Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/22/21

Area Forecast Discussion

National Weather Service Boston/Norton MA

 1012 PM EDT Tue Sep 21 2021

.SYNOPSIS...
High pressure centered south of the Canadian Maritimes moves
slightly farther offshore Wednesday, resulting in increasing
humidity and a risk for showers. A slow-moving front
approaching from the west will be accompanied bring showers into
western sections Thursday and spread across the region Thursday
night and Friday. Improving conditions expected Saturday, one
or two more periods of showers are possible Sunday. No big warm
ups or cool downs are expected.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
More minor tweaks to rainfall chances based on observed trends.
Latest runs for the HRRR and RAP seem to be verifying reasonably
well, as both captured the light showers across the Cape and
islands this evening. Since these were the only guidance sources
to do so, leaned heavily on their solutions to update the
timing and location of precipitation overnight.

Temperatures were also brought back line with observed trends
and updated expectations from near term guidance.

7 PM Update...

High pressure centered south of Nova Scotia. Local winds show
a southeast surface flow while winds at 2000 feet or higher, per
the KBOX VWP, are out of due south.

Increasing low level moisture. Radar shows light showers
popping near the Vineyard and moving toward Cape Cod. Another
batch of showers near Montauk Pt and along the RI Coast. All
showers moving north. Of the CAMS, the NAM Nest is the only one
to fully capture these showers. But it and the other CAMS
generate a new area of showers moving toward Wrn Long Island
near midnight that spreads across Srn New England overnight.

So expect some light rain/showers during the night. POPs at each
core should range from 25-30 pct, within a broader area of 20
pct.

The forecast expands the coverage of the rain but otherwise
follows the general theme of the previous forecast.

Previous Discussion...

The surface high pressure and mid level ridge move a bit
farther offshore, with a deepening mid level trough to our west.
Across southern New England, S/SE flow will bring increasing low
level moisture. This allows for an increase in clouds, and the
chance for patchy light rain and/or drizzle mainly over the
interior. Higher surface dew points will prompt a more mild night,
with overnight lows in the upper 50s to mid 60s, with areas of fog
developing.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Wednesday...Surface high and mid level ridge remain centered
offshore, while deepening mid level trough and associated surface
low move slowly eastward through the eastern Great Lakes Region/Ohio
River Valley. S/SE flow persists and pressure gradient tightens
somewhat. Saturated layer once again remains below 700 mb. Expecting
partly to mostly cloudy skies, with a continued chance of light rain
or drizzle mainly over the interior. Above normal temperatures, with
highs in the low to mid 70s.

Wednesday night...

Models show mid level trough becoming cut off/blocked and halting
eastward progression, with surface low retrograding somewhat. Low
level moisture remains in place, with a continued S/SE flow. Thus
expecting another night of considerable cloudiness, with patchy
light rain and drizzle mainly over the interior. Surface dew points
in the mid and upper 60s, very muggy for mid-September, with
overnight lows also falling into this range. Areas of fog will
likely redevelop.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Big Picture...

Closed and vertical low pressure over the Great Lakes lifts
north into Canada. A second upper low then drops southeast from
the Canadian Prairies across the Great Lakes and Northeast by
the weekend, with the axis crossing New England Sunday. High
pressure builds across the Northeast Monday and Tuesday.

Contour heights, reflecting the deep layer, are above normal
Thursday and Friday, then in the normal range Saturday through
Tuesday. This may briefly dip below normal Sunday night as the
trough axis moves through...but then recover to normal Monday as
the trough moves off through Eastern Canada.

Mass fields are similar through Friday, then show the same
trend but different positioning over the weekend. Greater
differences in the fields Monday and Tuesday. Overall confidence
is high Thursday/Friday trending to low-moderate early next
week.

Details...

Thursday-Friday

High pressure centered over the West Atlantic, while low
pressure moves slowly north through Michigan and Srn Ontario.
This pressure pattern maintains a southeast flow over Srn New
England, bringing low level moisture and marine temperatures.
Cross sections show plenty of convergence below 925-mb and just
as much divergence between 925-mb and 700-mb. Moisture cross
sections show plenty of moisture below 800-mb and pronounced dry
air above 700-mb. Low-end CAPE stretches north over the region,
with a limited 200-600 Joules/Kg available over the region.
Given the shallowness of the moisture, and the dry air aloft,
this seems more like a warm frontal pattern with rain/drizzle
rather than showers. Mid-level moisture is forecast to move into
Wrn New England Thursday afternoon as does the right entrance
region of the supporting upper jet. This may be enough to
mention chance pops for afternoon showers/thunder in the CT
Valley/East Slope regions.

The upper support shifts east Thursday night and Friday,
allowing the surface cold front to enter Western MA/CT Friday
morning. The front crosses to the Central Hills by early
afternoon and the East Coast Friday evening. The cold front
should provide good low level convergence, with adequate mid
level moisture with the front. PW values increase Thursday and
peak near 1.75 inches along/ahead of the front Friday, high
enough above normal to support local downpours. CAPE builds to
1000-1500 J/Kg Friday, especially in RI and Central/Eastern MA.
Convective parameters are favorable for thunder. Will forecast
chance pops for showers/thunder.

Mixing temperatures Thursday around 10-11C support max temps
mid to upper 70s. Similar temps aloft Friday but more rain
suggest max temps more broadly in the 70s.

Saturday-Sunday...

Cold front moves offshore Friday night but lingers over the
nearby offshore waters through the weekend. Passage of the
second trough on Sunday may generate a wave along the stalled
front. Also, the upper trough and its cold pool aloft may
generate enough instability for showers on Sunday. Will forecast
chance pops for showers over the southeast waters over
northern/eastern areas Saturday and northern areas Sunday. Will
also forecast chance pops for showers over Nrn MA Saturday night
and Sunday.

Monday-Tuesday...

Upper low moves off to the northeast, with showers diminishing
Sunday night. All models generate a wave passing south of New
England Monday. ECMWF then conjures up another system coming
through the Great Lakes Tuesday, while the GFS shows high
pressure. With low confidence in this part of the forecast, will
keep the forecast dry at this stage with mostly clear skies but
with limited confidence as noted above.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels.

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Tonight...Scattered to widely scattered light rain/showers moves
north from the South Coast. Greatest coverage should be over CT
and western MA around and after midnight. Conditions lowering
to MVFR/IFR across most terminals overnight into Wednesday
morning, from low clouds and areas of fog. Localized VSBYs as
low as 1/2 mile.

Wednesday...IFR/MVFR CIGs improving to VFR, except for far interior
terminals, where CIGs only improve to MVFR. Patchy fog lingers until
12-14Z. Patchy -RA mainly over the interior. SE wind 5-10 kts with
gusts to 20 kts possible south coast/Cape/Islands.

Wednesday Night...Conditions once again lower to MVFR/IFR across
most terminals, with low clouds and areas of fog. Slight chance -RA.

KBOS Terminal...High confidence in trends. Moderate confidence
in timing.

KBDL Terminal...High confidence in trends. Moderate confidence
in timing.

Outlook /Thursday through Sunday/...

Thursday: Mainly MVFR, with areas VFR possible. Breezy. Slight
chance SHRA, isolated TSRA.

Thursday Night: Mainly MVFR, with local IFR possible. Breezy.
Chance SHRA, slight chance TSRA.

Friday: Mainly MVFR, with areas VFR possible. SHRA likely,
chance TSRA.

Friday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA.

Saturday: Mainly VFR, with local MVFR possible.

Saturday Night through Sunday: Mainly VFR, with areas MVFR
possible. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels.

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Tonight through Wednesday Night...High Confidence

Tonight and Wednesday...High pressure centered offshore
maintains a south-southeast surface wind 10 to 15 kts. A few
gusts to 20 kts possible. Patches of light rain/drizzle with
patchy fog possible.

Wednesday Night....Seas building to 4 to 5 feet on the southern
outer coastal waters, thus SCA headlines may be needed there.
Otherwise SE winds 10 to 15 kts continue. Patchy fog possible
with visibility as low as 1-2 miles.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Local rough seas. Slight
chance of rain showers, isolated thunderstorms.

Thursday Night through Friday: Winds less than 25 kt. Seas up
to 5 ft. Chance of rain showers, slight chance of
thunderstorms.

Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.

&&

.CLIMATE...
The latest first sub-70 degree high temperature heading into
astronomical Autumn for BOS was September 20, 1947. Still
waiting on the first sub-70 max temperature after Summer.

The latest first sub-70 degree high heading into astronomical
fall for PVD is September 26, 2015.

Both BDL and ORH have already recorded sub-70 degree highs
earlier this month.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...WTB/NMB
NEAR TERM...WTB/Belk/NMB
SHORT TERM...NMB
LONG TERM...WTB
AVIATION...WTB/Belk/NMB
MARINE...WTB/NMB
CLIMATE...



Area Forecast Discussion

National Weather Service Grand Forks ND

 1002 PM CDT Tue Sep 21 2021

.UPDATE...
Issued at 1002 PM CDT Tue Sep 21 2021

A few very light showers are still lingering in far northwest MN,
otherwise most activity has ended with loss of diurnal heating.
Weakly positive vorticity aloft may still support these
sprinkles/very light showers a few more hours before finally
falling apart. There may also be additional pockets of mid and
high level clouds through the night, though overall trend is
towards clearing skies. Winds should begin to shift to the
south-southwest on the back side of the surface high 5-10 mph, but
until then we should see good rational conditions and many
locations are already falling in the the 40s. It doesn`t appear
likely for frost impacts outside of isolated (traditionally
colder/sheltered) locations in northwest/north central MN.

UPDATE Issued at 635 PM CDT Tue Sep 21 2021

Isolated showers continue to track over northeast ND and latest
RAP shows this activity moving into northwest MN before
dissipating after sunset (may linger a bit longer). There is
sporadic lightning activity, but the intensity/frequency has
diminished. Where this activity has tracked surface obs have
reported anywhere from 0.03" to a little over 0.1" A quick
downpour and brief lightning through sunset will be possible where
this isolated activity tracks before low level
decoupling/stabilization gets underway. I made some adjustments to
match lingering trends in short range guidance/radar.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 158 PM CDT Tue Sep 21 2021

Current visible metsat imagery showing cu development across
northeastern zones as well as on the west side of the valley from
Grafton down to the state line. Enhanced cu development associated
with weak 250 J/Kg MUCAPEs in vicinity of H500 cold pool is over
SE Sask/SW Manitoba and will translate eastward along the
international border, with a few light showers possible as it
moves into northeastern ND and northwestern MN. At most would
expect a light dampening of surfaces, in otherwords very low
impacts anticipated. Loss of solar will quickly dissipate L1 cu
currently across the central and southern valley, while the deeper
L2 cu associated with any possible SHRA may persist to mid-
evening. Eventually, clearing overnight anticipated and lightening
winds will allow temperatures to fall to near 40, or even the
upper 30s in low spots where some very light frost is possible.
Warmer temperatures west of the valley where weak mixing may
continue throughout the night.

Warmer and breezier on Wednesday with highs in the 70s likely and
overnight lows back into the mid to upper 40s.

.LONG TERM...(Thursday through Tuesday)
Issued at 158 PM CDT Tue Sep 21 2021

The extended period continues to look fairly quiet, with minimal
impacts expected. From Thursday to Saturday, the 500mb ridge axis
shifts east of the FA, and is replaced by the next wave. There are
still lots of differences in the strength, timing, and location
of this next wave, which show up on the Day 3 WPC cluster analysis
of 500mb heights. Overall, the timing and location associated
with any precipitation still brings the lowest confidence. Some
solutions are highlighting the chance for rain both Friday and
Saturday, and some just Friday. However, confidence is greater
that amounts should remain on the lower side, with the NBM showing
rather low probabilities (ie 30 to 50 percent) for amounts
greater than a tenth of an inch. The ECMWF and GEFS means favor a
tenth or two mainly east of a Devils Lake to Fargo to Fergus Falls
line. In the wake of this system, 500mb ridging takes back hold,
resulting in warm and dry conditions for Sunday through Tuesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 635 PM CDT Tue Sep 21 2021

Early in the TAF period isolated showers with occasional
lightning activity will move from northeast ND into northwest MN
through sunset, dissipating by mid evening. Brief downpours and
variable gusty winds (localized gusts around 25kt) are possible
though confidence in thunderstorm activity is low at terminals.
Radar shows this likely to track over KGFK and possibly towards
KTVF early in the TAF period. VFR conditions should prevail
through the TAF period, with clearing of CU through the night.
Surface high should result in a period of light and variable
winds, before low pressure builds in the west and winds shift to
the south. During the afternoon period Wednesday sustained winds
should range from 12-15 kt and gusts around 20kt will be
possible.


&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$

UPDATE...DJR
SHORT TERM...Speicher
LONG TERM...Godon
AVIATION...DJR



Area Forecast Discussion

National Weather Service Greenville-Spartanburg SC

 1033 PM EDT Tue Sep 21 2021

.SYNOPSIS...
A moist wedge of high pressure will result in cloudy and rainy
conditions across the region through tonight. A strong cold front
will cross the area from the northwest on Wednesday, bringing the
potential for strong storms. High pressure will build in behind the
front and bring cooler and drier air for the rest of the week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 1030 PM EDT Tuesday: Shower coverage has remained basically
unchanged this evening with better coverage east of the I-77
corridor. Isolated showers and patchy rain and drizzle continue
elsewhere. This pattern should linger into the overnight as forcing
will be weak overnight. Very little in the way of instability
overnight keeps the thunder threat to a minimum. Can`t rule out a
rumble of thunder, but overall chance is very low. Deep moisture and
forcing return late tonight into Wednesday as an upper low rotates
through the OH River Valley pushing a cold front into the area. All
of the guidance shows the wedge over the area dissipating with
southerly flow developing. The guidance also shows CAPE values of
1000 J/kg or so developing over the I-85 and I-77 corridors. Despite
the strong forcing, shear looks to be the limiting factor with only
moderate shear at best and even weaker effective shear. Helicity
values also look to be on the low side without a strong low level
jet and no significant wedge boundary forecast. Still expect
numerous to widespread showers to develop along and ahead of the
front with scattered thunderstorms. With the potential for moderate
instability and some shear, isolated strong to severe storms are
possible. Isolated flooding may also develop if convective rain
rates can increase even with the lack of low level jet. Low end
gusty winds may develop ahead and behind the front. Drying does take
place behind the front with precip chances ending for many locations
by late afternoon. Lows tonight will be up to 10 degrees above
normal. Highs Wed will be near normal outside of the mountains and a
little below normal across the mountains.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of noon Tue: Some question as to whether front and/or convective
line will have cleared the area by 00z Thu, the beginning of the
short term period. Recent NAM runs have trended more "cut off" with
the upper low to our northwest, which lends itself to a slightly
slower fropa. The 12z HRRR and NAMNest depict convection still in the
I-77 counties in the 00-03z timeframe, so it looks wise to maintain
some PoP in that area thru the evening. Amplifying 925-850mb winds
associated with LLJ look to bring PWATs close to 2 inches around 00z,
and also should lead to strengthening 0-1km/0-3km shear. Although
0-1km shear is a better predictor of damaging QLCS threat, fwiw,
hodographs start to exhibit excellent curvature on NAM and NAMNest
soundings from Greensboro around 00z, moreso than at Charlotte.
HREF shows an uptick in the coverage of updraft helicity streaks
as the convection is exiting our area, reflecting the improving
environment. So, a narrow window exists for severe and flooding
threat to worsen around or just after sunset along our eastern
border, but the remaining threats will quickly ramp down after the
line exits.

High pressure will build into the area and make the remainder of the
short term quiet, dry, and cool, appropriate for the first weekend of
fall. CAA in ensuing northwest flow across the mountains should
result in gusty winds in high elevations overnight into Thursday
morning, although the mixed layer will be shallow beneath a strong
inversion, and advisory-level gusts look unlikely. Min temps will
drop a few degrees below normal in most locations Thursday morning,
trending still cooler in the calmer, better radiative conditions
Friday morning. Mins likely will fall into the upper 30s in the
highest elevations Friday morning, but it looks dry enough that frost
seems questionable. Maxes will generally be in the 70s, with 60s
expected on ridgetops.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 100 PM Tue: Dry high pressure will persist over the Southeast
through the weekend and into early next week. Another closed upper
low looks to rotate toward the area late Saturday, bringing a
reinforcing cold front across the Appalachians early Sunday. The
fropa is dry on the current slate of deterministic model runs and
almost all the NAEFS members, so PoPs will remain below the
mentionable threshold. While the period will start off with crisp
fall conditions, modification of the airmass and rising heights in
its wake suggest a warming trend, with max temps a shade above normal
to begin the work week.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and Elsewhere: Generally IFR cigs will continue this evening
with LIFR possible. MVFR vsby expected in showers. That said, an
outflow boundary moving toward KCLT may cause a brief lift in
restrictions and SE wind, but more in the way of showers. LIFR to
possibly VLIFR cigs expected overnight with MVFR to IFR vsby. NE
wind becomes light and variable overnight. SHRA coverage increases
during the day Wed ahead of a front along with a chance of TSRA.
Expect improving vsby but cigs remain MVFR to IFR. Winds become S to
SW with low end gusts possible. Cigs only slowly improve behind the
front late in the afternoon. Winds will eventually turn NW with low
end gust chance continuing.

Outlook: Dry VFR conditions move in behind the front Wednesday
night. Gusty winds will taper off. VFR conditions persist into the
weekend.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...JPT/RWH
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...RWH



Area Forecast Discussion

National Weather Service Marquette MI

 744 PM EDT Tue Sep 21 2021

.SHORT TERM...(This evening through Wednesday)
Issued at 253 PM EDT TUE SEP 21 2021

Latest RAP analysis and water vapor imagery show one shortwave
moving slowly w-e across the Upper Great Lakes this afternoon. As
this shortwave pushes e of the area late afternoon/early evening
expect any remaining isolated afternoon showers to end. Another
shortwave farther upstream over southern Manitoba/nw Ontario is
expected to move across the Upper Great Lakes late tonight/early Wed
and bring another chance for some lake-induced showers into the
north central U.P.

Tonight and Wednesday, models suggest 850mb temps will fall
slightly, closer to 0-2C and considering Lake Superior water temps
are near 15-16C, these temperatures will be near the pure lake-
effect threshold for lake showers as model soundings indicate
saturation through roughly 5kft. As a sfc high pressure ridge builds
in from the west tonight, winds will turn northerly across the area
and become slightly convergent into the north central U.P. late
tonight. The combination of the lake induced instability, convergent
northerly winds and perhaps some weak forcing from the nw Ontario
shortwave moving across the area could spawn some light isolated
showers into eastern Baraga, Marquette and western Alger counties.
These showers could continue into Wed morning, but then ridging
building in behind the weak shortwave trough should put an end to
any showers by afternoon with a trend toward clearing skies.

Under clear to partly cloudy skies, expect min temps ranging from
the upper 30s interior west to mostly the lower to mid 40s
elsewhere. Highs Wednesday under a mix of sun and clouds will range
from the mid to upper 50s north to around 60s along the WI border
and south central.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 236 PM EDT TUE SEP 21 2021

Long term period continues to present a few opportunities for rain
showers. While there still exists some uncertainty in the
Thursday/Thursday night low lifting north out of the Ohio Valley,
guidance is starting to paint a much clearer picture than earlier
runs. High temps through the period look to be mostly in the 60s,
with Thursday being the coolest with highs close to 60. Overnight
lows look to range from the 40s near the lakeshores, to 40s and some
30s in the interior spots.

Ridging extending out of the northern Plains is progged to extend
into western Upper Michigan Wednesday night. This should help
support mostly clear skies early on in the west, which will translate
into a decent amount of radiational cooling. Models have been
consistent with this thinking and bring lows down into the 30s in
the interior west half and 40s by the lakeshores. Areas of frost are
looking probable in the interior west given the light winds. More
cloud cover is expected in the east thanks to a system lifting
northward out of the Ohio Valley toward Lake Huron. There, lows
should bottom out in the low 40s to near 40F.

The aforementioned system lifting out of the Ohio Valley is progged
to take on a negative tilt, then close off aloft as it lifts
northward. The surface low is expected to move through or near Lake
Huron Thursday and then into Ontario Thursday night. The exact
position and track of the low varies among the guidance, but the
western edge of the low`s deformation zone is expected to bring rain
showers to the east through the day and gradually end through the
night. How far west this will extend is where the uncertainty lies.

As the low lifts out, brief ridging will shift eastward through
Friday night before the next upper level low dips southeast into the
region late Friday. Previous model runs either had this system
remaining an open wave, then quickly lifting out, or a close low
parking on top of the Upper Great Lakes for the weekend. Well, now
model runs now have honed on a solution with a mix of the two
solutions. Current thinking is for an upper level low dropping
southeast through the region and exiting by the later half of the
weekend. This suggests rain showers will progress west to east along
the low`s cold front late Friday into Friday night with periods of
showers afterwards as a secondary front/trough and some lake effect
rain showers follow on Saturday. As the system lifts out on Sunday,
rain showers should gradually end west to east.
&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 743 PM EDT TUE SEP 21 2021

VFR conditions should prevail at IWD/CMX/SAW thru this fcst period.
Later tonight, light northerly winds off Lake Superior may bring bkn
lower clouds near the high end of MVFR back to SAW. Could be a few
-shra as well. For now, kept cigs just above MVFR threshold.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 253 PM EDT TUE SEP 21 2021

With the exception of a few localized gusts near gale, northwest
winds have subsided blo gales over the east half of Lake Superior.
East half winds will then subside into the 15 to 25 knots range
through much of tonight. Winds will remain less than 20 kts over the
west half of the lake through tonight. A low developing over the
Ohio Valley on Wednesday is expected to lift north-northwest towards
Lake Huron by Thursday. Depending on the track and strength of this
low, there could end up being some gale force gusts on the far
eastern lake Thursday. However, confidence is still low at this
point, so have decided to just mention that here rather than
explicitly include it in the forecast. Light winds over the west
half of the lake will persist through Thursday. A trough moving
across the region will cause westerly winds to increase to around 20
knots Friday into Saturday.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Beach Hazards Statement until 8 PM EDT this evening for MIZ005-
     006-014.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Voss
LONG TERM...JP
AVIATION...Rolfson
MARINE...Voss



Area Forecast Discussion

National Weather Service Nashville TN

 841 PM CDT Tue Sep 21 2021

.UPDATE...
FOR EVENING DISCUSSION.

&&

.DISCUSSION...

Showers and thunderstorms continue this evening ahead of the cold
front that is just starting to move through the region. Still
plenty of moisture out there per the 00Z sounding showing 1.8
inches of PWAT. OHX radar estimating a few spots seeing 1-2 inches
of rainfall in an hour, so these showers are still packing a
punch. With widespread saturated grounds, it will not take much to
start seeing some flooding concerns. CAMs bring additional showers
and thunderstorms overnight after slowly dissipating/weakening
this current line of showers over the I-65/I-40 corridors as it
moves east. However, the latest HRRR shows this line maintaining
strength as it heads towards the Plateau, then weakens a bit.
Either way, any rainfall this evening will just add more saturated
ground for the next round of rain overnight into Wednesday
morning and keep the flooding threat going.

&&

.AVIATION...
00Z TAF DISCUSSION.

Showers and a few thunderstorms will move through the area this
evening and again overnight into the morning Wednesday. Cigs will
drop to MVFR and IFR at all terminals overnight, with some periods
of LIFR cigs possible. MVFR/IFR vis possible with showers/storms
as well as some patchy fog overnight. After a cold front moves
through this evening into the overnight hours, northwest winds
will pick up to be around 10 to 15 knots gusting up to 25 knots at
times especially after midnight through the end of the TAF
period.


&&

.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

DISCUSSION......Barnwell
AVIATION........Barnwell



Area Forecast Discussion

National Weather Service Reno NV

 208 PM PDT Tue Sep 21 2021

.SYNOPSIS...

Warm and dry conditions are expected through Wednesday with slight
cooling on Thursday. Areas of haze and smoke will once again drift
back into parts of the region today through midday tomorrow. An area
of low pressure moving through the area tomorrow will bring
increased southwest winds that should push most smoke out of the
area. A slight chance for an isolated shower or two are still
possible by Sunday over the eastern Sierra of Mono County but
confidence remains low.

&&

.DISCUSSION...through early next week...

* CHANGES: Only showers and possible thunder chances were retained
  for a small portion of higher terrain in Mono County for Sunday.

A low pressure system pressing east into the Pacific Northwest west
will drag the weak cold frontal boundary across the northern Sierra
into western Nevada. No precipitation will accompany this system but
it will tighten thermal gradients enough over the region to bring
breezy conditions tomorrow afternoon to the above mentioned areas.
Wind gusts will range between 20-30 mph with some gusts to 40 mph
higher Sierra ridges. Winds are still expected to diminish going
into the evening. Also, look for one to three hours of critical
fire weather conditions over parts of the Sierra into far western
NV during this forecast period. These conditions will not be
widespread enough for any highlights. It is significant enough to
emphasize the usual fire weather concerns seen most of this
parting summer period. Winds look to be mostly light the remainder
of this week with a NE-E flow increasing over the Sierra and
western NV as higher pressure exerts its influence Thursday into
Friday. Modest westerly breezes will make a return entrance by
this weekend with ensemble guidance poking at stronger breezes
once again increasing by the middle of next week.

Outside the wind factor, smoke and haze from Sequoia/Kings Canyon
fires will be added to still active Caldor fire and continue to be a
nuisance through this weekend. Downwind areas over the Sierra and
far western NV could see air quality impacts through the
foreseeable future. However, most areas should not have substantial
air quality impacts through this forecast period with the
exception for the Mammoth area, which could still see degraded
air quality due to its close proximity to the more active fires in
the central Sierra. This smoke should be pushed more east as
winds increase tomorrow afternoon. The brief return of a northeast-
east flow should keep smoke from existing active fires out of our
region Thursday and Friday.

Sunday could still see a few showers with possible thunder chances
developing over higher elevation areas near the Sierra crest/White
Mountains in Mono County. Both available moisture and instability
will be the limiting factor for any developing storms. Dont
expect any significant precipitation from these storms as well.
Temperatures will once again warm into the 80s for most lower
elevations and mid-upper 70s for Sierra valleys going into the
weekend. Thursday could be a few degrees cooler in the NE-E flow
expected behind the earlier trough passage. Ensemble guidance is
hinting at a pattern chance by the middle of next week so stay
tuned for further details. -Amanda

&&

.AVIATION...
This afternoon winds from the SW-W will gust 15-20 kts across much
of far western NV. Smoke trapped in the Central Valley of California
and the western slopes of the Sierra could filter across the crest
later this afternoon and create slantwise VIS issues for Sierra
terminals as well as KCXP-KMEV. Into west-central NV and Mono-
Mineral counties, lower-level flow forecasts remain light for much
of the day bringing an influx of more smoke over those areas.
Forecast smoke guidance also shows a change for southern Mono
County including KMMH as simulations bring thicker, lower smoke
layers early tomorrow morning. Hi-Res HRRR model guidance
continues to thicken smoke back into the Tahoe Basin/KTVL later
tonight as well.

For Wednesday, increasing gusty southwest winds to 20-25kts, locally
to near 30kts, are likely in the afternoon and evening mainly north
of US-50. Turbulence is also expected to increase along and east of
the northern Sierra crest through tomorrow as stronger down/up
drafts in the area of KRNO could impact arriving and departing
commercial airline traffic. Increasing winds tomorrow afternoon
should mix out most smoke affecting area terminals. -Amanda

&&

.FIRE WEATHER...

* Warm and dry with little to no rainfall chances the next 7 days.
* Breezy winds Wednesday may lead to localized areas of critical
  fire weather conditions.

Breezy winds Wednesday remain on track as a system passes to our
north. Expect gusts in the 25-35 mph range during the afternoon and
evening hours. In the higher elevations of the Sierra and northeast
California, peak ridge level winds may touch 45 mph. Combine the
wind with dry conditions there could be localized areas of critical
fire weather conditions especially the Sierra Front.

Beyond Wednesday winds will turn to the north and east for Thursday
but should be rather light. There could be a brief period of dry-
gusty northeast to east winds along the Sierra Crest Thursday AM.
Brong

&&

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

$$

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



For frequently asked questions about the Area Forecast Discussion

visit...

 http://weather.gov/saltlakecity/general/afd_faqs.php