Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/14/20
Area Forecast Discussion
National Weather Service Caribou ME
1134 PM EDT Sun Sep 13 2020
A cold front will cross the area later tonight into Monday.
High pressure will settle across the area Monday night into
Tuesday, and move south of the area Wednesday. A cold front is
expected to move into the region on Thursday and move out of the
area by Thursday night. High pressure will build in on Friday.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
11:35 PM Update...Lingering showers with the cold front are very
light and spotty so lowered pops to isolated showers with most
of the rain east of the area now. Also raised temps a couple
degrees, mostly over the north, where cloud cover is preventing
Sustained winds of 15-20 mph were gusting at times to 30 mph
across the open and higher terrain early this evening. The
gusty S winds will continue into the evening and there is
potential that some sites could see gusts up to 40 mph early in
the evening as a 45 kt llvl jet moves across the region. The
model soundings support this setup w/the strongest gusts across
northern areas. The pre- frontal trof ahead of the strengthening
cold front sweeps across the region this evening w/a broken
line of showers. The NAM/GFS and GEM show the best forcing to be
across northern border producing rainfall amounts of up to
0.25". The HRRR does point to some embedded heavier showers
along the line. The llvl jet and PWs climbing around 1.25 inches
lend support for the brief heavy rainfall. Further s into the
Houlton and Millinocket region, rainfall amounts fall back to
less than 0.15". The Bangor and Bar Harbor will see a brief
period of rain w/less than 0.10" expected. This first round of
showers will diminish by mid evening as the best forcing pushes
on out and winds drop off as the llvl jet pushes off to the
east. There is another round of showers expected later tonight
w/the arrival of the cold front. Not much rainfall expected
w/this round of showers, but cooler temps will accompany the
front. Winds will be veering to the SW later in the evening and
then to the W overnight w/the cold fropa. The front will tend to
slow up some as it moves into the Downeast region Monday
morning as it parallels the upper trof.
A breezy day on Monday and drier and a bit cooler w/some CAA
and a good NW wind. The cold front should finally make it off
the coast by early afternoon. The cooler air will be held up
some to the slower progression of the front. Thus, daytime temps
across the Downeast and coast should be able to warm to around
70 before the gradual cooldown in the afternoon. A look at the
momentum transfer indicates potential for gusts to be 30-35 mph
in the afternoon w/an increasing NW wind all the way through 15k
ft. The strongest winds will be across the nor Therefore,
decided to increase the wind speeds on Monday by at least 10 mph
from the previous setup. Clouds will be around in the morning,
but as drier air continues to work into the region, clearing is
expected by the afternoon w/a gradual recover in the temps.
Daytime temps will be a few degrees below normal.
.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
High pressure will just be nosing into western Maine Monday
night. Much of the CWA will remain in N flow ahead of this high,
and thus winds are expected to prevent much widespread frost
potential. Dew point temps will drop further than the air mass
earlier this week. Confidence for frost would increase if the
high was located closer to the region, and if low level winds
were lighter. At this time will forecast the greatest potential
for frost across the NW North Woods, with some patchy frost
possible across lower valleys in northern and central Aroostook.
The high will pass to the south of the state Tuesday. West
winds will bring in some warmer temps, however any clouds
developing across the north will limit highs to the upper 50s
and lower 60s. Otherwise dry conditions are expected.
Tuesday night will cool a little early, but be highlighted by a
weak warm front lifting through the region. Expect a warmer
night, and the chance of some light showers across the far
north. Behind the warm front, temps Wed will rebound well
towards the lower 70s. This southerly flow will feed into a low
pressure system passing to the north of Maine. Downeast and
along the coast will see a breezy day as warm air advection
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
A cold front will impact the area beginning early Thursday
morning, though guidance remains split on the timing of this
feature with GFS being on the early side and ECMWF following a
bit later Thursday afternoon. Best chance for rain across the
region will be during the day on Thursday as the front sweeps
southwards. Temperatures will dip behind the front, with lows
falling into the lower 40s across the north. Clouds will remain
in place during the day on Friday, keeping high temperatures
capped in the upper 50s to lower 60s. Skies will clear Friday
night, allowing for temperatures to plummet even further with
sub-freezing temps possible across the North Woods and lows in
the upper 40s along the coast. These falling temperatures will
also produce the best chance at frost, especially over the North
Woods where winds will be light early Saturday morning. High
pressure returns for the weekend, keeping skies clear and low
.AVIATION /04Z MONDAY THROUGH FRIDAY/...
NEAR TERM: VFR for northern terminals this evening. KBGR and KBHB
will see MVFR cigs w/the lower deck coming in off the Gulf of
Maine. This MVFR looks like it will lift n and move into the
northern terminals this evening. There could be a brief period
of IFR especially across the northern terminals in showers. LLWS
w/S winds 10-20 mph this evening w/gusts up to 35 mph.
VFR for Monday for all terminals w/WNW winds kicking in.
Sustained winds of 10-20 mph w/gusts possibly up to 35 mph.
Monday night: VFR, light NW wind.
Tuesday: VFR, Light W wind.
Tuesday night, VFR. Light S wind.
Wednesday: VFR, some showers near FVE and CAR. Gusty SW wind.
Wednesday night: VFR, possibly lowering to MVFR north. SW wind.
Thursday: VFR/MVFR. SW wind becoming W.
Thursday Night: MVFR improving to VFR. Light wind becoming NW
NEAR TERM: SCA remains in place for the outer zones. S wind 10-15 kt w/gusts
to 25 kt becoming SW toward the early morning hrs on Mon. SW
winds becoming W by later Monday afternoon w/similar speeds.
The bigger concern will be the wave heights. Seas 2-3 ft this
evening building to 4-5 ft by Monday morning w/highest waves
over the outer zones. Swells from Hurricane Paulette w/a period
of 14-16 seconds will begin to show up during the day on
Monday. The could be some rough surf given the longer period
swell and waves building to 5-6 ft
Swell from hurricane Paulette is expected to build seas to 5 to
6 ft on Monday and 6 to 7 ft on Tuesday. Seas may continue above
5 ft through mid- week. Additionally, long period swell of 10-15
seconds is expected through Wednesday. SW Winds will generally
be 15-25 kts through this period, increasing again Wednesday
behind a warm front, potentially towards Gale.
Long-period swell of 10 to 15 seconds will affect the coastal
waters tonight through Wednesday with near shore waves building
5 to 6 ft. As Hurricane Paulette tracks well off in the open
Atlantic, the incoming swell may generate elevated rip current
risk and high surf along the coast Monday into mid-week.
Additionally, astronomical high tides are due later this
week/weekend. Prevailing wave heights and wave periods will be
monitored for any spashover or coastal erosion threat to low
MARINE...Small Craft Advisory from 5 AM Monday to 5 AM EDT Tuesday for
Area Forecast Discussion
National Weather Service Des Moines IA
636 PM CDT Sun Sep 13 2020
.DISCUSSION.../Tonight through Sunday/
Issued at 250 PM CDT Sun Sep 13 2020
No appreciable weather impacts are anticipated through the
period, but smoke may affect temps and fog potential into at least
tomorrow. There are some features of note nearby, but with
limited moisture there is nil associated sensible weather. A
baroclinic zone is in place across the northern Plains with the
associated surface front from SD into MN and low just east of
Pierre. As the upper flow becomes a bit more zonal, the front
should ooze south into IA overnight before washing out and/or
retreating northward as the theta-e advection and baroclinic zone
lift farther north and east Monday. With clear skies,
light/variable wind, and lingering low level moisture (dewpoints
still in the 50s), expect a repeat of fog development overnight.
The question will be how much smoke impacts radiational cooling.
GOES-16 channel 1/blue imagery shows this nicely with an initial
lobe already into IA, and more widespread coverage over the
Dakotas upstream. Recent available RAP and HRRR smoke runs
suggest this will expand into IA tonight so there are
uncertainties regarding how much this will impact radiational
cooling, the degree of fog, and low temps. Little past experience
with how smoke affects fog development so confidence is low.
Some smoke aloft will linger through tomorrow and may even shade a
degree or two off highs, but beyond this there should be nil
weather for much of the week with little adequate moisture and
lift phasing for much of anything. Mild temps can be expected
through Wed, but a dry frontal passage late Wed will drop temps
somewhat below normal to end the work week. Although they get to
it different ways, most deterministic and ensemble solutions
suggest low PoPs at least NW Thu Night, and then also late Sun
again NW ahead of a cold front where there is somewhat better
.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 632 PM CDT Sun Sep 13 2020
VFR conditions are predominantly expected, but may be interrupted
by fog development tonight that could develop MVFR/IFR conditions.
Main sites of concern would be KALO/KOTM and to a lesser extent
KMCW/KDSM/KFOD. Otherwise, light winds will begin to turn
southerly and smoke streaming overhead will remain aloft and
provide some obscuration.
Area Forecast Discussion...UPDATED
National Weather Service Nashville TN
833 PM CDT Sun Sep 13 2020
FOR EVENING DISCUSSION.
Activity has decrease markedly over the last few hours. Just a few
light showers is all that remains. Latest Hrrr data supports
little if any redevelopment overnight. Sfc high to our north
should continue to build in slowly over the next 24 hours. Lower
dewpoints are noted across nrn KY and we will finally see some of
these slightly lower dewpoints, but probably not until tomorrow
afternoon. Therefore, will go ahead and add some patchy fog, but
development may be limited to the Plateau.
00Z TAF DISCUSSION.
Rains have come to an end, but MVFR to IFR conditions still exist
at KBNA/KMQY. These should improve in a couple of hours, but
with the slow movement of today`s front, look for conditions to
worsen at KCSV after 06Z.
Northerly winds will be light overnight, but look for the surface
pressure gradient to tighten quite a bit tomorrow morning,
leading to gusty NE winds throughout the day Monday.
Area Forecast Discussion
National Weather Service Pocatello ID
120 PM MDT Sun Sep 13 2020
.SHORT TERM...Tonight through Tuesday night. Smoke and haze remain
in the forecast through the period. Otherwise, we`ll see high
pressure shift slightly to the east tonight and tomorrow, allowing
for some stronger southwesterly winds to come into the area. Given
the widespread smoke and haze, have dropped high temps a few degrees
tomorrow. Cooler temps may inhibit, or at least delay, mixing
tomorrow afternoon. This gives a bit of uncertainty to the wind
forecast. Strongest winds may be over the Central Mountains tomorrow
with gusts to 25 mph possible. Ridging will begin to build back to
our west on Tuesday. Hinsberger
.LONG TERM...Wednesday through next Sunday. The models are in very
good agreement throughout the forecast period holding the upper
ridge firmly over the region through early Thursday then translating
it east and breaking it down Thursday afternoon though Saturday as
the upper low off the NW coast finally rotates inland across the NW
states and east of the region by Sunday. As for the details, we
should remain dry and seasonably warmer than normal through at least
Thursday with smoke filtering into the region from California. By
Friday afternoon and continuing into Saturday, the passing upper low
should bring enough moisture and instability to the region to
support scattered showers and afternoon thunderstorms along with
breezy conditions...all of which should help to mitigate any smoke
issues. By Sunday, the low shifts well east of the region leaving a
mostly dry WNW flow aloft across the area and cooler but normal
.AVIATION...VSBY impacts due to wildfire smoke will continue
through mid-afternoon with some modest improvements late this
afternoon and evening as mixing and venting increase across the
region due to diurnal heating. The southwest flow aloft will
increase across the region Monday which should help to alleviate
most of the VSBY restrictions across the region. Thus we should see
a transition from near marginal VFR VIS conditions early this
afternoon to VFR conditions through Monday. Huston
.FIRE WEATHER...Critical fire conditions are expected tomorrow
afternoon due to winds and RH for zones 475 and 476. Wind gusts to
25 mph are possible in the afternoon, though smoke may reduce
daytime heating, which will inhibit mixing. Given the extremely low
humidity, Haines indices of 6 and marginal wind gusts, we`ve
upgraded to a Red Flag Warning for 18Z to 03Z tomorrow. Winds will
increase again on Thursday and Friday as a deep upper trough is
expected to approach from the west. Thunderstorms are possible on
Friday ahead of the trough. Hinsberger
.AIR STAGNATION...Smoke concentrations will continue to gradually
dissipate late this afternoon as thermal mixing helps to ventilate
the region. The HRRR and NAAPS smoke concentrations show conditions
continuing to improve across most of the area later tonight and
Monday as the southwest flow aloft increases across the region.
Although the increased southwest flow is expected to bring some
relief, it will likely only be temporary as smoke from the
California wildfires eventually advects into the region. In fact,
the NAAPS guidance shows deteriorating conditions as early as
Tuesday afternoon. Huston
Red Flag Warning from Monday afternoon through Monday evening for
Area Forecast Discussion
National Weather Service Reno NV
201 PM PDT Sun Sep 13 2020
Widespread smoke and haze issues will continue much of this week.
Warm temperatures are expected through Thursday then a cold front
will drop readings back to near or even below normal for the
upcoming weekend. Increased winds could bring fire weather
concerns especially Thursday and Friday. A few light showers
possible in NE California Friday and Saturday.
Most of the forecast hinges on the progression of quasi-cutoff
low currently over NE Pacific Ocean and its progression inland
by mid to late week.
* Smoke: Well today sure started out nasty with hazardous air
quality in many areas. Smoke has been slow to clear from valleys
thus far relying mainly on vertical mixing. However, a little
bit more SW wind into the evening could allow for more
appreciable clearing, at least away from ongoing fires. Smoke
models are changing up the scenario some Monday-Tuesday versus
the last couple days with increased SW transport winds. Were
seeing two distinct plume areas in the models where smoke
concentrations are heaviest: one into NE California and far NW
Nevada (e.g. Susanville) and another from the E Sierra up into
parts of W Nevada (e.g. Mammoth, Carson Valley, Yerington,
Fallon). Elsewhere likely to still be somewhat hazy with periods
of smoke - low confidence scenario on where boundaries between
denser smoke and haze will be.
* Wind: Winds will be a little stronger the next few afternoons
compared to this past weekend, but where were really watching
is Thursday and Friday. Guidance projecting a cold front into
the area with stronger S-SW winds for most areas. An appreciable
number of ECMWF EPS members showing gusts 30-40 MPH from NE
California south along the Sierra Front into the Eastern Sierra
both days. Could see localized travel and recreation impacts,
along with critical fire weather (see below). The stronger winds
could either make the smoke situation in our area worse via
long range transport and increasing fire activity - or those
winds could thin it out alot. We shall see. Smoke models are
only reliable out to 24-36 hours.
* Rain: Sorry, but not much luck happening here next 1-2 weeks.
The best we can muster: ECMWF/GFS ensemble guidance brings the
remnants of a weak-moderate atmospheric river into N California
late this week. This could yield a few showers down into parts
of NE California Friday-Saturday but precip amounts look to be
0.1 at best. Only 3 out of 52 ECMWF members showing anything
above 0.25. Could be a good soaking rain further north into
Oregon which would help the fire situation up there.
* Areas of dense smoke will continue to impact aviation interests
in the region through at least Monday. Based on the latest HRRR
Smoke model two major plumes will affect the east side of the
Sierra tonight into Monday - Quincy to Susanville (SVE) and
Mammoth (MMH) to Yerington and Carson City (CXP). Conditions
likely to get into IFR or even LIFR levels in smoke in these
* Elsewhere including Reno (RNO) and Tahoe (TRK, TVL) smoke and
haze are likely however concentrations do not appear as severe
as they were this morning. Probably still a good bet to expect
some periods of MVFR in these areas.
* The slight increase in SW winds weve seen today will
continue into Monday with slightly higher gusts but nothing too
impactful. Generally at or below 25 knots for most areas. This
could be enough to really mix out the smoke in most areas except
near and downwind on ongoing large fires.
***Increased Confidence in Widespread Critical Fire Conditions
Changes this forecast cycle:
*Cancelled the Fire Weather Watch for the northern Sierra Front
for Monday. The Watch for northeast California and northern
Washoe County still remains.
*Increased winds for Friday, especially along the Sierra ridges.
Today through Wednesday will most likely see an uptick in the
southwest flow with low humidity and poor overnight recoveries.
Recent model guidance shows weaker winds overall during this time
and that could be the result due to the smoke impacts. With thick
smoke present, thermal gradients will be weaker which in return
would dampen the strength of the afternoon winds. With this in
mind, we have decided to cancel the Fire Weather Watch for NV zone
420, the northern Sierra Front, for Monday. There could be some
localized gusts of up to 30 mph with Sierra ridges remaining gusty
into the overnight hours, but widespread critical fire conditions
throughout the area is less likely at this time.
The Fire Weather Watch remains for CA zones 270, 271, & 278 and NV
zone 458 (northeast California and northern Washoe County) for
Monday afternoon through the evening thanks to gusty southwest
winds and low humidity. These areas look to be the best shot at
widespread critical conditions, however, confidence is medium at
this time which is why we have left the Watch versus upgrading to
a Warning. Expect southwest winds 10-20 mph with possible gusts of
up to 30 mph. Higher gusts of up to 35 mph are more likely for
wind prone locations as well as for the ridges.
Tuesday and Wednesday look similar with zephyr-like breezes each
afternoon/evening. Localized critical conditions are possible each
day with emphasis on the ridges, northeast California, and
northern Washoe County.
Forecaster confidence continues to increase in the potential for a
widespread critical condition event sometime during the
Thursday/Friday timeframe of this week. It`s still early and
things could change, for example the overall timing of the gusty
southwest winds, but for the most part it looks to be windy thanks
to more upper-level support rather than just thermal gradient
driven. Therefore, we have increased winds on Friday with the
strongest winds along the Sierra Crest (emphasis on Mono and
Alpine counties). Even though humidity both daytime and overnight
look to increase during this time, the presence of the gusty winds
could essentially negate the higher RH. Unfortunately, chances for
wetting rains (>0.10") across the region are unlikely at this
NV...Dense Smoke Advisory until 11 AM PDT Monday NVZ001>005.
Fire Weather Watch from Monday afternoon through Monday evening
CA...Dense Smoke Advisory until 11 AM PDT Monday CAZ070>073.
Fire Weather Watch from Monday afternoon through Monday evening
For more information from the National Weather Service visit...
Area Forecast Discussion
National Weather Service Seattle WA
810 PM PDT Sun Sep 13 2020
.SYNOPSIS...Smoke from wildfires will remain an issue into Monday
resulting in air quality impacts across the region. A frontal
system will bring some showers Monday night and Tuesday. An upper
low will slowly move onshore later in the week.
.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Stubborn smoke continues
to hang on around most of Western Washington with unhealthy air
quality expected to linger into Monday. Surface gradients remain
light and this will do little to disperse anything across the
lowlands. A broad upper trough offshore will send a weakening
frontal system into the region Monday night into Tuesday, but models
are backing off considerably with precip chances. The trend now
appears that the upper trough offshore will largely stay there until
later in the week. Will hold off on making changes to the forecast
this evening, but overnight shift may need to scale back precip
chances Monday night and Tuesday. 27
Previous discussion...Smoke and air quality
continue to be the main issues across the region. Most areas
continue to report AQI values in the Very Unhealthy and Hazardous
categories. And visibility is mostly limited to less than 2 miles
in a combo of smoke and haze. The HRRR model does show total
smoke thinning out over western WA with stronger winds aloft (and
there`s less smoke offshore). However, mixing and ventilation
remain poor and there`s still plenty of smoke trapped near the
A frontal system will move inland on Monday (mainly Monday
afternoon or Monday night) bringing much needed rain to the
region. This, along with a stronger air flow pattern and deeper
mixing, will help clean things out (at least for areas west of
the Cascades). So improvements are on the way. Moist southwest
flow sets up over the Pac NW on Tuesday as a upper level low spins
offshore. This brings another period of rain to western WA which
will further help our air quality.
More smoke on Wednesday? We`re under south flow on Wednesday with
light offshore winds as the low continues to spin off the coast.
This flow pattern could potentially bring more wildfire smoke
(especially from OR and northern CA) into the region. But the
extent over western WA is unclear at this time. The smoke should
be mostly aloft. We will see better mixing through the period
along with additional showers so this should help to limit
.LONG TERM /THURSDAY THROUGH SUNDAY/...Western WA will see
additional showers Thu-Sat as the upper low slowly wobbles
inland. The air mass is slightly unstable over the Cascades where
we may see a slight chance of thunderstorms (near the crest).
These showers will be wet, though, and critical fire weather
conditions are not expected. Onshore flow will prevail late in the
weekend as this system exits. This brings a drier start to next
week with temperatures near average. 33
.AVIATION...Southwest flow aloft continues this evening and into
Monday. While PIREPs indicate that smoke layer is beginning to thin
from the top, widespread 1/2 to 2 sm visibility continues across
nearly all of the lowlands into the evening. With continued weak
onshore low-level flow expect lowering MVFR to local IFR ceilings
again tonight. An approaching front late Monday will bring
increasing mid level clouds and rain chances, but may provide enough
mixing to increase visibility late Monday afternoon.
KSEA...Visibility remains 1 to 1 1/2 SM this evening with light
surface winds. Expect little change tonight with restricted
visibility and lowering ceilings through early Monday. Increasing
mid clouds late Monday afternoon ahead of front, but increased
mixing may lead to better visibility. Cullen
.MARINE...Smoke will reduce visibility - especially over the inland
and inner coastal waters into Monday. A frontal system lifts north
through the waters on Monday into Tuesday. A surface low will
develop west of the waters Tuesday then drift towards the Oregon
coast Wednesday and Thursday.
Small craft advisory southeast winds may develop Monday night ahead
of the front over the coastal waters. Meanwhile, seas will build to
around 5 to 7 feet behind the front. Increasing onshore flow on
Thursday may bring small craft westerlies to the Central and Eastern
Strait of Juan de Fuca Thursday afternoon and evening. Cullen
.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
Area Forecast Discussion
National Weather Service San Diego CA
200 PM PDT Sun Sep 13 2020
High pressure aloft will remain in control of the weather over the
Southwest much of this week. The center will shift farther south by
midweek, which will result in warmer weather here, and should help
reduce the areas of smoke and haze. This last full week of Summer
will be a warm one, even as onshore flow prevails. A weak sea breeze
will moderate afternoon temperatures along the coast each day, with
some patchy low clouds and fog possible nights and mornings. Cooler
weather will arrive late in the week with an incoming Pacific
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
The weather pattern this week will see gradual warming conditions
through Wednesday as upper ridging builds over Southern
California, followed by gradual cooling late in the week as an
upper level trough passes by to the north.
Smoke fills the sky again today and is creating very hazy
conditions with visibility in the 3-5 mile range across the area.
HRRR integrated smoke shows little changes through at least
Monday, so we will continue under this very hazy, smoky sky.
Visibility could come down some near the coast tonight, but we
are not anticipating widespread dense fog.
Temperatures will gradually warm through Wednesday as the ridge
builds. Heat risk isn`t quite there for headlines, but it will be
noticeably hotter through mid week. A day or so of near 110 is
possible over the lower deserts with around 100 for the IE and
mostly 90s for the high deserts and inland valleys. Cooler at the
coast. The extent of smoke will depend on how hot temperatures
get. If thick smoke hangs around, which certainly is a
possibility, then temps would be a few degrees cooler than
An upper trough will remain situated off the Pacific Northwest and
finally move fully inland to our north late this week. This will
lower heights and allow for a cooling trend, but no rain here,
which is no surprise in September.
131945Z...Coastal Areas...A few low clouds with fog will linger at
the beaches this afternoon. Coverage will begin to increase after
06Z Mon and spread a few miles inland by 14Z Mon. Bases are likely
to be around 500-900 ft MSL, with vis locally 1-3 miles on higher
coastal terrain. Partial clearing to the immediate coast expected
between 15Z and 17Z Monday.
Elsewhere...Widespread smoke with variable thickness will continue
through tonight, mainly at/above 5,000 ft MSL, reducing vis down to
4-6 miles for most TAF sites west of the mountains. Smoke reducing
vis 3-5 miles at desert TAF sites this morning. Local near-surface
smoke will reduce vis down to 2-4 miles in the vicinity of ongoing
No hazardous marine conditions are expected through Thursday.
High pressure aloft will hold across the region and strengthen a bit
into midweek. This will bring a warming trend, but also some
moderation in RH as northwest flow aloft becomes more southeasterly.
Winds overall will remain light, except for afternoon sea breezes,
which could get gusty locally for a few hours. Relative humidities
will only see subtle moderation through Tuesday. The heat will
build, peaking Wednesday when daytime highs could be 8-14 degrees
above average. Despite the heat, minimum RH values and wind
speeds are expected to remain below critical values much of this
week. Conditions will gradually cool late this week.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
513 PM MDT Sun Sep 13 2020
.DISCUSSION...(This Evening Through Sunday)
Issued at 157 PM MDT Sun Sep 13 2020
Mean upper ridging expected over the western CONUS in most of the
period. The Northern Plains will remain on the NE edge of this
feature as increasingly active flow persists over southern Canada.
This will support an undulating frontal boundary over the region
with passing sfc lows. Backdoor cold front has settled further
south than expected today, with much cooler conds in the northern
third. In addition thick smoke has settled into the region aloft,
which has also sig limited insolation keeping temps cooler than if
it were clear. Decided to add haze to the forecast through
tomorrow, given HRRR vertically int smoke which supports high
layer smoke over the region. Approaching low will support
increasing southerly flow over the region tonight as a warm front
shifts north. Hot day expected Monday as the thermal ridge times
over the region at peak heating. Did not raise temps to near abs
guidance max, which has worked well since it has dried out, given
concerns on the amount of thick some aloft, which could certainly
limit temps. Low level smoke is also expected in the far west by
afternoon, per HRRR near sfc smoke progs, which will also limit
insolation. Expect breezy SW flow should help mechanically mix
which should allow temps to rise pretty well. Cool front will
shift south Tues with warm but breezy northerly winds. Upper ridge
will flatten some toward the middle and end of the week as an
upper low pushes into the western CONUS. This will result in more
unsettled flow locally, with perhaps increasing chances for
showers and thunderstorms if enough low level moisture advects
into the region.
.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 513 PM MDT Sun Sep 13 2020
VFR conditions are generally expected tonight and Monday. Hazy
skies due to smoke from western US wildfires will persist. Breezy
south to southwest winds will develop across northeast WY later
tonight and across a good portion of western SD late Monday
morning and afternoon.
Issued At 157 PM MDT Sun Sep 13 2020
A warm front lifting north on Monday will result in a deeply
mixed atmosphere and very dry and breezy southwest winds
developing across northeast WY and much of far western SD.
Upgraded the fire weather watch to a red flag warning, adding a
few zones on the east side. Cold front moves through early Tuesday
with elevated to near Red Flag conditions again possible although
the window looks to be small.
SD...Red Flag Warning from noon MDT /1 PM CDT/ to 8 PM MDT /9 PM CDT/
Monday for SDZ319>327-329-331>334.
WY...Red Flag Warning from noon to 8 PM MDT Monday for WYZ314>318.