Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/25/21
Area Forecast Discussion
National Weather Service Cleveland OH
943 PM EDT Sat Jul 24 2021
A warm front will move eastward across northwest Pennsylvania
late this afternoon. A cold front is expected to sweep across
the region on Sunday. High pressure will increase its influence
on the region from the west Sunday night with the high located
over Ohio by Monday night. The next cold front crosses the
region on Wednesday.
.NEAR TERM /THROUGH SUNDAY NIGHT/...
930 pm update...
We made some minor adjustments to the hourly pop chances during
the late evening and overnight time frame to better reflect the
latest radar trends and HRRR guidance with convection across
southern Michigan heading our way. The broken line of convection
will start to enter in our NW Ohio area around 2z and closer to
the lakeshore by 3z to 4z and south of the lakeshore and Ohio
Turnpike by 5z or 6z. The will be gradual weakening trend by 6z.
Warm front continues to move eastward across NW PA
taking the remaining showers with it. Our attention will then
shift to Michigan where a cold front will assist with the
initiation of thunderstorms through the evening. A few of these
storms during the evening could drift across NW OH and maybe
cross Lake Erie with some stronger wind gusts. For the most part
it looks like the storms will be decreasing in intensity as
they cross the region late this evening into the overnight.
However we will need to monitor closely. Brief heavy rainfall
will accompany the the thunderstorms that move southward through
the morning. Fortunately these storms should have a good
forward speed so the threat of flooding is low.
There should be enough breaks in the cloud cover this afternoon
to allow highs to reach the mid 80`s across the central and
western CWA. It will definitely feel much more humid into the
overnight. Lows tonight will be on the warm side with upper
60`s to lower 70`s common.
Outflow from the thunderstorms should move southward across the
CWA through the morning hours and should become the primary
focus for thunderstorms through the afternoon. So for now the
thinking is that most locations will be dry by mid afternoon.
One thing for us to monitor will be the actual cold front that
will lag its southward movement slightly. This boundary could
generate a few showers late afternoon into the early evening
across the southeastern half of the CWA. COnfidence is not high
in this potential but it is something for later shifts to
monitor. Highs on Sunday look to be in the 80`s for most
High pressure is expected to increase its influence on the
region Sunday night. Clearing skies, light winds and recent
rainfall may allow for fog formation early Monday morning. Lows
will range from the lower 60`s across inland NW PA to near 70
along the lakeshore.
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
By Monday morning, west to northwest flow aloft will be entrenched
across northern Ohio and northwest Pennsylvania. Precipitable water
values will range from 0.8 to 1 inch across the forecaster area and
deeper moisture will be displaced south from Mid Mississippi Valley
to Mid Atlantic state line early Monday. Surface high is expected to
be positioned over central Illinois on Monday. Expecting dry
conditions with temps slightly above norms for lows and highs Monday
and early Tuesday.
Upper level ridge over the plains is expected to build and amplify
yielding a more northwest flow across the Great Lake region. Euro
and GFS are showing a wave diving southeast from Lake Superior to
Lake Ontario late Tuesday. This feature may yield a few showers and
isolated thunderstorms across the forecast Tuesday afternoon and
Tuesday night. Surface base capes of 1500 to 2000 j/kg Tuesday
afternoon and 800 to 1000 j/kg Tuesday night may be in play.
Precipitable water values are expected to rebound to 1.25 to 1.5 by
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Lingering showers and a few storms are possible across the central
Ohio Wednesday morning. The synoptic pattern will remain in place
through the week with the ridge building over the Plains. This will
allow the trough remain over the northeast and northwest flow over
the forecast area through week. Precipitable water values will
decrease with the passage of the wave Tuesday night...expecting
values to drop to slightly below 1 inch Wednesday afternoon and
rebound Wednesday evening. As a result, moisture will increase from
west to east Wednesday night into Thursday. A stronger wave is
expected dive southeast and track across the forecast area Thursday
morning. A possible thunderstorm complex is possible associated with
this wave. There is still a great deal of uncertainty with the
placement of the initial convection on Thursday. Will maintain rain
chance with thunderstorms for Thursday and linger into Friday.
High temperatures for this period will begin in the mid to upper 80s
on Wednesday and a slight cool down to the low to mid 80s by Friday.
Overnight lows will also follow a gradually cooling trend, beginning
in the mid to upper 60s on Wednesday night to the low to mid 60s on
Thursday night into Friday morning.
.AVIATION /00Z Sunday THROUGH Thursday/...
Generally VFR ceilings this evening will transition to MVFR
ceilings with a broken line of showers and storms associated with
a cold front moving through the region overnight. MVFR ceilings
will linger through much of Sunday morning with a improvement
back to VFR conditions around midday Sunday through the
afternoon. TEMPO have been timed accordingly for each TAF site
with a 2 hour window for the likely impacts of lower
visibilities and ceilings with the heavier downpours. It appears
this convection will be on the weakening trend as it starts to
move into local area overnight. Southwest winds this evening
around 5 to 10 knots will gradually become westerly overnight
initially with the front passage. Winds on Sunday will become
northwest around 5 to 10 knots.
Outlook...Non-VFR possible in fog Monday morning. Non-VFR also
possible in showers/thunderstorms Tuesday night into Wednesday.
Southwest winds of 10-15 knots as the warm front moves across the
lake this evening. Waves should remain between 1-3 feet. A cold
front will move east across Lake Erie on Sunday. This will yield a
wind shift to east to northeast or 5-10 knots. High pressure will
build across the lake behind the frontal passage which will allow
calm conditions across the lake to persist through mid-week. Due to
the relaxed pressure gradient flow, a wind shift is expected along
the lakeshore associated with a lake breeze during the afternoons.
No marine headlines are expected at this time.
Area Forecast Discussion
National Weather Service Cheyenne WY
507 PM MDT Sat Jul 24 2021
.SHORT TERM...(Tonight - Sunday Night)
Issued at 211 PM MDT Sat Jul 24 2021
Isolated to widely scattered showers & thunderstorms are currently
developing across the higher terrain of southeast WY & the western
NE Panhandle late this afternoon. Forecast soundings for KCYS/KSNY
& SPC Mesoanalysis indicate strong capping & very weak instability
along the I-80 corridor, suggesting it will be tough for showers &
storms to be sustained as they move away from terrain features. Do
not expect any severe storms today, but the higher probability for
any stronger storms w/ small hail or gusty winds should be focused
across east central WY into the northern Panhandle where up to 500
J/kg CAPEs were analyzed. Effective bulk shear of less than 20 kts
should significantly limit updraft intensity. A similar pattern is
expected to remain in place for Sunday w/ most convection expected
to remain confined to the Laramie Range and/or the Pine Ridge. The
overall threat for severe weather will be low. Trending warmer and
drier as we head toward Monday.
.LONG TERM...(Monday - Saturday)
Issued at 315 AM MDT Sat Jul 24 2021
Good run-to-run model consistency with the large scale pattern next
week. Model consensus favors a strengthening of the upper ridge center
across the Central Rockies and High Plains early in the week. This
position of the ridge will keep the monsoon plume confined to the
south and west of the CWA. Large scale subsidence will limit convective
development and produce afternoon temperatures in the lower 90s to
lower 100s. The upper high center drifts slowly eastward Wednesday
through Friday, opening the monsoonal moisture tap and increasing
chances for mainly afternoon and evening showers and thunderstorms.
Models continue to show a backdoor front pushing south and west into
the CWA Thursday, with temperatures cooling closer to seasonal normals
with highs in the 80s to around 90 Friday.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 455 PM MDT Sat Jul 24 2021
VFR conditions likely through the forecast period for all
terminals. Current radar imagery indicates some showers and
thunderstorms east of Lusk, with a east to southeasterly movement.
Might see some light thunderstorm activity in the northern
portion of the Nebraska Panhandle, with the potential for VCTS
near KCDR. Otherwise, the extent of the forecast through early
tomorrow morning has most terminals experiencing some wind gusts
around 20 to 25 knots. Looking ahead over the next 24 hours, the
HRRR has been fairly consistent with depicting cell locations and
movement, and has some isolated to widely scattered showers &
thunderstorms developing west of the Panhandle. Went ahead started
trending terminals in southeastern Wyoming for VCSH beginning
around 20z tomorrow.
Issued at 215 AM MDT Sat Jul 24 2021
A weak surface front across northwest Nebraska and southeast Wyoming
will slowly sink south into northern Colorado this morning. High
temperatures this afternoon will be slightly cooler but still above
normal for late July. The upper ridge of high pressure will be the
dominating feature this weekend, suppressing the monsoonal plume
of moisture to the south and west. Widely scattered mainly afternoon
showers and thunderstorms are expected to develop, producing light
rainfall and gusty winds. The ridge will strengthen over the region
early next week, resulting in hot and dry weather. Minimum relative
humidities will fall into the low and mid teens each afternoon,
however wind speeds will be light. Shower and thunderstorm chances
will increase mid to late next week with the return of monsoon
Area Forecast Discussion
National Weather Service Des Moines IA
613 PM CDT Sat Jul 24 2021
...Updated for 00z Aviation Discussion...
.DISCUSSION.../Tonight through Saturday/
Issued at 250 PM CDT Sat Jul 24 2021
Today and Tonight:
Cloud cover throughout the late morning and early afternoon has
resulted in some limitation of insolation today, which kept air
temperatures a few degrees cooler. As noted overnight, moisture
pooling ahead of the boundary kicked dewpoint temperatures up a few
degrees, keeping heat index values above 100 across much of Iowa
this afternoon. The trough that has provided some deamplification to
the strong ridge and provided zonal flow across the Midwest is
currently located north of the Great Lakes. The stronger vorticity
with this trough remains well north of the area, but there have been
subtle height falls over Iowa and throughout the northern Plains and
upper Midwest regions. This was just enough to kickoff a weak
surface low and thermal boundary, which has been setup across the
eastern Dakotas and eastern Nebraska this afternoon. The parent
short-wave well to the north will begin to lift this afternoon, but
will drag the weak low pressure and boundary across Iowa this
evening. There is a chance for convection initiation in southeast
portions of the forecast area as this boundary approaches. RAP and
HRRR soundings throughout this afternoon depict a considerable EML
from about 850 to 750mb, with weak capping around 900 mb below the
EML. Diurnal heating may be able to erode capping below the EML
across southeast Iowa. If this ends up being the case and updrafts
are able to develop from an air mass with dewpoints well into the
70s, precipitation loading would be favored in this environment. As
a result, thunderstorms would have downburst potential, which could
produce a few severe wind gusts. Late morning runs of the HRRR
initiate convection around 00z in the far southeast portions of the
area. By the time the boundary starts to produce stronger
convergence in southeast Iowa, the deep-layer shear will be rather
weak (25 kts at best) and thus difficult for convection to organize.
The severe threat for damaging winds appears to be very small in
coverage area, and will have a narrow window. The timing is playing
out for a greater chance in Illinois and Missouri. The boundary
passage will bring in drier air overnight, lowering dewpoints into
the lower 60s.
Rest of the Week:
Sunday, dewpoints will be lower on the backside of the boundary, but
the air temperatures will not be drastically cooler. With lower
dewpoints, heat index values will be much less, and closer to the
air temps on Sunday. The ridge begins to re-amplify over the western
CONUS on Sunday, leaving the central Plains and upper Midwest
downstream in northwest flow. This will likely put Iowa in favorable
position for more smoke and haze in the skies from the western
wildfires. If this ends up being a bit heavier in sky cover,
temperatures may be a degree or two cooler. This ridge will dominate
through most of the week across the central CONUS. Low-level flow
will maintain a southerly component and keeps Iowa open to moisture
from the Gulf of Mexico. Model consensus is strong for H5 heights to
reach 597dam. This will keep weather conditions very hot and humid.
Tuesday and Wednesday look to be the warmest days, and also the most
hazardous with respect to heat. Wednesday, with air temperatures in
the upper 90s, possibly up to 100 in some spots, and dewpoints well
into the 70s, heat index values of 105 or maybe even higher can be
achieved. Outdoor activities Tuesday and Wednesday will be difficult
in these conditions. No precipitation is currently in the forecast
through Wednesday, will just need to keep monitoring any localized
sources of convergence though with this warm and moist of an
atmosphere for an air mass thunderstorm. Synoptic support for any
activity will not be strong. The ridge will remain over the Front
Range toward the end of the week. There are a few signals in
extended guidance for a short-wave perturbation to ride through the
northwest flow downstream of the ridge, which introduces some
precipitation chances by Thursday. Stronger short-wave perturbations
then move through the northwest flow Friday into Saturday, which
will present a better chance for precipitation and thunderstorms.
But until Thursday, warm and humid will be the main story, with
little rain. This will not be favorable for areas struggling with
.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 613 PM CDT Sat Jul 24 2021
A few storms have developed this afternoon from east of IKV to
over GGI with another, slightly stronger line from just east of
OTM to southeast of LWD. For the TAF sites, outside of the chance
of lightning near OTM the next few hours and a too low to mention
chance of 6SM BR at OTM Sunday morning, VFR conditions will
prevail with light winds through the period.
Heat Advisory until 8 PM CDT this evening for IAZ062-073>075-
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1052 PM CDT Sat Jul 24 2021
.SHORT TERM...(This Evening through Sunday)
Issued at 255 PM CDT Sat Jul 24 2021
Fairly quiet weather expected through the daytime hours Sunday, as
weak surface ridge slides through the forecast area. Will continue
to see filtered sunshine as smoke aloft streams across the region.
Could see briefly reduced visibility at the surface this evening as
well, as HRRR smoke model indicates potential for near surface smoke
currently across southwest ND/northwest-north central SD, streaming
eastward in a narrowing band behind a weak boundary before generally
dissipating later tonight. Visibility in these areas, as far east as
Mobridge as of 18Z, generally 5-6SM, so really a minimal impact in
that regard, but could result in a faint smoky smell if outdoors.
Also of note in the near-term is advancing of drier air behind the
aforementioned boundary. Dew points mixing down quite well across
northwest SD and far western ND, with readings in the 30s and even
some upper 20s as of 18Z. This in contrast to our readings still in
the mid 60s-around 70 over most of our forecast area. Feel this dry
air will be tempered slightly by evapotranspiration from the more
robust crop coverage in this part of the region, but still expect
dew points to fall into the 50s-lower 60s through this evening.
Along these same lines, some models, largely those with FV3 core,
are depicting these ultra-low dew points mixing down into our
northern counties Sunday afternoon. Again, though, recent rain in
the Highway 14 corridor, along with evapotranspiration may have some
impact in holding these readings higher. Thus will favor blended
solutions which keeps afternoon dew points in the mid 50s across our
north, with some lower 60s in northwest Iowa, as the surface winds
turn light southerly behind the exiting weak surface high.
With this drier air in place, and lack of any trigger prior to 00Z,
think it will be tough to see storm development during the afternoon
hours. Exception may be in our extreme west, as a mid-level wave
approaches the Missouri River through western SD, though timing of
this wave may favor early evening development after 00Z.
.LONG TERM...(Sunday Night through Saturday)
Issued at 255 PM CDT Sat Jul 24 2021
As a weak mid-level shortwave slides east across South Dakota late
Sunday into Sunday night, could see isolated-scattered storms across
mainly our western and northern counties. Deep mixing results in dry
lower levels with inverted-V profiles beneath 650-600mb. If storms
develop with this wave, could see isolated strong to severe winds,
as indicated by the Day 2 SPC Marginal Risk across our far western
counties. Similar to last night, though, think this threat should
wane as we progress through the late evening/nighttime.
First half of next week will be dominated by strengthening upper
ridge which once again builds over the InterMountain West through
Tuesday. NBM continues to project potential for high temperatures
topping the century mark in several portions of our forecast area by
Tuesday and Wednesday, but these values are running higher than the
50th percentile of NBM members. Given the continued potential for an
elevated smoke layer across the region with the upper ridge axis to
our west and northwest flow into the Upper Midwest, have nudged the
highs for these days a bit closer to that 50th percentile. This
still yields some triple-digit readings in our western counties, and
triple digit heat indices farther east, though the latter will
highly depend on whether dew points hold in the upper 60s-lower 70s
or mix a bit lower in the low level southwesterly flow.
Slight breakdown of the ridge during the latter half of the week
could allow weak shortwaves to slide through the forecast area
Thursday into Saturday. Timing/strength at this range is uncertain,
so did not alter the smattering of 20-30 percent pops in the longer
range portion of this forecast period. More sensible impact of any
waves may be to bring some modest "cooling", though highs still
likely to hold above normal as we approach the end of July.
.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1052 PM CDT Sat Jul 24 2021
Winds have become light and variable tonight and will remaining so
before turning primarily southerly by the mid-late morning hours
Sunday. Patchy valley fog is possible tonight, though not likely
impacting a TAF site. Scattered showers and thunderstorms become
possible late tomorrow afternoon across central SD, but have left
mention out of this set of TAFs due to time and location
Area Forecast Discussion
National Weather Service Glasgow MT
819 AM MDT Sat Jul 24 2021
...Heat returns on Sunday...
Changes to the forecast this morning were fixated on refreshing
the 7 hour old HRRR data for smoke and haze. Reduction in
visibility have already reduced to 3 to 5 miles across Glasgow,
Wolf Point, and Poplar and air quality has recently changed back
to unhealthy for Malta. So, these updates were to help zero in on
impacts to our TAFs in aviation weather and public health hazards.
Visibility should improve slightly across the Hi-Line in the
afternoon as the atmosphere mixes out. GAH
A dry air mass and a ridge of high pressure will be over the
forecast area today. While skies will be clear, smoke and haze
from numerous wildfires will be over the area. Highs will be near
90 in most areas with cooler temperatures near the Canadian
The upper ridge builds into the area starting on Sunday which will
bring the heat back into the region. Sunday`s highs will be in the
90s in most areas with a few locations near 100. Most areas will
have highs on Monday between 100 and 105. The ridge peaks on
Tuesday and it looks to be the hottest day with highs 100 to 110
in most areas. Some areas near the Canadian border could stay
below 100. At this point, Monday will need either a Heat Advisory
or Excessive Heat Warning and Tuesday will need an Excessive Heat
Warning. It is far enough out at this point to wait on issuing
The ridge back slightly to the west Tuesday Night and Wednesday. A
cold front Tuesday Night will bring somewhat cooler temperatures
in the 90s on Wednesday.
Weak waves could bring a slight chance of showers and
thunderstorms Thursday and Friday.
LAST UPDATED: 1400Z
FLIGHT CAT: VFR - MVFR. Smoke might reduce visibility to MVFR at
SMOKE AND HAZE: Smoke and haze across the area are here to stay
for the next 3 to 4 days. These will reduce slantwise Visibility
to MVFR on occassion, especially during the morning hours. There
is already enough smoke and haze in the air that it is causing
the KGGW and KOLF to report a false ceilings of around 5000 feet
in the mornig hours.
DISCUSSION: Skies will remain clear/dry today and tonight with
high pressure over the area.
WIND: Light and variable this morning. Becoming northwest this
afternoon around 10 knots. Look for north to NE winds 5 to 10
knots this evening and east to NE winds around 5 knots late
Area Forecast Discussion
National Weather Service Green Bay WI
1025 PM CDT Sat Jul 24 2021
Updated aviation portion for 06Z TAF issuance
Issued at 228 PM CDT Sat Jul 24 2021
Less humid tonight through Monday, then humid conditions
returning with a few rounds of thunderstorms from Monday night
through Wednesday night. A little cooler and drier for the latter
part of the work week.
A strong band of westerlies (for mid-summer) will persist across
the northern CONUS and southern Canada throughout the period, with
a longwave ridge position in the west and a trough in the east.
Amplitude will initially be quite modest, but increase a little
late in the period as a broad upper anticyclone strengthens from
the Intermountain West to the mid/lower-Mississippi Valley.
The pattern favors above normal temperatures through at least the
middle of the upcoming work week, with at least a little cooling
possible late in the period as the upper flow tilts more
northwesterly. The reservoir of very humid air will shift south of
the area for a time early in the period, then return north into
the area for a few days before shifting south again. Precipitation
totals are tough to gauge as they will depend on the behavior of
convection. The humid air mass across the area in the Mon night/Wed
time frame will likely support some heavy precipitation--the big
question is how widespread it will be and where it will occur.
.SHORT TERM...Tonight and Sunday
Issued at 228 PM CDT Sat Jul 24 2021
The latest RAP analysis and satellite/radar imagery show a cold
front extending across northern Lake Michigan to the central WI
lakeshore early this afternoon. Strong mid-level drying is
occurring in the wake of the thunderstorm activity and along and
behind the front. A strong push of lower dewpoint air trails well
behind the front, however, across northwest WI. A few convective
allowing models regenerate a few showers/storms along this
moisture gradient late this afternoon (like the NamNest), but
think this may be overdone considering mixing has started over
north-central WI, convergence is weak, and boundary layer moisture
is likely too high. Based on the latest trends, added an isolated
shower mention over far northeast WI for the rest of the afternoon.
Other than the possibility of redevelopment of convection this
afternoon, forecast concerns mainly revolve around temps through
Tonight...High pressure from the northern plains will build into
the region. The airmass will be very dry as evident from a lack of
convective clouds over the northern Plains where precipitable
water values fall to 0.50 inches at KBIS. Will therefore have
mostly clear skies with haze from smoke aloft. Stayed closed to
low temps from the previous forecast.
Sunday...High pressure along with the very dry airmass will be
hanging across the region. Under sunny skies, low level temps
support highs in the middle 80s to low 90s. But with seasonably
low dewpoints, apparent temps should be near actual air temps.
.LONG TERM...Sunday Night Through Saturday
Issued at 228 PM CDT Sat Jul 24 2021
The focus of the long-term portion of the forecast was on
conditions Monday through Wednesday night. That is when the return
of very warm/hot and humid air will correspond with seasonably
strong WNW upper flow, possibly setting the stage for a few rounds
of storms--some of which could be severe.
Dew points will begin to increase Monday, but the day should be
rain-free across most of the area. It is possible some convection
may affect the far north/northeast as a weak boundary lingers just
to the north and the area gets brushed by the tail of a shortwave
sliding SE across Ontario. The potential for storms to build
south into the forecast area will increase Monday evening/night.
SPC has outlooked the NW 2/3 of the forecast area with a Marginal
Risk during this time.
A very humid and unstable air mass will be in place across the
area by Tuesday. It is possible that temperatures around
850-800mb will be warm enough to provide a cap and inhibit
convection. But it is also possible an outflow from any storms
Monday night may be lingering across the area and provide
convergence which could break the cap. A similar set-up will
persist Tuesday night into Wednesday, then a more substantial
synoptic scale cold front will shift through the area. The medium
range models were not in good agreement on the placement of the
front/timing of FROPA. The large scale pattern certainly seems
supportive of a severe threat at some point during this period.
Right now, Wednesday night looks like the most likely time,
though that may change with time as smaller scale details become
Another round or two of scattered convection is possible during
the remainder of the period as shortwaves drop SE in the
strengthening NW upper flow across the forecast area.
.AVIATION...for 06Z TAF Issuance
Issued at 1025 PM CDT Sat Jul 24 2021
Very minor changes to 06Z TAFs. VFR flying conditions are expected
with mainly clear skies and good visibility. Winds will remain
light from the west overnight, and then increase Sunday afternoon
with gusts ranging from 15 to 20 knots. Winds will once again
subside Sunday evening.
Area Forecast Discussion
National Weather Service Shreveport LA
907 PM CDT Sat Jul 24 2021
Dry and stable conditions to continue overnight as surface and
upper-level ridging prevail areawide. Warm temperatures expected
overnight with lows forecast in the mid to upper 70s. Otherwise,
light winds and clear skies to prevail. No updates necessary at
this time. /05/
.PREV DISCUSSION... /issued 619 PM CDT Sat Jul 24 2021/
VFR conditions to prevail across area terminals through the
forecast period ending 26/00Z. Could see VCTS conditions across
MLU from 25/18Z through 26/00Z. Otherwise, light and variable
winds tonight to become southwest at 5 to 7 knots on Sunday.
PREV DISCUSSION... /issued 307 PM CDT Sat Jul 24 2021/
SHORT TERM.../Tonight through Sunday Night/
A strong upper level ridge continues to move slowly westward into
Central Texas while a surface ridge in the Northwest Gulf of
Mexico has drifted towards the Southeast Texas coast. The approach
of the ridges and increased subsidence have kept the forecast area
precip-free so far today. Westerly or northwesterly winds south
of the area have prevented any intrusion of the sea breeze. With
the decrease in cloud cover and rain chances, temperatures warmed
fairly quickly, especially across Southern Arkansas and Northern
Louisiana. Heat index values have already started to fall below
criteria over portions of Northeast Louisiana as increased
vertical mixing have finally brought dry air advecting into the
region in the 925-850 hPa layer down to the surface. However, the
current advisory will be maintained through 00z.
The HREF and HRRR continue to suggest isolated to widely scattered
convection will develop during the overnight through mid morning
hours of Sunday over Eastern Oklahoma and into Southwestern
Arkansas. This is expected to occur along an elevated theta-e
ridge. However, most of the other model guidance, including other
high-resolution CAMs remain dry. Given the uncertainty, I decided
to keep the forecast tonight/Sunday morning dry, but later shifts
may need to introduce PoPs in convection appears more likely.
Sunday should be relatively similar to today. The two ridge will
move farther inland over Texas, which may allow for some an
expansion of chance for isolated convection Sunday afternoon.
Decrease vertical mixing should create a more humid airmass.
Daytime highs should be a few degrees warmer than today, which
means more of the area will likely see heat index values above
advisory criteria. Therefore, another Heat Advisory was issued for
Sunday for Southeast Oklahoma, all of Southwest Arkansas, most our
Louisiana parishes, and portions of Northeast Texas. I would not
be surprised if heat indices climb above 110 degrees F over portions
of Northeast Louisiana. An upgrade to an Excessive Heat Warning
for a part of the area may be needed by later shifts.
LONG TERM.../Monday through Saturday/
The dogs days of summer are pretty much upon us, but we are
fortunately hanging on to all the green-up of our wet Summer start.
As our rain chances drop off again for mid to late week, we will
further erode this albedo benefit with upper 90s becoming a bit more
common during this timeframe and perhaps some triple digit air as
well. The upper level heights have already been creeping upwards,
boosting the mercury just a bit under the recent 594 core, but a
window of brief reprieve is approaching.
Overall, we are looking at the front range breeding the higher
heights this week as compared to the more forgiving Bermuda ridge,
which will keep just offshore of the SE U.S. However, a weak frontal
boundary will drop out of the Great lakes into the Ohio Valley on
Monday with a 1017mb surface high. There is also a weak upper low of
589dam associated with an inverted trough over the coastal bend of
Texas which will help to foster a decent sea breeze push for Monday
over our East and hopefully a bit more areawide into Tuesday.
Beyond this window for opportunity for better than average rainfall,
the heat will build under better subsidence and heights building
through midweek as the inverted trough dampens while sliding down
toward the Mexican coast over the west Gulf. The dominant upper
ridge over the high plains will drop into the plains and MS river
valley. This will effectively squash the sea breeze except for our
southern tier of Parishes for the most part. On Tuesday the core
will be near 595dam over the central plains and by the mid and
ending part of this work week, we will see this upper level feature
build to 597dam on both GFS and ECMWF centered right over Kansas,
while covering a vast expanse of the nation`s heartland. Coverage of
convection for us will be slim to none for many of our zones.
Afternoon heat indices will be around the 105 range every afternoon,
possibly higher by a few degrees during the hottest hours of the
day. The issuance of Heat Advisories continues daily for now, but
may come to include the overnights by late in this period. Remember
to move strenuous activity to early or late in the day, try to stay
hydrated by drinking water before, during and after exposure. Try to
take frequent shade or A/C breaks, and wear loose, light-colored
clothing and hats. Special care should be taken to ensure the well-
being of the elderly, young children and a pets and livestock during
late July. /24/
.PRELIMINARY POINT TEMPS/POPS...
SHV 77 99 77 98 / 0 10 10 20
MLU 77 97 76 97 / 0 20 10 50
DEQ 75 97 75 97 / 10 20 10 30
TXK 77 99 77 97 / 0 10 10 30
ELD 75 96 74 97 / 0 20 10 40
TYR 75 96 76 98 / 0 0 0 10
GGG 74 96 74 97 / 0 10 0 10
LFK 74 97 75 98 / 0 0 0 20
AR...Heat Advisory from 10 AM to 7 PM CDT Sunday for ARZ050-051-
LA...Heat Advisory from 10 AM to 7 PM CDT Sunday for LAZ001>006-
OK...Heat Advisory from 10 AM to 7 PM CDT Sunday for OKZ077.
TX...Heat Advisory from 10 AM to 7 PM CDT Sunday for TXZ096-097-
Area Forecast Discussion
National Weather Service Sacramento CA
150 PM PDT Sat Jul 24 2021
Dry weather with temperatures warming into the weekend. Chances
for mountain thunderstorms this weekend through next week.
High pressure building over the Desert Southwest is setting up
for a prolonged monsoonal moisture push into Northern California.
In the short term there may be an isolated shower or thunderstorm
later this afternoon around Alpine county southward along the
crest. Smoke from the Dixie wildfire has been slower to improve
over the interior than what the HRRR is suggesting but does have
it improving overnight and Sunday as it pushes the smoke towards
More moisture will arrive starting on Sunday but the big increase
will occur late Sunday night and Monday morning when we should see
a noticeable increase in cloud cover. Precipitable waters will be
high so any thunderstorms should have heavy rain associated with
them. Questionable time period will be Monday night through
Wednesday when there would be some potential for storms at lower
elevations. For now most of the activity is forecast to stay over
the mountains but that could change.
A decent Delta breeze will occur through Monday before becoming
lighter on Tuesday. Temperatures will trend cooler through Monday.
By Tuesday the low clouds along the coast will likely be getting
mixed out which in turn will lead to a weaker Delta breeze and
warmer inland temperatures.
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Wednesday there is an interesting feature that we will need to pay
close attention too. An upper level circulation will move
northward through the valley during the day. This time of year and
with the moisture that will be in place showers and thunderstorms
will probably have there greatest chance of getting into the
valley. For Thursday through the rest of the extending period the
monsoonal moisture gets pushed to the crest. There may be some
slight warming late next week then cooling over next weekend as
the high pressure weakens over the Desert Southwest.
VFR conditions are generally forecast to prevail over the next 24
hours except for areas of MVFR as a result of wildfire smoke
generally north of I-80 in the mountains and over the far north
end of the valley. Conditions should improve overnight in the
valley with a chance for the foothills improving Sunday morning.
Areas of smoke will also persist around Alpine county. Surface
wind gusts under 12 kts except local southwest gusts 20-30
kts vicinity west Delta.
Area Forecast Discussion
National Weather Service Las Vegas NV
823 PM PDT Sat Jul 24 2021
.SYNOPSIS...A large circulation moving in from Arizona will bring
additional moisture and lead to extensive showers and thunderstorms
across our region through Monday. After this disturbance passes by,
lower thunderstorm chances are expected Tuesday through Thursday.
.UPDATE...We are monitoring one final cluster of storms over
northwest Clark County, near Indian Springs. Storms have produced up
to 0.40" of an inch of rain in the past hour with some reports of
winds around 50 mph. Area is moving southwest into less favorable
environment over southern Nye County and would expect this area to
dissipate over the next 2-3 hours. Otherwise, we are seeing some
light showers or sprinkles from Las Vegas southeast across central
Mohave County. Area of stratiform light rain over Mohave County is
forecast to hold together as it moves south toward the lower
Colorado River Valley and Bill Williams River overnight. Rainfall
amounts on the Flag Burn Area and the rest of the area should be
less than 0.10". Touched up the forecast for the rest of tonight
limiting any threat of thunderstorms to northwest Clark County and
parts of Mohave and eastern San Bernardino County.
.AVIATION...For McCarran...Southeast wind less than 10 kts favored
overnight with winds eventually becoming light and variable toward
daybreak Sunday. Scattered to broken clouds above 12 kft tonight
and Sunday with an east or southeast wind less than 10 kts favored
Sunday afternoon. Low confidence if thunderstorm will impact the
valley terminals Sunday evening.
For the rest of southern Nevada, northwest Arizona and southeast
California...Thunderstorms will be dissipating across southern
Nevada and northwest Arizona by lat evening. Partly to mostly cloudy
skies overnight with light showers possible overnight across
southern Nevada, northwest Arizona and eastern California. Ceiling
will range between 6 to 10 kft AGL. Expecting another round of
storms to develop over the higher terrain of southwest Utah and
northwest Arizona Sunday afternoon and drift southwest toward
southern Nevada, lower Colorado River Valley and eastern California.
Heavy rainfall and gusty winds may impact some terminals.
.SHORT TERM...through Sunday night.
Scattered thunderstorms moving from northeast to southwest during
the late afternoon and evening hours will remain a threat for
northwest Arizona and southern Nevada through Sunday. The northeast
steering flow driving the thunderstorms out of southwest Utah and
southern Lincoln county is a result of the approaching large
inverted trough crossing Arizona and the counterclockwise flow
around the 500 mb high which will remain centered between Reno and
Tonopah through Sunday afternoon. Recent mesoanalysis reveals a
tongue of precipitable water values 1.5-1.9" extending from central
and eastern Clark County down through Mohave and eastern San
Bernardino counties. This area has been under considerable cloud
cover this morning but more heating will occur through the afternoon
as clouds breakup somewhat. The best ML CAPE values of 1000-1500
J/kg will be over northeast Clark county extending down across Lake
Mead into central Mohave County providing the most unstable
environment for storms to move into. However, as storms coming from
southwest Utah gain momentum, outflow could merge with storm outflow
from southern Lincoln County leading to storms developing toward the
Las Vegas Valley this evening. However, the latest HRRR and HREF
members focus the majority of storms over Mohave County and Lake
Mead to Laughlin-Bullhead City and even Lake Havasu this evening
with Las Vegas mainly getting brushed by gusty northeast or east
winds. Storm coverage will diminish overnight then a very similar
setup remains in place for thunderstorms that develop Sunday
afternoon and evening.
The axis of the inverted trough is forecast to move over southern
Nevada and southeast California between 00Z and 12Z Monday, so
showers will likely expand Sunday night into Monday morning across
Clark and eastern San Bernardino counties due to the dynamic forcing
along the leading edge of the trough. However, the 12Z HREF members
show little any the way of thunderstorms across our region between
06Z and 12Z Sunday night. This would not support expanding the Flash
Flood Watch beyond Mohave County and the Colorado River Valley.
Western San Bernardino, Inyo, Esmeralda and Nye counties will see
showers and thunderstorms spreading across late Monday morning
through the afternoon.
.LONG TERM...Tuesday through Saturday.
Chances for showers and thunderstorms decrease Tuesday through
Thursday as drier and more stable air moves in behind the inverted
trough as it lifts away.
Another inverted trough is forecast to lift from northern Mexico up
across our region late in the week leading to another injection of
moisture into our region. NBM probabilities of precipitation trend
upward into the 20-40 percent range for much of the region Friday
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
SHORT TERM/LONG TERM...Adair
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