursday Night: Mainly MVFR, with local IFR possible. Chance
SHRA.
Friday: MVFR/IFR conditions possible. Slight chance SHRA.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.
&&
$$
SYNOPSIS...Hastings/Sisson
NEAR TERM...Hastings/Sisson
SHORT TERM...Kutikoff
LONG TERM...Kutikoff
AVIATION...Hastings/Sisson
Area Forecast Discussion
National Weather Service Buffalo NY
1020 PM EDT Sun Jul 25 2021
.SYNOPSIS...
High pressure across the Mid-West will gradually move eastward
across Ohio, keeping our area mostly rain-free through Monday night.
A cold front will drop across the region on Tuesday with some
showers and thunderstorms possible. High pressure will then build
back across the area providing dry weather for Wednesday.
&&
.NEAR TERM /THROUGH MONDAY NIGHT/...
The axis of a ridge of high pressure centered to our west will
ridge across the region tonight. This will maintain dry weather
and mostly clear skies. This will support fairly good
radiational cooling, especially across interior valleys where
temperatures should drop into the 50s tonight. Fog may develop
across the Southern Tier valleys.
Mainly dry again on Monday as the surface high moves closer and
provides mostly sunny skies south of Lake Ontario. The St. Lawrence
Valley will be closer to a mid-level trough, perhaps enough to
support a stray showers or thunderstorm along the lake breeze
boundary northeast of Lake Ontario. Otherwise, it will be a bit
warmer than today with highs in the upper 70s to mid 80s.
Visible satellite and observations show near surface smoke from
the western wildfires across Northeastern Ontario this evening.
HRRR guidance depicts this area moving near northern NY Monday
which may produce hazy conditions across north central NY.
A cold front will approach late Monday night, but model consensus
keeps any precipitation associated with the front to our north
and west. Fair radiational cooling with partly to mostly clear
skies. Lows in the upper 50s to mid 60s.
&&
.SHORT TERM /TUESDAY THROUGH THURSDAY/...
There will be two systems that impact our region this period, both
occuring with a west to northwest flow aloft.
The first system will arrive Tuesday. Two shortwaves aloft will help
to push a cold front across the region...with the first shortwave
near the Saint Lawrence Valley and a second shortwave later across
Western New York. Showers and thunderstorms blossoming along the
cold front and ahead of the shortwaves will likely first be
concentrated east of Lake Ontario by early afternoon Tuesday...and
then later in the afternoon and early evening across WNY. There
continues to be sufficient instability ahead of this front, along
with 0-6km bulk shear values 35 to 40 knots to support the potential
for a few stronger storms.
As the cold front pushes across our region from northwest to
southeast, showers and thunderstorms will taper down Tuesday Night.
Much drier air aloft will push into the North Country by early
evening, and then across WNY through the night. Lingering low level
moisture could bring some patches of fog late Tuesday Night.
Weak high pressure near the region Wednesday should bring a dry day
with a mix of clouds and sunshine.
Wednesday Night the next system will impact our region, mainly
during the second half of the night. A mid level shortwave will
cross our region, bringing renewed chances for showers and
thunderstorms. PWAT values a little higher with this second
system...nearing 1.75 inches could allow for heavier
downpours...though at this time, an earlier timing in the day
Thursday of convection could lower the threat for severe potential.
With a decent amount of clouds around, especially Tuesday and
Thursday high temperatures will be near or just below normal...while
overnight lows dip to near normal levels.
&&
.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
In the wake of the cold front, high pressure builds east across
the lower lakes bringing cooler and drier air to the region. The
high will maintain dry conditions through Saturday. An area of
low pressure moving across Ontario will bring the risk of some
showers Saturday night and Sunday.
Highs Friday will be in the upper 60s to low 70s, about 5 to 10
degrees below normal, followed by a slow warming trend with
temperatures within a few degrees of the norm by Sunday.
Overnight lows too will start cool with some interior sections
of the southern tier and north country seeing lows in the 40s
Friday night gradually moderating to near normal upper 50s to
low 60s Saturday night.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Mainly clear tonight will support mainly VFR flight conditions.
Fog is likely to develop across the Southern Tier Valleys, with
a period of IFR likely at KJHW. Any fog will dissipate quickly
on Monday. Prevailing VFR flight conditions expected during the
day however haze from upstream smoke may track into the region.
This may cause MVFR conditions at KROC and KART through the
afternoon.
Outlook...
Monday night...VFR.
Tuesday and Tuesday night...VFR/MVFR with showers and thunderstorms
possible.
Wednesday...VFR.
Thursday...VFR/MVFR. A chance of showers and thunderstorms.
Friday...VFR.
&&
.MARINE...
High pressure will build across the lower Great Lakes tonight and
Monday. Pressure gradient will relax some across Lake Erie with
lowering winds and waves, while winds remain somewhat elevated on
Lake Ontario keeping choppy conditions in place, however waves
should be less than 2 feet.
&&
.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.
&&
$$
SYNOPSIS...Apffel
NEAR TERM...Apffel/HSK
SHORT TERM...Thomas
LONG TERM...Levan
AVIATION...Apffel/HSK
MARINE...Apffel/JM
Area Forecast Discussion
National Weather Service Caribou ME
1127 PM EDT Sun Jul 25 2021
.SYNOPSIS...
A warm front will lift across the area tonight. A cold front
will cross the area on Tuesday. High pressure will build over
the area Wednesday. Low pressure will approach on Thursday.
&&
.NEAR TERM /THROUGH MONDAY/...
11:30 PM Update...A line of showers and embedded thunderstorms
can be seen moving toward the northwestern part of our area from
the west. Increased pops and put isolated thunderstorms in as
this moves through. However, anticipate it may weaken overnight
as it moves across. Otherwise, no major changes this hour.
Prev Disc: The warm front and transition to a more humid air
mass is the dominant feature tonight into Monday morning with
fog developing across the entire area tonight. A Dense Fog
Advisory may be needed but will hold off for now. Rain will
taper off by early evening ahead of the warm front, but light
rain and drizzle is certainly possible throughout the night.
Later tonight, an upper level shortwave will cross the area.
This shortwave is currently associated with thunderstorm
activity in southern Ontario and western Quebec. Although not
all guidance shows it holding together across the northern half
of the forecast area later tonight, some CAMS output has shown
it for days and continues to do so. There`s some decent cooling
aloft while a low level thermal ridge builds at the top of the
frontal inversion tonight. This generates some elevated CAPE
later tonight and shear also increases. Will maintain mention of
isolated thunderstorms across Aroostook County late tonight
into early Monday morning. Low clouds and fog will slowly burn
off Monday morning. By this time the occluded front has moved
across the area, leaving a much warmer and humid air mass. The
morning low clouds will slow production of SBCAPE, but
eventually there should be sufficient instability for isolated
to scattered afternoon thunderstorms. The best CAPE and shear
will be in southern Penobscot County and interior Downeast for a
brief time in the early to mid afternoon. Shear looks marginal
for strong storms. There`s also the remnants of the washed out
occluded front in that area. There`s several factors inhibiting
convection such as very dry air aloft, lack of a decent upper
level shortwave like earlier in the day, and a cap near 500mb.
Will mention thunderstorms across the area in the afternoon, but
hold off on enhanced wording.
Smoke is the other emerging issue for Monday. Have not added
smoke or haze in the gridded forecast database at this time, but
HRRR guidance and METSAT imagery shows smoke from Manitoba and
Ontario fires heading this way...and it may mix towards the
surface by Monday morning. That usually generates a lot of
confusion and concern from the public. By the time clearing
occurs later Monday morning into the afternoon, the smoke will
likely be more noticeable.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Area wl be split btwn two fronts on Mon evening. Cannot rule out
lingering showers over srn and nrn areas with an isold tstm
still possible but coverage wl likely be on the decrease with
loss of diurnal htg. Given moist and humid airmass still in
place wl likely see areas of fog acrs the area Mon night.
Depending on how quickly high pressure builds south out of
Canada Tue morning wl determine where storms wl develop in the
aftn as s/wv heads south and east out of Canada. This wl allow
storms to develop along front dropping thru the CWA and shud
allow storms to develop across central and srn zones aft 18z.
Given the uncertainty have hesitated to call it chc showers and
tstms and hv only worded it as isold tstms until details can be
better ironed out.
Secondary front wl mv offshore Tue evening with showers winding
down aft midnight along the coast. Patchy fog expected to
develop acrs the north as skies clear but drier dwpts may
prevent fog to increase in coverage drg the overnight. Downeast
coast may see patchy fog as well as humid airmass rmns in place,
however skies wl still be cldy and prevent more widespread
coverage.
Sfc high pressure wl be building into nrn New England with cool
northerly flow draining out of Canada. Skies will be mocldy on
Sunday with nw winds ocnly gusting drg the afternoon.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Flow rmns out of the nw aloft thru Wed night and wl gradually
transition to a s/wv ridge acrs Maine Thu morning. Sfc high
pressure wl be building well offshore Wed night and with skies
clearing and light winds cannot rule out areas acrs the
northwest dipping into the mid-40s.
Next system wl be heading in fm the west and guidance fairly
consistent in bringing showers, possibly stratiform rain, in wrn
areas on Thu afternoon. Rain continues Thu night with showers
expected especially across the north on Friday as upr lvl trof
mvs thru Quebec into the Maritimes. Temps likely to be below
normal thru the end of the long term and into next weekend.
&&
.AVIATION /04Z MONDAY THROUGH FRIDAY/...
NEAR TERM: Conditions to continue to deteriorate this evening to
IFR and then LIFR due to low cigs, drizzle and fog. Fog is most
likely for GNR towards HUL and points south...especially on the
coast. FVE will also have fog. LLWS is expected late this
afternoon into the early evening. Thunderstorms are possible
north of HUL and GNR after midnight into early Monday morning.
Isolated afternoon thunderstorms are expected Monday afternoon
after morning fog and low clouds dissipate.
SHORT TERM: Mon night...Potential IFR in areas of fog
developing late at all terminals. Light WSW wind.
Tue...Becoming VFR late morning with localized MVFR restrictions
in -tsra, mainly at HUL and BGR. W 5-10kts.
Tue night...VFR early, decreasing to localize IFR in fog late.
NW 5 kts.
Wed-Wed night. VFR. NW 5-10kts Wed becoming light SW Thu
morning.
Thu-Fri...Lowering to MVFR/IFR in rain and fog. S 5-10kts,
becoming SW Fri morning.
&&
.MARINE...
NEAR TERM: Fog will thicken and become more widespread tonight
and slowly move offshore Monday afternoon...returning again in
the evening. S Wind Gusts will reach as high as 20 kts ovrngt
before subsiding by daybreak, but will fall short of advisory
criteria. These south winds will generate south seas reaching up
to 4 feet by late tonight, then subsiding durg the day Mon.
SHORT TERM: Winds and seas to remain below SCA thresholds
through the week. Expect that humid airmass will bring areas of
fog to the waters Mon night and Tue night before a cold front
crosses the waters Wed morning.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...None.
&&
$$
Near Term...VJN/MCB
Short Term...Farrar
Long Term...Farrar
Aviation...VJN/Farrar
Marine...VJN/Farrar
Area Forecast Discussion
National Weather Service Cheyenne WY
458 PM MDT Sun Jul 25 2021
.SHORT TERM...(This evening through Monday)
Issued at 158 PM MDT Sun Jul 25 2021
Latest satellite displaying cumulus field across good majority of
the forecast area as Td depressions over SE WY remain about 40-50
degrees. Ongoing pockets of isolated to scattered convection
remains along and nearby elevated terrain in Albany and Carbon
Counties early this afternoon. With growing cumulus field, expect
to see some enhancement in overall coverage. Wind shear is lacking
this afternoon over ongoing convection to limit and reduce any
severe convection potential. A few brief gusty winds and moderate
rainfall may be possible in the strongest of storms but overall
precipitable water values hovering around 0.7 inches. Some
storms late this afternoon into early evening may move off the
higher terrain into portions of the high plains in SE WY.
High pressure continues to build over the region as upper level
low near the Four Corners continues to spin moisture northward
aiding in our shower and thunderstorm potential today.
Area haze on webcams from distant fires across the west continue
to warrant inclusion in the forecast grids with high pressure
building centered on us Monday should keep skies hazy and
sunrise/sunset picturesque. Lows tonight front he upper 50s into
middle 60s. Highs Monday a few degrees warmer into the upper 80s
and middle 90s for SE WY and middle 90s to low 100s for the NE
Panhandle.
.LONG TERM...(Monday night through Sunday)
Issued at 158 PM MDT Sun Jul 25 2021
Overall ridging pattern persists into midweek as midlevel trough
digs into the west coast and slowly erodes the ridge as it
drifts eastward. Warm and dry conditions continue Tuesday as
subsidence continues though models have begun some trend to some
western-based convection Wednesday across the southern mountains
as pockets of vorticity and monsoonal moisture are advected in.
Continued warm temperatures into the upper 90s and low 100s
Wednesday for the Panhandle and upper 80s to upper 90s across SE
WY.
Long-range models continue consensus of weather pattern shift
late in the week going into the next weekend as better moisture
flow enters the region with elevated precipitable water values
around an inch or so. Backdoor cold front expected to stall over
the region in same timeframe with more widespread showers and
thunderstorms. Severe threat late in the week remains fairly low
as surface-based CAPE around 500 J/kg with some pockets of CIN
available. Lapse rates in the low levels remain fairly weak under
7 degrees/km. Concern as stated by previous forecast remains with
heavy precipitation and flooding potential that will have to be
monitored over the next few days. Cold front though will usher in
some cooler temperatures into the weekend from the upper 70s into
low 90s across much of the forecast region.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 453 PM MDT Sun Jul 25 2021
VFR conditions likely through the forecast period for all
terminals. Minimal concerns outside of some gusty conditions
around 20 to 25 knots, and some lingering convection from some
outflow boundaries pulsing through the region. Will likely see
shower and thunderstorm potentials drop off after 01z. Looking
ahead into tomorrow, the HRRR is hinting at some convective
development across Wyoming. However, confidence is low at this
time as subsidence is expected to prevail.
&&
.FIRE WEATHER...
Issued at 126 PM MDT Sun Jul 25 2021
Fire weather concerns remain fairly limited through the week with
isolated to scattered chances of showers and thunderstorms ahead
of monsoonal moisture and widespread precipitation chances
heading into next weekend. Min RH values will generally range from
10 to 20 percent though wind speeds are not expected to exceed
criteria for any immediate headline concerns. Seasonably warm
temperatures to persist.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...WM
LONG TERM...WM
AVIATION...MD
FIRE WEATHER...WM
Area Forecast Discussion
National Weather Service Des Moines IA
547 PM CDT Sun Jul 25 2021
...Updated for 00z Aviation Discussion...
.DISCUSSION.../Tonight through Sunday/
Issued at 259 PM CDT Sun Jul 25 2021
Today through Early Monday Morning:
Surface high pressure has been developing along the NE-KS state line
this morning as the remnants of the convective cluster from last
night dissipate. Low-level flow across the High Plains and Front
Range will be southerly on the back side of the high pressure. This
will result in strong WAA and will amplify the ridge. For Iowa, this
will switch the mid and upper-level flow back to northwesterly. Low-
level flow will be rather weak as the high pressure centers over the
area, thus no overly strong temperature advection for Iowa today.
Expect more smoke/haze to be in the skies this afternoon through
evening with the northwesterly upper-level flow, which may provide
some limitation to insolation, as well as the clouds emanating from
tops of remnant convection over the central Plains. However, still
expecting warm air temperatures today as the airmass is now slightly
drier and will heat up more efficiently. The lower dewpoints though
will keep heat index values close to the air temperatures. This
evening, low-level jet develops over the Central Plains providing
strong theta-e advection into the region. There is not much at the
surface or low-levels other than the LLJ itself, but there is a
signal for some convergence in southern South Dakota right where the
H5 height gradient becomes stronger. Expect elevated convection to
develop late in the evening, and will begin to move toward the
southeast. There is potential for a cluster of thunderstorms move
into northern potions of the forecast area overnight or by early
Monday morning. The HRRR has been the most robust CAM thus far,
attempting to bring weak showers to around Hwy. 20. However, not
entirely convinced the instability and moisture needed to maintain a
thunderstorm cluster will be present over Iowa at this time. Thus,
will keep slight chances POPs along and north of the Hwy. 18
corridor. At this time, there does not appear to be any severe
weather potential for the forecast area. Prior to any rain shower or
convection activity, areas of fog may develop as dewpoint
depressions may drop in an environment with weak winds.
Heat Through Midweek:
A subtle short-wave trough across the western Great Lakes Monday
through Tuesday will provide a weak block to the ridge, while
persistent WAA on the backside of the surface high pressure across
the central Plains will further amplify the H5 ridge, with heights
likely reaching 597dam! Temperatures will steadily rise throughout
the week. The surface high pressure will need to slide a bit further
eastward before this truly ramps up for the forecast area, but by
Tuesday late afternoon and through Wednesday, the stronger axis of
WAA/theta-e advection will arrive, and the ridge axis will also
slide eastward across the Central Plains and into the upper Midwest.
This will send temperatures into the mid 90s on Tuesday, with
dewpoints in the upper 60s to lower 70s. Wednesday is still looking
to be the warmest day for Iowa, with air temperatures in the upper
90s and dewpoints in the low to mid 70s. This will send heat index
values to 105, and may be able to reach 110 in some places. These
heat conditions will be hazardous for outdoor activities. There is
some uncertainty regarding the maximum extent of dewpoint
temperatures for the middle of this week. GFS soundings have been
showing a prominent EML, and stronger flow on the backside of the
high pressure. During the afternoon, lower dewpoints may be able to
mix down closer to the surface. It will be a battle between
evapotranspiration from the crops, and mixing down. If the mixing
ends up being weaker, then the dewpoints will be able to surge
considerably in the middle of the weak. For the exception of early
Monday morning (discussed in previous section), there is no definite
signal for precipitation activity through Wednesday, as any forcing
is shoved way northward during this time. There will be some forcing
in portions of southern Minnesota and southwest Wisconsin, but
current thinking is the amplifying ridge will keep this out of Iowa.
Thursday and Beyond:
Thursday afternoon the amplified ridge will still be present, with
the axis centered over the High and Central Plains, but a short-wave
perturbation will begin to travel through the northwest flow over
Iowa and will allow a thermal boundary to move through the area.
This will finally introduce more considerable precipitation chances
into the forecast, as well as provide some relief from the heat.
This will continue into Friday, with chances for at least some
shower activity, and cooler temperatures. The northwest flow pattern
across the upper Midwest will remain active into Saturday, with
another short-wave or two that will travel through the flow. These
short-waves will be moving over a warm moist air mass, thus it won`t
take all too much forcing to generate a shower. At this time, it is
hard to pinpoint if any of these short-waves will pose a severe
weather risk. These northwest flow perturbations tend to generate a
decent amount of forecast uncertainty beyond just a few days, and
that is the case again with this setup. If one of these short-waves
pairs up with some kind of surface feature, one of these setups
could produce some stronger storms. But at this time, that call
cannot be made.
&&
.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 547 PM CDT Sun Jul 25 2021
While official TAFs are VFR with SCT250 for high level smoke,
there are two concerns that will bear watching this evening.
First, fog development is once again possible after midnight
tonight over southeastern Iowa. At this time, it looks to be east
of OTM. Second, thunderstorms are expected to move into southern
Minnesota, but are expected to weaken as they move into northern
Iowa and its terminals. With low confidence on impacts, have left
out any mention. Will monitor trends this evening and address if
needed at 6z. Wind will be light overnight, but become from the
south or southwest at 7 to 13 knots at all but OTM by Monday
afternoon.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Krull
AVIATION...Ansorge
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1041 PM CDT Sun Jul 25 2021
.SHORT TERM...(This Evening through Monday Night)
Issued at 246 PM CDT Sun Jul 25 2021
Spotty convective chances are the main challenge for the near-term.
On the larger scale, we have an area of low pressure in western SD,
with a weak boundary extending east-northeast into northeast SD.
Meanwhile, a subtle upper level wave is seen in water vapor entering
the western Dakotas. This wave may interact with the boundary by
early evening, bringing a small chance of storms into our northwest
this evening, and if this occurs, inverted-V soundings and DCAPE
values above 1000J/kg would support an isolated strong wind threat.
Slightly greater potential for a few storms appears to be in far
north to northeast portions of the forecast area later tonight, as a
modest southwesterly low level jet develops across the area. Nose of
the jet focused near/northeast of the Buffalo Ridge, and will carry
higher pops for the overnight period in this area. DCAPE values not
quite as strong with this activity, but still quite a deep layer of
dry sub-cloud air to accelerate the low level jet to the surface, so
an isolated strong wind threat will continue.
The convective forecast becomes more muddled for Monday, dependent
on whether activity linger across northeast portions of our forecast
area into the later morning hours, as depicted by several HRRR runs
today. Tend to think this projection is overdone, as the waning LLJ
convergence should be pushing off to the northeast, so have trended
pops downward through the morning hours. Could still be a few weak
boundaries lingering from overnight convection, but diurnal mixing
should reestablish a primarily southerly flow across the forecast
area, with consensus showing the main warm front again from central
SD into central MN by late Monday into Monday night. Cannot totally
rule out a few stray storms into southwest MN Monday night, but as
with later tonight, think main focus for activity will be off to our
north/northeast.
Aside from these uncertain convective chances, the next 24-36 hours
will feature modest humidity levels with dew points largely in the
60s tonight through Monday night. Abundant smoke aloft as indicated
by HRRR Smoke model will have a continued impact on high temps, and
have nudged readings for Monday down a few degrees from previous
forecast.
.LONG TERM...(Tuesday through Sunday)
Issued at 246 PM CDT Sun Jul 25 2021
Heading into midweek, Tuesday-Wednesday continue to look like our
period of greatest concern with regard to excessive heat/humidity.
Very strong upper ridge builds into the northern Plains, with both
NAEFS and ECMWF ensembles depicting 500mb heights across eastern
SD/northeast NE near the highest in the climatological period by
early Wednesday morning. Heat begins to build into our western CWA
in earnest on Tuesday, before extending eastward on Wednesday as
the thermal ridge is flattened by an approaching cold front. Low
level temperature projections support highs in the mid 90s to low
triple digits, though question remains if we mix high enough to
attain these temperatures, how will the dew points respond. With
evapotranspiration nearing its peak, overnight/morning dew points
in the upper 60s to lower 70s seem reasonable. But soundings show
plenty of dry air aloft, so suspect these may drop off a bit more
than indicated. Confidence not quite high enough to adjust these
values 2-3 days out, but will be something to consider in later
forecasts. Almost certainly will see some variety of excessive
heat headlines for these days, but given the uncertainty in dew
points/humidity levels, still unsure whether that headline will be
an advisory or warning.
Relief comes in Wednesday night through the end of the week, as
the upper ridge is flattened in response to a stronger jet diving
southeast from the Canadian Prairies into the western Great Lakes.
Transition to northwest flow may bring a somewhat more active
pattern for the latter half of the week, with temperatures cooling
off to much closer to normal
&&
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1039 PM CDT Sun Jul 25 2021
Remnant scattered showers and isolated thunderstorms continue to
move across portions of the area west of I-29, now moving
south/southeasterly. Could see some more redevelopment of showers
and thunderstorms along and north of the highway 14 corridor through
tomorrow morning, but confidence not high enough to include in the
HON TAF at this time.
Winds will become gusty tomorrow morning predominantly from the
south, with gusts in the 15-25 mph range throughout the
afternoon.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&
$$
SHORT TERM...JH
LONG TERM...JH
AVIATION...APT
Area Forecast Discussion
National Weather Service Green Bay WI
639 PM CDT Sun Jul 25 2021
Updated aviation portion for 00Z TAF issuance
.SYNOPSIS...
Issued at 250 PM CDT Sun Jul 25 2021
Very warm and humid through the middle of the work week, with a
few rounds of thunderstorms from Monday evening through Wednesday
night. A little cooler and drier for the latter part of the work
week.
A strong band of westerlies will persist across the northern
CONUS and southern Canada throughout the period. A longwave ridge
position will be in the west, with a trough in the east. The
westerlies will initially be quite flat, but gradually gain
amplitude during the period.
The pattern favors very warm temperatures through the middle of
the upcoming work week, with a little cooling thereafter as the
upper flow tilts more northwesterly. The reservoir of very humid
air will shift back into the area for a few days, then get shunted
south again. As typical during the summer when precipitation is
almost exclusively convective, the 7-day total is tough to
estimate. The best guess is for AOA amounts.
&&
.SHORT TERM...Tonight and Monday
Issued at 250 PM CDT Sun Jul 25 2021
The latest RAP analysis and satellite/radar imagery show high
pressure stretching across the northern Plains into the mid-
Mississippi Valley early this afternoon. Quiet conditions thanks
to a very dry airmass (pwat of 0.74 inch of the 12z GRB sounding)
remain in place with only some fair weather clouds over far
northern WI. Looking west, quiet conditions remain present over
Minnesota, but pressure falls along a developing warm front will
likely lead to thunderstorm development over South Dakota later
today. As this frontal boundary lifts northeast, thunderstorm and
severe weather chances are the main forecast concerns on Monday
afternoon.
Tonight...High pressure will be sliding southeast across the
middle Mississippi Valley as the warm front lifts northeast across
the northern Plains. Focus for thunderstorm activity will
therefore remain well west of the region closer to the warm front.
The airmass will moisten somewhat, but probably not enough to
influence temps very much under a mostly clear sky. Warmer lows
ranging from the mid 50s to mid 60s.
Monday...Backing low level flow to the southwest will push the
warm front into northern Minnesota and near the U.P./Wisconsin
border by the afternoon. Some uncertainty exists where this front
will lay out by the time of peak heating, when mixed layer instability
upwards of 1500 j/kg is forecast to develop. In addition to the
position of the front, some guidance indicates deep mixing taking
place over northern WI that could bring down dewpoints and
diminish instability. While upper support is negligible, surface
pressure falls and increasing low level convergence leads to a
general consensus of thunderstorms developing around mid-afternoon
over northern WI to the Upper Peninsula. Deep layer shear of
35-40 kts and mid-level lapse rates of 7-7.5 c/km are supportive
of the potential for large hail and damaging winds. Highs will
again range from the mid 80s to low 90s.
.LONG TERM...Monday Night Through Sunday
Issued at 250 PM CDT Sun Jul 25 2021
There has not been much change to the forecast scenario since
yesterday. A weak boundary will shift toward northern Wisconsin
Monday, providing a focus for convective development during the
evening/overnight hours. The more organized the convection
becomes, the farther south/southeast it will probably propagate
into the warm/unstable air mass across the forecast area. The
expected combination of shear and buoyancy will be sufficient for
severe storms, with the best chance for severe across the north
closer to the front.
The greatest uncertainty early in the week will be the weather
conditions on Tuesday. The possible presence of an outflow
boundary across/near the area and perhaps some rain-cooled air
from Monday night storms will impact temperatures as well as the
possibility for additional thunderstorm development. On the large
scale, forcing Tuesday will be subtle at best so the day may end
up being rain-free unless low-level convergence near a boundary
can kick something off.
The next round of storms will probably be Wednesday afternoon
through Wednesday night when a cold front accompanied by some
forcing crosses the area. The large scale pattern certainly seems
supportive of another risk for severe storms and possibly heavy
rainfall.
The very humid air mass across the area will raise the risk of
heat-related issues, especially Monday and Wednesday
afternoon/evening. Heat indices are not expected to be sufficient
to warrant a headline, but will mention the possible hazard in the
HWO.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 639 PM CDT Sun Jul 25 2021
Will continue to see VFR flying conditions through the TAF period
at most locations. The main feature will be wind gusts to 20
knots, which will continue to subside over the next hour or two
this evening. West winds increase again late Monday morning with
afternoon gusts to 20 knots. Rain and thunderstorms are possibly
across north-central WI late Monday afternoon which could result
in lowered cigs and vsbys. Confidence on timing was too low to
include in KRHI this TAF issuance. Rain and thunderstorms are
possible area wide Monday evening (after 00Z) and overnight.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS.......Skowronski
SHORT TERM.....MPC
LONG TERM......Skowronski
AVIATION.......KLJ
Area Forecast Discussion
National Weather Service Gray ME
1016 PM EDT Sun Jul 25 2021
.SYNOPSIS...
A frontal system will continue to cross New England through this
evening with scattered showers and isolated thunderstorms
possible. Weak high pressure will build into the region on
Monday before a cold front approaches from the west on Tuesday
bringing scattered showers and thunderstorms. High pressure then
briefly builds back in on Wednesday before a series of fronts
return to the area through the end of next week.
&&
.NEAR TERM /THROUGH MONDAY/...
10:00 PM Update...Quick update this evening to increase POPS
across Northern NH as cells continue to fire along an
approaching vort max and associated jet streak. MUCAPE is
beginning to trend down as the cells move further east towards
ME, so feel the storms should begin to weaken as they move into
Carroll County. Further north across the boundary mountains,
chance for storms will continue through most of the night.
Patchy fog is beginning to form and that should be the trend
for the remainder of the night.
6:45 PM Update...A few cells are firing across VT at this hour
as a jet streak aloft begins to move into the region along with
general cyclonic 500mb flow. SPC surface analysis is still
showing CAPE around 500 to 1000 J/KG, kept isold 20 pops in the
region as a stray thunderstorm is still possible before
midnight. In addition, smoke is beginning to stream in aloft,
with some visibility restrictions being reported currently in
upstate New York, won`t be an issue tonight, but could have some
haze tomorrow morning at sunrise. Have also put in patchy fog
after midnight with elevated dewpoints in the 60s and mostly
clear skies expected with light winds. Should have valley and
low-lying shallow fog across most of the forecast area.
Warm front moved through the region today leaving 1/4 to 1/2" of
rain in its wake. SKies have started to clear across NH and will
continue to clear across Maine over the next few hours. Upstream
there are two features we`ll be tracking into the area. First is
thunderstorms which have initiated along a line extending from
Val D`or to Georgian bay associated with a cold front. These
storms will slowly move towards the northern portion of our area
overnight.
Between that front and our CWA is a broad warm sector with
temperatures in the mid 70s and dewpoints in the 60s. This puts
SBCAPE around 1000 j/kg widespread to our west. Additionally Bulk
shear of up to 40kts makes the airmass favorable for convection. Had
expected at least a few cells within this warm sector but none have
initiated yet, and CAMs continue to push back any convective
initiation for this afternoon leaving the threat of thunderstorms
smaller and smaller.
What is visible on satellite in the thunderstorm-less warm sector is
smoke. A solid haze is discernible on visible satellite imagery
and GOES smoke detection also shows a broad swatch of smoke.
Surface observations show this haze is thick enough to decrease
visibility to around 6SM, and it may also be enough to dampen
any convection from popping in the warm sector this afternoon.
&&
.SHORT TERM /MONDAY NIGHT/...
Overnight the thunderstorms and front will move southeast, reaching
the Canadian border after midnight where a chance for thunder
remains in the forecast. Elsewhere the main concern overnight will
be fog as dewpoints remain in the mid 60s overnight along with the
overnight lows. With this kind of widespread rain it feels like a
fog type night and have added it especially to the coastal plain and
all valleys where dense fog is possible.
Tomorrow expect fog to linger in the valleys but ultimately lift
within 2hrs of sunrise, however that won`t be the end of the
obscuration. The haze currently in Quebec will drift southeast ahead
of the front and HRRR Smoke indicates it being widespread
across most of our area during the day tomorrow. I can think of
very few times including haze in a forecast but with such a
clear smoke plume on satellite already reflected in the surface
obs and supported by the models have opted to add it for the
area tomorrow. Have additionally hedged a bit lower on the high
temperatures due to this haze, although even a degree or two
lower, most of the area will see the upper 70s to low 80s.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Overview: Broad troughing over New England will continue through
at least the end of the upcoming week as a series of passing
shortwaves and embedded frontal systems bring multiple chances
for unsettled weather. Temperatures will be near to slightly
below normal through next weekend.
Impacts: No significant weather impacts are currently expected.
Forecast Details: A frontal system and shortwave trough will
approach from the north and west on Tuesday with increasing chances
for scattered showers and isolated thunderstorms during the
afternoon and evening. There are some differences in the timing of
this front, which will play a large role in determining the
likelihood for thunderstorm activity. A slower arrival of the front
would favor more thunderstorm coverage, especially if it aligns with
peak daytime heating. While widespread severe weather currently
looks unlikely, steep low-level lapse rates and high DCAPE suggest
that any stronger thunderstorms would have the potential to produce
locally gusty winds. For now, have kept general thunder wording into
the grids, especially across the north. southwesterly winds at the
surface will allow Tuesday to be the warmest day of the week with
many locations reaching the lower to middle 80s.
Behind the front, a cooler and drier airmass will move in on
Wednesday with high temperatures only reaching the 60s to 70s from
north to south. This will then be quickly followed by the arrival of
another shortwave trough from Canada on Thursday, which will once
again bring increased chances for showers and possibly isolated
thunderstorms. A 300 mb jet streak will be located nearby,
which would support lift for convection, but given the low
surface dew points and temperatures severe weather does not
currently look likely. A few lingering showers will then persist
through Friday, especially across the north where there will be
upslope flow. High temperatures on Thursday and Friday will
primarily be into the 70s with 60s across the north and
mountains. Another system may then arrive by Sunday but forecast
confidence remains low at this time.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Short Term... Ceilings will improve across NH and western Maine
through sunset as the band of rain associated with the warm
front exits the area. Continued low level moisture overnight
will bring a return of fog and IFR for both the coast and
river valleys. Tomorrow will be clear, but haze will be
widespread with visibility dropping to 5-6SM in HZ possible.
Long Term...VFR conditions expected through the entire period
outside of any SHRA or TSRA, which could result in brief MVFR/IFR
conditions. The best chances for precipitation currently looks to
occur on Tuesday afternoon and Thursday. Some patchy fog will
also be possible on Tuesday night, especially across the
valleys.
&&
.MARINE...
Short Term...SCA remains in effect through 11pm, will likely be
able to end early as front is already pushing into New Hampshire
and will clear the waters early this evening. Behind it winds
decrease and become more westerly.
Long Term...Winds and seas are expected to remain below SCA criteria
through Friday. A cold front will cross the waters on Tuesday
afternoon or evening with southwest winds turning northwesterly
late. Another system will arrive on Thursday with increased
chances for scattered showers.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.
&&
$$
SYNOPSIS...Curtis/Tubbs
NEAR TERM...Curtis/Dumont
SHORT TERM...Curtis
LONG TERM...Tubbs
AVIATION...Curtis/Tubbs
MARINE...Curtis/Tubbs
Area Forecast Discussion
National Weather Service Jackson MS
904 PM CDT Sun Jul 25 2021
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
Tonight`s temperature forecast was slightly adjusted to be higher
due to observations being warmer than forecasted for central MS.
Otherwise, no major updates were made. Overnight lows will be
ranging in the mid to upper 70s, allowing for another warm and
muggy night. Light winds and enhanced surface RH will allow for
some patchy fog to develop in the region in the early morning
hours. Similar to this morning, the patchy fog is expected to
dissipate by daybreak. /AJ/
Prior discussion below:
Tonight and tomorrow...
Weak surface high pressure under a broad upper level ridge
dominates the weather map again today. Afternoon showers and
possible thunder continue to reinforce llvl moisture in a hot and
humid airmass. Winds very light/calm on obs across the area this
afternoon enhancing the impacts of the high heat index values
across the region. Same lack of flow is causing most showers to be
stationary...and areas under the few showers out there are
locally seeing some rain...but the bulk of the region is seeing
very little relief from the heat. Overnight tonight, the enhanced
llvl RH will result in some patchy fog in low lying areas...best
chances will be the same area that gets any precip today. Tomorrow
will bring much of the same, and temps and heat indices on par
with todays forecast with the airmass largely unchanged. Starting
with the area with the greatest chances for exceeding heat
advisory criteria...roughly along and west of a line from
Greenwood to Columbia. But tomorrow`s Heat Advisory will likely
get updated with the newest guidance... expect more of the same
muggy conditions from the weekend. HRRR coverage of the showers
and thunderstorms tomorrow seem to focus more in the south and
east...and slightly more convection overall in a relatively
stagnant airmass. /HJS/
Monday night through Wednesday: As the East Coast upper trough
amplifies through midweek, the mid/upper ridge will retreat at
least temporarily. While this trough will bring a weak front into
the Mid South, it will not be potent enough to keep the front
together through our area. Instead, the remnants of the front will
serve as a focus for convergence and deep moisture, resulting in
higher rain chances Tuesday and Wednesday. The added clouds/rain
may also help to knock a few degrees off our high temps, perhaps
offering a slight reprieve from the recent heat stress concerns.
Still with moisture levels remaining high, any areas that receive
a good bit of sun could still possibly reach advisory thresholds
during this time frame.
Thursday through next weekend: The ridge will begin to build back
in late Wednesday into Thursday, with richer deep layer moisture
pushing south. This will begin to limit rain chances, especially
in the northern portion of the area, and usher in a return of
warmer conditions with high temps again into the upper 90s and
possibly pushing triple digits in a few spots and heat indices
into the triple digits areawide, continuing to push heat advisory
criteria. Yet another dip in the East Coast upper trough and
accompanying moisture return may cause rain chances to creep back
up heading into next weekend. However, otherwise warm and muggy
conditions will continue through the end of the forecast period.
/DL/
&&
.AVIATION...
00Z TAF discussion:
VFR conditions will prevail through the forecast period with the
exception of potential brief impacts from diurnally driven
isolated/scattered TSRA, and possibly from early morning IFR/MVFR
category fog given light surface wind, mostly clear skies, and
humid boundary layer. /EC/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 76 93 76 94 / 17 65 22 68
Meridian 75 94 75 94 / 17 60 21 71
Vicksburg 77 95 77 95 / 16 51 18 55
Hattiesburg 76 94 75 95 / 17 51 15 60
Natchez 76 93 75 93 / 17 55 17 51
Greenville 76 94 76 92 / 13 47 19 54
Greenwood 76 95 75 93 / 14 55 21 64
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory from 10 AM to 7 PM CDT Monday for MSZ018-019-025-
034>036-040>043-047>049-053>055-059>064-072.
LA...Heat Advisory from 10 AM to 7 PM CDT Monday for LAZ007>009-015-
016-023>026.
AR...Heat Advisory from 10 AM to 7 PM CDT Monday for ARZ074-075.
&&
$$
AJ
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
645 PM CDT Sun Jul 25 2021
.SHORT TERM...
227 PM CDT
Through Monday night...
Much more tranquil and less humid conditions have prevailed
across the area today after Saturday`s scattered thunderstorms.
Daytime mixing has tapped into significantly drier air aloft
across northern Illinois, allowing dew points to lower well into
the 50s and locally upper 40s (more than 20F lower than 24 hours
ago). So while the overall airmass that arrived behind the cold
front early this morning is slightly cooler in the lower half of
the troposphere, the drier air has allowed temps to climb into the
upper 80s and locally low 90s even as thinning upper-level cirrus
spreads over the area. The drier air has also resulted in a
noticeable reduction in haze, though some western wildfire smoke
continues to advect into the region.
The surface high, currently centered over south-central Iowa,
will drift ESE to central Indiana through Monday night. Resulting
light and sometimes calm winds tonight amid lower dew points will
support generally seasonable temps under mostly clear skies.
Light north winds will prevail on Monday amid another dry and
mostly sunny day. Low-level thermal profiles support max temps
solidly in the low 90s provided somewhat thicker smoke aloft over
the northern Great Plains does not filter over the area.
Otherwise, an early- arriving lake-enhanced boundary will limit
temps to the mid 80s along the shore.
Monday night is expected to remain dry as convection initiating
over the north half of Minnesota Monday evening encounters
increased capping and the noted dry air mass over Wisconsin.
Kluber
&&
.LONG TERM...
248 PM CDT
Tuesday through Sunday...
Hot summertime weather is expected to continue across the area
through Wednesday. Increasing dewpoints for Tuesday and
especially Wednesday will make for increasingly uncomfortable
conditions as heat indices rise well into the 90s (possibly
around 100 degrees on Wednesday). Fortunately a welcome break from
this heat and humidity should occur for the later part of the
week following a cold frontal passage expected sometime on
Thursday. Shower and thunderstorm chances during the period will
be the greatest Wednesday night and Thursday as this cold front
approaches and moves into the area, but there is a low possibility
for some storms shifting into parts of the area from the northwest
both Tuesday and Wednesday.
Following the eastward passage of the surface high moving across
the area on Monday winds will turn back to the southwest on
Tuesday. This will in turn allow a much more humid airmass to
return to the area. High temperatures are likely to be in the
upper 80s to the low 90s both Tuesday and Wednesday. However, with
increasing dewpoints into the lower to mid 70s, we are likely to
see heat index readings well into the 90s for Tuesday, and
potentially topping 100 on Wednesday. This will make for very
uncomfortable and increasingly hazardous heat conditions for the
area, and we could be close to heat advisory criteria (heat index
105+) Wednesday.
While the threat of showers and storms looks fairly low for
Tuesday and much of the day on Wednesday, we will have to keep a
close eye on convective trends to our north across parts on MN
and northern WI Monday night into Tuesday and again Tuesday night
into Wednesday. Any well organized MCS`s that develop there could
try to propagate southeastward along the northeastern periphery
of the large upper ridge centered over the central Plains. If it
does so, the 850-300mb thickness gradient suggests it could get
steered in our direction into Tuesday. Its really just a question
of if increasing capping will prevent these storms from shifting
this far south. For this reason we will have to watch for the
possibility of storms and/or an outflow boundary moving into parts
of southern WI and possibly far northern IL on both Tuesday and
Wednesday. Confidence remains low on this scenario, but if it
occurs temperatures would be cooler than currently forecast across
parts of northern IL Tuesday into Wednesday.
The later Wednesday night through Thursday period remains the
roughly 24 hour window where guidance is providing the strongest
signal for convection in the area along the southward-shifting
frontal zone. There is potential for some form of MCS late
Wednesday night in the western to central Great Lakes that could
be shifting southeast near or into the area, but this remains far
too uncertain yet. The 00Z GFS and slightly slower ECMWF both show
a not-so-favored diurnal time for the frontal passage in terms of
maximizing strong convection and heavy rain potential. Obviously,
plenty of time for things to shift some though.
Behind the front, northeast winds look to pick up and steer in
drier air fairly quickly. These forecast winds presently have the
pattern to provide a high swim risk period for Lake Michigan
beaches from approximately Thursday afternoon through Friday
morning. The drier air mass looks to bring precipitation-free
conditions for Friday and potentially most of the day Saturday.
For Saturday, it looks to depend on how far southwest the frontal
zone moves on Friday. This zone is forecast to be active Saturday
and Saturday night, and this could remain southwest of the CWA.
KJB/MTF
&&
.AVIATION...
For the 00Z TAFs...
Aviation Forecast Concerns:
* Wind directions in otherwise light surface flow through period.
Early evening surface analysis depicts high pressure centered to
the west of the forecast are cross the mid-Missouri River Valley.
With the surface ridge axis extending eastward into our region,
the weak surface pressure gradient has allowed light, generally
west to northwest surface winds across the terminals through the
late afternoon hours. A lake breeze has moved through GYY, but
only came up to the very east side of the field at MDW and did not
approach ORD. Thus, wind directions should remain generally
westerly at all but GYY this evening. High-res model guidance has
generally trended toward a more westerly direction for a good
portion of the night as well, shifting more north-northwest toward
sunrise. With the relatively warm/dry air mass we should decouple
quickly this evening with the approach of sunset, so light/less
than 10 kt conditions are expected.
On Monday, the surface ridge slides south of the area. Within the
light gradient, winds are expected to shift northeast by mid-
morning across ORD/MDW and GYY, with a more easterly lake breeze
push developing in the afternoon. Winds for these locations should
then veer southeast Monday evening. Farther west, winds should
eventually back more westerly at DPA and RFD, and eventually
southwesterly in the afternoon at RFD. Again, speeds should
generally remain less than 10 kts.
Forecast soundings maintain dry moisture profiles across the
region through Monday evening in the vicinity of the high pressure
ridge, with the only exception being some high cirrus occasionally
streaming into the region from the southwest from convection
across the Plains. Skies will continue to appear milky aloft due
to smoke from western wildfires, though 18Z HRRR forecasts suggest
a decrease in near-surface smoke due to northerly flow above the
boundary layer. Thus no horizontal surface visibility issues are
expected.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Lubbock TX
619 PM CDT Sun Jul 25 2021
.AVIATION...
Scattered thunderstorms may affect KLBB and/or continue to affect
KPVW through 26/03Z. Pilots should expect strong downburst winds
beneath cloud base, confirmed by a surface gust of 42 kt by the
KPVW METAR at 2235Z. PIREP from 2305Z out of KLBB reported
moderate chop at FL340, and a convective SIGMET remains in effect
through 26/0055Z for all three terminals. A few cumulonimbi may
have maximum tops to 50 kft with hail up to 1 inch aloft.
Thunderstorms should quickly wane in intensity and coverage after
dark, with VFR prevailing otherwise for the TAF period.
Sincavage
&&
.PREV DISCUSSION... /issued 221 PM CDT Sun Jul 25 2021/
SHORT TERM...
Westerly surface winds across the South Plains early this afternoon
should back to the south by 21z. Weak inhibition should erode
allowing widely scattered showers/thunder to develop as advertised
by CAMS taking advantage of around 1000 J/KG MLCAPE. Favored area of
concentration according to the HRRR and the 12z Tech WRF run is from
the Caprock Canyon/nrn Rolling Plains region, developing farther
south/southwest along an axis through the central South Plains into
areas S/SW of Lubbock as cap erodes around 21z (4 pm). Given weak
winds aloft and fairly high PWATs (1.3 - 1.7 inches), isolated cells
could produce some brief heavy rain. along with gusty winds and
occasional lightning.
Activity should decrease rapidly with loss of heating around 01-02z
(8-9 pm), although did keep slight chance pops across the SE
Panhandle overnight. Similar situation with slightly less coverage
on Monday, and much less activity across the northeast where pops
fall below mentionable. Temperatures/dewpoints near persistence,
which are also very near climatological averages. James
LONG TERM...
We`ll keep a slight chance of showers and t-storms going Monday
evening, as models continue to show some kind of convectively
induced mesoscale vortmax sliding southwest from the Panhandles
into eastern NM by evening, and this may generate enough lift
despite evening stabilization to maintain any ongoing activity.
Tuesday appears to be mostly dry however, with the upper high in
close proximity and the mid-level moisture plume shunted farther
north into the plains. Tuesday`s highs should climb a few degrees
area-wide with mid to upper 90s on the Caprock and upper 90s to
around 103 or 104 in the Rolling Plains.
By Wednesday, the center of the upper-high should be in the
central plains and this should place our forecast area more
squarely under easterly flow aloft. Thus we expect daytime
temperatures to back off some from Tuesday`s readings. In
addition, a weak disturbance undercutting the ridge will bring
some mid-level moisture back into the area. The ECMWF is a little
weaker and farther south than the GFS with this westward-moving
wave, and the forecast remains dry for now, but there is a chance
that we might need to raise PoPs across the south.
Beyond Wednesday, the upper-ridge looks like it will expand
south and east, becoming centered roughly over north-central Okla
by Friday. This should bring hot (the heat does not appear
exceptional at this time) and mostly dry weather to the forecast
area to close out July.
&&
.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
09
Area Forecast Discussion
National Weather Service Medford OR
859 PM PDT Sun Jul 25 2021
.DISCUSSION...Just a couple of tweaks to the forecast this
evening. The radar shows a few returns mainly across Modoc and
Lake counties and earlier this evening there was a report of
sprinkles in Lakeview. Therefore the forecast has been updated
this evening for a slight chance of showers in these areas, and
then a slight chance of showers overnight across mainly Siskiyou
County based on the SREF model. Otherwise, we hope for rain over
the next two days but with little to no thunderstorms.
Sandler
&&
.AVIATION...For the 26/00Z TAF Cycle...Along the coastal
areas, expect LIFR/IFR conditions to return again early this evening
and persist through late Monday morning. For inland areas, expect
periods of MVFR visibilities due to wildfire smoke tonight east of
the Cascades then local MVFR visibilities in smoke on Monday. A few
cumulonimbi may be possible Monday morning as well as isolated
thunderstorms Monday afternoon along portions of northern
California and along and east of the Cascades. -Schaaf/CC
&&
.MARINE...Updated 800 PM PDT Sunday, 25 July 2021...High pressure
offshore and a thermal trough near the coast will persist into
Monday. This patten will result in gusty north winds and steep to
very steep wind-driven seas. Very steep and hazardous warning level
seas are expected from Gold Beach southward, with north gales
expected mainly beyond 5 nm from shore. North of Gold Beach,
advisory level conditions will continue into Monday. Winds will ease
some Monday and overall conditions will improve Monday night into
Tuesday, though seas will likely remain steep south of Cape Blanco
through Tuesday morning.
The thermal trough pattern will be disrupted Tuesday into Wednesday,
then likely return late Wednesday into Thursday. Although not as
strong as the current event, gusty north winds are expected to
return by Thursday and persist into next weekend. Conditions will
likely become hazardous to small craft then, especially south of
Cape Blanco. -Schaaf/CC
&&
.PREV DISCUSSION... /Issued 247 PM PDT Sun Jul 25 2021/
DISCUSSION...The majority of our team`s focus today was on thunderstorms
and communicating their potential, mainly because of lightning
and the potential for wildfire starts, given how extremely dry the
vegetation is. In general, we do expect a slight chance (15
percent) for lightning starting late tonight through Tuesday
morning, and we`re communicating that directly with partner
agencies mainly because it`s uncommon for us to forecast nighttime
or morning thunderstorms. That said, there aren`t the ingredients
coming together for an abundant lightning event through Tuesday.
Smoke coverage is once again extensive across the forecast area, and
it`s generally being transported from south to north aloft. At the
surface, smoke that has collected in some valleys should be pushed
off to the east this afternoon as daily afternoon breezes kick in.
The same general daily cycle of smoke should continue tomorrow,
but the latest HRRR smoke model run suggests surface smoke
trending slightly lower tomorrow compared to today.
Models suggest enough instability and moisture aloft tonight to
support a slight chance for thunderstorms. Any storms that form will
be mostly dry. That said, 500mb-300mb lapse rates, midlevel moisture
depth, and trigger, all indicators for how significant
overnight/morning storms can be, are marginal at best. So we
generally expect less than 50 cloud to ground lightning flashes
across the entire CWA through Monday morning.
Tomorrow afternoon conditions will be somewhat more favorable for
storms, but again not expecting abundant lighting. Instability is
moderate, and our most reliable post-processed guidance and high-
resolution model data are suggesting isolated storms, so that`s what
we`re forecasting. The best chance for storms is east of the
Cascades. Smoke is a variable that could limit surface heating and
subsequent storm development, but we don`t think it will preclude
seeing some lightning tomorrow.
Tomorrow night will feature more significant moisture and trigger,
so we are forecasting a slight chance for storms again, in a similar
area as tonight. On Tuesday a well-defined disturbance will move
from south to north through the area and will be accompanied by a
lot of moisture--with precipitable water values 300% of normal for
areas east of the Cascades. What this means is that we`ll likely see
lots of shower activity with some embedded thunderstorms possible.
The latest European model ensemble suggests a 30-50 percent chance
of 0.1 inches of rainfall from the Cascades eastward from Tuesday
through Tuesday evening. Temperatures Tuesday across the forecast
area will likely be below normal because of increased cloud cover.
Wednesday through Friday`s weather will feature a warming trend,
with temperatures jumping to 5 to 10 degrees above normal. Deep
southerly flow continues through the week, and as a result,
thunderstorm chances continue as well (though generally 20 percent
chance or less) from the Cascades and Siskiyous eastward. Keene
AVIATION...For the 25/18Z TAF Cycle...VFR will prevail for much of
the area away from the coast and away from area wildfires. Along the
coast and in the Coquille Basin, stratus is burning off the beaches
bringing VFR to the coast through this afternoon. Expect LIFR/IFR
conditions to return again early this evening. Expect periods of
MVFR visibilities due to wildfire smoke this afternoon, especially
east of the Cascades. A few cumulonimbus may be possible tomorrow
morning along portions of northern California and along and east
of the Cascades. -Schaaf
MARINE...Updated 200 PM PDT Sunday, 25 July 2021...A typical
summer weather pattern of high pressure offshore and a thermal
trough near the coast will persist into Monday. This patten will
result in gusty north winds and steep to very steep wind-driven
seas. Very steep and hazardous warning level seas are expected from
Gold Beach southward, with north gales expected beyond 5 nm from
shore. North of Gold Beach, advisory level conditions will continue
into Monday. Winds will ease some Monday and overall conditions will
improve Monday night into Tuesday, though seas will likely remain
steep south of Cape Blanco through Tuesday morning.
The thermal trough pattern will be disrupted Tuesday into Wednesday,
then likely return late Wednesday into Thursday. Although not as
strong as the current event, gusty north winds are expected to
return by Thursday and persist into next weekend. Conditions will
likely become hazardous to small craft then, especially south of
Cape Blanco. -Schaaf/BR-y
FIRE WEATHER...Updated 200 PM Sunday 25 July 2021...The upper
level ridge east of the area continues to weaken and our focus is
shifting to the potential for thunderstorms over the next several
days.
Water vapor imagery is showing southerly flow aloft taking hold
allowing monsoon moisture -- mostly over the Desert Southwest for
the past several days -- to surge northward across California. This
is evident with some high cirrus moving in and even some mid-level
cumulus/altocumulus across the south and east. We`ll see an area of
elevated instability move into the area tonight pushing north
across the area Monday morning. Forcing for convection is weak
and we don`t think there`ll be a lot of lightning (if any), but
some of the hi-res guidance is indicating a slight chance of
high-based showers and perhaps a stray CG flash or two developing
after 09z. Any rain will be minimal.
Hi-res guidance continues to show mid-level moisture increasing with
modest instability persisting into Monday afternoon/evening. Right
now, we`re not expecting widespread/abundant lightning. We`re
continuing to forecast isolated thunderstorms mainly east of a line
from the Jack Fire to the Illinois Valley. Best instability in the
guidance is being depicted from around Chemult/Crescent to the
Bootleg Fire down to around the Warner Mountains. In these
areas, however, instability may be somewhat limited by wildfire
smoke. Due to the dry air mass in place ahead of this, storms
that do form could be dry initially, but then get wetter with time
due to the increase in precipitable water (PW) to around 1.00 inch.
Elevated instability Monday night could result in nocturnal activity
in advance of another healthier disturbance arriving on Tuesday,
but again, activity appears to be isolated. Recent models are
still showing a fairly robust upper short wave moving northward
across California Monday night, then across the forecast area
Tuesday. PWs surge to and reach a peak of 1.00-1.50 inches during
this time period. With much more cloud cover expected, expect this
to be more widespread showers with embedded and isolated
thunderstorms, though any thunderstorms will be effective rain-
producers. Given the high PWs, we`ve increased our chances of
wetting rain (>=0.10") to around 30-50% in a corridor east of the
Cascades from eastern Siskiyou County to much of Klamath County and
into western Lake County, which would include the Bootleg Fire.
Wednesday-Saturday, it will heat up again. Since we`ll mostly
remain on the western periphery of the upper ridge axis to the east,
we`ll be under southerly flow aloft. Instability should be present
each afternoon/evening during this time period, and convective
activity will be dictated by short waves coming northward in the
flow. We`ve continued with a slight chance of pm/eve thunderstorms,
mainly from the Cascades eastward, but these areas can change, so
keep checking back. -Spilde
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...
CA...None.
Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Monday for
PZZ350-356-370-376.
Gale Warning until 11 PM PDT Monday for PZZ356-376.
$$
RES/RES/RES
AREA FORECAST DISCUSSION
National Weather Service Morristown TN
925 PM EDT Sun Jul 25 2021
.UPDATE...
EVENING UPDATE.
&&
.DISCUSSION...
Radar shows the convection over the area has been waning with the
loss of heating as expected. However, given the very moist air
mass over the area will need to keep at least slight chance to
low chance PoPs in for showers/possible thunderstorms overnight.
Will make some tweaks to temps/dew points to better fit latest
observations, but overall forecast for tonight generally looks to
be on track.
&&
.AVIATION...
00Z TAF DISCUSSION.
There will be mainly scattered convection around at times,
especially early and again late in the period. Will try to time
the higher probability times for thunder with VCTS/prob30 groups.
Fog development will be possible later tonight, with highest
chance for vsby restriction to MVFR or lower being at TRI. Will
include MVFR vsby at TRI but keep vsby no lower than 6SM at
CHA/TYS for now, but lower conditions are possible. Outside of
convection and any fog, conditions are expected to be mainly VFR
with light winds.
LW
&&
.PREV DISCUSSION...
/ISSUED 321 PM EDT Sun Jul 25 2021/
SHORT TERM...(This Afternoon through Monday)...
Key Messages:
1. Another weak wave in northwest flow aloft will bring another
round of scattered storms across the Plateau (especially northern)
and western Tennessee valley this evening. Isolated strong storm
with torrential rains, gusty winds up to 45 mph and frequent
lightning.
2. Increasing coverage of storms Monday, especially in the
afternoon/early evening due to daytime heating/destabilization.
Again, Isolated strong storm with torrential rains, gusty winds
up to 45 mph and frequent lightning.
Discussion:
Through this evening, another area of scattered storms over
south-central Kentucky is associated with a weak wave in northwest
flow aloft. MLCAPES from the RAP shows values of 1500-2200 over
most of the area, DCAPES of 700-900 and PWs of 1.6 to near 2
inches. This environment could produce isolated strong storms with
torrential rains, gusty winds up to 45 mph and frequent lightning.
Very localized flash flooding can not be ruled out.
For Tonight, diurnal convection waning and weak wave moving east
will diminish coverage and intensity. However, vertical profile is
very moisture so can not rule out isolated/widely scattered
convection almost anywhere. High moisture content will also
produce some fog.
For Monday, a frontal boundary will approach/move into the area in
the afternoon. Another weak wave in the upper flow along with the
boundary will focus the moist/marginal unstable airmass to produce
areas of convection. Airmass will remain very moist with MLCAPEs
again between 1500-2000. Again, isolated strong storms can be
expected producing torrential rains, gusty winds up to 45 mph
and frequent lightning. Very localized flash flooding can not be
ruled out.
LONG TERM...(Monday Night through Sunday)...
Key Messages:
1. Increasing heat this week peaking in the mid/upper 90`s Wed
through Fri, but cooling still expected next weekend.
2. Scattered convection will continue Tues, especially S of I-40,
but mainly dry Wed and Thurs before chances for convection slowly
increase Fri into the weekend.
Discussion:
Monday Night through Tuesday...
The cold front will continue to sag S and SW during this time as a
couple of mid/upper shortwaves progress across the Great Lakes and
NE CONUS, effectively deepening longwave troughing over the NE
CONUS. The S Appalachians will remain SW of the main trough axis, so
expect the boundary to stall and washout over our southern counties
as it runs into a building mid/upper ridge across the Plains and MS
Valley. The weak boundary in the area, some mid-level PVA, weak
upper diffluence, and heating of a moist boundary layer
characterized by Td`s in the low/mid 70`s and PWATs of 1.50 to 2.00
inches will allow for widespread convection during the afternoon and
evening as MLCAPES build to around 2000-2500 J/Kg. However, expect a
sharp gradient in the best coverage of convection with most of the
activity S of I-40 closer to the boundary. This is where pooling low-
level moisture will yield the highest Td`s and PWATs, and therefore,
the greatest instability. Forecast soundings suggest PWATs dropping
below 1.50 inches from the middle Valley northward into SW VA during
the afternoon as surface high pressure dropping into the OH Valley
allows for drier northerly low-level flow behind the front, so
convective coverage will be much less in those areas. Due to the
limited upper support with the main jet well to the N, do not expect
much organization to the convection with a pulse nature being the
most likely outcome. Locally heavy rain and gusty winds will
accompany the strongest cores, but still cannot rule out an isolated
severe cell with damaging winds due to high DCAPE values. Highs Tues
will reach the upper 80`s/low 90`s with morning lows in the upper
60`s/low 70`s.
Tuesday Night through Friday...
The big story in this period will be a few days of significant heat
with heat indices getting close to advisory criteria, especially in
the southern Valley. The aforementioned mid/upper ridge over the
Plains and MS Valley will strengthen to an impressive 598 DAM by Wed
and expand/elongate eastward across the TN Valley and deep South
through the end of the week. H5 heights peak at 592-594 DAM over the
S Appalachian region Wed and Thurs with an 850 mb thermal ridge
sliding into our region too. The building mid-level and thermal
ridge combined with low-level WAA will boost 850 mb temps to 20-21 C
Wed and 21-23 C Thurs, with the ECMWF being the warmest of the
guidance. Stout mid-level capping thanks to an EML tongue advecting
E should allow for mostly sunny skies and very limited convection
outside of the highest terrain, and since we are in the
climatologically warmest weeks of the year, feel that NBM highs of
mid 90`s Wed and mid/upper 90`s Thurs are realistic. If rainfall
coverage is less than expected early this week, then ECMWF highs
near 100 in a few places are possible. Regardless, Td`s in the low
70`s combined with the heat will yield heat indices near the 105
degree advisory threshold, especially over the S Valley, so those
outdoors will need to take frequent breaks and stay hydrated. By
Thurs night and Fri, shortwave energy will carve out a deepening
longwave trough over the Great Lakes and NE CONUS allowing a cold
front to approach from the N. Deterministic and ensemble guidance
agree on this, but timing of the fropa is low confidence. Will have
scattered showers/storms increasing from N to S late Thurs night and
Fri. The lowering heights and gradually cooling 850 mb temps, along
with possibly more cloud cover, will cap highs in the low/mid 90`s
Fri, but heat indices could still be near 105 in southern areas. Low
temps for mid and late week will be uncomfortably warm and muggy
struggling to fall out of the low 70`s, with some mid 70`s in the S
Valley.
Friday Night through Sunday...
The heat will diminish to more seasonable levels for the weekend as
a series of shortwaves deepen a broad trough across the Great Lakes
and NE CONUS leading to W/NW flow aloft and a cold front settling
into the TN Valley and S Appalachians. The front will likely stall
in this region, but tough to say exactly where this far out.
Continued low-level moisture and instability beneath lower heights
and the front in the vicinity will allow for scattered convection
each day, peaking during the diurnal cycle. Highs Sat will stay in
the upper 80`s/low 90`s with generally upper 80`s Sun.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 74 91 74 90 73 / 20 60 20 70 10
Knoxville McGhee Tyson Airport, TN 73 90 72 92 72 / 30 60 20 50 10
Oak Ridge, TN 73 89 72 90 71 / 30 70 20 40 10
Tri Cities Airport, TN 69 87 68 90 66 / 40 70 10 40 10
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
Area Forecast Discussion
National Weather Service Reno NV
128 PM PDT Sun Jul 25 2021
.SYNOPSIS...
Light westerly winds will continue to pour smoke into the region
from the large Dixie Fire through at least Monday. Monsoon moisture
will overspread the region leading to an increase in thunderstorm
chances each afternoon much of this coming week. After a hot day
Monday, temperatures will cool notably Tuesday before warming back
up again late week.
&&
.DISCUSSION...
* Smoke: Well, earlier there was some hope we`d see a (very)
gradual improving trend in the smoke out our window. That`s
pretty much dashed with worsening AQI as a likely smoke layer
aloft mixes down into the valley around Reno. Super light
westerly winds should kick in later today but the temperature
gradient to drive those winds will be made even weaker by the
thick smoke over W Nevada. In the end, based on HRRR Smoke Model
there may be some evening improvement but extra-low confidence
on extent.
* Similar situation Monday with light W/NW flow at night bringing
in Dixie Fire smoke to much of the region by daybreak, with
mixed confidence on improving conditions for late day, modulated
by t-storm outflows. The one area that escapes the thick smoke
is the E Sierra with more S/SE wind monsoonal trajectories
developing Monday.
* Thunderstorms: Respectable monsoon moisture push into the
region this week with a large high centered over the Four
Corners and Rockies. Thunderstorm probabilities will remain
elevated with precipitable water values rising to near 1" by
Tuesday afternoon in most ECMWF EPS members. Monday afternoon
looking active with slow moving storms in latest HRRR and HREF
guidance, and a wave lifting north out of SoCal could keep
faster moving t-storms going into the pre-dawn hours Tuesday.
Some possibility subsidence behind this wave + "too high PW"
could keep storm coverage down Tuesday PM but low confidence on
that this far out.
* We`ll really need to be on our toes with flash flood and debris
flow risks on the newer burn scars such as Beckwourth, and even
the ongoing Tamarack Fire especially on steeper slopes just west
of Hwy 395 + steep terrain of Alpine County. It only takes 5-10
minutes of heavy rain to cause major flooding on recent high
intensity burns. Will defer to the overnight shift to decide on
flash flood watch issuances each day, as flood flood
environments have limited predictability in our region more than
12-18 hours out.
* Most of the EPS guidance has drier air working in Wednesday
while some members keep moisture values high enough for a
continued storm risk. PW values rise again Thursday into the
weekend so better confidence of storms there. GEFS has a rather
robust QPF signal for Thursday, something to watch. We`re
definitely in a pattern over the coming week where at some point
over the next seven days, most areas will see some rainfall and
some could see rather heavy downpours. Now`s a good time to
ensure drainages are cleared out, and people near recent fires
are prepared for possible flooding.
-Chris
&&
.AVIATION (through Monday)...
Widespread smoke covering the area today mainly from the Dixie
Fire in NE California. Some aircraft holds into RNO due to low
visibility this afternoon. Any improvements will be very gradual
due to afternoon westerly winds being on the light side. HRRR
smoke shows some late afternoon and evening improvements for
TVL/TRK and possibly RNO/CXP/MEV, though confidence is only medium
as there is just a ton of smoke both at the surface and aloft to
move around.
Air flow turns more W/NW again tonight with smoke coming back in
overnight into Monday morning - MVFR to IFR conditions again well
into Monday. Highest risk of thick smoke is for SVE-RNO-NFL-CXP
areas, with less risk for TRK/TVL. Main exception to this will be
MMH where wind trajectories favor only minimal smoke or haze
impact through Monday.
Thunderstorms become more of a factor starting today with a solid
monsoon push working north into the region. Based on NBM and HREF
guidance, the best chances through this evening are between
TVL/MEV and MMH in the E Sierra. Somewhat slow moving storms with
areas of MVFR-IFR in heavy rain and outflows to 35 kts. For Monday
afternoon t-storms are more expansive ahead of an approach wave
aloft, including RNO and TRK/TVL and NFL vicinities. Outflows in
HREF look stronger, possibly up to 50 kts. T-storms of at least
isolated coverage will last into the evening and possibly
overnight to daybreak Tuesday.
-Chris
&&
.FIRE WEATHER...
The main concern for fire weather this week will be the increase in
thunderstorm activity that is expected to last throughout the week
as increasing monsoon moisture moves into the region from the
southeast. New fire starts in very dry fuels, along with gusty
erratic outflow winds and the potential for flash flooding on
current/recent fires are all hazards that could create issues
with the ongoing fire fights.
Today looks like a fairly typical thunderstorms day with build ups
beginning to develop late this morning along the higher terrain of
the eastern Sierra, with continued development and a few relatively
weak storms, expected through early evening.
Monday is a little more concerning as an upper-level wave brings
additional forcing while increasing moisture continues to flow
into the region. Stronger thunderstorms will be likely tomorrow
with the with elevated nocturnal convection possible lasting
overnight. Overnight storms are not clear cut at this point, but
the enough forcing and instability could be left over from to
keep some storms going after dark. Currently expecting a mix of
wet and dry storms tomorrow with the best chances for drier storms
north of highway 50 along the edge of the better increasing
PWATs, where storm motions will be faster with less available
moisture.
Storms will continue to transition to the wetter variety on Monday
(south of I-80), and throughout the region later in the week.
This will create flash flooding concerns, mainly in the more
vulnerable areas with fresh burn scars, especially near on the
Tamarack fire where considerable amounts of complex terrain has
burned near and above roadways.
Storms will continue throughout the week with varying degrees of
coverage and intensity. As moisture levels increase chances for more
widespread wetting rains will be possible this week, with the best
chances from Tahoe southward. -Zach
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno
Area Forecast Discussion
National Weather Service Las Vegas NV
207 PM PDT Sun Jul 25 2021
.SYNOPSIS...A moist weather system will bring widespread shower
and thunderstorm activity to the region today and Monday before
drier conditions resume Tuesday and Wednesday. Thereafter, another
uptick in monsoonal moisture is expected with increasing
thunderstorm activity through the weekend. Temperatures through
the week will be near to slightly below normal.
&&
.DISCUSSION...through next weekend.
As of 2 pm, convection was beginning to fire along the higher
terrain of Mohave county while working swiftly westward.
500-700mb mean flow of 20-30 knots has resulted in a quick storm
motion, with storms moving at near 25 mph from northeast to the
southwest. Meanwhile, SPC mesoanalysis indicates surface based
CAPE values of 1500-2500 j/kg pooled from southern Nevada
southward towards the Colorado River Valley. All in all,
conditions are primed for some robust thunderstorm development
through the afternoon and evening hours.
HRRR and HREF guidance has been quite consistent in
developing the strongest storms across northern/central Mohave
County with storms congealing and developing westward towards far
southern Clark county and the Mojave Preserve through the
evening. Storms may then eventually work west into the Western
Mojave Desert and Morongo Basin. While chances exist for storm
activity in the Las Vegas Valley this evening, the best signal for
storms is mainly south of the Vegas metro area. Given 25-35 knots
of effective shear, some storms could be severe with damaging
winds and even some quarter sized hail. Torrential rainfall is
also a possibility given highly anomalous precipitable water
creeping into the region, but quick storm motion will mitigate
the risk somewhat this evening.
Inverted trough will push into California tomorrow, with
precipitable water values peaking at 200% of normal or greater
across our western zones. Additionally, storm motion vectors will
slow down and shift to a more southerly direction, which will favor
both slower storm movement and the potential for training near
terrain features. Given the highly anomalous moisture in play and
signals from ensemble guidance for locally heavy rainfall, issued
a Flash Flood Watch for most of San Bernardino County, Inyo,
Esmeralda, Nye, and far western and southern Clark counties
through Monday evening. Coverage and intensity of activity Monday
will be dependent on how much instability can be realized amongst
the thick cloud cover in the moisture rich airmass, but it won`t
take a lot of heating to convect.
The inverted trough will weaken and lift north along the Pacific
coast on Tuesday and Wednesday with a drier and more stable
airmass working into the region. Drier conditions with only very
sparse thunderstorm activity are expected on these days along with
gradually warming temperatures. Thereafter, additional monsoonal
moisture and perhaps another weak inverted trough will push into
the region with thunderstorm activity increasing through the
weekend.
&&
.AVIATION...For McCarran...East to northeasterly wind around 10kt
will become more southeasterly this afternoon. Thunderstorm activity
in Mohave County will send east or southeast outflow wind toward
KLAS, but low confidence in timing and magnitude at this time.
Expect onset no sooner than 22Z. A change to southerly wind gusting
15-20kt with lowering CIGS aoa 8kft after 03Z is expected. Cannot
rule out a thunderstorm near the terminal later the evening.
For the rest of southern Nevada, northwest Arizona and southeast
California...Storms will move southwest this afternoon and evening
from SW Utah and Mohave County potentially bringing heavy rain and
strong outflow winds to southern NV and along the Colorado River
Valley, directly affecting KEED and KIFP and potentially KDAG later
in the evening. Lowering CIGS can be expected from east to west
across the area tonight with CIGS aoa 10kt expected.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
DISCUSSION...Outler
AVIATION...Berc
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