Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/26/21

Area Forecast Discussion...UPDATED

National Weather Service Amarillo TX

710 PM CDT Wed Aug 25 2021

.AVIATION...
For the 00Z TAFs, winds will diminish early this evening, then
increase again by mid to late Thursday morning. No precipitation
is expected through late Thursday afternoon. VFR conditions are
forecast to continue at KGUY, KDHT, and KAMA during this fcst
cycle.

.PREV DISCUSSION... /Issued 233 PM CDT Wed Aug 25 2021/

SHORT TERM...Tonight through Thursday

H5 high center remains near central KS with ridge extending SW
into the Panhandles, NM and SRN AZ. A narrow moist axis NW of the
ridge center, a weak boundary and strong heating may be enough to
spark a storm or two in the far NW late this aftn or evening. NAM
nest and HRRR forecast soundings show the window is there, but
brief. Keeping POPS around 10 to account for this potential.
While CAPE will strongly limit updrafts, DCAPE will be high and
couldn`t rule out a dry microburst if a storm does form, but
overall threat is very low given the POPs.

SE flow at H7 actually brings some drier air into the area at
least temporally on Thu and looks like the narrow moist axis will
push NW our of the area. The first of a series of S/WVs moving
across the rockies will lead to weakening of the ridge with H5
heights falling through the day. This will promote a dry forecast,
but will also allow for a slight decrease in high temps with
mostly 90s and maybe just a couple isolated 100-101 degree
readings. Weak to moderate SSE to SSW winds will continue.

Gittinger

LONG TERM...Friday through Tuesday...

The main high center will reform near the mid Atlantic coast with
weak ridging extending west towards far SRN NM and AZ while broad
troughing takes hold across the Rockies late in the week. By late
Friday the H5 heights will fall to below 590 DM locally as a
subtle weakness develops across the west and weak H7-H5 positive
vort moves into the region. There is just enough W-SW flow to push
the edge of some monsoon moisture into the far NW corner of the
Panhandles on Fri and the NW half to third of the Panhandles by
late Saturday (per H7 theta-e moisture progs). This will promote
a chance for storms in the far NW late Fri aftn and evening with a
slightly expanded area of SLT CHC POPs Saturday aftn and evening
(roughly north of Adrian to Canadian line).

The last few model runs have backed off bringing a weak front
into the region on Sunday. This change is due to a slightly
weaker and more northern track of a short wave the moves across
the NRN plains and the operational GFS and ECMWF now hang this
feature up across KS. The GEM brings it closer to the area, but
still falls short. Convective outflow from storms along the
boundary to the north the previous day could still help push it
further south. Until we see some CAMs and higher resolution
models reach out to Sunday, not sure we can completely rule a
boundary out. Despite the front likely remaining north, Sunday
remains the best CHC for storms with the entire area in play given
continued mid-upr level weakness over the area and spread of
higher moisture across the area from the south and west. That
said, NBM POPs have decreased Sun and esp Mon given good model
agreement in keeping the front north. As mentioned yesterday, the
boundary will be the difference between seeing isolated to low end
scattered coverage or high end scattered coverage, but for now
will stick with NBM POPS of just 20-30 percent based on potential
for no help from low level forcing associated with a SFC boundary.
High temps have also increased late in the period given changes
in frontal position described above.

Models are all over the map regarding the evolution and track of a
potential organized tropical system in the Gulf next week and
whether or not the system brings moisture or even the actual
remnant low to the area. Until a center forms for models to latch
onto, expect more potentially wild swings in next weeks forecast
for much of the country.

Gittinger

.AMA Watches/Warnings/Advisories...
TX...None.
OK...None.

Area Forecast Discussion

National Weather Service Binghamton NY

745 PM EDT Wed Aug 25 2021

.SYNOPSIS...
Hot and humid conditions are expected once again tomorrow.
However, scattered afternoon shows and thunderstorms may bring
temperature relief for some. Isolated to scattered afternoon
thunderstorms look to become a daily occurrence into the
weekend.

.NEAR TERM /THROUGH THURSDAY NIGHT/...
745 pm update...
A few showers and weak storms are developing over western
Steuben County this evening but remaining relatively short-lived
with a few of the cells producing around or just under an inch
of rain in 1-2 hours. There is some stronger more persistent
convection just to the west but this should lift gradually to
the north/ne this evening and dissipate after sunset. Made some
minor adjustments to the PoP and weather forecast for this
evening and overnight. Increased mention of showers and storms
this evening and cut back on precip during the overnight/early
Thu morning period. Rest of the forecast remains unchanged at
this time.

315 PM Update...

Hot and humid conditions continue this afternoon. Many areas are in
the upper 80s with Syracuse just now creeping into the 90s. Skies
are mostly clear with some fair weather clouds present. Some high
clouds/smoke have stretched from a portion of the Twin Tiers up
through the Western Mohawk Valley but have had little impact on the
temperatures. So it looks like most areas that were expected to
reach advisory criteria probably will.

A weak shortwave will pass through the area, which could bring some
isolated storms. PoPs were limited to the western portion of the
Finger Lakes and Southern Tier as most models keep any precip in
that general region. Things will be dry overnight though there is a
chance for some patchy valley fog to develop, but with the warmer
temperatures, it could take some extra time to develop. Overnight
lows will be in the upper 60s to low 70s.

There is a slight chance for some scattered showers and
thunderstorms along the Thruway and areas northward early Thursday
morning as a shortwave approaches the region. Coverage of PoPs
extends down to the Southern Tier by sunrise. Fog should also begin
to lift soon after sunrise. PoPs continue to increase into the
afternoon as this shortwave passes through and then a cold front
drops south and approaches the region by the late evening hours.
While there is some decent MLCAPE by late afternoon and evening, the
shear is lacking, so storms are not expected to be severe.

Another hot and humid day is expected Thursday as temperatures will
once again be in the upper 80s and low 90s and dew points in the
upper 60s and low 70s. A Heat Advisory has been issued for the same
area as before as heat indices approach 99 once again. The HRRR
smoke is showing some elevated smoke over the region, so that could
possibly have an impact on temperatures. However, if the smoke is
similar to today, then it will have little impact on temperatures
tomorrow. Any scattered showers/storms could bring cooler temps once
they pass through. There may be some lingering showers overnight.
Otherwise there is the possibility for fog to form again late
Thursday night and early Friday morning. Overnight lows will be
warm as temperatures will be in the 60s.

.SHORT TERM /FRIDAY THROUGH SATURDAY/...
330 PM update...

A frontal boundary will be settled over the area by Friday morning
with a flat upper ridge over the area. There is some disagreement
among models as to how far southward this will drop. Some runs keep
this a little more to the north, near the Thruway, while others drop
this a little farther southward towards the Southern Tier. South of
the boundary, greater destabilization amid dewpoints in the 60s and
lower 70s, as well as daytime highs in the mid and upper 80s, will
allow for better chances for scattered afternoon convection. North
of the front, dewpoints may mix out into the lower 60s by the
afternoon with a more stable airmass. Thus, kept chances for
afternoon showers highest along and south of the Southern Tier, with
mainly a slight chance to the north. Highs to the north should be
generally in the 70s and lower 80s, but the typically warmer
Syracuse metro may turn a couple degrees warmer.

Chances for showers and some thunder linger overnight with the
boundary in place, while temperatures range in the 60s under cloudy
skies.

Saturday, the front lifts northeast as a shortwave skirts the
periphery of the upper ridge. The airmass with destabilize nicely
behind the front for the afternoon, with our best chances for
showers and storms across our southwestern zones given a little bit
of uncertainty regarding just how far north the front will be able
to lift. There is no real dynamical support for any strong
thunderstorms, with the main threat being downpours amid slowly
eastward-moving storms.

Otherwise, expect a pretty steep temperature gradient with highs
only in the 70s across our northeastern zones ahead of the front,
and the lower to mid 80s to the west. Skies remain mostly
cloudy.

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
330 PM update...

Sunday will be warm and humid as the front finally migrates north of
our area into the afternoon. Scattered afternoon convection will be
possible given daytime instability, otherwise expect partly to mostly
cloudy skies while temperatures peak in the upper 70s to lower 80s.
Will keep chances for showers and some rumbles of thunder going
overnight into early Monday morning ahead of an approaching
shortwave. This will drag a cold front through the region Monday
evening - though some runs are a little earlier. Plenty of
instability and some modest shear ahead of the front would lead to a
potential for more organized convection depending on the timing of
the frontal passage, so this will be worth keeping an eye on.

Much of the area turns dry Monday night into Tuesday as the front
drops south of the area with more seasonal weather. Temperatures
starting in the 60s Tuesday morning peak in the 70s to lower 80s
Tuesday afternoon before temperatures fall back into the upper 50s
Tuesday night.

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Weak high pressure in place across the region should allow for
mainly VFR conditions through the next 24 hours. The only
exception continues to be ELM where fog is likely Thursday
morning. Prevailing MVFR vsbys with IFR or lower restrictions
are expected through 13Z, after which ELM will be back to VFR.

There is a chance for isolated showers/storms Thu afternoon,
mainly for RME, SYR and ITH. However, confidence is too low to
include in the TAFs at this time.

Light and variable winds are expected through the period.

Outlook...

Thursday Night through Sunday...Mainly VFR. A few afternoon and
evening showers or thunderstorms may cause brief restrictions,
and fog will be possible each morning.

.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...Heat Advisory from 11 AM to 7 PM EDT Thursday for NYZ009-
015>018-022>025-036-037-044-045-055-056.

$$
SYNOPSIS...BTL/MPK
NEAR TERM...BTL/BJT
SHORT TERM...HLC
LONG TERM...HLC
AVIATION...BTL/BJT

Area Forecast Discussion

National Weather Service Des Moines IA

655 PM CDT Wed Aug 25 2021

.DISCUSSION.../Tonight through Wednesday/
Issued at 303 PM CDT Wed Aug 25 2021

Key Messages:
- Low confidence in POPs through Thursday
- Low confidence in Severe Wx Potential Thursday
- Active Weather Likely to Continue Through Weekend

Tonight Through Friday Morning:

The multiple rounds of convection over the past 24 hours have left a
myriad of outflow boundaries across the region, and there is another
synoptic scale front further northwest into portions of Minnesota
and the eastern Dakotas. By 16z early this afternoon most of the
rain shower and thunderstorm activity had ended. Subtle H5 height
rises have been ongoing as the mid to upper-level high pressure
pushes a bit northward. This will also aid in clearing out skies
through this afternoon. For now, this is expected to stall the
boundary to the north of the forecast area. While there are several
outflows sitting across the forecast area, satellite trends over the
past few hours to do not show much in the way of new cumulus,
suggesting that any convergence from these outflows is hitting the
cap. While some boundary layer destabilization will be likely this
afternoon with clear skies, MLCIN values appear to be near 100 J/kg.
In addition, low-level flow will remain relatively weak through this
evening. This will greatly limit rain shower chances this afternoon
through evening. Attention turns to a pair of short-waves currently
present over the Northern Plains into parts of southern Canada.
Various GOES-16 imagery products show this enhanced flow through
these short-waves, attempting to ride along the backside of the
ridge moving up from the south. Some convection has emanated from
these waves in Dakotas this morning. As these short-waves propagate
across the northern Plains this afternoon and evening, they will
eventually attempt to congeal and generate a stronger PV anomaly,
though there still appears to be two distinct areas of stronger
cyclonic vorticity. Model consensus remains very poor. 12z GFS has
remained much faster with the first wave, attempting to move through
Minnesota after 00z, and pushing the boundary into northern Iowa by
06z. The NAM and RAP have been much slower, waiting to push this
into northern Iowa until around 11z. In the CAM world, it is not
much better. 12z NSSL-WRF attempts to initiate convection around the
11z time frame, but never fully materializes until the second area
of enhanced vorticity comes through and pushes the boundary even
further south. Meanwhile, the HRRR initiates convection in Minnesota
with the first wave, but pushes this into southwest Wisconsin, and
does not bring convection into Iowa until after 15z coming from
northeastern Nebraska. The FV3-SAR and HiRes-ARW, have some
initiation, but struggle to maintain anything organized through the
late morning. These latter CAMs have a more organized system
developing ahead of the boundary after peak heating, where boundary
layer destabilization will likely occur. For the overnight hours
into Thursday morning, will focus higher POPs along the IA-MN state
line close to the boundary, where at least some weak shower activity
should get going. For the rest of the forecast area, will limit POPs
to chance and slight chance only, given the uncertainty with how the
forcing will play out. Should convection overnight through Thursday
morning occur, there is some potential for elevated severe storms.
RAP and NAM soundings across much of Iowa have forecast lapse rates
over 8.0 C/km. If the initiating boundary does not jump far ahead of
the short-wave, increased mid-level level flow could send 2-8km
shear values to near 50 kts, with MUCAPE above 2000 J/kg. This could
support a severe hail threat, and some potential for damaging winds
(especially if strong MCS with a healthy cold pool develops).
However, this is conditional on convection being able to develop in
the first place, and this remains very uncertain. The threat for
convection and severe weather Thursday afternoon also remains
conditional. While confidence is a tad bit higher for afternoon or
early evening initiation, the current outflow boundaries and any new
outflow boundaries that may develop from overnight activity could
drastically change the mesoscale environment. If there is not much
in the way of cloud cover debris, boundary layer destabilization
should be expected, steepening low-level lapse rates to nearly 8.0
C/km, and MLCAPE values up to 2000 J/kg. Mid-level lapse rates will
also likely remain steep into the afternoon. The question is will
there be enough mixing to erode any surface or mixed-layer cap that
may be in place? It is possible that MLCIN values could be as high
as -150 J/kg in the morning leading into the afternoon. Even if the
synoptic boundary drops south, there will still be a lot of work
left to be done. If the scenario plays out where parcels can be
surface based or very near the surface within the boundary layer,
the surface low moving out of Colorado should enhance southerly low-
level flow enough to increase deep layer shear values with the jet
streak above, with 0-6km bulk shear in the range of 30-40 kts. Along
the main synoptic boundary, or perhaps along some kind of remnant
outflow boundary, a few discrete cells may able to develop by mid-
afternoon. However, the orientation of the deep shear vectors to the
initiation boundary is unknown at this time. If discrete supercells
do develop, or strong multicells, large hail, damaging winds, and
even a tornado is possible. If there were to be a tornado threat,
this would like have to be closer to the boundary to ensure strong
enough storm-relative inflow. If the cap erodes but the deep layer
shear vectors are more parallel to the initiating boundary,
multicells may quickly grow upscale into an MCS of some kind. The
thermodynamic environment would still be able to support a damaging
wind threat, and may produce some severe hail. Quick upscale growth
would likely limit any tornado threat. If MLCIN remains too strong,
the short-wave may be able to still provide enough convergence above
800mb to generate some elevated convection. As mentioned before,
steep mid-level lapse rates could continue to support storms with
severe hail, and precipitation loading could lead to elevated storms
posing a damaging wind threat. With anything elevated, the tornado
threat would be very low. Overall, a very complex picture for
convection and severe weather Thursday Morning through Thursday
evening. If showers and thunderstorms develop Thursday Morning and
again on Thursday afternoon, be prepared for changing conditions
that could lead to stronger storms. It is possible the critical
details may not be well understood until radar and satellite trends
can be analyzed thoroughly after initial convection develops.
Heading into Friday morning, the surface low pressure begins to exit
Colorado, and will start to push the boundary back north. If there
is not already convection ongoing from Thursday Night, isentropic
ascent should be able to force more shower activity into Friday.

Extended:

With a warm humid airmass in place Friday and through the weekend,
more rain shower and thunderstorm activity will be possible.
Dependent on what happens Thursday Night into Friday morning, there
may enough storm modification to the environment to support a few
severe storms again on Friday. Currently though, with the boundary
being forecast northward into the Minnesota, the severe threat
appears low for Iowa. This is highlighted by the SPC SWODY3 marginal
risk in southern Minnesota. With the boundary being pushed further
north, warmer temperatures will filter back into Iowa. This may send
heat index values into the 100s again, especially for southern Iowa.
Beyond the weekend, more short-wave perturbations are forecast to
eject from the Pacific Northwest and attempt to deamplify the ridge
and upper-level high across the southern CONUS. With the active flow
across the upper Midwest, expect more rounds of rain showers and
thunderstorms through the middle of next week. While it cannot be
determined at this time, a day with stronger to severe storms cannot
be completely ruled out. This may be able to alleviate drought
issues in northern portions of the forecast area.

Hydrology:

Heavy rainfall is possible with storms. North of Hwy. 30, a
widespread 1-2 inches is possible thorugh Thursday evening, with
locally higher amounts possible. More problems would arise if storms
train along either the synoptic boundary, especially if deep layer
shear vectors are parallel to the initiating boundary. This is all
conditional on robust convection developing. WPC has placed northern
portions of the forecast area in a slight risk for excessive
rainfall. In discussion with other NWS offices, have held off on
Flash Flood Watch issuance at this time because the flooding threat
would be very localized. With the uncertainty in storm occurrence
and tracking of any MCS, it is hard to pinpoint the greatest Flash
Flood Threat area with a watch at this time. In addition, rivers and
streams may rise with heavy rainfall. As the convection evolves, the
flooding threats will be better known.

.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 655 PM CDT Wed Aug 25 2021

Confidence is fairly high that VFR conditions will persist through
at least the evening with nothing beyond patches of mid clouds.
Beyond this period confidence decreases quite a bit however due to
uncertainties in convective evolution. Northern sections appear to
be the most likely to see storms tomorrow (Thu) so have added a
period of VFR VCTS at KFOD/KMCW/KALO during the day until details
in timing and location become more clear.

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

DISCUSSION...Krull
AVIATION...Small

AREA FORECAST DISCUSSION

National Weather Service Eureka CA

445 PM PDT Wed Aug 25 2021

.SYNOPSIS...Seasonable temperatures will occur across the interior
3hile coastal areas experience nightly stratus development followed
by afternoon clearing. Thereafter, a warming trend is forecast to
occur across the region going into the weekend. Moderating
temperatures will also be possible at the coast as marine air is
shunted offshore.

.DISCUSSION...A weak upper-level trough continues moving east
across NRN CA early today. As that feature departs east, midlevel
heights will rise slightly, and a warmer airmass will gradually
develop across the WRN CONUS during the remainder of the week. The
warming trend will yield high temperatures from 95 to 110 on
Saturday and Sunday across interior portions of Mendocino and Lake
Counties, and a heat advisory will likely be needed as a result.
Otherwise, an offshore component to the flow will develop in the
low to midlevels of the atmosphere Friday through the weekend.
That change in the flow regime will aid in shunting marine air
westward away from the coast, which will potentially favor mainly
clear skies and mild temperatures for many sea level locations.

Smoke from the active wildfires in the Trinity and Siskiyou
counties continues to be pushed toward northeast with the
southwesterly breezes aloft to bring some improvement in the air
quality for areas in and around Trinity, Mendocino and Lake
counties. Air quality is expected to deteriorate again across
most of the Trinity County on Thursday afternoon as the wind
aloft switch to west to northwest. HRRR model indicates smoke
will spread into the east of Trinity county Tuesday afternoon, and
drifting into Mendocino and Lake counties on Friday as the
offshore winds develops.

Garner/Velez

.AVIATION...Low clouds and modest visibility reductions in fog were
widespread over the coastal waters and adjacent coastal plains and
river valleys. However, due to a weak inversion and lack of
significant coastal eddies, clouds cleared effectively along the N
Coast, with sunny skies as of this writing. Clouds continue to hug
the Mendocino and S Humboldt county coasts, but even these clouds
are shrinking fairly rapidly. Smoke continues across mainly Trinity
County, and this is forecast to remain mostly in place for the next
24 hours. Expect low clouds to develop again tonight and spread
inland along the coast. Conditions are expected to remain VFR at
KUKI. Winds will be generally light. /SEC

.MARINE...Northerly winds will continue through the period. Advisory
level winds will continue across the S outer waters until winds
further increase to near gales. Across the N outer waters, winds
will remain generally light until gales kick in late Thursday night
and Friday morning. Have hoisted a Gale Watch for the outer waters
that starts at 6 AM Friday. This will mainly be for gusts, but
sustained gales are possible Friday night. /SEC

.FIRE WEATHER...Periods of gusty upvalley and ridgetops afternoon
winds will be possible during the remainder of the week, with
peak speeds ranging from 20 to 25 mph. On Friday, offshore
component is expected to develops on Friday. CANSAC and HRRR
models are indicating gusty north to northeast winds developing
across zones 203 and 204 above 1500 feet Friday and Friday night.
Warming and drying trend is expected on Thursday into the weekend
as the high pressure build in, with high temperatures across the
interior valleys peaking in the 90s to low 100s on Saturday. The
afternoon RH values will likely be in the teens across Trinity,
Lake and eastern Mendocino counties. Humidity recoveries will
gradually diminish through the weekend, with locally poor
recoveries by Sunday.

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...Gale Watch from Friday morning through Saturday morning for
PZZ470-475.

Small Craft Advisory until 6 AM PDT Friday for PZZ475.

Visit us at https://www.weather.gov/eureka

For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png

AREA FORECAST DISCUSSION

National Weather Service Sioux Falls SD

1030 PM CDT Wed Aug 25 2021

.SHORT TERM...(This Evening through Thursday Night)
Issued at 317 PM CDT Wed Aug 25 2021

This afternoon, a weaker MCS has formed oriented N-S as a weak wave
transversed the upper ridge, with one stronger cell on the southern
end tracking east across the MO River Valley. See no reason why
this cell wouldn`t continue to track east along the instability
gradient into the early evening. Given favorable deep layer shear,
weak instability, and strong mid level lapse rates present, could
see isolated large hail up to 1 inch in diameter and 60 mph wind
gusts possible.

Early this evening, most model guidance supports develop of
scattered elevated showers or storms lingering central to eastern
SD as the right entrance region of the northern SW-NE oriented
jet builds east into the Northern Plains. While a stray strong to
severe storm cannot be entirely ruled out amidst broad weaker
ascent aloft, most model soundings keep the environment capped
further north. The more mixy GFS and HRRR solutions continue to
suggest that areas of evening convection are possible if the
instability gradient can continue to shift northward this evening,
but exactly where is uncertain with the GFS/HRRR taking a more
southerly solution and the NAM much further north near the Hwy 14
corridor.

The latest deterministic runs have somewhat better agreement on
where the best chance for severe weather resides overnight and point
to two areas of focus: northern and east central SD to western MN,
and further south near the MO River Valley into northwest IA. This
is dependent on how far north the LLJ, and thus the instability
axis, extends and when a weak wave to the north tracks into the
region (overnight vs early in the morning). There is a signal for
both areas, or perhaps one and not the other, to materialize,
depending on how evening activity and the LLJ evolve.

Ultimately, the greatest severe weather threat likely resides from
4-10 AM Thursday morning, as favored by the 12z HREF UH tracks.
Anticipate more isolated severe weather with a southern MCS (MO
River Valley/Hwy 20 or further south) and potentially scattered to
numerous strong to severe storms with an elevated MCS further
north closer to the Hwy 14 corridor and extending into southwest
MN. Storms should initially develop in clusters, merging into an
MCS as motion would be more parallel to the front/instability
gradient, with the main threats being large hail and damaging wind
gusts. Pwat values of 1.5-2.0+ and storm training will support
locally heavy downpours with isolated amounts up to 2-3 inches
possible, especially in southwest MN. While there is some nice low
level hodograph curvature, 0-3 km shear vectors remain parallel
to the line so deem tornado threat unlikely at this time.

The progression of one or several morning MCSs will greatly impact
the evolution of the warm front on Thursday with the deterministic
guidance still very split on solutions. Should see a lull in
activity with some instability recovery around mid day to early
afternoon, despite a cloudy, muggy day unfolding. There is high
uncertainty in the timing/location of the next round of severe
weather on Thursday. For example, the 12z NAM keeps convection
going on and off during the day, preventing any organized stronger
complex from forming until later Thursday evening, and the 12z
GFS holds strong capping for a quiet day and early evening
initiation. As mentioned in previous discussions, the environment
remains favorable for severe weather throughout Thursday and
Thursday night as strong deep layer shear, steep mid level lapse
rates, and moderate instability linger in the warm sector across
the region. Be prepared for more isolated severe threat during
the day Thursday after the initial morning MCS, with more
widespread severe threat with any complex developing late
afternoon or through Thursday night. All threats will be possible
with activity Thursday afternoon and night, including isolated
tornadoes and localized flash flooding.

Most model guidance supports locally heavy downpours and isolated 1-
3 inch amounts again Thursday night, though this time the atmosphere
is even juicier with 1.5-2.5 inch Pwats and the MCS would likely
have a longer residence time in the region, as highlighted by the
Day 2 WPC Excessive Rainfall Outlook. If some locations,
especially in southwest MN, get multiple rounds of 1-3 inches of
rain over the next 2 days, wouldn`t be surprised to have some
flash flooding issues. However, given the uncertainty in any MCS
tracks over the next few days, held off on a Watch issuance for
now.

.LONG TERM...(Friday through Wednesday)
Issued at 317 PM CDT Wed Aug 25 2021

Main concern through extended period continues to be several periods
of potential for severe weather with the greatest threat
developing Saturday/Saturday night.

Friday looks a bit quieter for the region behind the departing
system. The unstable warm sector should recover and build further
north through the region during the day, leading to another warm
muggy day. Despite enhanced 500mb jet and moderate instability,
latest model soundings maintain capping in the forecast area and
slide a strong shortwave to the north across ND and northern
SD/MN. This would likely keep severe weather chances north of the
region (unless the wave tracks further south).

On Saturday, the upper trough meandering along/north of the
International Border finally digs into the Northern Plains. Height
falls aloft combined with upper jet right entrance ascent, moderate
to strong instability in the warm sector ahead of an approaching sfc
cold front, and increasing mid level winds support the better chance
of severe weather through this active week, as highlighted by the
SPC Day 4 threat area. There is low confidence in details such as
timing or sub-region with highest threat at this range, but the
Saturday afternoon/night period certainly bears watching for severe
weather threat in the coming days given the strong forcing for
ascent.

Behind Saturday`s departing system, Sunday is poised to be cooler
and dry/quiet. Early next week, zonal flow aloft transitions to
ridging building over the Rockies, which favors some periods of rain
chances, but progression of the upper ridging and resultant warming
is very uncertain as the Gulf is poised to become more active
again.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1028 PM CDT Wed Aug 25 2021

While most of the night should remain VFR by early Thursday
morning thunderstorms may become more numerous, with the better
chances north of Interstate 90. By afternoon into tomorrow night
occasional showers and thunderstorms are expected over much of the
area. Thursday is likely to be a busy day with severe weather and
heavy rain possible. Some MVFR ceilings will also be possibel with
the better chance north of Interstate 90.

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

SHORT TERM...BP
LONG TERM...BP
AVIATION...08

AREA FORECAST DISCUSSION

National Weather Service Hastings NE

908 PM CDT Wed Aug 25 2021

.DISCUSSION...(This evening through Wednesday)
Issued at 327 PM CDT Wed Aug 25 2021

Tonight and Tomorrow...
Most forecast models are dry for most of our forecast area. The
12Z NAM NEST was an exception in trying to develop a thunderstorm
complex to our northwest that could track into our northern
counties late tonight. However, the 18Z NAM NEST has backed off of
this solution and now more closely followers other model solutions
like the HRRR and NAM that are mainly dry for our forecast area.
Therefore, will lean towards the NBM for POPs but decrease POPs a
bit and only keep rain chances in across far northwest zones with
just a slight POP.

Thursday...
This will be another hot and humid day ahead of the cold front,
thus have extended the heat advisory into Thursday
afternoon/evening for our more humid southeastern zones. The
frontal boundary will likely move into our northwestern zones by
Thursday afternoon and evening bringing at least a slight chance
for thunderstorms primarily across our western and northwestern
Nebraska counties. This does not appear to be a big widespread
rain event, but a few spots could see a decent rain by Thursday
evening. There is a marginal to slight risk for severe
thunderstorms across our western and northern zones from Thursday
afternoon into Thursday evening.

Friday...
Forecast models vary on where the surface front will be situated.
It does appear that an upper trough will be working its way east
into the northern high plains and we could see some thunderstorms
move into our forecast area primarily during the evening and
overnight hours, but chances are on the lower end at this point
given model uncertainty. It will be hot again, especially across
southeastern zones and can not rule out possibly having to extend
the heat advisory yet another day forward in time.

Weekend...
Saturday should still be rather hot especially across southeastern
zones. However a pretty good cool front will bring one of our
better chances of thunderstorms to the forecast area Saturday
afternoon into Saturday night. Sunday will then be much more
pleasant behind the cool front with less humidity and highs maybe
only around 80 in many areas.

Early Next Week...
An upper level ridge will try to build back north across the
plains, so it appears to be mainly dry with warming temperatures.
Sunday really seems like the best day of the week.

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday)
Issued at 624 PM CDT Wed Aug 25 2021

VFR conditions expected through the end of the TAF period. There
is the potential for a little bit of low stratus to develop around
dawn tomorrow, but right now it only looks to be scattered. Still
something to keep an eye on though. As far as winds go, they will
remain mostly southerly and will calm down to light and variable
overnight and through tomorrow morning before picking up again in
the afternoon. Expecting gusts tomorrow to be around 20-25 kts at
times.

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory from noon to 8 PM CDT Thursday for NEZ064-077-086-
087.

KS...Heat Advisory from noon to 8 PM CDT Thursday for KSZ007-018-019.

DISCUSSION...Wesely
AVIATION...Shawkey

Area Forecast Discussion

National Weather Service Goodland KS

810 PM MDT Wed Aug 25 2021

.MESOSCALE DISCUSSION...
Issued at 759 PM MDT Wed Aug 25 2021

Key Message: Storm continues to maintain severe intensity as
environment stabilizes. However the storm is beginning to show
signs of becoming more elevated with a lower intensity.

Latest satellite imagery shows the storm maintaining its
intensity. There have periods where the cloud tops warmed, but the
storm then intensified again. Latest mesoanalysis guidance is
suggesting the supercell thunderstorm is starting to become more
elevated. This should start to lower its intensity as the
environment becomes more stable this evening. As the storm
continues to move north the environment will continue to
stabilize which should cause the storm to weaken. Since this is a
supercell thunderstorm it will not be affected by the environment
as quickly.

Severe weather reports with this storm show the intensity waning.
Hail reports are half of what they were, and wind reports are now
closer to 60 MPH instead of 70.

.SHORT TERM...(This evening through Thursday night)
Issued at 300 PM MDT Wed Aug 25 2021

Overview: An expansive upper level ridge will persist over the
Southern Plains and southern MS River Valley.. downstream of
persistent troughing aloft along the Pacific Coast. The Tri-State
area will remain situated on the N-NW periphery of the ridge.. at
the far southern fringe of the mid-latitude westerlies. In the
lower levels.. a weak/broad thermal low will persist in the lee of
the central Rockies.

In a rather stagnant synoptic pattern one would generally expect
little change in sensible weather conditions, however.. in such
close proximity to the mid-latitude westerlies, the Tri-State area
will, nevertheless, remain within the `sphere of influence` of
small amplitude waves progressing northeastward from the
Intermountain West into the Northern Plains -- whether that
influence be direct or indirect. In general, well-above normal
temperatures and dry conditions are anticipated to persist.
Isolated afternoon and evening are possible during the aft/eve
hours Today and Thursday.. generally in northeast Colorado and
southwest Nebraska (in closer proximity to the mid-latitude
westerlies).

Convection Today: At 20Z, isolated diurnal convection was
developing invof a weak sfc cyclone /thermal low/ in far southwest
KS and far southeast CO.. as simulated reflectivity forecasts via
the HRRR and NAM NEST have suggested. Recent HRRR/ NAM NEST runs
have backed off on isolated development along the CO Front Range
and/or Palmer Divide late this afternoon.. perhaps due to
considerable convective inhibition assoc/w persistent stratus in
northeast CO. While effective deep layer shear is on the order of
35-40 knots invof the NE/KS border.. values sharply decrease with
southern extent into KS.. closer to the ridge aloft. Assuming
isold development does not occur in northern CO, organized
convection appears unlikely. South of I-70 -- mainly in
Greeley/Wichita counties -- strong insolation, near dry-adiabatic
SFC-H5 lapse rates, moderate instability, and extreme DCAPE
suggest that any high-based updrafts (short-lived, as they may
be) will be capable of producing brief severe downbursts.

Convection Thursday: Southwest flow aloft will modestly
strengthen over the central Rockies as cyclonic flow aloft
broadens/expands eastward from the Pacific Coast to the
Intermountain West.. yielding a somewhat deeper lee cyclone in
eastern CO.. and noticeably breezy south winds in western KS.
Expect a greater potential for convection (compared to today)..
with activity most likely emanating from the CO Front Range during
peak heating. With strong insolation, steep low-level/mid-level
lapse rates, moderate instability, and extreme DCAPE, any high-
based updrafts will be capable of producing damaging winds. At
this time, the greatest potential for organized severe weather
appears to be further north.. in central/northern Nebraska.. an
area more firmly entrenched in the mid-latitude westerlies.

.LONG TERM...(Friday through Wednesday)
Issued at 238 PM MDT Wed Aug 25 2021

At the start of the extended period, the CWA lies underneath a
trough yielding a mostly southwesterly flow during the Friday.
Models show redevelopment of the trough occurring near the far
western U.S./Canada border throughout Friday. On Saturday, the
southwesterly flow looks to continue as the redeveloped trough
progresses eastward into the Northern Plains region. A shortwave
disturbance appears to pass over the CWA during Saturday evening as
well. On Sunday, models depict the trough moving into the Great
Lakes region with a trailing ridge moving over the western CONUS
giving the CWA a westerly flow aloft. Another shortwave disturbance
is seen moving over the CWA on Sunday evening. Going into Monday,
the ridge continues to be the dominating feature over the central
CONUS with another trough building in the Pacific Northwest. On
Tuesday, forecast guidance shows the flow aloft turning
northwesterly as the upper air ridge in the central CONUS becomes
sandwiched between two upper air troughs. This pattern looks to
continue going into Wednesday with the GFS showing an upper air high
possibly forming over the CWA while the ECMWF does not currently
have this feature.

At the surface, the CWA looks to have some precipitation chances
during the long term period. While Friday looks to stay dry in the
CWA, the first chance for showers and thunderstorms appears to be
around Saturday afternoon and evening for the eastern half of the
CWA as a surface trough sets up in eastern CO. Sunday sees a slight
chance for showers and thunderstorms mostly for areas along and east
of KS-25 ahead of an approaching cold front that passes through the
CWA during the day though the timing of the frontal passage still
has some model uncertainty. Monday and Tuesday look to have minimal
precipitation chances being due to the upper air pattern. Wednesday
evening sees a possible return for showers and thunderstorms as
models show a possible surface low setting up in northeastern CO.
Elevated fire weather concerns are possible for areas along and west
of the CO border on Friday and Wednesday with minimum RH values
around or just below 20%. Near critical fire weather may be possible
for the same area on Tuesday with forecasted minimum RH values as
low as 15% are seen. Maximum wind gust speed may be the limiting
factor for fire weather conditions on these days, but the situation
will be monitored for changes in future model runs.

The Tri-State area should see high temperatures on Friday and
Saturday between the lower and upper 90s. On Sunday, daytime highs
cool to the lower to upper 80s with a cold front passage followed by
Monday`s highs being in the lower to middle 90s. Tuesday`s highs
expect to be in the middle to upper 90s while Wednesday`s highs stay
in the lower to middle 90s. Tri-State area overnight lows for Friday
expect to be between the lower 60s and lower 70s with Saturday
seeing overnight lows in the middle 50s to the middle 60s. Overnight
lows for remainder of the long term period look to be in the upper
50s to middle 60s range.

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 527 PM MDT Wed Aug 25 2021

VFR conditions forecast for the TAFs. A line of thunderstorms is
slowly moving north over West Central Kansas. At this time, do
not foresee these storms moving over KGLD. Current data is
indicating the storms should either end in the next hour or two or
shift to the west site as the storms move north. KMCK should not
have any storm activity.

Am not expecting the stratus that was over the sites earlier today
to return tonight. Thursday both sites will have breezy south
winds.

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

MESOSCALE...JTL
SHORT TERM...VINCENT
LONG TERM...076
AVIATION...JTL

Area Forecast Discussion

National Weather Service Lincoln IL

808 PM CDT Wed Aug 25 2021

.SYNOPSIS...
Issued at 251 PM CDT Wed Aug 25 2021

Hot and humid conditions will continue across the region the next
couple days, with periodic chances of showers and thunderstorms.
A few of the storms may be strong or locally severe, especially
in the afternoon and evening hours.

.UPDATE...
Issued at 802 PM CDT Wed Aug 25 2021

Thunderstorms continue across central Illinois this evening,
though seeing signs of overall weakening trends this hour. An
outflow boundary has surged well ahead of a complex of storms,
reaching roughly Rushville to just north of Springfield then NE
through Le Roy as of 8 PM. Wind gusts of around 30 to 40 mph are
being reported with the gust front, and a few showers and storms
are briefly pulsing up along the boundary. Weak deep layer shear
and diminishing diurnal instability should keep the severe threat
in check for the remainder of the evening, and SPC has pulled the
marginal risk as a result. Storms may still briefly pulse up and
become strong with 3500 J/kg MLCAPE still in place, but slow storm
motions mean these storms quickly fall behind the outflow
boundary. Locally heavy rain is expected with the strongest cores
producing 1.5 inches per hour.

.SHORT TERM...(This evening through Thursday)
ISSUED AT 251 PM CDT Wed Aug 25 2021

Outflow boundary that pushed through earlier today has washed out
without doing anything, though a boundary from convection in
Indiana has fired a few storms along the border near Danville and
Paris. Some new development southwest of the Quad Cities may be
associated with an earlier MCV, and will be curious to see how
much expansion takes place with it. NAM Nest was the only CAM that
hinted at that possibility with the morning model runs, and it
brings showers/storms across mainly the northwest third of the
forecast area through mid evening. Latest HRRR is more
disorganized and later with its development. Will mainly keep
evening PoP`s in the 30% range for this activity with all the
uncertainty, with slight chances after midnight.

No significant pattern change is expected Thursday, with
boundaries still driving the rain chances. Outside of the storms,
another hot and humid day on tap. No changes will be done with the
heat headlines at this time.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 251 PM CDT Wed Aug 25 2021

Several models indicate the potential for one or more MCS`s to
move through the upper Mississippi Valley Thursday night. Most
take them just to our north, though the morning HRRR dives one
southeast into central Illinois Thursday evening. Will include
some 30-40% rain chances around Peoria northward for that. After
that, the general storm track pushes further north, with mostly
dry weather the first half of the weekend.

Forecast complications increase next week. Longer range models are
generally in agreement with a shortwave tracking across the upper
Mississippi Valley late Sunday, with shower and thunderstorm
chances increasing again. After that, the forecast will be driven
by a potential hurricane in the Gulf of Mexico. Models currently
have it arriving in Louisiana, though the GFS is much stronger
and slower with it. By Wednesday, its remnants are progged to be
in the vicinity of Arkansas. This would cause a bottleneck in
progression of the lingering front, though a stronger northeast
flow over our area would bring some welcome cooler conditions.

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 624 PM CDT Wed Aug 25 2021

Thunderstorms are moving across the Peoria area this hour and may
reach BMI between 00-01Z. Elsewhere, storms cannot be rule out but
confidence and coverage is expected to be lower. Light and
variable or southeast winds will set up overnight and will veer to
S/SSW during the day Thursday.

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT Thursday for ILZ040>042-047>057-
061>063-066>068-071>073.

UPDATE...Deubelbeiss
SYNOPSIS...Geelhart
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Deubelbeiss

Area Forecast Discussion

National Weather Service North Platte NE

629 PM CDT Wed Aug 25 2021

.SHORT TERM...(This evening through Thursday night)
Issued at 338 PM CDT Wed Aug 25 2021

20z Vsby satellite this afternoon suggests a weak upper level
disturbance is operating across nern Colorado. This disturbance has
set off thunderstorms across swrn Nebraska. Satellite and KGLD VWP
suggest the storms are forming just above the stratus layer
associated with a sfc inversion a few thousand feet deep. Another
disturbance is shown on satellite across swrn UT which could affect
wrn and ncntl Nebraska late tonight. Timing tools suggest this
disturbance will affect wrn Nebraska by 08z tonight.

The basic thunderstorm forecast tonight revolves around the
development of a low level jet across KS which will lift a warm
front into swrn or wcntl Nebraska by morning. The POP forecast
follows the trusty SREF which has been performing better than the
HRRR. The HRRR was the best model earlier this week but fell behind
last night and this afternoon.

The very strong shear associated with the 25-35 kt low level jet and
a belt of 25-40kt westerlies at h500-300mb, PWAT 1.25-1.5 inches and
fairly steep lapse rates could support severe storms. A strong cap
at 800mb shown by the NAM and RAP models appears to holding back
storm development. Presumably, the cap will limit storm coverage to
isolated. Only the NAMnest suggests more than isolated severe storm
coverage but this model is a sfc based CAM and the convection
tonight will be mostly elevated forming north of a warm front.

This storm activity will probably be across SD or nrn Nebraska
Thursday morning. The sfc warm front should be near the SD border
with a large warm sector open across wrn and ncntl Nebraska. The NAM
will then sink a cold front into or toward swrn Nebraska during the
afternoon. The front, robust moisture, steep lapse rates and a model
predicted UA disturbance moving off the Colorado Rockies are the
basis for chance to likely POPs across wrn and ncntl Nebraska
beginning late Thursday afternoon and continuing overnight.

The best focus for severe weather Thursday might be across nrn
Nebraska where winds aloft increase to 40-50 kts at h500-300mb.
Weaker winds aloft across srn Nebraska will support more of a
locally heavy rain threat. The NAM suggests conditions would be
prime in both areas by 22z. Later in the evening and overnight,
temperatures aloft may warm due to diabatic heating from heavy rain.
The time of storm initiation will probably be dictated by upper
level support which is difficult to predict beyond 12hrs, especially
if it is associated a subtropical disturbance which tend to amplify
crossing the Rockies.

.LONG TERM...(Friday through Wednesday)
Issued at 338 PM CDT Wed Aug 25 2021

A dry forecast is in place Friday. A plume of deep moisture should
be south and east of wrn and ncntl Nebraska. The models continue
to draw this moisture back north and west Saturday. A fairly
strong upper level disturbance will move through the nrn Plains
and reach south into Nebraska. The best rain chance for this
system is currently advertised across ncntl Nebraska but moisture-
PWAT greater than 1.25 inches, will be available across swrn
Nebraska if the dynamics can reach farther south.

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 624 PM CDT Wed Aug 25 2021

VFR conditions expected to largely prevail through tomorrow
evening. Isolated thunderstorm development will continue for a few
more hours this evening across portions of central Nebraska,
generally south of a TIF to ONL line. Some guidance hints at
development of low stratus overnight across southwest Nebraska,
though confidence remains too low for inclusion at LBF at this
time. Additional thunderstorm development is expected tomorrow
afternoon, though confidence remains low in placement and timing
for now. Winds will gradually shift southeasterly overnight, at
around 5 to 10kts.

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Brown

Area Forecast Discussion...UPDATED

National Weather Service Twin Cities/Chanhassen MN

1057 PM CDT Wed Aug 25 2021

.UPDATE...
Issued at 932 PM CDT Wed Aug 25 2021

00Z model guidance is trickling in and it appears trends are being
established. 00Z NAM/NAMnest and the HRRR for the last few runs have
high-based thunderstorms developing over SE MT late this evening.
There have been attempts of development already, but so far those
attempts have fizzled. A shortwave should nonetheless eventually get
a cluster of thunderstorms going over the high plains tonight with
the development of a LLJ. This cluster will grow late tonight into an
MCS, track along or just south of the ND/SD border, and approach
western MN by late morning. It`s possible additional thunderstorm
activity (a W-E oriented band) could form in advance of this MCS. If
that occurs, heavy rainfall totals will result due to training over
parts of western MN. This may be where the heaviest rain will fall
Thursday, and there could be several inches. Eventually the MCS will
catch up with the secondary development to the east and track along
an instability gradient through the afternoon, likely along the MN
River into southeast MN. Sufficient instability ahead of it will
sustain it or strengthen it to severe levels. The main threat would
be wind damage. There may be another area of convection that forms on
the tail of the MCS or outflow boundary, again most likely along the
MN River. Confidence decreases significantly Thursday night. The
afternoon MCS may very well organize any future activity farther to
the south in Iowa and leave the region dry. Global models up to this
point, as well as their ensembles (particularly the GEFS), would
argue for thunderstorms to refire much farther north into central MN
and northwest WI. At this point, that seems to be an unlikely
scenario if the MCS does in fact track across the southern third of
MN.

This trend would result in a significant reduction in QPF north of
I-94 through Thursday night. The main focus would become along the
MN River and west central MN, where not only the MCS will track, but
the preceding development and subsequent development would also
occur. These areas are very dry and can take a lot of water, even in
a non-drought year due to crops. These areas also have smaller urban
footprints and flatter terrain making flooding less likely as well.
Therefore, will hold off on any Flash Flood Watches this evening and
will await further trends.

.SHORT TERM...(This evening through Friday)
Issued at 300 PM CDT Wed Aug 25 2021

Winds have shifted to the northwest in the wake of the cold front.
Dew points have dropped off across central and western MN but remain
in the mid to upper 60s to lower 70s across southern MN and western
WI. These should continue to drop into the lower 60s and upper 50s
this evening before increasing again Thursday morning. Scattered to
broken cloud cover has pushed into western MN and is expected to
continue eastward this evening. There is an elevated smoke layer but
that should remain elevated throughout the short term period with
little impact at the surface.

For Tonight into Thursday, thunderstorms are expected to develop in
the Dakotas this evening and trek eastward along the thermal
gradient/850 mb front overnight. These are expected to move into
Minnesota near the SD/ND border and toward the Twin Cities by
Thursday morning. It`s important to note that there is still some
uncertainty on the exact evolution, but confidence has increased
that we`ll see an initial round Thursday AM and a second round
Thursday late PM. CAMs are also beginning to come together to
support this outcome but vary on the exact track and location
impacted. PoPs gradually increase overnight from SW MN to the Twin
Cities by Thursday afternoon. One feature that guidance has been
consistent with is a potent southwesterly low-level jet developing
across the Central Plains overnight into Thursday. The LLJ will push
further north on Thursday, eventually overrunning the warm front.
This will ultimately fuel a large region of precipitation due to
strong moisture advection and lift along the frontal boundary. All
of this adds up to heavy rainfall with the potential for high
rainfall rates. Various models bring an area of 2.0" + PWAT air over
the CWA Thursday afternoon effectively re-priming the atmosphere for
another round of heavy rain and thunderstorms Thursday night. The
Weather Prediction Center has a slight risk in the excessive
rainfall outlook (ERO) for day 2 due to the threat of heavy rainfall
and potential for flash flooding. Thursday night into Friday, the
warm front lingers over the CWA with the potential of showers and
thunderstorms likely. A second round of showers and thunderstorms
are expected to develop and should linger through Friday afternoon.

Model guidance struggles to get a good handle on the timing and
location specifics, but the best chance for multiple rounds of
convection and heavy rainfall looks to be between the I-94 and I-90
corridors. Both 12Z ECMWF and GFS ensembles have trended a touch
northward with the highest QPF through Friday. This places the
highest totals along the thermal gradient that remains over south-
central MN and western WI.

.LONG TERM...(Friday night through Wednesday)
Issued at 300 PM CDT Wed Aug 25 2021

The main impact for this long term period will be the continued wet
period with multiple chances for rainfall. The first of these
chances will be continued rainfall associated with the warm front on
Friday night. The next chance for rain arrives on late Saturday into
early Sunday with the passage of a cold front. The next round is
less certain with another round of rain possible early next week
near the Iowa border. General high pressure though after the front
passes Sunday suggests that widespread rainfall is not likely Mon to
Wed. Outside of a warmer day on Saturday near to just below normal
temperatures expected behind the cold front Sunday into next week.

Friday night to Sunday... High precipitable water values continue
Friday night into Sunday with NAEFS percentiles ranging from 90% to
above 99%. This means that there will be plenty of moisture present
for heavy rain to occur. With strong forcing Friday night from the
warm front and then the cold front Saturday into Sunday rainfall is
likely across much of the Upper Midwest. As with all convective
summer rainfall though the highest totals with vary significantly
locally. Despite this there should still be widespread rainfall.
What areas get the greatest rainfall will become more apparent when
we get into the 24 or so hours out period when there is more CAM
guidance and the current observations fit better into our conceptual
models. The timing for the cold front this weekend has come into
better agreement among deterministic models with a Saturday evening
into early Sunday morning passage now looking most likely from
northwest to southeast. The set up for this weekend rain looks
similar to what we saw on Tuesday morning with a line for storms
with heavy rain and some chances for severe weather along the line.
The Storm Prediction Center has highlighted this area in a day four
15% risk as daytime heating should provide sufficient instability,
forcing front the front, and sufficient shear is present in guidance
for some chance for a severe risk.

Monday to Wednesday... With a ridge building in and surface high
pressure it appear likely that most will see quieter weather. There
has been some suggestion that the rain to our south could extend
into parts of southern Minnesota on Monday or Tuesday.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1057 PM CDT Wed Aug 25 2021

A complex of storms over the Dakotas tonight will track southeast
along the MN River Thursday. Introduced TEMPOs for TS with passage
of this complex, mostly at RWF, MKT, and MSP. There is low confidence
in convective chances Thursday evening following the complex, so left
all sites dry but cigs could lower to MVFR or IFR.

KMSP...No concerns tonight or Thursday morning. TSRA chances increase
in the afternoon as a complex of thunderstorms approaches. Wind could
shift to the WNW and increase in speed with the line, perhaps gusts
to 40 kts.

/OUTLOOK FOR KMSP/
Fri...TSRA/MVFR likely early. Wind SE 10-15 kts becoming SW.
Sat...TSRA likely late. IFR or lower possible. Wind SW 5-10 kts.
Sun...Chc SHRA, best chance in the morning. VFR likely. Wind WNW
10-15 kts.

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&

UPDATE...Borghoff
SHORT TERM...BPH
LONG TERM...NDC
AVIATION...Borghoff

Area Forecast Discussion

National Weather Service Pocatello ID

120 PM MDT Wed Aug 25 2021

.SHORT TERM...Tonight through Friday night. An upper trough is
sitting over WA/OR, and will offer support for some showers/isolated
thunderstorms over eastern Idaho this evening. High-res models place
the best precip chances over the MT border and around Driggs. The
trough will slowly progress eastward tonight and tomorrow with the
trough axis pushing through tomorrow evening. Models are keeping
things dry for the most part, making it difficult to include any
mention of precip. A secondary trough will move into the area on
Friday, but again models are keeping us dry in southeast Idaho.
Winds will pick up tomorrow and, especially, Friday as the surface
gradient increases. Expect to see a bit of a cool-down on Friday as
a weak surface cold front pushes through. Smoke remains in the
forecast for the short-term periods, being transported from
wildfires in OR and CA. Hinsberger

.LONG TERM...Saturday through next Wednesday. A dry and warm
westerly flow prevails across the region until Tuesday. The next
upstream trough hits WRN Canada Tuesday morning, resulting in
increasing southwest flow across the region and what appears to be a
monsoon intrusion into the southeast portion of the forecast area
Tuesday night continuing into Wednesday as the trough lingers across
WRN Canada and the NW states. Huston
&&

.AVIATION...Early afternoon satellite imagery continues to show
active smoke production from NRN California fires which will likely
advect north into SRN Idaho possibly impacting VSBY from time to
time. Otherwise, a dry upper trough will advance into and through
the region tonight and Thursday resulting in locally breezy diurnal
winds at the terminals. Huston
&&

.FIRE WEATHER...Mostly dry conditions are expected this evening,
though some areas along the MT border and the Island Park area may
see some isolated thunder. Otherwise, the forecast will remain dry
at least until Tuesday. Winds will pick up on Thursday and Friday
afternoons. Look for gusts to 25 to 30 mph across the Snake
Plain/Arco Desert, though humidity is expected to stay above 15
percent. There is some concern for fires as Haines indices of 6 are
forecast, but that persists mostly in areas where fuels are not
critical. Hinsberger
&&

.AIR STAGNATION...Southwest flow aloft through Thursday will keep
the trajectory in place for smoke intrusion from California fires.
A few weak features will move through, providing variable relief in
some areas. Flow changes and becomes more westerly Thursday night
through Friday, which should keep the denser California smoke to the
south, though this would allow for smoke from Washington/Oregon
fires to make its way into the region. HRRR model smoke production
holds smoke across the region except the far southeast corner of the
forecast area waiting to fill that in later this evening. We most
likely won`t see any changes in current conditions until the west
flow kicks in Thursday night as previously mentioned. DMH/Huston
&&

.PIH WATCHES/WARNINGS/ADVISORIES...None.
&&

Area Forecast Discussion

National Weather Service Reno NV

248 PM PDT Wed Aug 25 2021

.SYNOPSIS...

Lighter breezes and some warming are expected late week and for
the weekend. There is a chance for less smoke into western Nevada,
especially north of Highway 50, as light westerly afternoon winds
retreat to the Sierra late week; however, some smoke and haze will
remain with potential air quality impacts. Westerly afternoon
winds next week may bring back heavier smoke into western NV.

.DISCUSSION...

Lighter winds return Thursday through much of Sunday (westerly
breezes look to return Sunday afternoon). As far as direction at
the surface, northerly flow is possible for far northeast CA and
northwest NV starting Thursday night, with areas down to around
I-80 seeing light north winds by Friday night and Saturday
morning.

The light winds from the northwest to northeast at the low levels
is simulated by the HRRR to shift the densest smoke plume from the
Caldor Fire to areas south of Hwy 50. This northerly push isn`t
expected to be strong enough to flush the smoke completely out of
western Nevada valleys until at least Friday afternoon, especially
as some some from the Dixie Fire may eek into far western NV.
Therefore, expect particulates/haze to remain along with some
continued air quality impacts; however, air quality may at least
be better, at least from a relative sense after the unhealthy to
hazardous air quality that we have seen for what seems like ages.
Unfortunately, the Sierra may see daily pushes of smoke up the
west slopes with northeast CA south of Susanville continuing to
see Dixie Fire smoke. Still, with less wind, the air quality east
of the Sierra crest may be marginally better than recent days.

Aside from the smoke, temperatures will remain a couple of degrees
below season averages through Thursday before high pressure starts
a modest warming trend through the weekend. Temperatures look to
warm roughly 5 degrees above average with mid 80s to mid 90s for
valleys over the weekend.

As we head into next week, the pattern again favors a broad and dry
trough setting up near the West Coast and over the Pacific Northwest.
This is expected to result in a gradual cooling trend with breezy
conditions for the first half of next week. Unfortunately, it also
brings the potential for more smoke to pour into western Nevada if
the Caldor Fire remains active. -Snyder

.AVIATION...

A shift to more westerly flow (rather than SW-W) is expected to
push the worst VIS with dense smoke from the Caldor Fire to areas
near and south of Hwy 50 tonight through Thursday, although some
new smoke input from the Dixie Fire may eek down through northeast
CA and into western NV. A shift in low-level winds to a lighter
and more northerly direction may bring more improvement to VIS/
smoke CIGS for western NV and far northeast CA by Friday. However,
for eastern CA south of Susanville down to at least Alpine County,
modest afternoon and evening westerly winds may prevail for a
higher threat of lowered VIS/smoke CIGS through Friday. -Snyder

.FIRE WEATHER...

*Breezy southwest-west winds this evening; gusts 20 to 30 mph.

*Wind direction change Friday afternoon into early Saturday.

*Poor mid-slopes recoveries expected through the weekend.

Modest breezes will continue into this evening with surface gusts 20-
30 mph. Isolated critical conditions could linger especially east of
Highway 395 and along exposed ridges and slopes. Winds will weaken
sharply after 2000 for most locations. Until then, expect increased
ventilation and potential for enhanced fire activity.

Winds will be much lighter Thursday with potential for a northerly
shift late in the afternoon out of the north. A dry surface boundary
could push through portions of the region down to around a Susanville
to Lovelock line. These winds will remain light through Friday until
another dry boundary pushes through Friday afternoon/evening.
Northerly flow could marginally increase with breezes around 10 mph.
A concern for the Dixie Fire will be a more easterly flow pattern
Friday night into Saturday; some winds along the Sierra could become
breezy ridges north of Interstate 80.

Otherwise, poor mid-slope and ridge top recoveries are expected
through the weekend. Next week, breezes may increase and become
gusty again as the pattern shifts.

-Boyd

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

For more information from the National Weather Service visit...
http://weather.gov/reno