Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/14/21
Area Forecast Discussion...UPDATED
National Weather Service Albuquerque NM
555 PM MDT Mon Sep 13 2021
.AVIATION...
00Z TAF CYCLE
Broad high pressure remains over southern NM/AZ with very dry west
and northwest flow aloft over NM through Tuesday. A backdoor cold
front will result in a wind shift and isold to wdly sct showers and
thunderstorms to the northeast quarter Tuesday afternoon. Elsewhere,
VFR will be the rule with continued haze mainly south of I-40 and
east of I-25.
33
&&
.PREV DISCUSSION...254 PM MDT Mon Sep 13 2021...
.SYNOPSIS...
Hot, dry and hazy conditions persist across the region under the
influence of strong high pressure. A weak backdoor front will bring
chances for storms to northeast and east central New Mexico late
Tuesday, some of which may become strong to severe. Isolated storms
are possible Wednesday, mainly along the central mountain chain. Hot
and dry conditions will persist across most of the area Thursday
through Saturday, with above normal temperatures. Breezy conditions
will develop late Sunday into Monday ahead of the first notable cold
front of the season, forecast to move across our area early next
week.
&&
.DISCUSSION...
SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)...
Another hot, hazy and dry day is underway as high pressure aloft
continues to reside over the American Southwest. The high has
stretched along a west-east axis, an orientation that has kept mid
level moisture intrusions cut off from NM. Any cumulus over northern
and western NM have generally stayed flat with little vertical
development thus far this afternoon, and temperatures are on their
way to near-record or even record values. The remnants of this
afternoons cumulus will slowly dwindle overnight, and latest HRRR
runs suggest near-surface and vertically integrated smoke
concentrations should continue decreasing overnight.
A shortwave trough moving through the northern Great Plains today
will slide over the Great Lakes area early on Tuesday, and this will
send a surface cold front southward down the plains. This front is
modeled to make a entrance into northern Colfax and northern Union
counties by Tuesday afternoon, introducing increased surface
convergence along the boundary while also advecting increased low
level moisture and interjecting deep layer directional shear in the
lower half of the troposphere. Scattered thunderstorms are expected
along and east of the Sangre de Cristos as the front arrives late
Tuesday afternoon and into the evening with a few strong to perhaps
briefly severe cells. Aside from a modest cooldown in the far
northeast, the above average and near-record warmth will continue
Tuesday. Most areas outside of the northeast will remain dry, but a
stray anemic cell or two cannot be ruled out over the southwestern
or south central high terrain. The front will then advance farther
south and west Tuesday night, eventually inducing gusty canyon winds
in centrally favored locales.
LONG TERM...(WEDNESDAY THROUGH MONDAY)...
Breezy east canyon/gap winds will persist into Wednesday morning from
the middle RGV south to the upper Tularosa valley. The front will
introduce sufficient moisture for late day build-ups west of the
central mountain chain Wednesday afternoon, but little-to-no
measurable rainfall is expected as this round of convection will
favor strong/erratic wind gusts. The southern Sangre De Cristos and
the south central mountains could see some deeper convection late
Wednesday with wetting rainfall due to a deeper moist layer
along/east of the central mountain chain.
The upper high will pump back up over our area Thursday into Friday,
keeping well above normal temperatures going with near-record or new
daily record highs possible. Isolated thunderstorms are possible late
Thursday from the south central mountains east into Chaves Co., but
our entire area should be devoid of storms on Friday due to a lack of
moisture.
The 12Z model solutions are at odds with the exact timing of an upper
level trough and associated cold front moving southeast out of the
Pacific NW late in the weekend and into early next week, but at least
are in agreement that we`ll be getting our first notable cold front
of the season at some point Mon/Tue. Breezy conditions will likely
develop Sunday as the westerlies increase across the region in
advance of the approaching upper level trough, with windy conditions
likely to accompany the fropa. Above to well above normal
temperatures will persist until we get some relief from the cold
front.
52/11
&&
.FIRE WEATHER...
Fuel moisture will continue to dwindle over the next several days as
above normal temperatures and mostly dry conditions persist.
Afternoon humidity will commonly drop to or below a 10 to 20 percent
range in the days ahead, and many northern and central zones will
struggle to recover to 35 to 50 percent in the overnight and early
morning periods. The northeastern plains and adjacent highlands will
receive scattered footprints of wetting rainfall on Tuesday, but the
cold front responsible for the storms will provide only short-lived
relief from the hot temperatures. The front will also be responsible
for the primary wind concerns (other than thunderstorm outflows) as
it is expected to surge through central gaps and canyons with
accelerated gusts Tuesday night and Wednesday morning.
52
&&
.ABQ WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Gaylord MI
1155 PM EDT Mon Sep 13 2021
.UPDATE...
Issued at 942 PM EDT Mon Sep 13 2021
Low pressure is lifting across the central plains. Surface front
is easing northward toward the IL/WI border, though is still
largely stalled along the southern lower MI border. Return flow
continues to increase into the western lakes, and this is
supporting a skinny band of convection north of the front. This
extends from GRB to MBL to far southern Lk Huron. This is also
along the MuCape gradient per SPC mesoanalysis, with MuCape values
of 1-1.5k j/kg over most of the GRR/DTX forecast areas. Have
accelerated the onset of pops a bit in the far sw (MBL/Frankfort/
CAD).
Anticipate the existing band of showers to lift northward with
time, initially quite slowly, but more quickly overnight. Expect
showers/t-storms to also become more common along this band, as
theta-e advection increases. Very late overnight, the more
widespread area of precip over MN and environs will push into nw
sections of this forecast area.
Would not preclude a near-svr cell within the band(s) of
convection as they develop and lift northward tonight (as we saw
earlier in the evening over the Thumb). However, the possible
development of MCS(s) ahead of the advancing low in se MN/central
WI poses the main svr threat (which is not large). Some HRRR runs
do bring an MCS into w central lower MI after 6 am.
Have lowered min temps a smidge in many areas, given present
opportunity for cooling before clouds thicken and the pressure
gradient tightens further.
&&
.NEAR TERM...(Through Tonight)
Issued at 355 PM EDT Mon Sep 13 2021
High impact weather potential: Marginal risk for severe
thunderstorms tonight.
Pattern synopsis/forecast: Fairly zonal upper-level flow across the
Great Lakes this afternoon will quickly be shunted eastward as mid-
upper level ridging encroaches on the region from the west. Our well-
advertised nearly stationary boundary remains downstate attm, but
will begin its northward shift this evening into the overnight hours
as a warm front, in response to strengthening low pressure lifting
northeast out of the central plains into the upper Mississippi
Valley. Increasing moisture/forcing/instability through tonight
will yield increasing scattered shower/storm chances.
Primary forecast concerns/challenges: PoPs and severe chances
through tonight.
Little in the way of sensible weather ongoing this afternoon as the
focus remains downstate tied closer to the aforementioned stationary
boundary. As was alluded to, this boundary begins its northward
progression as a warm front this evening, and especially tonight.
Increasing south-southeasterly return flow/warm air advection will
aid in increasing deep layer moisture evident by PWs climbing to
more than 1.5" by sunrise Tuesday. Better forcing will accompany
this boundary, ultimately yielding increasing shower and storm
chances from southwest (as early as mid-evening) to northeast (by
late tonight). Not incredibly impressed by instability parameters
during this overnight period, but none the less, do expect at least
some elevated instability (~500-1,000 J/kg) to advect into the area.
Combined with increasing wind fields (bulk shear values increasing
to greater than 50 kts), still can`t rule out an isolated strong to
severe storm, especially across the southwestern half of the
forecast area. By no means expecting widespread organized severe
weather through tonight as the gut feeling is shower/storm
development will largely remain isolated-scattered in nature.
Worth watching very late tonight toward sunrise Tuesday for the
potential for a MCS to be approaching parts of northern Michigan,
especially across the tip of the mitt and eastern upper given the
aforementioned unidirectional shear already in place by this point
and better dynamics across far northern areas.
Overnight lows a bit warmer than last night...generally ranging from
&&
.SHORT TERM...(Tuesday through Thursday)
Issued at 355 PM EDT Mon Sep 13 2021
High Impact Weather Potential: Severe thunderstorms Tuesday.
Pattern Synopsis/Forecast: Low amplitude jet stream pattern exists
across North America and across the northern Pacific though jet
level winds speeds much faster across the Pacific. Short wave
trough was crossing the Canadian Prairies/northern Plains...with an
upper low over southwest Alaska. Zonal flow across the Great Lakes
region ahead of upstream troughing. At the surface...stationary
front has settled along the Michigan/Indiana/Ohio border stretching
back into northern Illinois/Iowa/Nebraska. 1022mb surface high over
northwest Ontario ridging south into the Great Lakes on the cool
side of the boundary. Definite moisture contrast along the boundary
with 1.50 inch precipitable water values pooled along this front
with things drying out quick as you go north (0.71 inch PWAT off 12z
APX sounding).
Lead piece of short wave energy coming out of the western Dakotas
this afternoon will spin up a weak surface low that will track
northeast across Wisconsin/Upper Michigan Tuesday. Stationary front
to the south will lift northward as a warm front Tuesday across
Lower Michigan...with a cold/occluded front pushing east across the
Lower Peninsula Tuesday afternoon/evening. This will be followed by
a second short wave trough Wednesday but very little surface
reflection of that across the Great Lakes with weak high pressure
crossing the region. This high moves into New England Thursday with
rising heights as upper level flow backs a bit with a stronger short
wave trough and associated cold front front reaching the upper
Midwest by Thursday evening.
Primary Forecast Concerns: Thunderstorms on Tuesday will be the main
forecast focus...and it is likely that convection will already be
ongoing as part of an overnight MCS rolls into northern Michigan
along a 30-40kt southwesterly low level jet. Strong mostly
unidirectional shear in place already to start the day (45 to 65kts
0-6km bulk shear)...so at the very least the potential for severe
storms will be there to start the day. Mostly unidirectional
vertical wind profiles will support bowing segments...whether we can
see stronger wind gusts reach the ground is another issue that will
depend on boundary layer stability. But severe hail is also a
threat early on...and with the surface warm front lurking across
northern Lower could see some funkiness if storms can interact with
that. Cold/occluded front then crosses Lower Michigan during the
afternoon...with perhaps a second round of convection if things can
destabilize again and will mention potential for two rounds of
strong storms in the afternoon Hazardous Weather Outlook. Locally
heavy downpours a good bet as well given precipitable water values
in the 1.50 to 1.75 inch range...though think convection will be
progressive enough to keep total rainfall amounts from getting out
of hand. Looking like a gusty day tomorrow especially assuming some
mixing during the day with southwesterly low level jet crossing the
forecast area. Non-convective wind gusts to 35mph appear to be a
good bet...with winds remaining gusty post-cold front into the
evening from the west/northwest before subsiding overnight as
pressure gradient flattens out.
Beyond Tuesday however the midweek period is looking dry...with
seasonable temperatures Wednesday and warmer on Thursday.
.LONG TERM...(Thursday night through Monday)
Issued at 355 PM EDT Mon Sep 13 2021
High Impact Weather Potential: Minimal as of now.
Pattern Forecast: Short wave trough moving into central Canada and
the northern Plains Thursday will clip the upper Lakes with some
height falls Friday...but the majority of the dynamics as of now are
getting pulled well north into Ontario. Associated cold front...as
it parallels the upper level flow...may also slow/stall in the
vicinity of Wisconsin/Michigan for Friday/Saturday. Rising heights
will then be the predominant feature to start next week as overall
pattern becomes more amplified with troughing in the west and
ridging in the east. Uncertainty with the position/strength of the
western trough which will ultimately have downstream impacts on
strength of the ridge over the eastern third of North America and
position of baroclinic zone which will set up across the nation`s
midsection.
Forecast Trends: Definitely warm especially this weekend with highs
in the 80s which could threaten a few records on Sunday. Rain
chances increase Friday and may linger into Saturday depending upon
&&
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1154 PM EDT Mon Sep 13 2021
SHRA/TSRA chances increasing tonight and Tuesday. IFR at times Tue
morning PLN/APN.
A front along the southern lower MI border will return northward,
with low pressure eventually lifting into the northern Great Lakes
on Tuesday. Sct SHRA/TSRA are expanding into nw lower MI, and
these will lift across the area tonight. Brief cig/vsby restrictions
possible, but at least for tonight VFR will be more common.
Toward morning, cigs should lower toward IFR conditions at
MBL/APN, before improving later in the day. Cold front passage
from w to e Tuesday afternoon will end the precip threat and
improve cigs.
Increasing se winds tonight will veer s and sw Tuesday. LLWS
MBL/TVC late overnight.
&&
.MARINE...
Issued at 355 PM EDT Mon Sep 13 2021
Winds and waves will strengthen to SCA criteria late tonight thru
Tuesday evening ahead of strong low pressure lifting northeast out
of the central plains into Lake Superior. Scattered showers and
storms are also possible in associated with this system as early as
this evening, but more so late tonight into Tuesday with a low
chance of a few severe storms.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY from 5 AM Tuesday to midnight EDT Tuesday
night for LHZ345>348.
SMALL CRAFT ADVISORY from noon Tuesday to midnight EDT Tuesday
night for LHZ349.
LM...SMALL CRAFT ADVISORY from 5 AM Tuesday to midnight EDT Tuesday
night for LMZ323-341-342-344>346.
LS...SMALL CRAFT ADVISORY from 5 AM Tuesday to midnight EDT Tuesday
night for LSZ321-322.
&&
$$
UPDATE...JZ
NEAR TERM...MG
SHORT TERM...JPB
LONG TERM...JPB
AVIATION...JZ
MARINE...MG
Area Forecast Discussion
National Weather Service La Crosse WI
1057 PM CDT Mon Sep 13 2021
.SHORT TERM...(Tonight through Tuesday)
Issued at 250 PM CDT Mon Sep 13 2021
Main forecast concern rests on the strong/severe storm question
tonight. Where various elements lay up/track will have a large
bearing on whether severe weather is realized, and what kind.
SETUP: Warm front currently lays out west to east across central IA
and northern IL with a band of low clouds just north of it. Gradual
progression northward today, with general consensus of making the
IA/MN border by 00z. Warm front should get a push northeast this
evening as upper level shortwave trough pushes into MN with
strengthening sfc low lifting through MN into northern WI overnight.
Low level jet/moisture transport kicks in before 00z, focusing
northward across the sfc front in NE IA/SE MN, also making steady
progress into northern WI as the evening wears on.
In addition, 900-800 layer of frontogenetic lift helping spark a
west-east narrow band of convection north of the sfc boundary,
progged to advance to I-94 by 00z.
INSTABILITY/SHEAR: steady, but limited advancement of instability
northward of the sfc front. RAP MUCAPES roughly 500-1250 J/kg, but
rather skinny profiles per RAP bufkit soundings (not great for
updrafts). 0-1 km shear pretty stout along front and to the south,
but CIN quickly increases this evening around and northward of the
front - limiting/inhibiting surface based convection (and tapping
into that shear and/or near sfc instability). 1-3 km shear roughly
20-25kts and upwards of 35 kts of 1-6km. All mostly due east. So
some storm organization possible.
SEVERE? Elements not syncing up well for severe storms. Surface
inhibition, timing, location of front, and CAPE profiles all working
against widespread severe storms. Certainly some strong, and
potentially a few severe - so need to keep a close eye on the radar
through the night.
Main threats are hail and wind, although wind will have to compete
with the near sfc stability.
With good turning and strong shear in the 0-1km layer, cannot rule
out an isolated tornado around the warm front. Short window/location
for that - looking like the I-90 corridor at this time,
.LONG TERM...(Wednesday through Monday)
Issued at 250 PM CDT Mon Sep 13 2021
An upper-level ridge builds across the region on Wednesday,
providing sunny and seasonable weather. Calm winds from this high
pressure will likely result in valley fog development Wednesday
morning. An upstream trough axis associated with lower heights in
Canada digs eastward across the northern plains on Thursday.
Associated surface boundaries begin to interact with our forecast
area late Thursday into Friday. Severe threat continues to look
minimal with the primary MLCAPE & shear axes focused along the cold
front north and west of our forecast area.
Due to the ostracized nature of the primary upper-level forcing,
models hint at the surface cold frontal boundary becoming stranded
for the weekend into early next week leaving our forecast area in
the warm sector. The previous few EPS runs have been alluding to
high temperatures in the mid to high 80s for Sunday and Monday as
well as the potential for unseasonably warm low temperatures. It
will be important to continue monitoring for unseasonably warm
temperatures.
&&
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1057 PM CDT Mon Sep 13 2021
The initial convection this evening has primarily stayed to the
north of both sites other than a few sprinkles. Watching a second
line farther west ahead of a developing area of low pressure and
cold front. This activity is expected to push through overnight
with the bulk once again going north of both sites. However, there
should be a broken line along the cold front that could bring a
couple hours of showers and maybe a storm to the area. IFR/MVFR
ceilings already in place behind the area of low pressure and
these will likely spread over both sites late tonight or early
Tuesday morning as the winds swing around to the west with the
passage of the front. Ceilings should go up to MVFR by late
morning with these clouds then scattering out around sunset.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...Rieck
LONG TERM....JAR
AVIATION...04
Area Forecast Discussion
National Weather Service Cheyenne WY
531 PM MDT Mon Sep 13 2021
.SHORT TERM...(This evening through Tuesday)
Issued at 225 PM MDT Mon Sep 13 2021
Showers and thunderstorms associated with the vort max passing
over the region this morning have moved off to the east into
north- central Nebraska this afternoon. A few collapsing showers
produced wind gusts around 55 MPH near and west of Cheyenne right
around 18z. Skies have mostly cleared across SE WY and the NE
Panhandle, but scattered cumulus development has begun across
Carbon Co and the North Laramie Range. Additional showers and
thunderstorms are possible late this afternoon into tonight. Main
focus for late this afternoon will be along the CO/WY border where
additional shortwave energy will pass over the area with marginal
instability around 500 J/kg MLCAPE and 40 kts of 0-6 km shear.
Main hazards will be strong outflow winds with dry downbursts as
LCLs look to sit well above the freezing level, especially west of
I-25. Storms currently located north of Vernal, UT could continue
to approach southwest Carbon Co in the next few hours around 23z
so will need to keep watch. Hi-Res guidance continues to hint at
storms mainly along the I-80 corridor from Laramie to Sidney after
6 PM MDT to around midnight. Lastly, a secondary cold front north
of the CWA will continue to slide south providing the potential
for showers and thunderstorms overnight into early Tuesday morning
along the Pine Ridge area from Niobrara Co over to Chadron.
NAMNest is much farther south compared to the HRRR with the
location of these storms (~50 mi) so will all depend on placement
of best forcing after midnight. Clouds will continue to linger
around the NE Panhandle through much of the morning while most
areas east of the Laramie Range will see cooler temperatures (5-
10F) compared to today.
.LONG TERM...(Tuesday night through Monday)
Issued at 225 PM MDT Mon Sep 13 2021
Key Messages:
1) Well-above normal temperatures Wednesday through Sunday with near-
critical to critical fire weather conditions for portions of the
area each day.
2) A colder period looks to be possible early next week with
increasing precipitation chances but details on pattern and sensible
weather remain for just how cold and what type of precipitation
could be possible, especially for higher terrain locations.
Weather Details: Global model and ensemble consensus indicate a
broad flat H5 ridge to zonal flow across the Central Rockies to the
SW CONUS in place. H7 Temperatures will be above normal in the +13C
to +16C range over WY/NE. This will lead to above normal to almost
record temperatures mid to late week and towards the weekend. Ridge
slowly breaks down across the SW CONUS and SW flow develops across
central Rockies by the weekend with deeper Pacific NW trouging.
Embedded shortwave impulses are likely but overall precipitation
chances will be minimal with the dry air mass and weak forcing.
Elevated to critical fire weather conditions will be likely across
the region with red flag warnings probable.
A larger pattern change is advertised for Monday and Tuesday of next
week with deterministic GFS showing a deeper trough across the
Central Rockies with a solid cold tap from Canada with H7
temperatures falling below 0C to -3C. Latest deterministic ECMWF is
a little slower but coming on board with a deeper trough similar to
the GFS. Ensemble guidance in long term also hints at a cooler trend
with increasing preci[itation chances with the approach of the
trough signal. Too far out to go into sensible weather details but
snow levels looks to drop near 8/9KFT and while low at this time,
there is a hint of wintry possibilities for at least higher terrain
locations early next week. Stay tuned through the week as model and
ensemble solutions narrow in early next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 523 PM MDT Mon Sep 13 2021
Southeast WY (KCYS, KLAR, KRWL): Showers and thunderstorms possible
this evening and into the early overnight hours in southeast Wyoming.
Winds will diminish and gusts should subside as the evening progresses.
Expect skies to clear overnight in southeast Wyoming as this system moves
out of the region.
Nebraska Panhandle (KCDR, KBFF, KAIA, KSNY): Isolated showers and
thunderstorms are possible at KSNY this evening likely after 3Z.
Gusty and erratic winds are possible with these. Another line of
showers are expected to move through in the early morning hours
from the northwest, moving south/southeast. Ceilings and
visibilities may temporarily be lowered to MVFR or even IFR
levels. More confidence with these impacts will come with the 6Z
TAFs. After those showers move through, skies should begin
clearing by mid-afternoon.
&&
.FIRE WEATHER...
Issued at 225 PM MDT Mon Sep 13 2021
Scattered showers and thunderstorms are possible this afternoon
and overnight with a few storms lingering around the northern
Nebraska Panhandle through Tuesday morning. Afterwards, elevated
to near critical fire weather conditions are possible the rest of
the week into this weekend with drier weather expected. Afternoon
RHs will drop to into the teens for most areas Wed-Sun with near
to above normal temperatures. Gusty winds along and west of the
Laramie Range are expected during this period so may need to
monitor for potential issuance of RFW products in future updates.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...MB
LONG TERM...JSA
AVIATION...LK/SF
FIRE WEATHER...MB
Area Forecast Discussion
National Weather Service Des Moines IA
643 PM CDT Mon Sep 13 2021
...Updated 00z Aviation...
.DISCUSSION.../Tonight through Monday/
Issued at 241 PM CDT Mon Sep 13 2021
Forecast Highlights:
-- A few strong to severe storms northern Iowa tonight - main risk
is hail, but conditional, brief tornado cannot be ruled out
-- Perhaps a few strong storms far southern Iowa later Tuesday
afternoon
-- Pleasant Wednesday with seasonable temperatures/humidity
-- Return to warm, humid conditions late this week into this weekend
with a few opportunities for storms over northern Iowa
Details: Early afternoon surface analysis shows the warm front has
lifted to around Highway 20 and expect it to continue to lift to
near the Minnesota border by 0z Tuesday. Main shortwave trough is
moving east of the central Rockies and it is expected that as
surface low pressure traverses the front into Wisconsin this
evening, the low will be deepening. The risk for storms will likely
be delayed until better forcing arrives with the shortwave and
surface low toward and likely after 0z over north central Iowa.
Upstream 12z RAOBs from ABR/OAX/UNR/LBF show a warm environmental
mixed layer centered around 850mb. This warm EML is above northern
Iowa and early morning and midday initialized forecast soundings
from the NAM, GFS, HRRR, and RAP at MCW and EST show that this will
persist over northern Iowa likely limiting any surface based
convection. Shortly after sunset, model soundings all indicate the
EML remains and is enhanced/aided in strength as the boundary
layer decouples from the surface. With increasing inhibition/CIN
through this evening, storms over northern Iowa will at least not
fully be rooted at the surface with parcels being accelerated from
an elevated surface. This should limit the tornado potential, but
more on that in a moment. Elevated rotating storms will be
possible with deep layer shear over 40 if not closer to 50 knots,
though the effective inflow layer shear will be closer to 30
knots. While the main threat will be large hail and perhaps gusty
winds if the winds can make it to the surface, a conditional
tornado risk could briefly evolve this evening. With linear
segments expected to move across northern Iowa and possibly
favorable 30+ knot 0-3km shear orientation to the line, if a storm
can become or stay surface based, then a brief tornado is
possible. Latest runs of the 12z HREF members show only the HRRR
with updraft helicity tracks over far northern Iowa and given the
expected location of the warm front this evening, risk for any
tornadoes would be over our most far northern counties into
southern Minnesota. So, while the current forecast thinking is
that large hail will be the main concern, cannot rule out a brief
tornado and have coordinated with SPC to maintain the 2% tornado
at the 1630z update near/at the border. These storms should be
largely east of the forecast area around or shortly after
midnight.
Another shortwave trough moving east of the Cascade Mountains this
afternoon will be the impetus for additional storms across the
region later Tuesday. Scattered storms will develop along and
perhaps behind the front over far southern into far eastern Iowa
Tuesday afternoon and evening. For our forecast area, the 9z RAP/12z
NAM both have most of the storms developing near the Missouri border
if not over northern Missouri. Most of the latest convective
allowing model guidance agree that the more robust convection will
be close to exiting the forecast area with perhaps some elevated
showers or storms post frontal over southern Iowa. Thus, any window
for severe storms will be short-lived as the front moves into
Missouri.
As this shortwave trough moves eastward, surface high pressure will
move over the region Tuesday night through Wednesday. This will
provide a comfortable September day with low humidity and highs a
few degrees below normal ranging from the middle 70s over northern
Iowa to near 80 degrees over southern Iowa on Wednesday. The high
pressure exits into the Northeastern US Wednesday afternoon with
return flow from the south and later southwest allowing for
increasing heights/temperatures and moisture. This flow change will
also be aided by a longwave trough that will move primarily across
Canada and the far northern states. This may allow for a few
opportunities for storms Thursday night through early Saturday as
temperatures rise well into the 80s over central and southern Iowa
with dewpoints into the 60s statewide. 00z WPC cluster analysis of
the GFS, CMC, and ECMWF and their ensembles show the most likely
place for any QPF over northern Iowa and then northward into the
eastern Dakotas, Minnesota, and Wisconsin. Thus, PoPs from initial
guidance are highest in our forecast area over northern Iowa with
southern Iowa likley missing out on much if not all of the rainfall.
Instability and shear are favorable during this period so will need
to monitor trends for any severe potential late this week.
The next chance for rain and storms would be late in the weekend
into early next week as a more amplified longwave trough pushes
equatorward and through the central Rockies. Given the robustness of
the trough and amplified flow, this should yield widespread
rainfall and possible stronger storms early next week as the front
moves through the region.
&&
.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 636 PM CDT Mon Sep 13 2021
There is a warm front across north-central Iowa that will be the
focus for rain shower and thunderstorm development later this
evening and maybe overnight. This will present at least vicinity
impacts to FOD and MCW, and maybe ALO. Conditions across northern
and central Iowa will drop to low-end MVFR, and there may be an
hour or two of IFR ceilings across northern Iowa. By late Tuesday
afternoon, skies may remain overcast but will begin to improve to
MVFR. There will also be low-level wind shear concerns this
evening as the low-level jet strengthens.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Ansorge
AVIATION...Krull
Area Forecast Discussion
National Weather Service Quad Cities IA IL
919 PM CDT Mon Sep 13 2021
.UPDATE...
Issued at 901 PM CDT Mon Sep 13 2021
Have updated forecast to bump up storm chances tonight mainly near
and north of Hwy 30 corridor. Storms have developed over the past
60 mins between Sioux City and Omaha ahead of a cold front, and
approaching shortwave with additional lift from left exit region
of an upper level jet streak. Latest guidance is showing more
favorable forcing between the jet streak and wave overnight
especially across our northern counties, and last few runs of
HRRR appear to be latching onto this and baring out an uptick in
convection after 06z-07z N/NW counties. Small hail, gusty winds
and heavy downpours possible with a low risk for an isolated severe
storm.
&&
.SYNOPSIS...
Issued at 242 PM CDT Mon Sep 13 2021
Another beautiful day out there for much of the forecast area, with
some high clouds moving through and temperatures in the mid 80s.
Dewpoints are a little higher today, making it a little bit stuffy,
but far from oppressive. Areas in our northern tier of counties
continue to see some scattered showers moving through. Winds are
generally light and from the south, as the cold front that stalled
over our area overnight developed warm frontal characteristics and
has since pushed to the north. On the northern end of this boundary,
showers and thunderstorms continue, but mostly sunny and dry
conditions will be seen south of it. Through the remainder of the
evening, most of the area should stay dry, with some clouds
filtering through the area.
&&
.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 242 PM CDT Mon Sep 13 2021
Tonight, warm front has since lifted to our north and we sit within
the warm sector of the surface low out west. The weak wave in our
west will slowly makes its approach, with a cold front progged to
move through early tomorrow. The warm front in our north will set
the stage for another night of potential showers and storms north
of Highway 20. Most of the activity should stay to the north of
our forecast area, but a stray shower or storm cannot be ruled out
once the strengthening LLJ kicks in after dark. With strong warm
advection taking place over the area and clouds moving in ahead of
an approaching cold front, temperatures will stick in the upper
60s and low 70s in the area. Breezy southerly winds are expected
to continue through the night, as short term guidance indicates a
strengthening pressure gradient ahead of the front. This can lead
to gusts upwards to 20-25 mph at times. This will generally be
late in the night and closer to tomorrow morning.
Tomorrow, we will see a bit of a change. The cold front is progged
to start its push through our area mid-morning and be out by mid
afternoon. Given the timing of frontal passage, not much moisture
return, and relatively weak forcing, most of the area is likely to
stay dry tomorrow. Thus, I have cut back on PoPs for much of
tomorrow, generally keeping most in a slight chance, with the best
chances in our far southeast. The severe risk has also been pushed
out of our area, leaving us in a general thunderstorm outlook. Some
of the short term guidance hints at some showers developing mid day,
but this will generally be seen in our southern half of our forecast
area, where the moisture return is greatest and we can get some
daytime heating. Otherwise, there will be scattered clouds as the
front pushes through and some gusty winds out ahead of it. While a
slight temperature change will be felt tomorrow, the biggest change
will be felt tomorrow night and the following day.
.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 242 PM CDT Mon Sep 13 2021
Key Messages:
1. Confidence increasing on cold front being well south of the area
Tuesday evening and dry forecast
2. Increasing heat and humidity the rest of the period.
3. Low end pops to end the week
Discussion:
Zonal changing to SW flow is expected through the long term period
as the main message is hot and humid to continue. To start the
period a cold front will bring in a short reprieve to the heat and
humidity Wednesday into Thursday, then the heat returns. A cold
front is still forecast to glance the area later in the week and
continues to have low chc/schc pops associated with it. When it
comes down to it we will likely see dry conditions through most of
the long term period.
With the exception of the FV3 models, it appears that all of the
cams have us dry after 00z Wednesday as the front is well south of
the area. This is looking even more likely as festering convection
today has only resulted in the warm front mixing 60 miles north from
this morning. The FV3 brings an east to west moving MCS system
along the sfc cold front. Overspreading north of this boundary
leads to some pops across our area. Since only the FV3 model has
this, I don`t think it is likely. It will be one of those mental
models where if you see it occurring out west, then may need to
increase pops after 00z Wednesday. This system appears to be tied
to the upper wave and could lead to organized convection/updrafts
and strong storms if it happens. This would represent a low end
chance forecast.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
ISSUED AT 708 PM CDT Mon Sep 13 2021
A cold front is slated to push through the terminals Tuesday AM
12z-17z. Ahead of the front tonight expect S/SW winds occasionally
gusty, especially prior to sunset then again by late evening into
the overnight with a strengthening low level jet. The stronger
winds aloft of around 40-45+ kts descending to 1500-2500 ft agl
warrants a continuation of LLWS at all terminals roughly 06z-12z.
Can`t rule a few showers or storms ahead of the front, especially
at KCID and KDBQ with a warm advection wing attendant to low
pressure passing north of the region. However, chances look to be
lower than PROB30 at this time and therefore no mention was included.
Winds will veer to W/NW with the frontal passage Tuesday AM and
gust for a period to around 20-25+ kts, especially at KCID and
KDBQ before generally settling into 10-15 kt range. MVFR to local
IFR ceilings are likely to develop behind the front especially
upstream of the terminals. There is the potential for a period of
MVFR ceilings at KDBQ and KCID by mid AM through midday as hinted
by some guidance, but there`s a lot of guidance keeping these
lower clouds just north of the terminals. Also, frontal timing
during the daytime lends to potential for some mix out of the
moisture. As a result, confidence is not high enough to mention
MVFR ceilings yet at KCID and KDBQ.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
UPDATE...McClure
SYNOPSIS...Gunkel
SHORT TERM...Gunkel
LONG TERM...Gibbs
AVIATION...McClure
Area Forecast Discussion
National Weather Service Goodland KS
945 PM MDT Mon Sep 13 2021
.SHORT TERM...(This evening through Wednesday)
Issued at 244 PM MDT Mon Sep 13 2021
This afternoon, weak shortwaves are traveling along zonal flow
across the High Plains. These shortwaves are helping to push a weak
cold front east across the area while a lee trough sits along the
Rockies. As of 2 PM MT, the front is pushing across NW Kansas,
causing some breezy conditions with winds gusting up to 35 mph
along/ahead of the front. Today`s environment is more of a high
shear-low CAPE setup. CAPE values are less than 1000 J/kg over
eastern CO where this afternoon and evening`s storms are expected to
develop over the next several hours. CAPE does increase as you move
east into NW KS and S NE this evening. Shear isn`t much of an issue
with 20-40 kts across the area for locations west of US-83. Model
soundings and other convective parameters are favoring more of a
strong to damaging wind hazard with any convection that develops;
however, given a decent amount of moisture in the mid-levels large
hail can`t be ruled out during the early evening hours. The storms
are expected to move east through the overnight hours, with a few
more showers/storms possibly developing along and east of US-83
after sunrise. It`s possible these storms remain elevated as they
ride along the back of today`s front.
A moist airmass is expected to remain over the area on Tuesday while
another cold front moves south from the Northern Plains. As the
front moves down, the lee trough will push off the rockies during
the afternoon aiding with the development of storms during the
afternoon hours. Despite being cooler, the environment seems more
favorable for storms tomorrow afternoon. The CAMs are still
disagreeing on how storms move across the area, with the HRRR being
the most aggressive with a small line of storms developing off the
Front Range and moving across the area south of I-70. The 3km NAM
keeps us capped, despite an otherwise favorable environment.
Damaging winds and hail are also a threat tomorrow afternoon. If
these storms develop, they are expected to move out of the Tri-State
area by midnight. Dry conditions will return on Wednesday as a
surface high pushes south behind the front and the ridge builds over
the Western CONUS.
.LONG TERM...(Thursday through Monday)
Issued at 132 PM MDT Mon Sep 13 2021
The long term period looks to be warm and dry for the time being.
Upper ridging builds into the southern and central Plains on
Thursday from the Desert Southwest, leading to southwest flow aloft
by Friday. Meanwhile, an upper trough comes ashore over the Pacific
Northwest. This disturbance helps to amplify the ridge and gradually
shift it eastward through the weekend. On Monday, southwest flow
strengthens above the region between the incoming trough and
departing ridge.
Fire weather conditions will be the main concern during this
timeframe. While it is still a bit early to get too specific,
elevated to near critical conditions are possible each day of the
period. The area of most concern looks to be eastern Colorado on
Thursday, Friday, and perhaps Monday. However, the two days that
stand out the most are Saturday and Sunday, when relative humidities
fall as low as 10 to 20 percent for locations along and west of
Highway 25. Will continue to monitor in the coming days as winds
appear to be marginal at this time.
High temperatures range in the upper 80s to mid 90s for Thursday
through Sunday. Low temperatures are mainly in the low 50s to mid
60s through the period.
&&
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 945 PM MDT Mon Sep 13 2021
For the 06Z TAF time period scattered showers and thunderstorm
potential exists for KGLD through 09Z per recent runs of CAMS
however seems to have overdone reflectivity thus far this evening.
Shower and storm potential for KMCK still appears to be on track
with convection entering the radius of the terminal around 06Z.
Guidance indicates the potential for the threat of storms through
sunrise with additional chances lingering through the majority of
the day Tuesday. I opted to mention VCSH through at least mid
afternoon as numerous runs of CAMS have shown this solution. Tuesday
afternoon KGLD may see storms, perhaps severe with large hail and
damaging winds the main threat during the late afternoon. This
threat for KMCK looks to remain to the SW of the terminal so opted
not to mention the threat in the TAFS at this time. Winds during the
afternoon will gradually shift from from northerly to more ENE
during the afternoon and persisting through the end of the TAF
period.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
SHORT TERM...KMK
LONG TERM...JBH
AVIATION...TT
Area Forecast Discussion
National Weather Service Green Bay WI
547 PM CDT Mon Sep 13 2021
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Tuesday
Issued at 159 PM CDT Mon Sep 13 2021
The latest RAP analysis and satellite/radar imagery show a stalled
front positioned east to west across northern Illinois. Areas of
showers and storms have been developing north of the boundary at
times today. Farther north, southeast winds have contributed to a
field of broken convective clouds over northeast WI early this
afternoon. These clouds are relatively shallow and should mix out
later this afternoon. The next storm system is tracking east
across the northern Plains with widespread showers and storms. As
this system moves across the region tonight, details surrounding
storm chances and potential for severe weather is the focus of
this forecast.
Tonight...Shortwave energy will be moving across the northern
Mississippi Valley this evening and across northern WI overnight.
Ahead of the wave, a developing surface low and strengthening
south to southwest flow will push the stalled front northward
across Wisconsin this evening. Models, in general, are
unenthusiastic about thunderstorm development along this front as
it shifts north. But with elevated instability up to 1000 j/kg and
thunderstorm activity ongoing along it for much of the morning,
maintained chances in the forecast. The main swath of
showers/storms will sweep across the area after midnight. Strong
dynamics thanks to a 40-50 kt low level jet will advect elevated
instability of 1000-1500 j/kg across central to northeast WI ahead
of the surface low. This could lead to thunderstorm clusters with
bowing segments. The severe potential is relatively unclear,
however, due to the rather skinny nature of the instability
(limits hail potential) and an inversion centered around 900mb
which will make it difficult to get downburst winds to the
surface. But given the strong dynamics at play, think an isolated
severe threat could develop overnight. The heaviest rainfall will
likely occur over northern WI where amounts upwards of 1 inch may
fall. Lows ranging from the middle 50s to lower 60s.
Tuesday...The surface low will exit early in the morning, while
the trailing cold front will take until midday to exit the region.
Widespread low clouds will likely hang around northern WI for a
good chunk of the morning, and could be accompanied by drizzle at
times. Partial clearing is expected in the afternoon, with more
sunshine across the south than the north. Highs ranging from the
mid 60s north to mid 70s south.
.LONG TERM...Tuesday Night Through Monday
Issued at 159 PM CDT Mon Sep 13 2021
High pressure should bring mainly dry conditions Tuesday night
through Wednesday night, along with near normal temperatures.
Patchy/areas of fog are possible over north central and central WI
late Tuesday night into early Wednesday morning.
Precipitation chances for the extended forecast will occur in
association with a couple frontal passages. The first front is
expected to slowly move through the forecast area Thursday night
into Friday, then linger nearby into Saturday morning. This
front, combined with jet and short-wave energy, should bring a
chance of storms through the period. Another front is progged to
approach the region on Monday, and may bring another chance of
storms. Precise details are uncertain, given lingering timing
issues with the models. Temperatures are expected to trend well
above normal for the weekend and early next week.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 547 PM CDT Mon Sep 13 2021
A stalled frontal boundary is expected to lift northward tonight
as a warm front. A few showers and isolated thunderstorms have
develop to the north of this front along with some brief MVFR
ceilings.
As a stronger low pressure system and associated cold front
approach from the west toward midnight, expect widespread showers
and thunderstorms to slide through each of the TAF sites from west
to east. Made minor adjustments to shower/thunderstorm timing.
Otherwise, lower ceilings are anticipated with the increasing
low-level moisture and precipitation. MVFR and a few IFR
observations have been noted with this system across Minnesota and
the Dakotas.
Flight conditions will be slow to improve on Tuesday morning, but
its possible conditions will improve to VFR by midday or early
afternoon Tuesday as the cold front exits the area.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from 4 AM CDT Tuesday through Tuesday
afternoon for WIZ022-040-050.
&&
$$
SHORT TERM.....MPC
LONG TERM......Kieckbusch
AVIATION.......Cooley
Area Forecast Discussion
National Weather Service Lincoln IL
913 PM CDT Mon Sep 13 2021
.SYNOPSIS...
Issued at 251 PM CDT Mon Sep 13 2021
Hot and humid conditions will continue into the day Tuesday ahead
of an approaching cold front. Scattered showers and storms are
expected across portions of central Illinois Tuesday afternoon and
evening as the front moves across the region. Precipitation
chances linger into the day Wednesday, then expect dry conditions
through the remainder of the week.
&&
.UPDATE...
Issued at 829 PM CDT Mon Sep 13 2021
A surface warm front, which has been hung up along the IL/WI
border this evening, will begin to lift northward overnight as a
robust mid- level shortwave trough lifts into the Upper-
Mississippi Valley. This disturbance will help drive the surface
cold front into the Illinois River Valley by Tuesday morning. The
boundary layer will become moist and unstable by afternoon as a
plume of low 70s surface dewpoints advect into the region and pool
ahead of the cold front. MLCAPE values from the RAP exhibit
2000-2500 J/kg by late afternoon. Meanwhile, deep layer shear is
progged between 30-40 kts thanks to an upper-level speed max
nosing into the region from the west. This all adds up to a period
of deep, organized convection tomorrow evening, mainly for
locations east of I-55. Damaging wind gusts remain the prime
severe weather threat, with hail and tornado looking less likely
due to a skinny distribution of CAPE and straight-hodograph.
&&
.SHORT TERM...(This evening through Tuesday)
ISSUED AT 251 PM CDT Mon Sep 13 2021
This afternoon, a warm front is draped roughly along the IL/WI
state line with thunderstorm chances mainly north of the front
this evening and tonight. Across central Illinois, fair weather
will persist with a modest south breeze expected through the night
helping to prop up temps with overnight lows in the lower to mid
70s.
Low pressure over the central Great Plains this afternoon will
track across the Great Lakes Tuesday pushing a trailing cold
front across central Illinois. Ahead of the front, temperatures
warming into the upper 80s with dew points in the lower to mid 70s
will contribute to moderate diurnal instability with MLCAPE
values increasing to around 1500-2000 J/kg. Meanwhile, deep layer
shear will be marginal, but increases through the day to around
25-30 kt in the vicinity of the front during the afternoon.
Guidance is in reasonably good agreement that thunderstorms will
initialize along the front mid afternoon between the Illinois
River Valley and the I-57 corridor. Steep 0-3 km lapse rates of
7.5-8.5 C/km will support efficient mixing down of winds and
support a damaging wind threat with stronger storms. If shear is
able to be strong enough to support a few supercells, an isolated
hail/tornado threat will also be present.
.LONG TERM...(Tuesday night through Monday)
ISSUED AT 251 PM CDT Mon Sep 13 2021
By Wednesday morning, the slow moving front is expected to stall
near or just south of the I-70 corridor. A broad 500mb trough will
move across the region Wednesday providing additional chances for
showers and storms in the vicinity of the front, mainly south of the
I-72 corridor. Guidance suggests modest instability up to around
1000 J/kg MLCAPE will be in place near the front Wednesday
afternoon, but deep layer shear will be diminishing through the day
as the upper jet pulls away across the Great Lakes. 0-6km shear
values of 15-25 kt during the afternoon hours will be a limiting
factor in terms of any organized severe threat Wednesday.
After a brief moderation of temperatures Wednesday with passage of
the cold front, upper ridge builds back across the region while the
h85 thermal ridge builds just to our west and northwest through the
weekend. Veering low level flow and building heights will push
afternoon highs back into the mid to upper 80s Friday though
Monday. While couldn`t completely rule out some isolated diurnal
thunderstorm development, most of this time frame will be dry.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 611 PM CDT Mon Sep 13 2021
VFR conditions will continue through much of this TAF period ahead
of an incoming cold front that will impact the regional terminals
Tuesday evening. Breezy south to southwest winds will gradually veer
westerly beyond 21z/4pm Tuesday as the cold front pushes through
the region. Confidence and coverage are high enough to include
vicinity thunder mention in the TAFs with the arrival of the
front.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...MJA
SYNOPSIS...Deubelbeiss
SHORT TERM...Deubelbeiss
LONG TERM...Deubelbeiss
AVIATION...MJA
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
838 PM EDT Mon Sep 13 2021
.SYNOPSIS...
High pressure will remain anchored offshore through much of the
week. A backdoor cold front will approach from Pennsylvania tonight,
then retreat northward as a warm front Tuesday. Low pressure may
develop near the Carolina coast Thursday into Friday as a weakening
cold front approaches from the Great Lakes. This boundary
eventually stalls and remains well to the west of the region
over the weekend.
&&
.NEAR TERM /THROUGH TUESDAY/...
Clear skies and calm winds will be the story tonight, along with
warm and humid conditions. Low temperatures will be 10-15
degrees above normal for early to mid September. Given the
humidity, paired with calm winds and clear skies, could see some
valley fog west of the Blue Ridge. Otherwise a dry night, as the
convective activity mentioned in the previous forecast is
expected to stay well to our north. The MCS is currently over
east-central PA moving into northern NJ, and should pose no
threat to northeast MD. Given the continued unbreakable cap
present in the 00z IAD sounding, no amount of outflow is going
to get anything going tonight in our region.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
On Tuesday, a flat upstream trough is forecast to be crossing
through the Upper Great Lakes while what is Tropical Storm
Nicholas tracks toward east-central Texas. Over the course of
the following 24 to 36 hours, the former trough will accelerate
toward the northeastern U.S. with weak to neutral height falls
grazing the Mid-Atlantic states. While the more discernible
severe weather threat is more focused over New England, some
strong to severe convection may fire in advance of the cold
front over western Maryland and the eastern West Virginia
panhandle. There are some hints that mid-level vorticity centers
from the circulation of Nicholas may become ingested into this
trough by late Wednesday. This could easily augment some of the
lift along the advancing trough/frontal zone. Thus, the best
chance for showers and thunderstorms will be Wednesday afternoon
into the early overnight hours. While some non-zero convective
threat exists the prior day, robust instability will again be
offset by capping issues. Have maintained convective chances
along the Alleghenies with conditions more uncertain downstream.
The 12Z HRRR maintains the mid/upper plume of smoke into Tuesday
which could again offset high temperatures by a degree or two.
The current forecast calls from highs in the low 90s which is
around 8 to 12 degrees above average. A few additional clouds
the following day could trim numbers off a tad leading to more
widespread upper 80s, locally into the low 90s. The persistence
of modified tropical air over the region will keep mild
overnight lows. Expect low 70s inside I-95 with 60s elsewhere.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
A mid-level trough of low pressure across the region will be the
focal zone of possible shower and thunderstorm development on
Thursday. Shower and thunderstorm coverage will be mainly isolated
and occur during the afternoon hours. Severe potential is low at
this time. High temperatures in the lower to middle 80s.
As we get into Thursday night through Friday night and as the trough
of low pressure breaks down some, a tropical disturbance could move
northward and offshore of the Outer Banks. Models have some
agreement that this tropical disturbance, whether develops or not,
stays offshore of the Outer Banks before slowly moving out to sea
offshore of the lower Delmarva Peninsula and Tidewater of Virginia.
It is still early to rule out any impacts to our region from this
disturbance, but until it reaches the offshore, we need to monitor
it for any further development. Temperatures Friday will top out in
the middle 80s.
By the weekend of Saturday into Sunday, considering tropical impacts
could be lessened or nil, high pressure will make an attempt to
build into the region and bring drier air and tranquil temperatures
our way. Highs in the middle 80s.
&&
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
VFR conditions are anticipated through tonight across most of
the terminals. The only exceptions may be over KMRB with some
reduced visibility due to patchy fog. Given the anomalous low-
level moisture, calm winds, and mostly clear skies, fog could
become a bit more widespread than advertised. Otherwise, not
expecting any restrictions on Tuesday before sub-VFR conditions
are possible at times on Wednesday afternoon and evening due to
showers and thunderstorms. Regarding winds, they should
gradually shift to southerly for Tuesday and Wednesday.
Should the terminals encounter a Thursday or Friday afternoon heavy
shower or thunderstorm, then conditions may be temporarily MVFR.
Otherwise, expect VFR conditions with winds generally southeast
becoming northeast 5 to 10 knots throughout the period.
&&
.MARINE...
Increasing southerly flow on Tuesday evening and into Wednesday
should lead to channeling of the winds. Thus, SCAs will likely
be needed for that time period. Additionally, the threat for
convection on Wednesday may warrant Special Marine Warnings with
any of the stronger storms.
No marine hazards expected at this time Thursday through Friday
night. Should there be a close influence from a tropical disturbance
moving north offshore the mid-Atlantic region Friday into Friday
night, then we could see Small Craft Advisories. It is a little
early to make this confidence concrete.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.
&&
$$
SYNOPSIS...BRO/DHOF
NEAR TERM...BRO/CJL
SHORT TERM...BRO
LONG TERM...KLW
AVIATION...BRO/KLW/CJL
MARINE...BRO/KLW/CJL
Area Forecast Discussion
National Weather Service Las Vegas NV
816 PM PDT Mon Sep 13 2021
.SYNOPSIS...Dry conditions and temperatures several degrees above
seasonal averages continue through the week as afternoon breezes
pick up in the afternoons. The second half of the week will be
characterized by gradually decreasing temperatures and elevated
southwest winds each afternoon.
&&
.UPDATE...Allowed the Excessive Heat Warning and Red Flag Warning to
expire at the top of the hour.
Noticed visibility and air quality deteriorating in the Owens
Valley due to smoke from the Walkers and KNP Complex wildfires along
the western slopes of the southern Sierra in Tulare County. Great
Basin Unified Air Pollution Control District currently indicates
moderate AQI at Bishop while further south Lone Pine and Keeler are
unhealthy for sensitive groups and unhealthy for all. With not much
wind forecast the next two days 00Z HRRR Smoke indicates it will
remain an issue through Wednesday.
&&
.DISCUSSION...Today through next Monday.
Gusty southwest winds have picked up across the region this
afternoon with speeds between 20 and 25 mph observed across southern
Nevada due to a weak 250 mb jet streak passing aloft. These winds
will peak through the afternoon before subsiding around sunset. As
such, the Red Flag Warning that is in effect through 8pm PDT remains
in good shape, as elevated wildfire danger existing in the Spring
Mountains and lower elevations of Clark County.
Additionally, temperatures this afternoon are forecast to reach
between 5 and 8 degrees above seasonal averages, with portions of
the Colorado River Valley experiencing "High" to "Very High"
HeatRisk values this afternoon. An Excessive Heat Warning for Lake
Mead, Lake Mohave, and Lake Havasu persist through 8pm PDT tonight.
Those recreating on area lakes are encouraged to continue to hydrate
today, even if they`re not thirsty, and especially if they`re
consuming caffeine, alcohol, or drugs. Reminder that heat events
that occur at the end of the season like this one are likely to
result in an increased number of heat-related emergencies, as bodies
are exhausted from regulating internal temperatures during extreme
conditions all summer.
Windy conditions today will subside for Tuesday and Wednesday as
temperatures gradually decrease through the week as a dry, southwest
flow sets up over the region.
Models continue to differ regarding the weekend. The NBM continues
to remain dry, with breezy afternoon winds and afternoon
temperatures dropping into the 90s for the lower deserts, to all of
which I made no changes. An area of low pressure and associated
vorticity maximum may push inland across southern California next
weekend, with the GEFS Ensemble moving the vorticity maximum
directly across Las Vegas, and with the ECMWF Ensemble pushing it
out to sea. Additionally, as mentioned in the previous discussion,
the larger model disagreement persists regarding a trough pushing
inland across the Pacific Northwest. The strength and depth of this
trough will determine regional temperatures, wind speeds, and
precipitation chances, with increased fire danger likely.
&&
.FIRE WEATHER...A Red Flag Warning is in effect for much of Clark
County, Nevada, including zones NV-464 and NV-465, encompassing the
Spring Mountains until 8pm PDT this evening. Relative humidity
values in the single-digits will combine with sustained wind speeds
of 20-25 mph and critically dry fuels to create very high to extreme
wildfire danger.
&&
.AVIATION...For McCarran...Southwest gusts to 25 kts will persist
through the afternoon before waning around sunset. Winds for the
remainder of the TAF period will be light with diurnal trends. No
operationally significant cloud cover expected.
For the rest of southern Nevada, northwest Arizona and southeast
California...Southwest gusts to 25 kts will persist through the
afternoon for the Mojave Desert and Colorado River Valley before
waning around sunset. Winds along the Owens Valley and for the
remainder of the TAF period will be light with diurnal trends. No
operationally significant cloud cover expected.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
UPDATE...Pierce
DISCUSSION/AVIATION...Varian
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