Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/24/21
Area Forecast Discussion
National Weather Service Albuquerque NM
943 PM MDT Fri Jul 23 2021
Water vapor shows upper level low over E NM tonight with flow
curving around it from the east and northeast over C and W NM where
large scale lift exists to support thunderstorm activity. This
activity continues to decline both in intensity and coverage so any
flash flooding will be due to ongoing runoff. Forecast shows a
decreasing trend in PoPs which looks to be on track as dry slow from
the east works across C NM and to the west. Upper level low will
likely meander and perhaps combine with another low over AZ. This
will allow for deeper southerly flow through the atmosphere with
plenty of moisture for another round of storms tomorrow. Activity may
be focused more over W NM than central but will depend upon how much
the atmosphere recovers and becomes unstable again. We will likely
need another flash flood watch to cover any flood potential tomorrow
as the same areas that got heavy rainfall and flooding today will
probably have it tomorrow. WPC keeps slight to moderate excessive
rainfall outlook over W/SW NM which makes sense given the trends with
the upper low and antecedent conditions.
.PREV DISCUSSION...557 PM MDT Fri Jul 23 2021...
00Z TAF CYCLE
Area radar are busy this evening with scattered to numerous storms
over much of central and western NM. Water vapor imagery shows upper
low over Santa Rosa NM with the bulk of the storms on the west side
of that low. This low will continue to be supportive of storms
through the next 24 to 36 hours which will make timing convective
events at terminals a challenge. HREF has upper low slowly moving
west towards AZ putting NM in a more favorable southerly upper level
flow and PWAT supportive of convection.
KGUP/KFMN...Will need to monitor for storms the next 3-6 hours as
storm motions will be towards these terminals. Hi-res models have
decent handle on storms affecting these sites this evening. Once
storms clear...several guidance including GLAMP show ceilings
dropping to MVFR for KGUP through the morning hours. Another round of
storms again tomorrow afternoon.
KSAF/KLVS...Storms impacting KSAF now through the next few hours and
then clearing up. KLVS should be east of the storms and not have any
impacts through the night. Look for storms to initiate again tomorrow
around 18Z but could be as early as 16-17Z.
KABQ/KAEG...thinking TSRA are done for the evening hours so will keep
TAFS VFR. Concerned HRRR runs showing activity beginning in the late
morning hours so have mention of VCSH at 17Z. Just have little
confidence as it will take some time for the atmosphere to recover
from today`s convection. Given the upper low and day time heating
that is possible, but may take more heating for it to happen.
Hopefully newer guidance for 06Z TAF will provide more confidence.
KTCC/KROW...terminals should stay VFR. HREF shows most of the
convection over C and W NM with maybe an isolated storm in spots of E
NM so confidence is low in any storms affecting these terminals.
.PREV DISCUSSION...336 PM MDT Fri Jul 23 2021...
With a low pressure system moving westward across the state, combined
with abundant low-level moisture, the threat for localized heavy
rainfall and flash flooding will be a concern through Saturday. These
storms will be mainly focused along and west of the central mountain
chain. Heading into Sunday, storm coverage will begin to decrease
through next week, but daily rounds of showers and thunderstorms will
still continue through next week.
SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)...
Lots going on this afternoon with severe weather and flash flooding
in central areas and storms now developing in the west. Expect more
in the way of severe weather and flash flooding well into tonight.
This is thanks to the upper low in eastern NM. It is helping to
produce high PW values, up to 2000+ Capes, -7 LI`s and effective
bulk shear up to 40 knots, promising a busy period into tonight. The
upper low will trek across the state tonight into Saturday, then it
will turn southwest into into AZ later Saturday and Saturday night.
We will continue with the Flash Flood Watch currently in effect for
all of western and central NM through tonight. We will issue another
Flash Flood Watch for Saturday into Saturday night with this package
for a smaller area of our west and southwest zones. These areas will
still be impacted by the upper low. Elsewhere scattered to numerous
showers and storms will occur, expect the far eastern plains where
activity will be isolated, and possibly rain free in Curry and
Roosevelt Counties. The threat for severe weather will be less
Saturday as we lose the shear component.
LONG TERM...(SUNDAY THROUGH FRIDAY)...
By Sunday, the upper-level low will have scooted westward over Baja
California. Meanwhile, the high will elongate and shift north into
CO/WY. Drier air will begin to work its way into the northern part of
the state, leading to a downtick in storm coverage for Sunday. On
Monday and Tuesday, the high makes a trek southeastward into
Kansas/Nebraska, with scattered storms focusing over western and
central areas. The flow becomes more favored for east-southeast
Wednesday and Thursday feature even less convection, as the high remains
over the Great Plains and continues to bring in drier air.
Temperatures will gradually rise in most areas of the state as the
high strengthens. Despite the highs placement, a traditional
monsoon stream of moisture does not seem to materialize. Compared to
yesterdays 12z models with the immobile high to our northeast, the
12z GFS and ECMWF are now in decent agreement that the high meanders
back to the west and tries to re-station itself over the Four
Corners region by late next weekend.
Heavy rain from thunderstorms will produce widespread wetting rain,
some of it heavy, producing an inch or more of rain in 30 minutes,
and large hail is also possible through this evening. This weather
is thanks to an upper low over eastern NM. It will move across the
state well into tonight with more soaking rain and potential flash
flooding. With the upper low moving into AZ, Saturday should not be
as active, aside from the Northwest and West Central Highlands
closest to the low, where widespread wetting/soaking rains are
likely. High pressure to our east will move toward NM late this
weekend and early next week. The high will shift back east Tuesday
and beyond and strengthen. We will see a subtle decrease in storm
activity Sunday through much of next week, but overall it will still
be relatively active.
Flash Flood Watch until 6 AM MDT Saturday for the following zones...
Flash Flood Watch through Saturday evening for the following
Area Forecast Discussion
National Weather Service La Crosse WI
1054 PM CDT Fri Jul 23 2021
Issued at 942 PM CDT Fri Jul 23 2021
A complex weather pattern unfolding over the regional tonight with
overall weak forcing. At 9 pm, broad southerly flow continued to
hold dewpoints in the low 70s across the area. The cold front to
the northwest is slowly becoming more organized along a KINL-
KABR-KRAP line with northwest flow clearly behind it...and lower
dewpoints. Warm frontal convergence over northern MN erupted
storms several hours ago which are moving southeast near Duluth at
this time. Over South Dakota, weak shortwave trough energy is
trying to organize instability with a fair amount of warm air
aloft limiting mid-level lapse rates to 6.5C per SPC mesoanalysis.
These lapse rates are widespread over the entire pre-frontal
region. MUCAPE is out there in 2-4k J/Kg range but most is
elevated and the analysis seems a bit overplayed for the lapse
rates in place. To boot, the wind shear across the area is poor
and little storm organization is expected.
The main rain chances overnight will come from weak shortwave
trough energy oozing east now causing precipitation across South
Dakota. Cloud tops and lightning activity continues to show
development. There should be enough weak forcing with the SD
trough, cold front, and elevated instability evolving eastward to
keep a likelihood of showers and sct storms north of I-90 for the
3-9 am period. The HRRR model run-to-run consistency has been
giving and taking all night so the lesson seems to be
concentrate on the bigger picture forcing and instability.
Consistent signals have been in the energy emanating out of SD and
observational data supports this. The Duluth convection may clip
northcentral WI as well.
Overall, updated the northern rain chances to 80 percent and
increased the rainfall amounts. Rain chances still fall southward
but have increased the I-90 corridor for light rain in the 50-60%
chance range. Storms should be garden variety overnight and no
severe thunderstorms are expected.
.SHORT TERM...(This evening through Saturday)
Issued at 210 PM CDT Fri Jul 23 2021
Latest water vapor satellite imagery shows shortwave ridging over
the Upper Great Lakes region. Subsidence underneath ridge is
allowing for mostly sunny skies per visible satellite imagery.
Temperatures have warmed into the middle to upper 80s per latest
Tonight...Shortwave trough over the Northern Plains states is
expected to track across northern Wisconsin and the Upper Peninsula
of Michigan. The latest 23.12z NAM/GFS/RAP increase moisture
transport/convergence this evening and tonight across the northern
half of the forecast area. Showers/storms are expected to develop in
association with the shortwave trough and move across mainly the
northern half of the forecast area. The latest 23.12z NAM/23.16z RAP
show 20 to 25 knots of 0-3km shear and 0-6km Most Unstable CAPE of
up to 1500 j/kg across the far northern parts of the forecast area.
A few of the storms will be strong to severe with damaging winds the
main threats. Locally heavy rainfall is also possible...as
precipitable water values approach 2 inches.
The shortwave trough and associated cold front push southeast and
east of the forecast area by 18z Saturday. The 23.12z GFS/NAM
suggest warmer air aloft advects into the forecast area behind cold
front with 925mb temperatures warming to plus 26 to plus 28 degree
celsius by 21z Saturday. The 23.00z NAEFS show plus 1 to 2 degrees
standard anomalies across the forecast area. High temperatures are
expected to rise into the upper 80s to middle 90s at most locations.
The combination of dewpoints in the lower 70s or 70...heat indices
will be 95 to 105 across much of the forecast area.
.LONG TERM...(Saturday night through Friday)
Issued at 210 PM CDT Fri Jul 23 2021
The main weather story in the extended will be the very warm to hot
temperatures through Wednesday with periodic rain chances.
The 500mb pattern has the forecast area in northwest flow aloft
Saturday night through Friday. This puts the regional vulnerable to
shortwave troughs that move through the flow, however there are no
real high confidence periods where widespread soaking rains
forecast. Periodic rain chances occur starting Sunday night. The
GEFs plumes are quite dry and generally a half an inch or less for
both KRST and KLSE through the end of July. The EC EPS is
similar. They both have some outliers with wider spread starting
next Thursday night.
Temperatures during this prolonged period are not expected to be
record-breaking, but still above normal.
Highs Sunday through Wednesday should range from the lower 80s to
the lower 90s and in the 80s still for Thursday and Friday. We
expect a break in the high humidity Sunday and Monday, however
dewpoints climb again Tuesday and Wednesday.
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1053 PM CDT Fri Jul 23 2021
Convection has developed this evening over South Dakota along a
surface trough ahead of an incoming short wave trough. All the
hi-res meso-scale models suggest this activity will hold together
overnight as it moves east toward the area. There should be some
weakening of the activity as it moves past the best instability
gradient and into the mid-level warm air in place over the region.
This should result in mainly showers with some embedded
thunderstorms probably impacting both airports, with the chances
a little bit better for KRST than KLSE. Will throw in a short
tempo group with some MVFR conditions at KRST while holding with
VCTS and VFR at KLSE for now. Once this activity moves past in the
morning, VFR conditions should return and then remain through
Area Forecast Discussion
National Weather Service Columbia SC
1033 PM EDT Fri Jul 23 2021
Drier weather is expected for the weekend, as seasonally low PWs
work into the region. By Monday, PWs are expected to gradually
increase ahead of an approaching cold front. Scattered to
numerous showers and thunderstorms are then expected from Monday
through Wednesday evening. Uncertainty then develops by Thursday
and Friday. Temps will be near normal - highs in the 90s and
lows in the 70s.
.NEAR TERM /UNTIL 8 AM SATURDAY MORNING/...
High pressure continues to ridge into the area from the north
with low level ENE flow and mid level NW flow leading to drier
air moving over the forecast area as PWATs in the northern
forecast area have dropped to below 1.5 inches. Surface trough
over the Upstate with a sliver of higher moisture developed some
isolated convection this evening but by after sunset, any
lingering showers or storms are expected to dissipate. Lows a
bit cooler tonight, dropping into the upper 60s and low 70s.
.SHORT TERM /8 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
The short term period is looking fairly benign, and should set
up for a really nice weekend across the CWA. General troughing
is expected to continue dominating the eastern US, and with that
will be a surface high pressure influencing the region. This
will move eastward from the Ohio Valley into the Atlantic by
Sunday, but will help to push some lower (1.3-1.5") PW air into
the region for Saturday. Additionally, flow will be weak
throughout the atmosphere, with backing wind profiles in model
soundings indicative of weak cold air advection. Overall, I
can`t rule out a weak/isolated shower Saturday, especially
across our northwestern counties. One fly in the ointment to a
beautiful forecast would be the presence of haze from smoke.
HRRR-smoke products push the smoke westward tomorrow, but I
wouldn`t be surprised if more stayed around the area given weak
atmospheric flow. Either way, highs look seasonal - in the lower
90s most places. Overnight, lows should be a bit below guidance
with lower dewpoints across the area. Expect lows in the upper
60s to around 70.
Sunday looks to be more of the same, albeit with some increasing
moisture. Ensemble guidance continues to suggest low chances of
instability developing, and forecast soundings fall in line with
that as well. Without any obvious forcing mechanisms in place,
Sunday should be another benign day. Highs will be a touch warmer as
heights rise a bit, topping out in the low and mid 90s. Overnight,
lows should be back to where they have been with higher surface
dewpoints returning. Expect low 70s.
.LONG TERM /MONDAY THROUGH FRIDAY/...
Little has changed with the long term period over the last day or
so, with the exception of some increased uncertainty with the
pattern towards the end of the period. Overall, it looks seasonal
with regards to temperatures and rain chances.
By Monday, PWs will begin increasing again as heights rise slightly
and southerly and southwesterly flow increases. This will be ahead
of a cold front that will drag through the region during the week.
Troughiness is expected to follow this in the eastern US through
Wednesday/Thursday as shortwaves reinforce the parent trough over
the Northeastern US. Some uncertainty develops with how this evolves
towards Friday as some ensemble members show a more amplified trough
by the end of the week, which would change the forecast. Will side
towards an expectation of rising heights during this time. Sensible
weather will be very seasonal. Monday will be quite warm with
slightly rising heights and southwesterly flow ahead of the front.
Some isolated showers & storms may keep this in check, but I`m
expecting mid 90s everywhere. Tuesday-Wednesday looks active, with
widespread showers and thunderstorms developing along the front.
Ensemble guidance indicates >70% chances of 1000 j/kg of CAPE
developing both days, giving confidence that we`ll see numerous
storms develop both days. This should limit overall high temps a
bit, and I`m going slightly below guidance. There is a good bit of
uncertainty on Thursday and Friday, owing to pattern evolution
questions and uncertainty about where the front will eventually set
up. I really don`t think the front will push through the area, and
expect at least scattered shower/storm chances to remain. Highs will
continue to be in the 90s throughout the week, with lows in the
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Visibility has been reduced a bit due to haze/smoke from the
Western U.S. wildfires. As the upper trough along the eastern
seaboard shifts east tonight, the smoke may diminish. The trend
in LAMP guidance has been less fog/haze early Saturday morning
with MVFR just before sunrise. HRRR Smoke product continues show
some smoke across the area producing hazy conditions overnight
with vsby improving from east to west beginning around 06z. Will
continue mention of MVFR at AGS 09z-12z due to persistence.
Mostly clear skies overnight as surface high pressure ridges in
from the north. Scattered cumulus with bases 4kft to 6kft
expected to develop Saturday afternoon. Winds will be E/SE 10
kts or less.
EXTENDED AVIATION OUTLOOK...Early morning restrictions possible
at fog prone sites AGS/OGB. Scattered showers and thunderstorms
Tuesday and Wednesday as a frontal system moves into the area.
Area Forecast Discussion
National Weather Service Cheyenne WY
442 PM MDT Fri Jul 23 2021
.SHORT TERM...(This evening through Sunday)
Issued at 221 PM MDT Fri Jul 23 2021
Latest radar/satellite loop was showing the frontal boundary
continuing to surge south across northeast Colorado and recently
exited the southern Nebraska panhandle. Behind this boundary
convection has continued to develop along and just behind the
boundary. However, this convection has been fizzling out across
south of the CO/WY border during the last hour or so. A couple of
possible reasons for this convection deteoriating is due to a warm
nose aloft and limited cape depicted by the HRRR and local
soundings. In addition, we are also seeing a cirrus shield over
Laramie County. This cirrus shield may keep things capped for a
little while longer, but still cannot rule out some isolated
thunderstorms developing mainly along and south of a Laramie to
Scottsbluff line late this afternoon and early this evening with
lighting and heavy rainfall being the main threats. Otherwise, we
will see showers and thunderstorms clear out fairly quickly after
sunset. Cannot rule some patchy fog in the North Platte River
Valley tonight, but most places will be partly to mostly cloudy
with a broad swatch of mid and high clouds across southern
The precipitable water values will be quite a bit less tomorrow
over areas mainly over the southern half of our forecast area, due
to good subsidence building in behind the shortwave. We will need
to keep our eyes on another shortwave transversing across southern
Montana and northern Wyoming tomorrow. This feature may trigger
some scattered thunderstorms over the northern sections of our
forecast area. For now, we are continuing to favor a downward
trend on the thunderstorm chances.
Saturday night and Sunday will see the upper level ridge continue build
over the area which will tend to suppress any convection lower the
precipitable water values along with a return of warmer
.LONG TERM...(Sunday night through Thursday)
Issued at 230 AM MST Fri Jul 23 2021
The medium range models/ensembles are in good agreement with the
building of the upper ridge (~597 dm) over the Central Rockies next
week. Monsoonal moisture will be suppressed early in the week, but
return by the middle of the week as the ridge drifts east into the
High Plains. Expect dry conditions Monday. Isolated to scattered
mainly diurnal showers and thunderstorms are forecast Tuesday
through Thursday. The severe weather threat will remain low due to
weak shear. Locally heavy rain will be possible east of the Laramie
Range with precipitable water values around an inch.
Well above normal temperatures are forecast early in the week with
700 mb temperatures between 16 and 20 degrees Celsius. High
temperatures Tuesday and Wednesday will range from the lower 90s to
lower 100s. A weak backdoor front will push into the plains Thursday
lowering high temperatures into the lower and mid 90s.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 439 PM MDT Fri Jul 23 2021
Cold front well south in Colorado this afternoon has kept much of
the monsoonal moisture south of us. Pretty stable air over
southeast Wyoming and Nebraska Panhandle...so thunderstorms look
to be minimal tonight. VFR conditions overnight.
Issued at 221 PM MDT Fri Jul 23 2021
The upper level ridge is expected to continue to dominate the area
this weekend into early next week. This will allow for low
afternoon humidities (15-25 percent) and high mixing heights
around 8-12kft. Wind speeds will remain fairly light and variable.
A subtle pattern change is expected at the end of the week as the
upper level ridge slides southeast into the central Plains and
brings deeper moisture and northwest upper level flow which may
favor better precipitation chances.
Area Forecast Discussion
National Weather Service Des Moines IA
804 PM CDT Fri Jul 23 2021
Issued at 804 PM CDT Fri Jul 23 2021
A warm and humid, but quiet evening is in store across the region.
With some residual smoke around, some locales are likely to see a
vibrant sunset. Temps are still running in low to mid 80s, as of
8pm with dewpoints ranging from the upper 60s to lower 70s.
Keeping our eye on a few features attm. First - showers and storms
are ongoing across portions of SD into far western MN. Still
expecting a weakening line of showers and isolated thunderstorms
to dribble into northern Iowa very early on Saturday morning /3am-
6am/. No severe weather is expected, although a few of these
higher based cells could produce gusty winds. Most areas will
pick up only very light amounts of rainfall. Second - decided
against any expansion of the Heat Advisory at the moment. Current
forecast of 95F at KDSM is on the high side of temperature
guidance envelope on Saturday, and expecting a fair amount of
clouds around so we might even be a touch too high. The one caveat
is dewpoint pooling ahead of the front. Currently forecasting Tds
from 70-75F which appears reasonable. However, if more widespread
mid 70s show up - we could then approach heat indices around
105F. The midshift will have one more look tonight in case of
drastically different trend.
.DISCUSSION.../Tonight through Friday/
Issued at 237 PM CDT Fri Jul 23 2021
-Heat and humidity settles across the area this weekend through the
upcoming week. Peak heat this weekend will occur Saturday with a
Heat Advisory in effect over southern Iowa.
-Spotty chances for convection Saturday morning, then perhaps Monday
and Thursday, though impacts remain fairly low
Smoke from wildfires across western portions of North America
continues to create hazy skies over Iowa and especially eastern
Iowa, as seen on GOES-East true color imagery this afternoon (or
taking a peek out the window). Latest HRRR runs indicate that this
higher concentration of smoke aloft should clear the area
overnight, with better - albeit still slightly hazy - conditions
Overnight a shortwave trough will traverse the ridge with a weak
line of precipitation to move across northern Iowa in the early
morning hours. Better forcing remains north of the area, however a
broken line of showers or perhaps thunderstorms will still travel
across northern counties. CAM guidance remains mixed regarding
whether activity will be squashed by midday (HRRR, ARW, Fv3, RAP)
or progress into central and southern Iowa later in the afternoon
(NAMnest, NSSL-WRF). For now have sided with majority and kept the
afternoon precipitation chances fairly low since forcing remains
weak and may struggle to overcome the cap.
Of greater concern Saturday is the heat as afternoon temperatures
climb into the mid 90s and dewpoints sit in the low 70s. Heat
indices, especially across southern Iowa, will top out around 100-
105 so a Heat Advisory remain in effect Saturday across southern
Iowa. Hot and humid conditions settle in through the upcoming week
thanks to a western US ridge that doesn`t budge much. Heat is
expected to peak again this Wednesday when high will reach the upper
90s and dewpoints will likely be in the 70s area-wide.
The forecast remains fairly subdued outside of heat impacts. there
is a window for precipitation on Monday as another shortwave
moves across the area, however models struggle with timing and
placement of this system. The airmass certainly supports more than
sufficient instability and shear is around 30-40 kts, however
with a cap in place convection may struggle. Any storm that does
manage to get going would certainly have severe potential.
Following that the next window for precipitation at this time
appears to be Thursday though details are fuzzy at this time
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 618 PM CDT Fri Jul 23 2021
Mainly VFR conditions are forecast this period. Plume of thicker
mid/upper level smoke continues to push ewd with mostly clear
skies this evening. A weak frontal boundary currently extending
from SD into MN will slowly sag swd into IA overnight. A
weakening line of showers and thunderstorms is expected to impact
northern Iowa, including KMCW and possibly KFOD. Cloud bases
should remain VFR with only brief/transient reductions to
visibility possible. Otherwise, the remainder of the area will
just see periods of mainly mid-level cloudiness. There is a low
probability of a few thunderstorms developing across southeast IA
Saturday afternoon, but highest threat is east/south of KOTM.
Southwest winds will shift n/nwly behind the front by Saturday
Heat Advisory from noon to 8 PM CDT Saturday for IAZ062-073>075-
Area Forecast Discussion
National Weather Service Grand Forks ND
1007 PM CDT Fri Jul 23 2021
Issued at 1005 PM CDT Fri Jul 23 2021
Cluster of thunderstorms along the ND/SD border near Eureka/Ashley
moving east...some earlier wind reports of 55-68 mph in the
Linton/Wishek area. Seems a bit less now. Hail threat seems
greatly diminished though attm. But will watch these as they move
east. In general with 500 mb wave moving thru general support for
some shower and t-storms eastward thru far SE ND and eventually WC
MN overnight. border thru 06z.
.SHORT TERM...(This afternoon through Saturday night)
Issued at 320 PM CDT Fri Jul 23 2021
Short term weather impacts include potential for scattered severe
thunderstorms this afternoon and evening, with near critical fire
weather conditions possible Saturday.
Surface trough axis has acted as a focus for early thunderstorm
development this afternoon, with high Td values in the 70s
along/east of this supporting ML CAPE 1500-2000 J/KG and heat index
values near 100F. Weak forcing associated with subtle waves within
mid level westerly flow and PWATs 1-1.5" are supporting isolated to
widely scattered activity this afternoon. Main period of forcing is
still this afternoon with the main frontal passage, but at that
point there is potential that Td values will be decreasing along
with instability lowering potential severe threat between the trough
axis and frontal zone as this transitions east. Latest trends in
HRRR has picked up on this showing weakening trends in
coverage/intensity by 00-01Z. Due to at least elevated instability
and better forcing though I wouldn`t want to rule out original CAM
solutions supporting clusters forming during the evening hours.
Effective shear 30-40kt and straight hodographs clouds support
supercells/splitting, but due to weak low level shear/higher bases
tornado threat is limited (though can`t be ruled out). Primary
threats in this environment will tend to be damaging winds to 75
mph/hail to 1.75". PWATS 1-1.5" and slower storm motions along
surface boundaries does raise the possibility for localized heavy
rain/excessive rain threat.
Rest of tonight-Saturday: After the cold front passes there will be
a slight drop in temps aloft but a much greater change in Tds and
drier/stable air aloft. While westerly BL flow keeps above average
temps in place it will tend help scour out any smoke and HRRR smoke
model keeps smoke out of our area (possibly the most clear
conditions we`ve had in weeks at the surface and aloft). Sunny skies
and westerly BL flow will support efficient mixing and potential for
temps in the lower 90s, RH values in the 20-30 percent range, and
gusty winds 20 to 35 mph (highest mixing potential in northeast ND).
This raises the possibility for near critical fire weather
conditions across the region. The best chance for critical fire
weather conditions will be dependent on rain this evening and winds
within or west of the RRV.
.LONG TERM...(Sunday through Friday)
Issued at 320 PM CDT Fri Jul 23 2021
Upper level ridge in the south west and southern United States
continues to take hold bringing hot conditions. Troughs move up and
over the ridge through the early and middle part of the week
increasing the chances for showers and storms. Near the end of the
week ensembles hint at the ridge moving eastward pushing the track
of the troughs further north bringing drier and warmer air into the
The week ahead...
Conditions look to be dry throughout Sunday, with temperatures in the
upper 80s to lower 90s. RH values remain fairly low in the 30s, with
winds on the lighter side. Warm and dry conditions provide elevated
fire concerns for the afternoon, but not as elevated as Saturdays
impact since winds will be on the higher side. As we head into the
early part of next week another trough makes its way up and over the
ridge out in the south west. The frontal boundary associated with
the trough encounters CAPE values in the 1500-2000 j/kg range.
Moisture flow turns more southerly allowing for a stream of higher
dew points into the 60s toward our area. Taking a look at ensemble
soundings shear has been decent in both directional and speed
components through multiple runs. Effective shear in the low and mid
levels are around 25-35kts.
Lapse rates look decent, but very between different ensembles
bringing low confidence in that category. The exact timing of the
system is different between runs, with some bringing the trough
through early eliminating the daytime heating ingredient which is a
key component in initiating storms. Precipitation amounts of
exceeding 0.1 inches continue to lie between 40-60% for western MN
and eastern ND. Continued chances for precipitation and storms are
possible mid week before the ridge begins to push further east
increasing heights and tracking troughs further north. This would
bring drier conditions and a continuation of the heat. Temperatures
through the long term remain consistent with highs in the upper 80s
to lower 90s.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 718 PM CDT Fri Jul 23 2021
VFR expected thru the pd as skies clear overnight/Sat AM and winds
turn more west to northwest all areas. Sct tstorms remain psbl but
most likely not impact any TAF sites after 02z.
Area Forecast Discussion
National Weather Service Green Bay WI
753 PM CDT Fri Jul 23 2021
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Saturday
Issued at 236 PM CDT Fri Jul 23 2021
The latest RAP analysis and satellite/radar imagery show a rather
ill-defined warm front extending across northern Minnesota and
northeast Wisconsin early this afternoon. Northeast of this front,
winds are southeast off Lake Michigan, which is setting up a weak
convergent zone over northeast WI with the prevailing southerly
flow. Mixed layer instability is 600-1000 j/kg, but it is yet to
be seen if convergence is strong enough to produce a shower or
storm given mid-level shortwave ridging overhead. Will leave a
slight chance in the forecast. Also added a chance to far north-
central WI where a cell developed just south of Bayfield. Further
west, a prefrontal trough extends across the northern Plains into
eastern Manitoba. As mid- level height falls overspread this
region, thunderstorms are expected to develop during the middle to
late afternoon hours along this trough before spreading southeast
into the area late tonight. The severe weather chance with these
storms is the main forecast concern.
Tonight...If any storms develop this afternoon near Lake Michigan,
they should fizzle relatively quickly this evening. Given the weak
forcing, don`t think a strong or severe storm is possible. Then
attention turns towards the potential for severe storms as they
move in from the northwest towards late evening or overnight. The
cams/href indicate a slower arrival of the strongest convection,
most likely after midnight, although could have a few cells
popping up over north-central WI ahead of the main line. The
slower timing reduces the severe threat somewhat and consequently,
SPC lowered the threat from a slight risk to a marginal risk over
north-central WI. In general, storms will be undergoing a gradual
weakening trend as they move southeast across northeast WI
overnight. Most unstable capes of 1000-1500 j/kg and effective
shear to 25 kts will lead to an isolated severe threat over
north-central WI as the storms arrive overnight. Damaging winds
will be the main threat. Otherwise, it will be a warm and muggy
night with lows ranging from the upper 60s to lower 70s.
Saturday...Thunderstorm activity will be ongoing at the start of
the morning from northeast to central WI. It will continue to
weaken through the morning hours, possibly dissipating or exiting by
the end of the morning. The surface cold will trail the convection
and will move across northeast Wisconsin during the afternoon.
Thunderstorm and severe weather chances along the front will be
conditional in the afternoon, dependent upon the duration of
thunderstorm and resultant cloud cover left over from the morning.
The later arrival of the precip tonight will not help
thunderstorm redevelopment in the afternoon, but perhaps a few
hours of clearing could occur, resulting in instability in the
2500-3000 j/kg range according to models. This instability
coupled with deep layer shear of 35-40 kts could lead to severe
storms if sufficient heating occurs. Highs will range from the
middle 80s to lower 90s.
.LONG TERM...Saturday Night Through Friday
Issued at 236 PM CDT Fri Jul 23 2021
The main forecast concern will be the potential for severe
thunderstorms toward the middle of next week.
Weak high pressure will dominate the region for the end of the
weekend and the early part of the next work week, with mainly dry
but very warm weather expected.
A warm/stationary front will bring a renewed chance of thunderstorms
Monday night into Tuesday night, with a cold frontal passage
occurring sometime Wednesday into Wednesday night. Through this
period, strong daytime instability (CAPE 2000-3000+ j/kg) and
strong deep layer shear (35-50 knots) will be supportive of
organized severe thunderstorm development, though confidence is
low in the timing and coverage. CIPS analogs (centered on 00z 7/28)
support the threat.
After the cold front shifts south, Canadian high pressure will
bring mainly dry conditions for Thu/Fri, along with less humidity
and temperatures closer to normal.
.AVIATION...for 00Z TAF Issuance
Issued at 753 PM CDT Fri Jul 23 2021
VFR conditions will prevail at least through about 06Z with
occasional patches of mid-level clouds drifting southeast across
the forecast area. A few isolated showers and thunderstorms may
also develop near the UP/WI border during the evening hours with
some brief MVFR CIGS/VSBYS.
After midnight a complex of thunderstorms over northcentral
Minnesota will gradually work its way into far northcentral WI and
central WI after midnight. Latest shorterm model guidance
suggests this complex of storms will eventually work its way SE
across the remainder of the forecast area through the early
morning hours, and eventually exit eastern Wisconsin by mid-
morning Saturday. Confidence remains low on exactly how the
convection will evolve during the early morning. Central and
northcentral TAF sites will likely see few hours of MVFR CIGS and
VSBYS with the thunderstorm activity. The storms will be strongest
across central Wisconsin before weakening as they move into
eastcentral Wisconsin after daybreak.
Additional shower and thunderstorms are possible by early
afternoon over eastern WI associated with cold frontal boundary
passage, but this will be conditional on how quickly the
atmosphere can recover from earlier storms.
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1044 PM EDT Fri Jul 23 2021
Air quality should improve somewhat over the weekend while afternoon
showers and thunderstorms increase in coverage and intensity through
Monday. A backdoor cold front builds into the forecast area early
next week, bringing more active weather at least through Tuesday.
.NEAR TERM /THROUGH SATURDAY/...
As of 1030 PM: Still a few cells popping up near the escarpment
and across the western Upstate, but not as much coverage as earlier
runs of the HRRR and NAMnest were advertising. The current forecast
looks largely on track. Did bump up sky cover a little bit to line
up with trends. Otherwise, no changes were needed with this update.
Isolated showers may linger well into the night, especially in
upslope areas, as a moist, low level southerly flow continues. This
flow may also help low clouds to develop near or just after
sunrise. Mountain valley fog and stratus is expected once
again. Lows will be near to slightly above normal.
Heights rise slightly through the period in the northwesterly flow
aloft as a short wave ridge moves over behind a departing trough.
Guidance generally agrees on a lee trough developing and some
weak upper divergence moving through despite the slight increase
in heights. The guidance disagrees on the resulting coverage of
convection. They do agree that the mountains have the best chance,
but some guidance moves the convection off the mountains and across
the Piedmont during the late afternoon. Others show only isolated to
low end scattered across the Piedmont. Have gone with the guidance
blend which favors the mountains and foothills, with less coverage
over the Piedmont. Highs will be near to slightly below normal.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 145 PM EDT Friday: With a 500mb ridge entrenched over the
western CONUS, Sunday`s opportunity for synoptic forcing will be
severely restricted. A Bermuda high over the western Atlantic will
help to maintain southerly surface flow...which in turn will help
PWATs ramp up to near 2" by Monday afternoon. A deep 500mb trough
will spread eastward, though the best DPVA will remain well north of
our CWA. Global models at least indicate some enhanced QPF response
starting Sunday night and extending through Monday evening, ahead of
a slowly-advancing cold front swooping in from the north. PoPs on
Sunday afternoon are largely restricted to slight/chance in the
mountains and foothills, as points east appear to be increasingly
well-capped in model soundings, which should inhibit widespread
coverage of convection despite modest SBCAPE of 500-1000 J/kg.
Monday afternoon should fare somewhat better as increased moisture
content, lowered LFCs, and less-stable profiles allow for more
scattered showers and embedded thunderstorms to crop up ahead of the
advancing front. Activity gradually winds down late Monday night
into Tuesday morning, as the front attempts to clear the region.
For now, have lowered temps a degree or so to more closely match
the latest guidance, which seems to be trending toward slightly
cooler temps for the next few days. This does little to offset
the unseasonably warm temps forecasted for the weekend.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 200 PM EDT Friday: Upper ridging continues to dominate
the western half of the CONUS. Following Monday night`s frontal
passage we should at least see some improvement in air quality, as
the intrusion of continental air clears out any residual low-level
smoke/haze in the area. There`s a good bit of uncertainty in
the forecast following this fropa, however, as the models haven`t
yet reached a consensus on whether the front clears the Carolinas
entirely or stalls for a bit. What`s clear is that the Bermuda high
refuses to budge, and as such we should retain our diurnally-driven
afternoon convection on Tuesday and Wednesday afternoon - something
that the presence of a stalled boundary might work to enhance.
Late week may feature the arrival of another robust midlevel
trough, which would drive a wave of renewed precipitation by
Friday afternoon. Expect temps to remain at least a few degrees
above normal throughout the medium range forecast.
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Scattered showers and tstms will continue
into the evening near the Blue Ridge escarpment, so VCTS will
be carried at KAVL/KGSP/KGMU for the first few hours of the 00z
TAFs. From there, showers may linger, but overall coverage should
diminish overnight. Another concern will be how much fog and low
stratus develops outside the usual mountain valleys. For now,
think the TAF sites will be mostly VFR outside any precip. Greater
coverage of convection is expected Saturday, with the usual diurnal
trend of starting in the mountains, and then expanding/drifting
E/SE into the Piedmont by early evening. Going with PROB30 for
all sites for TSRA. Winds will be light thru the period, generally
out of the SE to SW.
Outlook: Diurnal thunderstorm chances will steadily increase through
early next week. Early morning fog or low stratus will be possible
each day, primarily in the mountain valleys.
02-08Z 08-14Z 14-20Z 20-00Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 95% High 95% High 100%
KAVL High 93% Low 44% High 100% High 100%
KHKY High 100% High 100% High 100% High 100%
KGMU High 100% High 97% High 93% High 100%
KAND High 100% High 97% High 95% High 100%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:
Area Forecast Discussion
National Weather Service Gray ME
1019 PM EDT Fri Jul 23 2021
Scattered showers and thunderstorms are across the region this
afternoon and will wane as the sunsets. High pressure will build
in with clear skies tomorrow. A front will approach the region
overnight Saturday and cross the area on Sunday morning bringing
widespread rain and thunder.
.NEAR TERM /TONIGHT/...
Only remaining cloud cover left out there is associated with two
small areas of continued shower activity. This will continue to
decrease in coverage through the remainder of this evening with
little if any additional rainfall expected. With a mostly clear
sky and calm winds, we should see good cooling tonight. Areas
that had rain this evening will be most susceptible to fog
formation and this has already occurred in some spots.
It seems the most active of the convective activity has
subsided. Outflow still pushing southwest across York County and
through central New Hampshire. This is the most likely area for
further convection this evening. Even this, though, is on the
decrease. Areas that had rain this evening will be prone to fog
overnight. Otherwise no significant changes in forecast
Scattered showers and thunderstorms persist across the region
this afternoon as upper level trough keeps freezing levels low.
Most of these storms are Pulse type, quick to intensify and
quick to pass. With the low freezing levels have had reports of
hail and expect some very isolated wind damage with the
strongest cores collapsing. Convective initiation is very much
tied to the diurnal heating and thus expect the reverse later
this evening with coverage rapidly decreasing after sunset. HRRR
has done a good job with the timing and general coverage of the
convection and have leaned on it for the PoP for the next
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
Overnight after storms decrease we`ll see clear skies.
Satellite reveals a broad area of dry air to our west and expect
temperatures to fall rapidly as a result. Lows will drop the
low 50s with some northern valleys in the 40s. While it`s
generally dry, midday dew points are in the 50s and expect fog
to form in the CT river valley, and possibly up into the
For Saturday expect clear skies with high pressure. A robust
seabreeze will likely push inland as far as Sebago lake and keep
temperatures cooler along the coast.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Low pressure will be passing well north of the area as it travels
through central Quebec Sunday morning, with a warm front associated
with the system approaching the area at this time. Widespread shower
ahead of the front will be ongoing Sunday morning. The rain will
mostly end across western New Hampshire by the early afternoon as
the region tries to break into the warm sector behind the warm
front. The warm air is notoriously stubborn to actually make it in
with these type of set ups, but if and where it does make will stand
the best chance of seeing a few stronger thunderstorms Sunday
afternoon as the cold front approaches. Areas farther east into
Maine will likely hold onto the showers for more of the afternoon
hours, thus minimizing the risk of storms across these areas.
The front will most likely be clearing the coastline by Monday
morning, with our trough dominated pattern continuing for the
foreseeable future. Next week will continue to be characterized by
temperatures generally near to below normal, with frontal passages
roughly every other day and broad surface high pressure in between.
High pressure looks to be in control for Monday, with seasonable
highs and mainly sunny skies. A cold front will approach later
Tuesday, likely brining a round of afternoon showers and
thunderstorms. The front will likely clear the area on Wednesday,
yielding clearing and improving conditions during the daytime
on Wednesday as weak high pressure builds into the area for
Wednesday night and Thursday. Another front will likely approach
the area by late next week, but it`s too early to tell and
there is significant model divergence on where and when the low
will track through, so at this time I`m keeping an increased
chance of POP`s for the end of the time period.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Fog tonight is most likely in valley locations affected by
evening rainfall. That includes Whitefield but confidence is
lower for Lebanon. Otherwise expect VFR conditions through
Widespread showers will bring restrictions Sunday morning,
lasting through most of the afternoon across eastern terminals,
while western terminals see a period of VFR/MVFR conditions Sunday
starting late morning before scattered thunderstorms develop in the
late afternoon hours. VFR conditions return Monday, with
another chance of showers and storms returning Tuesday
afternoon. VFR conditions likely return later on Wednesday.
Short Term... Calm winds and seas will hold through the start
of the weekend.
A front will cross the region on Sunday morning with rain, and
thunderstorms. Winds will go NW behind the front.
High astronomical tides will bring water levels just to minor
flood stage across New Hampshire and southwest Maine. With calm
seas and little wave action have opted for a Coastal Flood
statement to highlight the elevated water levels.
NEAR TERM UPDATE...Kimble
Area Forecast Discussion
National Weather Service Indianapolis IN
1145 PM EDT Fri Jul 23 2021
...Updated Aviation Discussion...
Issued at 933 PM EDT Fri Jul 23 2021
While isolated convection across the western portions of the
forecast area has dissipated, persistent convection continues across
the far northeast area. However this is showing signs of weakening
as heating is lost. Upped PoPs where needed for this convection.
With nothing to really sustain the convection after the heating is
lost, expect it to continue to weaken and dissipate, and will allow
PoPs to lower this evening with this trend. Given how slowly its
weakening though, did extend PoPs in time a bit across portions
of the northeast.
Elsewhere just made some tweaks to hourly forecasts to match current
.Short Term...(This evening through Saturday night)
Issued at 244 PM EDT Fri Jul 23 2021
Much of the focus for weather later today and tonight will be on an
exiting complex of thunderstorms that has moved now into
northwestern Ohio. Latest GOES16 visible satellite imagery is
showing a diffuse outflow boundary that is now stretching from south
of Muncie up through Lafayette. This boundary has been a focal
point for convection this afternoon with showers and a few rumbles
of thunder ongoing. Don`t think that any widespread convection will
occur, but do think that the latest HRRR runs showing isolated
showers looks very reasonable with this area of enhanced lift across
an area with over 2000 J/kg of surface CAPE. Surface visibilities
haven`t been impacted by the hazy conditions today and don`t
expect much through the rest of the day.
During the overnight hours, convection will gradually dissipate with
the loss of diurnal heating. Low clouds associated with peak
heating should also be gone by 10 PM with mostly clear skies outside
of the continued thin smoke layer. Do think that areas of ground
fog are likely again tomorrow morning with the mostly clear skies
and gradually increasing surface moisture levels. Any fog that
forms will be brief. During the daytime hours, a few showers and
storms are possible during peak heating, but think that any
convection would be later in the day when a more robust convective
system may drift as far south as the northern counties. SPC placed
that area in a Marginal Risk which seems fairly reasonable at this
time with the potential for an MCS to dive further south that models
currently suggest in order to tap into the better instability.
Exact timing is very uncertain with the potential anytime from
late evening through the overnight hours.
In addition to the precipitation chances, temperatures and surface
dew points will gradually continue to rise with highs reaching the
low 90s in spots tomorrow along with max heat indices greater than
.Long Term...(Sunday through Friday)
Issued at 244 PM EDT Fri Jul 23 2021
Much of the extended period will be highlighted by a stagnant...
classic mid summer pattern as deep upper level ridging remains
quasistationary focused over the central and southern Plains. While
the Ohio Valley will reside on the periphery of the ridge through
much of next week...it appears very warm and humid conditions will
be the norm with the potential for periodic isolated to scattered
convection on most days driven by mesoscale details that have yet to
be worked out at this stage.
The best threat for storms at any point throughout the extended
likely focuses on Sunday in association with a weak southward moving
boundary. The boundary will interact with a hot and unstable airmass
to initiate scattered storms that will gradually focus near and
south of Interstate 70 by late day and into Sunday night. The
boundary will settle into the lower Ohio and Tennessee Valleys
before washing out on Monday...close enough to maintain a low
threat of convection across southern counties through the day. By
Tuesday and Wednesday...the threat appears even lower as weak high
pressure attempts to expand into the region. While the northwest
flow regime aloft cannot be ignored...the presence of the surface
high presents enough uncertainty into the forecast to go dry both
days at this time.
The upper level ridge appears to retrograde slightly by late week as
a sharpening trough amplifies over eastern Canada. This in turn will
sharpen the northwest flow in between the two features and across
the region...potentially opening the door for a greater influence
from waves traversing through the flow to produce convection or even
convective clusters. There are hints of a stronger surface low
tracking to the northeast of the region as well with the possibility
of a trailing frontal boundary back into the forecast area. Really
impossible to pin anything definitive down for the 5-7 day period at
this point...but it seems entirely plausible all things considered
that higher pops will eventually be needed at some point in the
Wednesday night through Friday period with a greater potential for
storms over parts of the region.
Highs in the upper 80 and low 90s will be common through the period
with even higher readings in spots. A cooldown back to more near
normal temps does appear on the horizon by next weekend.
.Aviation...(06Z TAF Issuance)
Issued at 1145 PM EDT Fri Jul 23 2021
- MVFR visibility likely at most sites at times overnight
- Low VFR cumulus will develop again Saturday.
- Some convection possible, mainly after 250300Z.
DISCUSSION: Some MVFR ground fog is likely at KLAF and KHUF
overnight, with KBMG also possible. Current thinking remains that
KIND will avoid the fog. Additional cumulus will develop on
Saturday. Brief MVFR ceilings cannot be ruled out during the
Convection is possible Saturday evening, spreading from north to
Area Forecast Discussion
National Weather Service Louisville KY
726 PM EDT Fri Jul 23 2021
...Updated Aviation Discussion...
.Short Term...(This evening through Saturday)
Issued at 300 PM EDT Fri Jul 23 2021
North-northwesterly winds aloft along the eastern edge of the
central CONUS ridge will continue to filter upper level smoke from
western US wildfires across our region. At the sfc, broad sfc high
pressure currently stretching across the Ohio Valley will slowly
slide eastward into New England tomorrow, changing our winds from an
ENE flow this afternoon and evening to more of a SE flow by tomorrow
morning. However, by tomorrow afternoon, sfc winds will be
southwesterly, which will help bring warmer and more humid air to
Dry wx remains in the forecast for tonight and into tomorrow. A weak
stationary frontal boundary stretches across the Mid-Atlantic and
cuts up through western Kentucky and into IL/IN. Most near-sfc smoke
looks to cling to this boundary through this evening and into
tomorrow. For our region, HRRR Smoke guidance suggests most smoke
will be 6000ft and above, primarily due to a shallow inversion that
is located around 850mb (5000ft). Could see an isolated shower/storm
outside of our CWA to our west or south tomorrow afternoon, but with
model soundings suggesting we`ll have convective temperatures in the
mid-upper 90s, we won`t reach that to fire off any convection in our
region. We could have a shower sneak into our southwestern CWA, but
not entirely confident that will happen either so will leave dry wx
grids for this forecast package.
Winds look to go calm overnight under clear skies, so once again
could have some early morning patchy fog possible south of the
Pkwys, but not expecting this to cause too many issues. With
southwesterly winds picking up tomorrow afternoon, temps will rise
to the upper 80s and low 90s.
.Long Term...(Saturday night through Friday)
Issued at 318 PM EDT Fri Jul 23 2021
...Saturday Night through Tuesday Night...
Upper level pattern looks to start off with a broad ridge over
western US with an upper trough axis moving out of New England. This
will place the Ohio Valley within a northwest flow regime. Within
this northwest flow pattern, a short wave trough axis is forecast to
move through the southern Great Lakes and weak frontal boundary will
drop southward through the region on Sunday. This should result in
shower and thunderstorm activity returning to the region. Highest
coverage looks to be on Sunday afternoon as the front drifts through
In terms of severe risk, the overall setup remains generally
marginal. Best bulk wind shear will remain within the faster flow
well to our north. We will have a build up of instability in the
afternoon. PWATs will be up near 2 inches, so storms will be
capable of torrential rainfall, gusty winds, and lightning.
Convection should diminish in coverage Sunday night with the loss of
The front will slowly push through southern KY on Monday and we`re
likely to see a gradient of PoP from south to north. The lesser
chances will be across southern IN with the greatest chances down
near the KY/TN border region. The front should slowly drop into
Tennessee on Tuesday. However, will keep some low chance PoPs going
for southern KY with the front in the area. If future model runs
push the front further south, then subsequent forecasts may trend
As for temperatures, highs Sunday and Monday should top out in the
upper 80s to near 90 with overnight lows in the upper 60s to around
70. Highs on Tuesday will again reach the upper 80s to near 90.
...Wednesday through Friday...
By mid-week, the western US ridge is forecast to strengthen and
build eastward. Center of the ridge looks to develop across the
high Plains. The eastern nose of this ridge may push into the
western part of the Ohio Valley for Wed/Thu for a time, but I
suspect that a deepening trough axis over the northeast will shove
it back to the west a bit. This would leave the Ohio Valley in a
notorious northwest flow regime with the possibility of mesoscale
convective systems dropping in from the northwest. The timing of
those are very uncertain at this time frame, but there are strong
signals in the data that we`ll be dealing with it by the end of the
As for temperatures, much of the temperature forecast depends on the
amount of upper level ridging building into the region. Confidence
on temperatures is lower than average here. For now, am going to go
a little more conservative than the ever increasing blended temps. I
think upper 80s and lower 90s are a safe bet through this time frame
with overnight readings in the upper 60s to the lower 70s.
.Aviation...(00Z TAF Issuance)
Issued at 725 PM EDT Fri Jul 23 2021
VFR conditions are expected throughout most of this TAF cycle with
the exception of potential MVFR VIS in fog at BWG and HNB. Latest
surface analysis continues to show high pressure centered over the
eastern Great Lakes with a weak boundary running N-S through W KY.
Best chance for fog development will be along and on the warm side
of this boundary with HNB likely experiencing longer and greater
restrictions. Otherwise, Saturday will be another VFR day with light
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1044 PM CDT Fri Jul 23 2021
.SHORT TERM... (Through Late Sunday Night)
Issued at 311 PM CDT Fri Jul 23 2021
Currently aloft, the CWA is under weak northwest flow thanks to a
broad ridge positioned over the western United States. At the
surface, the area of high pressure responsible for our recent
weather continues to drift slowly eastward away from our CWA. This
feature has kept southerly flow sustained over the Middle
Mississippi Valley today, which in turn has advected warm, moist air
into the region. This has allowed heat index values to reach the mid
to upper 90s for most locations, with a few more degrees of warming
left in the day. Also, these warm and humid conditions have allowed
for the atmosphere to become quite unstable over the CWA. Here,
current SPC mesoanalysis shows 2,500-3,000 J/kg of SBCAPE that a
subtle short wave has tapped into to produce isolated showers mainly
across southeastern Missouri. As the shortwave moves through the
Middle Mississippi Valley, I expect the chance for isolated showers
and maybe a brief, weak thunderstorm to continue mainly over
southeastern Missouri through early evening. The 12z HREF and recent
HRRR runs have also shown convection further northward over the St.
Louis metro area and into portions of western Illinois. Given the
passing shortwave and how unstable the environment is, I feel this
is a reasonable solution, and have expanded a slight chance of
convection into these areas through early this evening.
Tonight into tomorrow morning, another round of fog/haze is
possible, as the smoke from the western wildfires has been slow the
clear the CWA. Guidance currently gives me confidence that
conditions tonight and tomorrow morning will be better than what was
experienced last night with the smoke clearing to the east, but I
can`t rule out some lingering pockets of haze/fog late tonight and
During the day tomorrow, continued southerly low-level flow will
keep temperatures warm and humidity high. Current indications are
that temperatures will at least reach the low 90s area wide, with
some locations reaching the mid 90s. This will be the case
particularly in the St. Louis metro area, where heat index values
are anticipated to reach 105 during the afternoon, and the current
Heat Advisory looks to be on track. Later in the day, a cold front
will approach the CWA from the north, bringing with it the chance of
isolated to scattered convection. Model solutions differ on the
timing of the front, with faster solutions pushing the front and
associated convection into portions of northeastern Missouri and
west-central Illinois during the evening. The timing of slower
solutions would bring the front and convection into this portion of
the CWA later overnight. Widespread severe storms are not
anticipated, but with some guidance showing around 25 kts of 0-6 km
bulk shear, I can`t rule out an isolated damaging wind gust and some
hail with storms that form with the front.
The differences in frontal timing continue on Sunday, leading to
much uncertainty in how warm temperatures will get. If the front is
slower, a repeat of Saturday`s temperatures will be possible across
much of the region. If the front is faster, the frontal passage and
associated cloud cover and convection will help subdue temperatures.
I currently do not have confidence in either solution, and the
current temperature forecast reflects a blend of both with a lean
toward the warmer solution. If the slower front solution becomes
reality, the heat advisory may need to be continued and possibly
expanded on Sunday. Instability will be sufficient along the front
for convection, but 0-6 km bulk shear looks to be 20 kts or less, so
severe weather is not anticipated.
.LONG TERM... (Monday through Next Friday)
Issued at 311 PM CDT Fri Jul 23 2021
For Monday, the western upper-level ridge mainly stays in place,
but surface conditions are not as steady. Deterministic guidance
has varying solutions for the progression of the front and the
surface high behind it, which has lead to a notable increase in
the spread in ensemble guidance surface temperatures on Monday.
Like the forecast for Sunday, and more progressive front would
help curb temperatures by a couple of degrees and reduce humidity,
where a slower solution would lead to the CWA remaining just as
warm and humid as over the weekend, as well as linger the chance
for scattered convection.
These different solutions impact our weather through Tuesday and
Wednesday. WPC cluster analysis shows all four clusters supporting
the western ridge staying mostly in place. This gives me confidence
in NAEFS and EPS guidance holding 850 mb temps around 21 degrees C,
supporting surface temperatures across the CWA in the low to mid
90s. However, the placement of the aforementioned front and post-
frontal high will determine how humid we`ll get, and therefore, what
heat index values will be. Some guidance has the front stalling to
the south of the CWA and easterly/northeasterly flow around the
surface high keeping higher dewpoints shunted south. Other guidance
has uninhibited southerly low-level flow over the CWA, advecting
greater moisture into the area. If the first solution is realized,
the CWA will still see highs in the low to mid 90s, but relatively
lower humidity, whereas if the second solution is realized, highs
will be in the mid 90s and humidity levels will be uncomfortable.
Solutions begin to diverge considerably near the end of the extended
period. Ensemble guidance differs on the phasing of the western
ridge, the evolution of a trough over the eastern U.S. and its
associated shortwaves, and the potential passage of another cold
front through the CWA. This leads to much uncertainty as to how warm
temperatures will remain at the end of the week or if a potential
break from the heat is in store.
.AVIATION... (For the 06z TAFs through 06z Saturday Night)
Issued at 1044 PM CDT Fri Jul 23 2021
VFR flight conditions expected through the forecast period.
Otherwise, light south winds will veer to the southwest to west
and increase to near 10 kts by 17z Saturday. Also, diurnal cu
will develop across the region through the afternoon hours, before
dissipating towards sunset.
Precipitation chances will be on the increase Saturday night,
mainly over northern portions of the forecast area as a cold front
approaches. For now confidence is low that precipitation will
develop over KUIN before 06z Sunday, so kept TAF dry for now.
MO...Heat Advisory from noon to 8 PM CDT Saturday for Jefferson MO-
Lincoln MO-Saint Charles MO-Saint Louis City MO-Saint Louis
IL...Heat Advisory from noon to 8 PM CDT Saturday for Calhoun IL-
Jersey IL-Madison IL-Monroe IL-Saint Clair.
Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
700 PM CDT Fri Jul 23 2021
.SHORT TERM...(This evening through Saturday night)
Issued at 249 PM CDT Fri Jul 23 2021
A warm front resides over far NW MN over northern WI while a cold
front is draped over ND into MT, associated with a low pressure
center over southern Manitoba. Squarely within the warm sector of
this system is the WFO MPX coverage area. This has allowed areas
under full sun to reach the low-mid 90s for highs (while areas under
cloud cover are still in the 85-90 degree range with still several
hours of warming available). With dewpoints into the upper 60s to
lower 70s, this has allowed heat index values to climb to the 95-100
degree range for much of the area. However, this has also allowed
MUCAPEs to climb to over 2000 j/kg for much of the area, particularly
in western MN where values are 3000-4000. This available instability
will be tempered a bit going into tonight as the cold front drifts
closer to the area but the bigger concern will be an upper level
shortwave expected to move across Manitoba/Ontario through northern
MN/WI late this evening into the overnight hours. While the cold
front will help enhance low-level convergence, increasing low-level
jetting in conjunction with the arriving disturbance will enhance
divergence aloft, allowing for loosely-organized clusters of storms
to develop overnight in western MN and progress eastward through
sunrise in eastern MN and western WI. Bulk shear will increase to
around 30kt, so there is still some potential, isolated at best, of
some strong to severe storms with damaging wind gusts or large hail
overnight. The storms will diminish in coverage and shift east after
daybreak as the cold front sweeps through the area, resulting in
clearing skies behind his system. However, "clear" skies refers to
the lack of cloud cover. HRRR Smoke model indicates a swath of upper
level wildfire smoke returning to the area behind the cold front so
while there may be little to no cloud cover, hazy skies will likely
result and make for filtered sunshine during the day Saturday.
As for temperatures, very little drop in temperature from today to
tomorrow for highs is expected behind what is essentially a "cold"
front. Highs will be more in the upper 80s to lower 90s, rather than
hitting the mid 90s as today. That said, much less humid conditions
are expected as the cold front will bring much drier air into the
region as it passes through. Thus, this will make for slightly more
tolerable conditions in terms of heat index. Therefore, once the Heat
Advisory expires later today, no additional advisories will be needed
for Saturday as heat index values will top out 90-95 degrees, highest
of which will be east and south of the Twin Cities metro.
.LONG TERM...(Sunday through Friday)
Issued at 249 PM CDT Fri Jul 23 2021
Not much has changed during the long term period, the upper ridge
slowly builds east out of the Great Plains into the Upper Mississippi
valley. Locally, we`ll continue to experience above normal
temperatures through the middle of next week. As per the previous
AFD, the 12Z guidance continued the trend with a deepening trough
across eastern Canada by the end of the week, with slightly cooler
temperatures for next weekend. How far west the upper ridge retreats
will be key for temperatures next weekend.
A strong upper ridge develops over the center CONUS with heights
reaching 597+ dm by mid week. We`ll remain on the edge of this ridge
throughout the long term. This set up allows for potential shortwaves
to move along top of the ridge, favoring the development of
potential convective complexes. Forecast models like to develop
convection during this pattern and as a result the NBM has 20-30 PoPs
each night until Thursday. On Monday, moisture return kicks in and
the humidity returns as dew points increase into the 60s. For us, the
warmest temperatures arrive on Tuesday and Wednesday. Barring any
convective debris or dense smoke layers, highs in the low to upper
90s and dew points in the upper 60s and lower 70s are expected. A
frontal passage Wednesday night could trigger a round of
thunderstorms across the region and provide some relief for
temperatures on Thursday.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 700 PM CDT Fri Jul 23 2021
VFR this evening, then showers and thunderstorms build late this
evening and track across central/southern MN and western WI
overnight. MVFR or IFR conditions possible with the showers and
KMSP...TSRA chances increase after 06Z through about 11Z. IFR
conditions possible within heavier cores. Skies clear quickly
Saturday morning with much drier air moving in.
/OUTLOOK FOR KMSP/
Sun...VFR. Wind W 5-10 kts.
Mon...VFR. Slight chc SHRA/TSRA. Wind S 5-10 kts.
Tue...VFR. Wind SW 5-10 kts.
Issued at 249 PM CDT Fri Jul 23 2021
While scattered convection is expected overnight, the hit-and-miss
nature of the thunderstorms plus short-duration rainfall is not
expected to make any appreciable dent in the ongoing drought. In
addition, the strong drop in dewpoints with highs still in the 90s
will force RH values to 20-25 degrees for much of the coverage area,
particularly west of I-35 and north of I-90. However, winds look to
fall short of Red Flag criteria with speeds of 15-20mph and gusts
20-25mph. In addition, collaboration with MNCC officials indicated
that the increase in humidity recently has allowed some smaller fuels
to be reinvigorated, helping mitigate fire weather concerns despite
the overarching drought. Thus, we have agreed to issue a Fire Danger
(Special Weather) Statement to highlight the Critical RH and near-
Critical RH values expected on Saturday. Should rainfall be less than
advertised overnight, the situation could change and additional
collaboration with surrounding offices and fire weather officials may
MN...Heat Advisory until 8 PM CDT this evening for Anoka-Blue Earth-
Kandiyohi-Lac Qui Parle-Le Sueur-McLeod-Meeker-Nicollet-Ramsey-
WI...Heat Advisory until 8 PM CDT this evening for Polk.
...Updated Aviation Forecast Discussion...
Issued at 223 PM CDT Fri Jul 23 2021
A heat advisory is in effect tomorrow for southeast Nebraska and
southwest Iowa. Maximum afternoon temperatures are expected to
remain above 90 degrees for the next 7 days. Temperatures at or
above 100 degrees are expected Tuesday and Wednesday.
Today and Tomorrow:
Most locations in the forecast area have reached at least 90
degrees so far this afternoon. Maximum temperatures should peak
in the 91 to 99 degree range with the warmest temperatures along
the NE/SD border. Dew point temperatures have outperformed by 2 to
4 degrees so far today which will increase the effects of the
heat. The increased moisture will likely result in many locations
reaching a heat index of 100 degrees.
Mid-level height falls are forecast across the northern Plains in
response to a couple of shortwaves moving eastward. One of those
shortwaves in combination with a surface frontal boundary may lead
to some non-severe thunderstorms along the NE/SD border. The best
chances for precipitation will be between 10 pm tonight and 6 am
tomorrow morning. Rainfall amounts of less than a tenth of an inch
Tomorrow, the HRRR smoke model indicates a higher presence of
smoke across Nebraska and Iowa. The smoke may not be noticeable
at the surface as it`ll be mostly aloft. The increased smoke in
combination with height falls in the mid-levels may lead to
slightly cooler temperatures than today. Temperatures will still
be above 90 and dew point temperatures of least 70 degrees will
result in a muggy afternoon.
Sunday and Monday:
Sunday and Monday will be the cooler days in the forecast period.
Another weak mid-level shortwave is forecast to move through
Nebraska and Iowa. A few non-severe thunderstorms will be possible
Sunday evening into Monday morning. Whether precipitation is
realized, temperatures these two days will depend on how much
cloud cover develops from the passage of that weak shortwave.
Tuesday through Thursday:
Medium range guidance is still in good agreement in the
intensification of a mid-level ridge across the central CONUS.
NAEFS analysis of temperatures from 850 hPa up to 500 hPa show
temperatures at those levels to be at least in the 99th percentile
of climatology. All signs point to Tuesday and Wednesday being
dangerously hot days. Maximum temperatures are expected to top
100 degrees in many locations. Minimum temperatures won`t drop
below 75 degrees in southeast Nebraska and southwest Iowa. If the
forecast doesn`t change, a heat headline will be needed for these
Some relief from the triple digit heat is forecast for Thursday.
The mid-level ridge retrogrades to the West Coast leaving the
central portion of the country in northwest flow.
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1028 PM CDT Fri Jul 23 2021
VFR conditions are expected through the TAF cycle. A weak frontal
boundary is forecast to drift south overnight and will provide a
subtle wind shift turning winds from southwest to north. There is
a remote possibility that a few showers could develop along this
boundary overnight to just past sunrise on Saturday. Did add a
TEMPO group for KOFK but left KOMA and KLNK dry at this point. A
few sprinkles are possible Saturday morning at these sites, but
any associated clouds should remain at VFR category.
NE...Heat Advisory from noon to 8 PM CDT Saturday for NEZ051>053-
IA...Heat Advisory from noon to 8 PM CDT Saturday for IAZ079-080-090-
Area Forecast Discussion
National Weather Service Reno NV
1133 AM PDT Fri Jul 23 2021
Smoke and haze from multiple wildfires will continue to produce
areas of reduced air quality over the next few days. Temperatures
will gradually rise into the weekend with highs pushing above 100
degrees for most lower valleys by Saturday. Confidence is increasing
for showers and thunderstorms returning to the region Sunday through
much of next week.
* Smoke and haze with air quality impacts likely through the weekend
for much of the region.
* Hot temperatures return for lower valley areas with triple digit
heat in the mix again. Some heat-health impacts possible.
* Monsoon moisture will begin to build along the Eastern Sierra into
southern Lyon/Mineral Counties Sunday with chances for isolated to
scattered thunderstorms. Impacts include localized heavy rain,
with higher risk of debris flows, especially for burned areas.
An easterly wave will progress across the desert southwest through
the weekend while high pressure strengthens across the Great Basin
and northern California. This wave will help to eventually sweep up
monsoon moisture into the eastern Sierra and western Nevada with
increasing chances for shower and thunderstorms late this weekend
into next week. For now through, the warming trend continues into
the weekend with high temperatures around 5-8 degrees above typical
late-July values, upper 80s-lower 90s for the Sierra and into the
triple digits for western Nevada valley locations.
If the hotter temperatures don`t get you to take a break indoors
this weekend, then the smoke and haze certainly should. Weaker
westerly winds the next few days will limit smoke/haze clearing
across western Nevada and the Tahoe Basin today and Saturday.
Multiple ongoing wildfires, Dixie and Fly in Plumas County and
Tamarack in Alpine/Douglas Counties, will continue to produce
smoke the next couple of days. The trend will be for increasingly
poor visibility and air quality conditions, especially as winds
shift west to northwesterly overnight. Latest HRRR smoke
simulations funnel the smoke directly into Reno-Tahoe tonight into
early Saturday. Keep those windows closed tonight!
The next order of business headed into the weekend will be the
potential for showers and thunderstorms as monsoon moisture begins
to make a push for the region. Shower and thunderstorm potential
will be rather isolated today and Saturday, with the best potential
confined to far southern Mono and Mineral counties. Precipitable
water parameters really ramp up by late Sunday into next week with
values between 0.8 - 1.0 inches. These values are quite anomalous
for the eastern Sierra and western Nevada. Confidence is high for
the moisture to inundate the region, but the nature of showers or
thunderstorms have yet to be determined. There doesn`t appear to be
an obvious trigger or mechanism, for now, to facilitate deep
convection, but that can change in these situations. We will
continue to highlight the following risks with thunderstorms/showers
for next week: (1) lightning may impact fire suppression,
firefighter safety, or new fire starts (2) heavy rain: increased
threat for flash flooding and increased risk of debris flows in
steep terrain or burned areas. Areas south of Highway 50 have the
best potential through Monday of receiving a wetting rain or
thunderstorm, and the chances will expand northward for Tuesday and
the remainder of next week.
Greatest impacts through the weekend will be smoke/haze from ongoing
wildfires. KMMH looks to largely avoid any big impacts, but most
other terminal sites are likely to experience degradation in
visibility. The worst visibility reductions with smoke ceilings will
be at KCXP-KMEV (due to the Tamarack fire) and near Lake Almanor-
KSVE-KLOL-KNFL (from the Dixie and Fly fires). All other terminals
may only experience slantwise visibility reductions with periods of
lower surface visibility.
Westerly flow weakens today which will limit smoke clearing out of
the Tahoe Basin and Sierra Front. There will be some improved mixing
late in the afternoon for KTVL/KTRK/KRNO, but conditions will likely
stay relatively poor for KCXP and KMEV. Smoke from the Dixie and Fly
fires in Plumas County will flood into western Nevada late
tonight into early Saturday as flow gradually shift west and
northwest. Sunday may be very similar with little change in the
wind direction early Sunday. The flow Saturday could bring smoke
to all areas north of KMMH, with similar conditions for Sunday.
For this afternoon and evening, there may be a few stray
thunderstorms around KMMH and the White Mountains eastward as well
as Saturday afternoon. There are slightly better chances (15-20%)
Sunday from KBAN-KHTH south. A moisture push early next week will
bring increasing chances for showers and thunderstorms across
the eastern Sierra and western Nevada.
No significant changes to the ongoing fire weather forecast.
The gradual heating trend continues through the weekend with late
afternoon/evening winds gusting into the 20-25 mph range. For
northeast CA, humidity recovery will continue to be poor to moderate
at best until the bulk of the moisture surge arrives early next
week. For the eastern Sierra up to Tahoe, recoveries will improve
faster as moisture builds on the edge of an approaching monsoonal
push. A few buildups are anticipated in these areas today and
Saturday with an isolated thunderstorm for southern Mono into
southern Mineral Counties.
Thunderstorm and shower potential will be on the increase Sunday and
through next week. Ensemble simulations are showing a decent push of
monsoonal moisture into the eastern Sierra, Tahoe Basin, northeast
CA and western Nevada with precipitable water values nearing
1.00" for some locations. There is a high probability for
localized wetting rains with an increased potential for flash
flooding. Steep terrain and burned areas will be the locations to
keep an eye out for flash flooding and higher risk for debris
flows. Lightning will also pose a danger to ongoing fire
For more information from the National Weather Service visit...
Area Forecast Discussion
National Weather Service Sacramento CA
103 PM PDT Fri Jul 23 2021
Dry weather with temperatures warming into the weekend. Chances
for mountain thunderstorms in the northern Sierra return late
weekend into early next week.
A brief period of northerly winds has pushed fire from the Dixie
and Fly fires south into central valley. This was picked up pretty
well by HRRR smoke. Expect a little of a delta breeze later this
evening to push it back north and east. Have added it to forecast
though for this afternoon and evening.
Beyond that forecast still on track which is that upper level
ridge will retrograde back over California slowly. Monsoonal
moisture will begin effecting the far southern portion of our
forecast area in the Sierra with isolated thunderstorms. PW`s
looking pretty high so they shouldn`t be dry but will for sure
have gusty winds and brief downpours.
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Large area of high pressure will dominate the forecast during the
extended period. Monsoonal moisture and instability will likely
lead to at least isolated thunderstorms. Timing and coverage is
always tricky with these patterns but for now pretty high
confience activity will remain in mountains and upper foothills.
Have expanded coverage of pops a bit Tuesday to include higher
terrain of Shasta County. Otherwise for the most part chances are
for Sierra south of I-80. Rasch
VFR conditions are generally forecast to prevail over the next 24
hours. Exception would in the mountains and foothills where areas
of IFR visibilities and mountain obscurations are possible as a
result of wildfire smoke. Winds generally less than 12 kts except
gusts up to 25-30 knots in the vicinity of the Delta.
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
530 PM MDT Fri Jul 23 2021
.DISCUSSION...(This Evening Through Friday)
Issued at 1230 PM MDT Fri Jul 23 2021
The latest water vapor images and RAP model 500-mb height
analysis showed an upper high anchored over the Southwest U.S.
with quasi-zonal flow across the CWA. One short-wave trough was
evident over central/eastern WY and it was associated with
considerable cloud cover. This will dampen heating and thus result
in less MLCAPE and more MLCIN than previously expected. Better
insolation was over central SD, which should be more favorable for
later convective development. Otherwise, another short-wave
trough was moving across central MT in association with a 70-90kt
jet streak. Q-vector convergence supports stronger lift with this
system; lapse rates, CAPE, and 0-6km bulk shear will be better
with this wave, and thus convective development appears better.
Based on this and the CAMs it seems probable that weaker storms
will form over the BLKHLS, with strong-to-severe storms (and
supercells) over parts of northwestern into central SD, and then
some severe storms with a wind threat over south-central SD where
inverted-V soundings, a weak boundary, and weaker 0-6km shear
exist. PWATs of 150-200 percent of average favor locally heavy
rain, but the lack of a focusing boundary and mean winds of
15-20kt should preclude organized heavy rainfall. Otherwise, these
storms/small MCSs should be mostly east of the CWA by 04z.
Convection will be relatively diminished Saturday and Sunday as the
monsoonal moisture plume is shunted south of the CWA. However, some
warm advection and steeper lapse rates over the southwestern CWA
will favor elevated storms late Saturday, and possibly Sunday too as
monsoonal moisture creeps back into the CWA.
Monday through Wednesday look to be exceptionally hot as the
Southwest U.S. upper high builds northward. Record highs and record
high lows appear likely on Tuesday based on the latest ensemble and
NBM guidance. The main limiting factor is the potential for smoke to
reduce insolation. The upper ridge then appears to retrograde
Thursday and Friday as upper low pressure deepens over the Hudson
Bay area. Monsoonal moisture also should spread back across the
CWA. This will bring a modest reprieve from the heat along with
slightly better chances of showers and thunderstorms.
.AVIATION...For the 00Z TAFS Through 00Z Saturday Evening
Issued At 523 PM MDT Fri Jul 23 2021
Thick band of mid level clouds streaming over southwestern into
central SD will shift to the east overnight, leaving mostly clear
skies Saturday. Thunderstorms moving across northwestern SD. Heavier
smoke is moving into northeastern WY and will spread across the
area, reducing visibility occasionally.
Issued At 1230 PM MDT Fri Jul 23 2021
Minimum relative humidities will fall to 10-15 percent on Monday
and Tuesday across northeastern WY and northwestern SD as high
temperatures soar into the upper 90s and 100s across most of the
area. However, at this time it appears that wind speeds will
remain below red flag warning criteria.
Area Forecast Discussion
National Weather Service Las Vegas NV
230 PM PDT Fri Jul 23 2021
.SYNOPSIS...Moist and unstable air will remain in place through the
weekend, providing fuel for thunderstorms. A large circulation
moving in from Arizona will likely bring additional moisture and
more extensive thunderstorm development across the entire region
especially late Sunday into Monday.
.UPDATE...Another monsoon day for the desert Southwest, though
coverage was less than what we have seen the past few days. Main
areas that saw afternoon convection were through Lincoln County as
well as eastern Mohave County. Some training storms with high
rainfall rates did cause some flash flood concerns in southeast
Mohave County, but further north the concern was more about the
potential for strong winds. An outflow developed from decaying
storms in southwest Utah later this afternoon as has been tracking
southeast through eastern Lincoln County, northeast Clark County and
northern Mohave. Along the outflow, gusts 40 to 50MPH have been
reported. In addition, the outflow has allowed for additional
thunderstorms develop as it unzips the atmosphere and allows for the
extra kick to cause thunderstorm initiation.
Moderate confidence that this outflow will continue to track
southwest through much of Clark County and the Lake Mead area. With
current mesoanalysis showing MUCAPE values still over 1000 J/Kg,
additional isolated to scattered thunderstorm development is
possible over the next few hours as the outflow moves through. The
storms are moving quickly and diminish fairly soon after
initiation, so the threat for flash flooding is not high. However,
DCAPE values remain in the 1500-2000 J/Kg range over Clark County
and the Lake Mead area, and dry air was noted both in the low levels
as well as above the main cloud layer. A few downdrafts and sudden
gusty winds 40-50 MPH are possible with these storms.
The other area of concern tonight is in eastern Mohave County. A
complex has been pushing west through Arizona and is almost at the
county border. This area of precipitation should continue to push
west tonight, and though the complex should diminish over the next
few hours, high PWAT values over this region could cause some heavy
rain and isolated flash flooding. A couple of the Warn on Forecast
ensemble members do show "paintballs" of 1 in/hr rain rates around
the Valentine and Fort Rock area, and there is a non-zero
probabilities of over an inch QPF through central Mohave County
until 06Z on the HREF 3hr PMMs. Precipitation may linger through
southern Mohave overnight before ending Saturday morning, but the
heaviest and most widespread precipitation should be through 06Z.
.SHORT TERM...tonight through Sunday.
A favorable setup continues to come together for thunderstorms to
converge around northeast Clark County early this evening and push
down the I-15 corridor which will likely impact Lake Mead and
possibly the Las Vegas Valley. The HRRR and various HREF members
continue to show this trend which should materialize between 7 PM
and 11 PM PDT/MST. The main threat would be winds 40-50 mph, and
possibly higher. Heavy rain and localized flash flooding will also
be possible, but the storms should be progressing toward the
southwest fairly quickly. Storms should continue developing after
midnight as the outflow boundary pushing southward through Mohave
Saturday and Sunday will see the approach of the large slow moving
inverted trough moving westward across Arizona which will produce
thunderstorms propagating from northeast to southwest. The latest
HREF members indicate an organized cluster of storms Saturday
evening bringing the threat of heavy rain and flash flooding to
central and southern Mohave county and the nearby Colorado River
Valley from Laughlin-Bullhead City to Lake Havasu. Favorable
conditions will continue for large organized clusters of
thunderstorms into Sunday. A Flash Flood Watch is in effect Saturday
afternoon through Sunday evening for Mohave County and the Colorado
River Valley from Lake Mead to Lake Havasu.
As the wave slowly progresses, the potential for numerous
thunderstorms with heavy rainfall may expand into southern Nevada
and eastern San Bernardino County by Sunday night.
.LONG TERM...Monday through Friday.
The latest ECMWF and GEFS ensemble means indicate the axis of the
easterly wave will be centered about over southeast California and
northwest Arizona by 12Z Monday then will continue lifting toward
the northwest during the day. This will be favorable for generating
showers and thunderstorms on the leading edge of the ridge which
will increasingly favor western San Bernardino and Inyo counties
along with south central Nevada Monday afternoon and evening.
Convection should diminishing on the back side of the wave and the
forecast area will be under a general southeast flow Tuesday through
Friday with moisture decreasing somewhat, but there will still be
sufficient for afternoon showers and thunderstorms the rest of the
.AVIATION...For McCarran...Thunderstorm formation on area mountains
to the south and west of the Las Vegas Valley are possible today.
Prevailing wind speed and direction should veer from 160 to 220
through the afternoon with speeds generally around 8 kts. However,
storm formation could result in wind shifts as well as gusty winds
from their direction this afternoon. Between 03 and 08Z this
evening, there is a chance of a gusty northeast outflow reaching the
terminal. Confidence regarding timing and strength is low at this
time, and will continue to update the TAF accordingly. SCT-BKN
cloud bases down to 10 kft possible.
For the rest of southern Nevada, northwest Arizona and southeast
California...Focus area for storms today are in Lincoln/Mohave
counties and Mohave County tonight. Storm formation is possible on
Clark County mountains that could result in wind shifts and gusts
from either the southeast or west this afternoon. Otherwise, storm
formation is not anticipated directly over any terminals, with
diurnal wind patterns otherwise expected. SCT-BKN cloud bases down
to 10 kft possible.
.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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