Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/24/21

Area Forecast Discussion...UPDATED

National Weather Service Albuquerque NM

537 PM MDT Mon Aug 23 2021

.AVIATION...
00Z TAF CYCLE
Isolated to scattered showers and thunderstorms will continue into
the early evening and then mostly diminish before midnight. Activity
will remain concentrated along and south of the Interstate 40
corridor with a few strong to briefly severe cells capable of
producing heavy downpours, small hail and gusty downburst winds.
Thunderstorms on Tuesday will likely be fewer in number, remaining
concentrated over the southwestern to west central mountains of New
Mexico while just a few isolated cells develop along and east of the
central mountain chain. Hot temperatures and high density altitude
readings, especially in the eastern plains of New Mexico, will create
difficult ascents for some aircraft.

.PREV DISCUSSION...304 PM MDT Mon Aug 23 2021...
.SYNOPSIS...
Fewer storms and above average daytime temperatures will be the trend
for Tuesday through Wednesday. Highs in the mid 90s to near 100 are
expected across eastern New Mexico while upper 80s and 90s will
be common for the central and west. These readings will be 5 to 10
degrees above seasonal averages for most locales. Storm coverage
will then ramp up on Thursday, especially for the northern half of
the state, as a disturbance passing north of the state draws
moisture northward. A relatively active monsoon pattern will
persist Friday into the weekend with daily rounds of thunderstorms
favoring the west and north. Daytime highs should trend closer to
seasonal average for Thursday through the upcoming weekend.

.DISCUSSION...
SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)...
594dam 500mb high centered near the ArkLaTex and extending a ridge
axis west into southern NM per the 12Z upper air analysis. The latest
water vapor imagery shows moisture from the eastern Pacific, where
TS Marty resides, being pulled northeast across northern Mexico and
into southern NM. The 12Z KEPZ sounding confirmed this with a well
above normal PWAT of 1.5" and even the KABQ sounding had a PWAT near
1". Surface dewpoint temperatures were an average 4 degrees higher
across portions of central and western NM at 1PM compared to 24hrs
prior. Given some daytime heating, all of this adds up to a decent
round of storms this afternoon, with the focus for deeper convection
and stronger storms capable of producing locally heavy rainfall
generally south of I-40 in the higher PWAT airmass. Storms closer to
our southern border under the ridge axis will be moving slower and
more capable of producing torrential downpours with localized flash
flooding. Both the latest HRRR and HREF show convecting winding-down
shortly after sunset, but the NAM shows precipitation continuing
overnight across southern portions of our area similar to last night.
Regardless, coverage and intensity will trend down with the loss of
daytime heating this evening.

Tuesday is looking very similar to today overall with slightly
higher pressure heights near 593dam at 500mb and above normal high
temperatures, especially across eastern NM. A drier airmass to our
west is forecast to get wrapped into the upper high circulation
across northwest and north central NM Tuesday and should put the
brakes on convection north of I-40 and west of I-25. Storms across
the southern high terrain will be capable of producing locally heavy
downpours Tuesday afternoon, with the potential for localized flash
flooding once again.

LONG TERM...(WEDNESDAY THROUGH MONDAY NIGHT)...
Wednesday looking to be among the least active days of the
forecast period. Shortwave trough modeled to move inland long the
northern CA and PacNW coasts early Wednesday resulting in weak
compensatory height rises downstream over our part of the world.
As a result, the models generally show the strong 595 dam H5 high
over the Southern Plains briefly expanding westward. Latest
blended PoP guidance trended a little downward for Wed PM and this
seems reasonable under what should be slight warming aloft and A
weakly forced environment.

The above mentioned upper trough to cross the Great Basin eventually
nearing the central Rockies late Thursday. Ahead of this wave, a
corridor of enhanced forcing for large-scale lift should develop and
support a noticeable uptick in storm coverage particularly from WC
through NW and NC areas for Thursday afternoon and evening. We would
not rule out the possibility of strong if not severe storms in this
regime given increasing swly flow aloft though storm motions may
preclude significant FF potential. PWAT time series reflect values
generally at or just above seasonal averages. And with the west to
east oriented upper ridge axis getting forced southward, we are not
likely to see a significant moisture tap during this period. The
tail-end of this upper wave should graze northern New Mexico
Thursday night. Thereafter, GEFS and EPS mean 500mb height fields
suggests the upper high reorganizing over the area this weekend with
the ridge axis near the NM/AZ line. Meanwhile, this forecaster was
expecting to see a weakening backdoor cold front appear across
northeast NM in wake of the upper trough passage through the Central
Rockies. There may be some evidence for late Friday with another
frontal feature for Sunday, but nothing too impressive. KJ

.FIRE WEATHER...
No fire weather concerns for at least the next seven days as
northern and central NM remain under the influence of ridging aloft
with bouts of wetting storms. Some drying through Thursday will
limit the wetting rain footprint, which should expand Friday through
the weekend as the ridge weakens and PWATS creek back to normal or
slightly above normal for the end of August. 11

.ABQ WATCHES/WARNINGS/ADVISORIES...
None.

Area Forecast Discussion

National Weather Service Denver/Boulder CO

906 PM MDT Mon Aug 23 2021

.UPDATE...
Issued at 906 PM MDT Mon Aug 23 2021

A couple of strong storms developed in Logan county over the past
hour. They`re on the edge of the better moisture, which is also
cooler. With the moisture and some convergence on the front of
these cells, they will probably continue as they are but we don`t
think they will get much stronger than they are now.

The rest of the forecast is looking good, with clearing skies.

.SHORT TERM...(This evening through Tuesday)
Issued at 252 PM MDT Mon Aug 23 2021

A persistent southwesterly flow aloft will be over the region
through Tuesday. Enough moisture entrained in the flow aloft to
produce a few high based showers or thunderstorms. Main concern
this afternoon and evening will be gusty outflow winds in the
40-50 mph range. The latest HRRR runs suggests this potential. The
storms will diminish by midnight. Too dry and stable on Tuesday
for thunderstorms with high temperatures back into the mid 90s.
Fire danger will be high over North and Middle Parks, reference
the fire weather discussion for details.

.LONG TERM...(Tuesday night through Monday)
Issued at 252 PM MDT Mon Aug 23 2021

Southwest flow aloft will persist over northeast Colorado for
much of the week between troughing over the northwest and ridging
over the southcentral and southeast parts of the country. Tuesday
evening will be clear and dry, and a weak cold front will move
over the plains Tuesday night as a disturbance moves through the
southwesterly flow aloft. The front will bring slightly cooler
temperatures to the lower elevations Wednesday, with highs down to
the upper 80s and lower 90s across the plains. Models are showing
an increase in low to mid level moisture as well, of maybe 2 to 3
g/kg in the specific humidity fields, which should be enough for
isolated showers and storms to develop in the afternoon and
evening. Greater low level moisture and instability on the
northeast plains, where there could also be around 30 to 40 knots
of bulk shear, might support a few severe storms in that area.

A stronger trough will move over the northern and central Rockies
Thursday and Thursday night, and model agreement is improving
about a deep enough trough far enough south to provide some
forcing over northeast Colorado. There should also be better
moisture ahead of the trough with precipitable water values up to
over an inch across the plains and to around two-thirds of an inch
over the higher terrain. Expect scattered showers and storms with
an isolated severe threat again. Heavy rain may also be possible
from the stronger cells but increasing mid level winds should keep
storms moving fast enough to mitigate the threat. I once again
primarily moderated increases in PoP and QPF in the extended
period.

Friday is expected to be drier behind the trough with
temperatures fairly similar to those Thursday. There could be
enough moisture in place for some more isolated, low impact
showers. It looks like there might be a westerly stream of smoke
in more zonal flow aloft between troughs as well. Another trough
should move over the northern and central Rockies Saturday, which
still looks to be a little too far north for serious impacts to
northeast Colorado. It may bring some more isolated to scattered
weak showers and storms, and another front over the plains late
Saturday with some cooler air for Sunday.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 906 PM MDT Mon Aug 23 2021

VFR through Tuesday. Winds will become southerly by 06z. A period
of west winds around 10 knots is expected Tuesday morning before
winds go northerly by 18z.

.FIRE WEATHER...
Issued at 252 PM MDT Mon Aug 23 2021

Hot and dry on Tuesday with a moderate southwesterly flow aloft
over the forecast area. The fire danger will be high over the
mountain valleys of Jackson, Grand and Summit counties. Gusty
winds to 30 mph and RH values down near 10 percent enough to
warrant a Fire Weather Watch for Tuesday afternoon.

The Fire Weather Watch for North and Middle Parks will continue
into Tuesday evening until 8 pm, as there is potential for
critical humidity in the 10 to 15 percent range and with gusts
exceeding 25 mph to persist in these areas. We have issued
another Fire Weather Watch in those same areas for Wednesday, from
noon to 8 pm, due to the potential for similarly hot, dry, and
gusty conditions. By Thursday, greater moisture over the area with
scattered showers and storms are expected to alleviate this fire
danger.

.HYDROLOGY...
Issued at 252 PM MDT Mon Aug 23 2021

Low chance of flash flooding through this evening, with decent
storm motion and limited storm coverage. Nil on Tuesday with no
thunderstorms forecast.

Tuesday will be dry and clear, then isolated showers Wednesday
will bring a very low threat of flooding. Greater moisture
Thursday will allow scattered showers and increase the threat of
burn area flash flooding, with localized heavy rain possible
though storms are expected to be moving more quickly. The threat
should remain limited. Precipitation should decrease in coverage
and intensity again for the weekend.

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Tuesday afternoon through Tuesday
evening for COZ211-213.

Fire Weather Watch from Wednesday afternoon through Wednesday
evening for COZ211-213.

UPDATE...Gimmestad
SHORT TERM...Cooper
LONG TERM...EJD
AVIATION...Gimmestad
FIRE WEATHER...Cooper
HYDROLOGY...Cooper/EJD

Area Forecast Discussion...Updated

National Weather Service Billings MT

849 PM MDT Mon Aug 23 2021

.UPDATE...

Tweaked the winds this evening with the front coming through the
area. It looks like the main front is about through Billings as of
830p. There have been some showers and thunderstorms that have
developed mainly from Wheatland County to northern Rosebud County
with this front, but most have been quick to develop and then
dissipate. Have kept the broad bushed slight chance PoPs across
the area. Reimer

.DISCUSSION...

Tonight through Wednesday...

Cold front was just through KTFX at 18Z and was progged to move
into the NW corner of the forecast area by 00Z tonight. HREF
focuses on the SE for isolated thunderstorms from 22Z into the
evening, and showed possible strong winds with the storms. RAP
soundings showed inverted-v`s across most of the area. SREF had
possible dry thunderstorms SE this afternoon. Kept slight chance
PoPs across the area this evening due to energy in SW flow aloft,
lift from the front and the soundings. Models bring front through
KBIL around 03Z, and through the entire area by 09Z. Front will
usher in cold advection and there will be a tight pressure
gradient. Front will also be accompanied by decent pressure rises.
As a result, expect windy conditions with N to NW gusts around 30
mph behind the front. Winds will drive smoke and haze out of the
area. Went above NBM winds which were not strong enough. Temps
will fall into the 40s and 50s behind the front.

Upper trough crosses the area on Tuesday and cold advection
continues until winds turn easterly late in the day. Highs will
mainly be in the lower 70s. Expect gusty winds over the E half of
the area. Humidities will range from the mid 20s to 40 percent.
Few showers and storms are possible over the southern mountains.
Anticyclonic flow aloft moves over the area Tue. night and
continues on Wednesday. Warm front pushes N into the eastern part
of the area on Wed. ahead of a surface low over WY. So had low
PoPs late Tue. night/Wed. morning with the warm front in the E,
and PoPs over the W in the afternoon due to upslope flow and
energy approaching ahead of next trough. E winds will be gusty
over the E on Wednesday and temps will reach the mid 70s to mid
80s. Only lower RH`s were in and near Sheridan County. Trough
continues approaching Wed. night and warm front remains over the E
with a low-level jet. PWAT`s also increase with the EC suggesting
values around 1 inch. SREF had 500-1000 j/kg MLCAPE over the SE
Wed. night with fairly strong shear across the area. Had PoPs over
much of the area Wed. evening with precipitation shifting N and E
overnight. Currently, SPC has a marginal risk over the E Wed. and
Wed. night, so will need to keep an eye on this period for strong
storms. Arthur

Thursday through Monday...

Unsettled conditions can be expected through the extended
forecast. Large upper trough is progged to move through the
region on Thursday bringing shower and thunderstorm chances.
Southeasterly flow out ahead of the trough looks to transport
moisture and instability into the east, where there is potential
for some stronger storms. Shower and thunderstorm chances look to
linger for Friday as cyclonic flow remains over the area. Yet
another disturbance looks to drop through the region over the
weekend bringing additional precipitation chances and slightly
cooler temperatures. Weak ridging builds back over the area for
Monday bringing drier and warmer conditions.

Generally below normal temperatures are forecast through Monday
with most places seeing highs in the 70s. A few locations could
nudge above 80 degrees Thursday ahead of the upper trough, and
again on Monday. Low temperatures in the 40s and 50s are forecast
most nights. STP

.AVIATION...

VFR conditions will prevail. Slant visibility may be reduced from
smoke.

A cold front will continue to move southeast this evening into
the overnight hours, switching winds to the north with surface
winds to 35 kts. Isolated showers and thunderstorms remain
associated with the front will continue through around 06Z. Breezy
winds will continue into the early morning hours.
Carrothers/Reimer

.PRELIMINARY POINT TEMP/POPS...

Tue Wed Thu Fri Sat Sun Mon
-----------------------------------------------------------
BIL 051/071 049/078 053/079 052/077 051/073 049/072 049/082
20/U 11/B 24/T 53/T 34/T 21/B 00/U
LVM 043/073 044/078 049/077 047/075 045/072 044/073 046/083
20/U 12/T 34/T 33/T 33/T 21/B 00/U
HDN 050/072 049/083 051/080 050/078 049/076 047/072 047/083
20/U 11/U 23/T 53/T 34/T 21/B 00/U
MLS 055/072 049/081 056/079 054/077 052/074 051/071 051/079
20/U 12/W 43/T 63/T 34/T 32/W 10/U
4BQ 056/073 050/084 057/083 054/079 052/077 051/070 050/079
20/U 21/U 33/T 53/T 34/T 32/W 10/U
BHK 054/074 046/078 054/077 053/078 051/076 050/072 049/079
20/U 12/W 54/T 64/T 44/T 42/W 10/U
SHR 049/073 046/085 050/081 048/079 047/076 045/071 046/082
21/U 11/U 22/T 42/T 33/T 31/U 10/U

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

weather.gov/billings

Area Forecast Discussion

National Weather Service Duluth MN

624 PM CDT Mon Aug 23 2021

.DISCUSSION...(This evening through Sunday)
Issued at 225 PM CDT Mon Aug 23 2021

Summary: Today will continue to be warm, windy and dry before a
much needed change to a wetter pattern with temperatures closer
to normal through the remainder of the week.

Warm, windy and dry is the main story today. Winds have been
mainly out of the west gusting at times to near 25mph with minimum
RH values near 30 percent from the Brainerd Lakes region
northeastward to the Arrowhead. This will continue the Near
Critical Fire Weather Conditions for NE MN.

The next chance of precipitation comes overnight tonight into
Tuesday morning. A warm front to our south from northeastern
Montana to southeastern South Dakota will begin to move northward
and develop elevated convection over eastern Dakotas. Bulk shear
of 40 knots parallel to the front will allow the convection to
continue to move eastward in a linear form. As the warm front
moves northward, this will set up the southern portion of our CWA
in a waa regime with strong theta-e north of the warm front along
with an EML above 700mb. Additionally, elevated lapse rates around
7-8C/km will be moving northward with the front. By 12Z the warm
front will be from northeastern SD to extreme southern MN as a
shortwave moves in from the SW overtop the warm front along with
isentropic lift at 310-315K will provide enough lift to keep
ongoing convection moving eastward along the instability axis. Due
to what is mentioned above, SPC has the southern portion of our
CWA in Marginal Risk. The question remains how long will the
convection stay organized and will it move into a Mesoscale
Convective Complex which would mean that there will be more of a
wind threat than a hail threat. Some models are indicating that
the shortwave will remain strong through the afternoon, but the
LLJ will decrease substantially by 15Z. Should also state that
model hodographs show a small chance of tornado development near
12Z, but quickly diminishes. The HRRR is bringing in additional
convection after the main complex moves eastward. This appears
that it could develop on a secondary shortwave that moves through
but have little confidence in its development given that the
previous complex could decrease instability.

The next chance of precipitation comes in overnight Thursday into
Friday morning. Some model data is showing higher precipitation
amounts which will be a welcome sight for drought stricken
northeastern MN.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 623 PM CDT Mon Aug 23 2021

An MVFR stratus deck continues to flow across the International
Border impacting INL. These clouds are expected to persist through
the early portions of the night before lifting further north.
Overnight, fog has the potential to develop across northern MN
primarily impacting HIB and possibly DLH. A challenging weather
system is projected to move in from the west tomorrow morning
bringing rains and possibly strong to severe thunderstorms across
the region. Model guidance continues to waiver in timing and
location so confidence is not high for the onset and duration.
Additionally, depending on how the morning convection goes there is
potential for a second dose in the afternoon and evening hours.

.MARINE...
Issued at 423 PM CDT Mon Aug 23 2021

Winds will be mainly out of the southwest 10 to 15 knots with
gusts to near 20 knots switching to the northwest around 10
knots later this evening. By Tuesday morning winds will be out of
the northeast 10 to 15 knots with gusts to near 20 knots. Waves
will be less than 2 feet. Showers and thunderstorms will develop
overnight into Tuesday morning possibly reaching the lake by early
afternoon. Strong winds and large hail is possible.

.PRELIMINARY POINT TEMPS/POPS...
DLH 57 69 60 76 / 10 70 50 0
INL 49 75 54 71 / 0 70 50 20
BRD 59 79 58 75 / 40 70 30 0
HYR 57 76 60 79 / 20 70 50 10
ASX 57 75 61 80 / 10 60 50 10

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

DISCUSSION...KSE
AVIATION...Britt
MARINE...KSE

AREA FORECAST DISCUSSION

National Weather Service Eureka CA

417 PM PDT Mon Aug 23 2021

.SYNOPSIS...Seasonable temperatures and generally light winds
will continue through Wednesday. The coast is expected to see
areas of nightly marine stratus with afternoon clearing. Smoke is
expected to remain near fires, flowing with daily diurnal winds.
Later this week, a warming and drying trend is expected with
marine stratus persisting.

.DISCUSSION...Visible satellite imagery shows coastal stratus
lingering along the Mendocino coast and smoke from the active
wildfires in Trinity and Siskiyou counties has pushed back
northeast as light southwest wind aloft develops. The weak upper-
level trough is bringing seasonably temperatures and is expected
to continue through mid week. Inland areas will see temperatures
topping out close to 90 each day in Mendocino and Lake counties
with low to mid 80s farther north. Temperatures may trend a degree
or two cooler each day as this trough deepens. This cooler air
aloft will continue to keep the marine inversion weak and limit
the coverage of marine stratus. Afternoon clearing remains likely
each day. Winds will be breezy along the coast, but inland areas
will generally see diurnal/terrain driven winds. Otherwise,
a brief period of increasing winds is expected tomorrow by late
afternoon/early evening with westerly to northwesterly flow as a
weak low level trough moves through.

Thursday high pressure starts to build in over the west coast
warming temperatures and increasing winds over the coastal waters
and on the immediate coast. Most inland areas are expected to see
around 5 degrees of warming. The ensembles have come into better
agreement on this.

Friday and into the weekend there is more uncertainty of on how
much warming is expected. Some of the ensemble clusters show an
upper level trough dropping down over Idaho, while others continue
to build the ridge in. The scenario with trough would keep
temperatures cooler, but may also increase north to northeast
winds and lower the RH. The ridge would warm temperatures and
keep the stronger northerly winds more confined to the coast. The
operational GFS, ECMWF, and CMC are all closer to the clusters
dropping a trough into Idaho and they are starting to show some
stronger NE winds Saturday morning in Del Norte county. MKK&ZVS

.AVIATION...Once again, stratus blanketed the coastal waters and
adjacent land areas this morning. These clouds eroded quickly over
land, but held until around midday for portions of the N Coast.
These clouds are now gone N of Cape Mendocino, but stratus continues
S of the cape and along the Mendocino and S Humboldt coasts. The
marine layer is presently about 2000 ft deep at the ACV profiler and
a bit deeper to the S at the Bodega Bay profiler. The marine layer N
of the cape is forecast to become even shallower later tonight and
Tuesday, and the low-level inversion is forecast to weaken. As a
result, low clouds which re-develop along the N Coast may clear more
quickly Tuesday morning.

Low clouds briefly advected N up the Russian River Valley to KUKI
this morning. The latest HRRR guidance suggests this may occur again
Tuesday morning. Winds will be generally light, with some gusts near
20 kt at KCEC and KUKI into the early evening. /SEC

.MARINE...Northerly winds will continue through the period.
There may be enough of a lull to drop headlines for the N outer
waters by Wednesday, but winds are forecast to increase once again
later in the work week, with gale force gusts likely by Friday
afternoon. For the update, have hoisted a Hazardous Seas Warning for
the N outer waters from this evening thru Tuesday afternoon to
account for an increase in wind over the extreme N portion of the
zone and northward. Have also extended the Small Craft Advisory for
the S outer waters thru midday Thursday. /SEC

.FIRE WEATHER...The upper level trough will remain over the west
coast through about Wednesday. The trough may deepen slightly and
this could cool temperatures by a degree or so each day. The
afternoon RH and overnight recoveries may diminish slightly as
well. Transport winds remain light, but are generally pushing the smoke
off to the northeast. Most of our areas will remain free from
the thicker smoke aside from areas of Trinity county to the
northeast of the fires. Surface winds will generally be light and
terrain driven. Tuesday, a brief period of increasing winds is
expected late afternoon/early evening with westerly to
northwesterly flow as a weak low level trough moves through. More
wind prone areas could sees gusts up to 25 mph.

Thursday models continue to come into better agreement on high
pressure starting to build in and bringing a warming and drying
trend. There is decent agreement in the ensembles that this
warming and drying trend will continue on Friday. For the weekend
the ensembles are starting to show a couple clusters. One brings
warming temperatures as ridge builds in. This would like keep
winds mainly terrain driven. The other two clusters show a trough
dropping into ID/MT and either slowing the warming bringing some
cooling. This would also bring some stronger offshore winds and
drier air. MKK&ZVS

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 4 PM PDT Tuesday for PZZ450.

Small Craft Advisory until 6 PM PDT this evening for PZZ470.

Hazardous Seas Warning until noon PDT Tuesday for PZZ470.

Small Craft Advisory until noon PDT Thursday 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 Chicago/Romeoville, IL

908 PM CDT Mon Aug 23 2021

.UPDATE...
908 PM CDT

Few minor tweaks made to going forecast this evening, mainly to
raise overnight min temps slightly. Thunderstorm forecast for
later tonight remains somewhat low confidence with CAM guidance
still offering diverging solutions on evolution of elevated
convection across the region. Chance pops across especially far
northern still appear reasonable at this point though, and no
changes made.

Early evening surface analysis depicts a west-east oriented
surface trough, stretching roughly along the I-80 corridor across
IA and northern IL. Mid-70s surface dew point temps were pooled
along and south of this boundary, with a northward drift noted
over the past few hours. Water vapor imagery indicates a mid-
level short wave trough propagating east-northeastward across the
mid-Missouri River Valley of eastern NE/western IA. This feature
will continue to translate east-northeastward tonight, reaching WI
and northern IL toward 10Z/4 am. Pooled low-level moisture and
the advection of steep mid-level lapse rates (OAX 00Z sounding
indicates deep layer of 7+ C/km lapse rates) would appear to
support the development of substantial elevated instability across
the region into early Tuesday morning, with the caveat being
sufficient moistening of a layer in the 800-850 mb range to allow
for a forced parcel to break the cap. 00Z upstream RAOBs don`t
depict this, though RAP analysis does depict a narrow axis of H8
dew points along the I-80 corridor from NE across IA. CAM guidance
has been somewhat split on the extent and location of elevated
convection development overnight, with the HRRR decidedly on the
dry side and the 18Z 3 km NAM maintaining that models earlier
trend of activity developing across northern IA and spreading into
northwest/northern IL toward Tuesday morning. Quick glance at the
newly arriving 00Z 3 km WRF still brings convection into the
IL/WI state line region early Tuesday, though not as extensively
and perhaps too slowly (per short wave timing). Basically, the
potential for thunderstorms remains across northern IL late
tonight/early Tuesday remains a possibility, though of somewhat
low confidence. Therefore hesitant to change our current 30-40
percent pops much, with some potential that guidance/RAOB network
is not handling moisture fields 100 percent correctly.

Otherwise, did raise overnight mins slightly tonight especially
across the southern cwa where aforementioned higher dew points
will likely keep temps from falling off too much. Can`t rule out
some patchy fog in a few spots with moist low levels, though 10+
kt flow atop the boundary layer should work against this somewhat.

Ratzer

.SHORT TERM...
330 PM CDT

Main concern beyond the near term is later tonight into Tuesday
morning for the potential of at least scattered storms to develop
overhead northern Illinois and gradually overspread points south
and east. This would have a heavy downpour and localized flooding
threat, especially if the convective footprint is larger.
Depending on how long into Tuesday the convection lingers along
with associated debris cloud cover, the potential exists for
parts of the area to reach or exceed 105+ degree heat index
criteria for Heat Advisory.

We`ve been tracking a convectively modified disturbance from
eastern Colorado that has reached the Missouri River vicinity near
the NE/IA border. After the wave responsible for the northwest
Illinois convection this afternoon exits, should have at least a
few hours of subsidence in the evening. Later tonight, a plume of
even steeper mid-level lapse rates will be advecting eastward as
the short-wave drifts overhead. Modest LLJ but decent isentropic
upglide on the 310K surface in response to the wave should work to
erode MUCIN assuming there`s enough moisture in the 850-800 mb
layer. While there`s variance in the details, much of the guidance
does indicate enough saturation to tap into large MUCAPE
reservoir. HRRR has been a notable dry outlier, though may be
starting to see a change on the 18z run. Conceptually do favor the
idea of convective initiation overhead in the pre-dawn hours,
though lower confidence in exact timing and coverage.

Given this, opted to largely forecast continuity though with a
modest increase in PoP magnitude into the 40%ish range. As alluded
to in intro, high column moisture with PWAT pushing 1.7" or more
would support torrential downpours especially in robust
convection. Slow storm motions would yield efficient rain
producers and will need to watch for training or backbuilding if
convective footprint is large enough. Lots of unanswerable
questions on how this all evolves through the morning, so needless
to say observational trends will be monitored closely.

Given the above uncertainty and overall expectation that
convection will occur farther east than it did earlier today,
confidence is rather low in the temperature and heat index
forecast. Convective uncertainty aside, the air mass with 850 mb
temps in the lower 20s Celsius amidst dew points into the mid and
even locally upper 70s would support heat indices near or above
105F if temps reach the mid 90s. Neighboring offices to the south
and west have gone ahead and issued a Heat Advisory, but decision
here was to hold off given the potential for convection and
lingering clouds to have a substantial effect on temps. Convective
trends beyond the morning are also uncertain - other than thinking
that there will be a lull after morning storms diminish (assuming
they do). We`ll have to watch for a semi-organized cluster of
convection to approach from the west and northwest Tuesday evening
and night. Have the highest PoPs overnight (30-40%) focused I-80
and north for this potential.

Castro

.LONG TERM...
301 PM CDT

Wednesday through Monday...

A persistent pattern of heat and humidity may finally break early
next week, but until then the mid to upper 90s heat indices will
linger into the weekend, with actual highs in the upper 80s to lower
90s. Relatively weak southerly flow for most of the period may
allow for lakeside cooling on some afternoons. The best bet for
significant onshore cooling winds comes on Thursday following the
passage of a weak frontal zone late Wednesday.

In this type of pattern with an upper ridge to our south and quasi-
zonal flow across the northern CONUS, heat headlines and afternoon
convection are usually the two competing questions. This certainly
will be true on Wednesday ahead of the approaching frontal zone. The
latest guidance suggests we might be very close to but just below
thresholds for a heat advisory, and additional uncertainty is
provided by the influence of possible convection along the surface
boundary.

Precip chances will remain elevated, though for now still in the
chance category, as the front pushes into the area late Wednesday,
stalls Wednesday night, then begins to lift back north on Thursday
as a warm front extending eastward from a surface low moving from
the Southern Plains toward Lake Superior. North of this front on
Thursday is also where the cooler easterly flow off the lake would
develop.

By late in the week and into the weekend, heat and humidity persist
but precip chances presently look lower with the lack of additional
shortwaves or low-level boundaries to provide a focus for lift.
Models then suggest a more significant cold front will move through
late Sunday and usher in cooler conditions to start next week, but
there is considerable uncertainty that far out in such a weakly
forced pattern.

Lenning

.AVIATION...
For the 00Z TAFs...

630 PM...Forecast concerns include...

Chance of thunderstorms Tuesday morning.
Chance of thunderstorms Tuesday afternoon/evening.
Chance for fog early Tuesday morning.
Possible gusty southerly winds Tuesday.

Showers and isolated thunderstorms earlier this afternoon have
dissipated and not expecting any additional activity this evening.
Focus shifts to the predawn hours Tuesday morning when the next
chance for thunderstorms will arrive but confidence remains low.
This time period is currently covered by prob mention and this
looks fine for now. Will need to assess thunder potential with the
03z update this evening. There is another chance of thunderstorms
Tuesday afternoon into Tuesday evening and these will likely be
dependent on morning activity though there seems to be a bit
better signal for activity Tuesday afternoon/evening. Opted for
just prob mention for now. Any thunderstorms that do form, at
either time period, will have the potential to produce very heavy
rain and gusty/erratic winds.

There will be some fog potential again overnight into early
Tuesday morning, mainly west and southwest of the Chicago
terminals. Already have lower vis mentioned associated with the
thunder potential but some prevailing mvfr vis may be needed,
especially at rfd Tuesday morning. Some patchy dense ground fog
may also develop in the usual locations.

Winds will remain southerly under 10kts tonight, with some
southeast directions possible this evening. Outside of any
thunderstorms or their outflow, generally southerly winds are
expected Tuesday and there is some potential for wind speeds to
increase into the 10-15kt range with some higher gusts. These will
be dependent on precip timing/location but medium confidence to
increase wind speeds for Tuesday. cms

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

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Area Forecast Discussion

National Weather Service Marquette MI

624 PM EDT Mon Aug 23 2021

.SHORT TERM...(This evening through Tuesday)
Issued at 351 PM EDT MON AUG 23 2021

Water vapor imagery and RAP analysis show a slowly-weakening
shortwave continuing to lift ne through northern Ontario this
afternoon. Over the Upper Great Lakes, mid-level ridging is fcst to
continue building into the region this afternoon and evening. Higher
dew points in the lower to mid 60s combined with steep low-level
lapse rates of 7C or greater has resulted in an expansive cu field
over much of the western half of the U.P this afternoon. Afternoon
temps have risen generally in the lower to mid 80s across much of
the area with cooler readings in the mid 70s along the Lake Mi
shoreline.

Big question late this afternoon/early evening: is will convection
initiate along weak sfc trough/convergence area over the nw U.P.? A
few of the CAMS still try to get some convection going in this area,
but looking at the fcst soundings mid-levels are very dry with even
some CIN noted, so I would doubt we`ll see showers forming. Kept
fcst dry, and expect diurnal cu to dissipate after sunset in the
west. Models indicate a shortwave late tonight could ride along
frontal boundary/instability gradient resulting in a possible MCS
over central/southern WI although it looks like any convection from
this system would stay south of the U.P. Expect min temps in the 50s
to lower 60s tonight, coolest over the western interior. Given
higher dew points and light winds, I guess it wouldn`t be out the
question there could be some patchy ground fog over the western
interior, but with low confidence decided not not to put it in
the fcst grids.

Model agreement/timing is poor for potential convection on Tuesday
although there is a signal with several of the CAMs that convection
forming over central MN later tonight could congeal into an MCS and
then track se or ese as a linear convective system across either
northern or central WI on Tuesday following the better instability
gradient along the sfc-850 mb warm front. Generally bring chc PoP
for showers/t-storms into mainly western and south central portions
of the cwa Tue afternoon where convection on northern end of MCS
could brush these areas. Expect max temps in the lower to 80s over
much of the interior and in the mid to upper 70s near the Great
Lakes shores.

.LONG TERM...(Tuesday night through Monday)
Issued at 423 PM EDT MON AUG 23 2021

We have a tricky forecast to start the extended period, as model
guidance is showing high divergence as to when, where, and if
convection will develop over the U.P. Tuesday night. As a sfc low in
the Northern Plains lifts northeast towards northern Ontario (ON)
Tuesday night, expect better synoptic forcing to remain northwest of
us. Meanwhile, some CAMs still show an MCS developing mainly just
south of the border in WI (such as the NAM4km and HiRESW-Fv3) during
the overnight hours. The Euro, NAM12km, and RAP13 still show
precipitation over the U.P. Tuesday night, so there is a chance for
some precip still, though it doesn`t look as favorable given the
lack forcing and the better instability being south of us; if an MCS
does develop in WI, I would expect chances for precip over the U.P.
to decrease Tuesday night. Therefore, I tried to keep only a chance
of showers and thunderstorms across the area, although I did adjust
to my neighbors to the south who had a much higher chance of seeing
precip in their areas (as the southern U.P. does have a better
chance of seeing something Tuesday night). Don`t think severe wx
should be a threat Tuesday night; again, the better instability
should be south in WI, and the better forcing should be closer to NE
MN, even though the 0-6 km bulk shear looks modest (30 to 40 knots).
As the low in northern ON combines with another low and shifts east
towards Quebec, expect a cold front to move through Wednesday. This
front should keep the highest temperatures confined to the south
central, where the front will more than likely have the least impact
given the jet stream should be north of Lake Superior then. As this
front passes through Wednesday, showers and thunderstorms should be
confined to the east; again, no severe weather is expected due to
most of the precip being done by noon, and the turning of the winds
with height is expect to not be as strong (even though the forcing
is better).

Expect cooler conditions Thursday as a high pressure over northern
ON should move cooler Canadian air over the U.P.. Meanwhile, a
pressure gradient aloft should begin moving slowly east over us and
tighten late this week as a troughing pattern sets up over the
Northern Plains. This should allow multiple shortwaves to cross over
Upper MI this weekend. Given that ensembles show PWATs in the 90th
percentile for these shortwaves (and the forcing doesn`t seem too
strong also, which should help with rainfall production), would not
be surprised to see a soaking rainfall event this weekend. Global
models also are showing some pretty decent winds with the shortwave
activity this weekend. Wouldn`t be surprised if we had some breezy
conditions, particularly in the Keweenaw. Eventually, we should have
a cold front move through next Sunday night into Monday as the
troughing pattern moves east. This should bring an end to the
precip, and we should also see temperatures become `cooler` and
closer to normal next Monday.
&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 623 PM EDT MON AUG 23 2021

VFR conditions should prevail thru this fcst period at all sites.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 351 PM EDT MON AUG 23 2021

Expect winds to remain generally under 20kt across Lake Superior
thru Wed. During Thu and Fri, pres gradient will tighten btwn high
pres moving from northern Ontario to Quebec and a low pres trof
lifting into the Upper Great Lakes. As a result, expect e to ne
winds to gust to at least 20-25kt over western Lake Superior on
Thu with e to se wind gusts to at least 20-25kt spreading to eastern
Lake Superior Thu night into Sat. Would not be surprised to see
gusts to around 30kt for a time as well.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

SHORT TERM...Voss
LONG TERM...TAP
AVIATION...07
MARINE...Voss

Area Forecast Discussion

National Weather Service Omaha/Valley NE

Issued by National Weather Service Hastings NE
535 PM CDT Mon Aug 23 2021

.DISCUSSION...
Issued at 530 PM CDT Mon Aug 23 2021

Hot and humid conditions, with occasional/conditional thunderstorm
chances, are the main forecast concerns.

Hot and humid conditions have developed across much of the CWA
this aftn, esp areas along and S of the Platte River. A weak
disturbance (as seen on latest WV imagery) ejecting from NE CO
into central NE has resulted in iso to widely scat elevated/weak
convection for areas around BVN to OFK. Short-term hi-res
guidance has not handled this well, thus far. Exactly how this
activity evolves is low confidence, but gut feeling is that it
will remain fairly weak/elevated as it continues to move NE over
next few hrs. Sfc based instability is strong, but MLCINH remains
fairly high at 50-100 J/kg per latest SPC mesoanalysis, further
supporting the idea this activity will struggle to become sfc
based. Appears greater potential for sfc based t-storm
development, and associated svr threats, will be closer to NE/SD
border, within zone of greater low level wind/moisture
convergence, and on edge of stronger mid level capping. Tstms have
blossomed over S SD last hr or two, and this activity is forecast
to move E/SE and may move into far NW portions of CWA towards
late eve. As such, this is where a Slight Risk for severe tstms
resides, with large hail and damaging winds the main concerns.
Current thinking is that 18Z NAMNest is overdone, and HRRR may be
underdone...so have focused 20-30 PoPs mainly NW of LNK/OMA.

The main forecast change for Tue was to issue a Heat Advisory for
S half or so of CWA for peak heat indices near 105F. Don`t think
there will be significant AM convection or clds, which should
allow for rapid warming through the AM. Guidance indicates pooling
moisture ahead of a dev sfc low along NE/KS border by aftn, which
combined with high temps in the upper 90s/near 100 should lead to
heat indices near 105F. Add in evapotranspiration from mature
crops and it could be even higher in spots. Winds over
central/western ares are lighter. So even though heat indices may
be a touch lower, it may actually feel as bad or worse in these
areas. Will let mid shift crew get a look at a couple more model
runs, but wouldn`t be surprised if current advisory is expanded NW
a county or two.

The next concern revolves around yet another chc for tstms during
the aftn/eve hrs Tue. A shortwave tracking across the N Plains
will force a cold front into central NE by late aftn. Intense
heating along/ahead of the front and impingement onto NW fringes
of low level moisture plume will probably support iso to scat
convection in the 21Z to 00Z time frame, probably over NW portions
of CWA or just W of there. Upper level support is not great, and
mid temps are quite warm at 14-16C, but magnitude of CAPE/shear
support a non- zero chc for strong/severe storms. Expect a gradual
eastward movement thru the eve. Intensifying low level jet Tue
eve could foster upscale growth during late eve, but magnitude of
mid level temps casts some uncertainty on size/scope of any
potential MCS. IF an MCS develops, will have to watch for locally
hvy rn given PWATs near 1.75" and perhaps some subtle training.
Again though, confidence on this is very low attm given high model
spread (e.g. 18Z HRRR much more active than 18Z NAM Nest.)

The rest of the forecast remains on the warm/hot and humid side, but
probably not as bad as Tue. Some areas along KS/NE state line
could see heat indices near 100F again Wed, and maybe even Thu,
but current thinking is that we`ll stay below Heat Advisory
thresholds. There are mentionable PoPs (15 percent chc or greater)
nearly every period through the extended, but this probably
sounds worse/wetter than it will be. This is fairly common for
late summer. Appears time frame of best chcs will be Wed night
into Thu, esp. for N half/third of CWA, then areawide Sat-Sat
night. Won`t go into much more details beyond that as
predictability is low.

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 619 AM CDT Mon Aug 23 2021

Expect mainly VFR conditions the next 24 hours. There are some MVFR
ceilings in the far northern parts of northeast NE north of KOFK
and some patchy areas of fog, but we don`t expect these to have
much of an impact at the TAF sites. Could see some scattered storms
in parts of northeast NE today and mentioned a PROB30 group at
KOFK for 21z-24z. Otherwise chances at KOMA and KLNK are not zero
but too low to include in TAFs.

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory from noon to 8 PM CDT Tuesday for NEZ051>053-
065>068-078-088>093.

IA...Heat Advisory from noon to 8 PM CDT Tuesday for IAZ069-079-080-
090-091.

DISCUSSION...Thies
AVIATION...Miller

Area Forecast Discussion

National Weather Service Pendleton OR

858 PM PDT Mon Aug 23 2021

.UPDATE...Based on surface observations and satellite imagery,
light winds and mostly clear skies are present across the
forecast area. This should allow efficient radiational cooling
tonight. As such, have lowered tomorrow morning`s minimum
temperatures in a few spots, mainly high valley locations.
Additionally, updated haze and smoke based on the latest HRRR
Smoke run. Otherwise, no major changes to the forecast. 86

.PREV DISCUSSION... /issued 425 PM PDT Mon Aug 23 2021/

SHORT TERM...
Tonight through Wednesday night...An area of low pressure was
located over British Columbia with weak troughing over northeast
Washington. However, further south, the flow is more zonal. Weak
ridging moves in overnight and into Tuesday before a trough off
the Pacific Northwest coast moves onshore Wednesday into Wednesday
night.

With a mainly clear sky and light winds expected tonight, it will
be a chilly night in most locations, the coolest night we have had
in some time. Most areas will be in the low to mid 40s with the
mountains in the 30s, and some mountain locations close to or
below freezing. Temperatures on Tuesday will be warmer than today,
as the ridging moves in, and many locations, will be close to 80
degrees, with the Basin in the low to mid 80s. Temperatures on
Wednesday will be a degree or two warmer than on Tuesday.
overnight lows will also warm with most locations in the 40s and
50s.

As far as sensible weather, with the trough moving in on
Wednesday, and several shortwaves, albeit weak ones, moving
though it on Wednesday, there is a small chance of showers or
thunderstorms mainly over the mountains. However, none of the
guidance is particularly excited about this potential at this time
and since the shortwaves aren`t particularly strong have opted to
leave the forecast dry for now. The HREF ensemble guidance places
a couple of enhanced showers in central Oregon Wednesday night as
does the ECMWF, while the GFS and NAM are dry. So it is possible
showers and or thunderstorms may need to be added for a portion of
the area at a later time.

LONG TERM...
Thursday through Monday...To begin the long term, an upper level
trough will be departing the region, promoting cooler weather and
westerly breezy winds. High temperatures look to remain below
average across much of the forecast region with 70`s to mid 80`s
expected Thursday through Saturday. The breeziest winds should
remain the usual locations of the Columbia Gorge and the Kittitas
Valley.

Into Sunday is where the greatest discrepancies lies in model
potential as high pressure ridging is expected to move in through
Monday and bring a warming trend for the region. Ensemble
clusters show that the strength of the ridge is not agreed upon,
but none of the models are stout with it. Rather, only a few
degrees of temperatures difference are expected, as we are getting
far enough along in the year that major heat events will become
more and more unlikely. For Sunday and Monday, current highs look
to range in the 80`s, peaking in the low 90`s for the Columbia
Gorge and Columbia Basins.

With all of this fair weather finally expected for our region, a
reprieve in the form of precipitation is not expected. Models
continue to keep us dry with only a chance at showers expected for
the WA Cascade Crests on Thursday. Goatley/87

AVIATION...00Z TAFS...VFR conditions should prevail over the next
24 hours. Some patchy smoke may drift near YKM/RDM/BDN but is not
expected to be as dense as previous days. Winds will generally be
under 10kts. 91

.PRELIMINARY POINT TEMPS/POPS...
PDT 42 80 49 82 / 0 0 0 0
ALW 47 83 55 84 / 0 0 0 0
PSC 47 84 51 85 / 0 0 0 0
YKM 42 82 49 85 / 0 0 0 0
HRI 45 84 49 85 / 0 0 0 0
ELN 45 82 49 84 / 0 0 0 0
RDM 34 79 42 80 / 0 0 0 0
LGD 39 79 45 80 / 0 0 0 0
GCD 41 82 51 82 / 0 0 0 0
DLS 50 86 54 84 / 0 0 0 0

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

SHORT TERM...86
LONG TERM....87
AVIATION...91

Area Forecast Discussion

National Weather Service Portland OR

230 PM PDT Mon Aug 23 2021

.SYNOPSIS...A very broad, weak upper level trough over the Pacific
Northwest will maintain near average temperatures through most of
the upcoming work week. Odds favor a brief return to hotter
temperatures late in the weekend.

.SHORT TERM...Tonight through Thursday...Water vapor satellite
imagery this afternoon reveals a broad shortwave trough over the
Pacific Northwest. As a lobe of this shortwave trough slides
southeastward across central Washington this evening, 850mb winds
will turn out of the east to northeast. This will limit morning
cloud cover across northwest Oregon and southwest Washington Tuesday
and result in temperatures warming well up into the 80s Tuesday for
inland valleys. The HRRR smoke model does suggest smoke from the
Schneider Springs fire in Yakima County, WA will shift into
southwest Washington and the northern Willamette Valley Tuesday.
While this may result in the sky being a little less blue than
normal, not expecting this smoke to bring noticeable impacts. This
is primarily based on the fact smoke from the fire today is very
limited per satellite imagery.

Models are then in good agreement a piece of the shortwave trough
currently over the Gulf of Alaska will slide southeastward into the
upper level trough currently sitting over the Pacific Northwest.
This will result in the upper level trough sharpening a bit and the
pressure gradient gradient force becoming more oriented from
southwest to northeast across the area. High resolution models are
not terribly keen on the idea of extensive marine clouds so have
kept sky cover closer to NBM guidance. This is partly due to the
fact that marine stratus is currently limited offshore and will
likely be so to begin the day tomorrow. As a result, it may not have
enough time to congeal despite the pattern looking favorable for a
fairly extensive marine cloud layer across northwest Oregon and
southwest Washington. Either way, with the loss of easterly winds at
850mb and a return to a more marine air spreading into the area,
temperatures should drop several degrees on Wednesday relative to
Tuesday.

Ensemble and model guidance suggests a weakening front will then
drop southeastward towards southwest Washington and northwest Oregon
Wednesday night into Thursday. Virga and higher level clouds will
likely spread across the area late Wednesday. However, a better
chance for rain to reach the ground arrives late Wednesday night
into Thursday as the majority of raw ensemble guidance available
suggests light rain will move into our northern coastal zones. PoPs
are still only the slight chance to chance category at this point
given some uncertainty in the exact timing of precipitation.
Nonetheless, think it`s safe to say some light rain and drizzle is
likely along our northern coastal areas some time late Wednesday
night or Thursday. The majority of ensemble guidance weakens the
front enough that measurable rainfall does not reach the Portland
metro, let alone places like Salem or Eugene or our wildfires in the
Cascades. Nonetheless, another push of cooler marine air into the
region should lower temperatures back below average for the date on
Thursday. /Neuman

.LONG TERM...Thursday night through Monday...Models and their
ensembles are in good agreement a low amplitude shortwave trough
will linger over the Pacific Northwest through Saturday. However,
the degree to which shortwave ridging develops over the northeast
Pacific and its proximity to the Pacific Northwest remains in
question as we move into late Saturday and Sunday. The probability
the area warms and dries out Sunday has gone up slightly when
compared to this time yesterday. NBM guidance now suggests the
probability of hitting 90F on Sunday is now 50% for Portland and
nearly 80% for Eugene.

WPC cluster analysis and a look at raw ensemble output does suggest
the odds of those hot and drier conditions lasting into early next
week is relatively low as another low amplitude shortwave trough
settles into the Pacific Northwest. For example, NBM guidance drops
the probability of 90F temperatures lasting into even Monday at less
than 10% for Portland and around 20% for Eugene. A bit beyond the
scope of this forecast, but there is very little sign in the ensemble
guidance of a major fall-like storm system bringing a much needed
widespread soaking rain event next week. /Neuman

.AVIATION...00Z TAF UPDATE: Northwest flow aloft continues over
the area through Tue. Stratocumulus clouds over southwest
Washington and northwest Oregon slowly diminishing during the
afternoon. As of 2030Z still areas of cigs around 045, but expect
these cigs to dissipate as the low-level flow becomes north to
northeast this evening and tonight. The 12Z high-resolution cloud
cover model suggests minimal marine stratus Tue morning, even along
the coast. Expect VFR to prevail across the area through the 18Z TAF
period. Cannot rule out isolated IFR or lower conditions along the
coast Tue morning, but confidence is low.

For detailed regional Pac NW aviation weather information, go
online to: https://weather.gov/zse

KPDX AND APPROACHES...VFR through the 00Z TAF period. However,
scattered clouds 040-050 will continue through early evening.
Northwest to North wind 10 kt or less, but gusts to 15 kt through
the evening. Weishaar

.MARINE...Strong surface high pressure remains over the eastern
Pacific through Tuesday. Thermally-induced low pressure along the
south Oregon coast will result in gusty wind over PZZ255 and
PZZ275. Will maintain the current small craft advisory through
06Z Tue. Latest model guidance shows wind speeds decreasing
overnight. Not expecting small craft advisory conditions Tue as
guidance suggests 15-20 kt boundary layer wind speeds. Surface
gradients weaken Tue night and Wed as another upper trough moves
over the waters. This will deepen the marine layer and result in
lighter west wind. Small craft advisory level wind speeds may
return south of Cascade Head Fri as gradients tighten and
thermally-induced surface low pressure strengthens over the south
Oregon waters.

Meanwhile, west-northwest swell around 5 ft at 8 sec will
gradually subside through Tuesday, leaving primarily wind-driven
seas by midweek. The next swell train of significance arrives
behind a decaying cold front Thu night/Fri, but latest wave
guidance suggests seas will remain well below 10 ft through the
upcoming weekend. Weishaar

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for coastal
waters from Cascade Head OR to Florence OR out 60 NM.

forecast discussion above for more details. I do want to note

that dense smoke will have impacts on predicted temperatures

(cooler daytimes). But for fire weather it is also having an
impact by limiting how strong the afternoon diurnal winds get by
reducing the Sierra to Nevada thermal gradient and vertical
mixing. So that could be an influence on the extent of near-
critical conditions Wednesday afternoon.

-Chris

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

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

Area Forecast Discussion

National Weather Service San Diego CA

134 PM PDT Mon Aug 23 2021

.SYNOPSIS...
Low clouds will continue the next few nights, but become
increasingly shallower and confined to coastal areas as high
pressure slowly expands. A gradual warming trend will bring us
near-normal temperatures by Wednesday, and above-normal
temperatures thereafter. Increasing smoke aloft may bring hazy
skies over the next couple of days, with some higher
concentrations near the surface possible as well for the mountains
and deserts. There are some indications of thunderstorm activity
returning to our mountains/deserts as early as Sunday, but
uncertainty remains in the pattern that far out.

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING
ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN
BERNARDINO COUNTIES...

Afternoon update...

Forecast temperatures were raised slightly for mid to late week.
With moderate to high heat risk now expected for the lower
deserts, an Excessive Heat Watch was issued Wed-Fri for the
Coachella Valley and San Diego County deserts. No other
significant changes made today. See below for previous discussion.

.SHORT TERM (Today through Wednesday)...

This morning`s satellite imagery exhibits little change from
yesterday, with an uncharacteristically deep marine layer (for
August) extending to the foothills. Signs of the rising heights
are evident though, with the thinner low clouds unable to produce
any measurable precipitation this morning save for two isolated
sites, and with a lesser inland extent in the Inland Empire. Thus,
look for slightly earlier clearing compared to yesterday (albeit
still slow). Smoke aloft is also faintly visible over SoCal and
the California Bight, with much more abundant smoke impacting
northern California and the Great Basin. With better clearing and
higher pressure, temperatures will be a few degrees warmer today,
though highs will nonetheless remain below normal across the
region.

Over the next couple of days, we`ll stay wedged between a
troughing pattern to our north, and high pressure to our east,
with prevailing southwest flow aloft. The primary change will be
the gradual westward expansion of the high pressure, which will
result in a steady warming trend that will return us to near-
normal temperatures by Wednesday. Meanwhile, a shrinking marine
layer will see low clouds reduce their footprint each night,
becoming increasingly confined to coastal areas with a possibility
of patchy fog by Wednesday morning.

An additional factor to consider over the next few days will be
the increased potential for both elevated and near-surface smoke.
HRRR smoke products are consistent in showing an area of higher
smoke concentrations - currently to our southwest - advecting
northeast into southern California through the next 24-48 hours.
Most of the smoke should remain aloft, with the main impact being
slightly hazier skies, however the mountains and deserts could see
a notable increase in near-surface smoke Tuesday as it mixes down.

.LONG TERM (Thursday through Monday)...

500 mb heights will continue to climb late in the work week, with
850 mb temperatures peaking near 29-30 C on Friday across southern
California. As such, warmer than normal conditions will return,
with highs around 100 F for the Inland Empire and High Desert, and
110-115 F in the Coachella Valley and San Diego County deserts,
which translated into moderate Heat Risk for many interior
locations. It`s likely that marine layer clouds will be minimal to
nonexistent during this period.

Differences in model guidance become more substantial for the
weekend and into early next week, with mixed signals when it comes
to the potential return of monsoonal activity. Higher pressure
looks to become somewhat more centered over the Four Corners, with
a corresponding increase in southeasterly flow near the surface.
For a considerable portion of the ensembles, this is reflected in
the form of higher PWAT values and indications of measurable
precipitation for mountain/desert locations as early as Sunday,
though with some uncertainty in timing. Of the GFS ENS members,
approximately half show precipitation at Big Bear on Monday,
although over 90% of them show precipitation at some point
between Sunday and Tuesday. The EC ENS system is less bullish,
however.

.AVIATION
232030Z...Coast/Valleys...Mostly clear skies with 6+ mile vis
despite smoke aloft over the region this afternoon. BKN-OVC stratus
will spread inland again tonight with onset mostly 03Z-07Z Tue at
the coast and 06Z-11Z Tue in the valleys with bases 1500-2300 ft MSL
and tops to 3000 ft MSL with higher terrain obscured and local vis
below 3 miles in the valleys in fog. The valleys will mostly clear
15-17Z Tue, and the coast will mostly clear 16Z-18Z Tue.

Mountains/Deserts...Mostly clear skies will prevail through Tue.
Smoke aloft will reduce vis somewhat, but the vis will remain mostly
6+ miles.

.MARINE...
No hazardous marine conditions through Saturday.

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch from Wednesday morning through Friday
evening for Coachella Valley-San Diego County Deserts-San
Gorgonio Pass Near Banning.

PZ...NONE.

PUBLIC...Rodriguez
AVIATION/MARINE...Maxwell

Area Forecast Discussion

National Weather Service Tucson AZ

252 PM MST Mon Aug 23 2021

.SYNOPSIS...High pressure will bring hotter temperatures the
second half of the week. A chance of thunderstorms today and
Tuesday before storm chances wane into the weekend. Conditions are
expected to be more favorable for thunderstorms early next week.

.DISCUSSION...We continue to see troughiness through the region
northwest of our area with a strong ridge building across southern
tier states. The subsequent southwesterly flow is on the dry side,
however a narrow area of high H7 theta-e values from eastern
Sonora into the AZ/NM border area is seeing some strong convection
this afternoon. On our side of the border that has mainly been
Cochise county with severe and flash flood threat. HRRR spreads
some of that into Santa Cruz, Graham and Greenlee counties over
the next few hours before typical diurnal trends knock things down
by early to mid evening.

Another chance of thunderstorms tomorrow afternoon before we fall
back to well below average coverage with limited moisture and an
unfavorable temperature profile the rest of the week.

That will open the door for heat, with excessive heat levels
possible Wed through Friday. Both NAEFS and ENS ensemble means
are above the 99th climo percentile at 850-500mb Thursday.

Beyond that, we`re seeing increasing likelihood that an active
tropics will help push a deep surge into southern Arizona over the
weekend. Next week is starting to look very interesting and
potentially very wet.

.AVIATION...Valid through 25/00Z.
Isolated SHRA/TSRA will develop east of the KTUS and KOLS this
afternoon but a brief VCSH is not out of the question for KOLS
through this evening. Better chances for SHRA/TSRA at the terminals
will be on Tuesday afternoon between 21z-03z, potentially lasting
through 07z at KOLS. FEW-SCT clouds are expected to develop at 8k-
12k feet this afternoon with decreasing coverage overnight. Winds
will favor a westerly component this afternoon, remaining around 10
knots before decreasing this evening. Aviation discussion not
updated for TAF amendments.

.FIRE WEATHER...
A near to below normal monsoon pattern is expected through late this
week. Isolated to scattered storms will be possible each afternoon
primarily east and south of Tucson and over the higher elevations.
An uptick in storm activity will be possible Friday into the
weekend. Temps will remain above normal Tuesday through at least
Friday with triple digit temps expected for much of the lower
deserts. 20-foot winds will generally be less than 15 mph when not
influenced by thunderstorms and RH values are expected to remain
above critical thresholds.

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Wednesday morning through Friday
evening for AZZ501-502-504-505.

Public...Meyer
Aviation...Guillet
Fire Weather....Guillet

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