Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/29/20
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
829 PM CDT Mon Sep 28 2020
Issued at 825 PM CDT Mon Sep 28 2020
Overall the forecast is in okay shape. Latest HRRR continues to
show some shower activity late tonight so will keep low pops in
place. Temperatures are already close to lows so did drop them a
notch. However, WAA clouds later tonight should stem the fall.
.SHORT TERM...(This Evening through Tuesday Night)
Issued at 254 PM CDT Mon Sep 28 2020
Forecast challenges revolve around WAA-forced precipitation chances
tonight/early Tuesday morning, as well as high temperatures Tuesday.
Currently, with the exception of the west-river counties, most of
this CWA is mostly cloudy, and temperatures are holding in the 50s
to low 60s. It`s breezy to windy again, today; northwest at 15 to 25
mph with gusts from 30 to 40 mph. There were a few showers earlier,
running down the I-29 corridor, but they have moved out of this CWA.
There is the potential for seeing a couple more showers out over and
east of the Prairie Coteau before sunset.
WAA gets going tonight and persists into Tuesday. Higher up in the
atmosphere, some of this WAA-forcing could end up generating some
light rainfall across the James River valley over into MN late
tonight into early Tuesday morning. Just a couple hundredths of
measurable precip. The rest of Tuesday and Tuesday night should be
dry. There is still a cold front forecast to work through the region
by Tuesday night, setting the stage for more cold air to enter the
forecast scene. Similar to the past couple of days, Tuesday should
pack some breezy, to windy at times, west to northwest winds.
Temperatures over the next day and a half should recover to
somewhere closer to climo normal for the end of September.
.LONG TERM...(Wednesday through Monday)
Issued at 254 PM CDT Mon Sep 28 2020
The main stories of the long term period include windy conditions on
Wednesday, and cold-enough-for-frost air Thursday night/Friday
morning. By 12z Wednesday, a colder air mass will be advecting into
the area following Tuesday`s cold frontal passage. Strong northwest
flow aloft (60 to 90+ knots at 500mb) will reside across the
Northern Plains, with a large upper-trough centered across the Great
Lakes and an upper-ridge over the Western US. Sfc low and high
pressure systems will mirror the positions of their upper-level
counterparts, and a tight pressure gradient will have set up across
this CWA. Mostly clear skies, especially across central SD (higher
probability for clouds closer to the lower pressure/colder air the
further east you go), will help mix down these stronger winds aloft.
Ensemble data pings on Wednesday as being similar to or windier
than any other day this week.
Temperatures may dip into the mid to upper 30s Wednesday night, but
winds should be strong enough to prevent frost. While Thursday
morning may remain breezy, winds will be on the decrease through the
day as sfc high pressure noses in. Dry and below average
temperatures for Thursday, with highs in the mid to low 50s. Given
the cold air aloft and sfc high pressure, frost is possible by
Friday morning. The NBM 1D Viewer gives an 82% chance for a low of
at least 34 degrees at Pierre Friday morning, and a 79% chance at
Aberdeen (48% for 32 F or colder at each location). The rest of the
long term looks to remain cool and predominantly dry thanks to a
continuation of a similar upper-level pattern.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
Issued at 618 PM CDT Mon Sep 28 2020
VFR skies/vsbys are expected overnight regionwide. There may also
be isolated to scattered showers late at KABR/KATY. Given the low
probabilities, they are not mentioned in the tafs for now.
***Construction to improve taxiways at both KABR/KPIR terminals
may cause an occasional temporary visibility reduction due
to blowing dust (bldu), mainly during daytime hours UFN.
Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
Issued by National Weather Service Jackson MS
953 PM CDT Mon Sep 28 2020
.NEAR TERM...(Rest of tonight)
Issued at 953 PM CDT Mon Sep 28 2020
The much-anticipated cold front has now cleared the Tennessee
Valley, with a cool and drier N/NW breeze and only isolated light
post frontal showers persisting over Lookout Mountain at this time.
The HRRR has hinted at the potential for some redevelopment of
showers closer to daybreak, but it has been struggling with overdoing
precip and slow timing through much of the day. Thus PoPs have been
cut back to only "isolated" for parts of NE Alabama for the
remainder of the night. There are a few breaks in the cloud deck
mainly west of I-65, which will allow some areas to go "partly
cloudy" through part of the night, but as the mid/upper trough
remains situated to the west, low level cyclonic convergence will
lead to another increase in clouds again toward morning. Otherwise,
the rest of the forecast is on track with no other notable changes
needed. Updated text products have been transmitted.
.SHORT TERM...(Tuesday through Wednesday)
Issued at 242 PM CDT Mon Sep 28 2020
A nice change in the airmass will be noted on Tuesday with daytime
highs about 15 degrees cooler than what we saw today. Highs Tuesday
will top out in the middle to upper 60s, with morning lows Wednesday
tumbling down into the middle to upper 40s! Cooler and drier air will
stream into the TN Valley, making for a very pleasant day both days,
albeit a bit more cloud cover Tuesday rather than Wednesday.
Otherwise, expect daytime highs on Wednesday to be about 5-7 degrees
warmer than that on Tuesday, topping out in the lower 70s. Be sure to
get out and enjoy the taste of Fall in the TN Valley as it`s not too
often that we get a *true* Fall. Remember that this time last year,
we were in the 100s heading into early October, and it was very hot
and dry (compared to this year), so be sure to enjoy it while it
.LONG TERM...(Wednesday night through Sunday)
Issued at 242 PM CDT Mon Sep 28 2020
Unseasonably cooler and drier wx is still xpcted to spread into the
region heading into mid week, as a large dome of high pressure out of
the Plains states builds to the SE. Upper low/trough axis will also
be moving ewd across the cntrl Gulf states on Wed, with NW flow aloft
developing in the wake of the exiting upper trough pattern. All of
this will translate into quiet and tranquil wx conditions prevailing
from Wed into the weekend period. The large sfc ridge will actually
become reinforced on Thu, thereby helping with the influx of cooler
and drier air. Afternoon highs Wed/Thu look to climb mainly into the
lower 70s for most spots, before dropping into the mid/upper 60s Fri
and Sat. Overnight lows early Thu morning look to start out in the
lower 50s, before dropping more into the lower/mid 40s to round out
the remainder of the forecast period. Temps in the latter half of
the forecast package easily look to be around 10-20F below normal
for this time of the yr.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 645 PM CDT Mon Sep 28 2020
Conditions should steadily improve to mainly VFR behind the cold
front this evening as cooler and drier air moves in. Sat trends
the cigs to midlevel before clearing considerably. Tomorrow will
see gusty winds return in the afternoon out of the northwest. A
sct/bkn cu deck is anticipated for the afternoon, but VFR through
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Area Forecast Discussion
National Weather Service Reno NV
256 PM PDT Mon Sep 28 2020
Easterly winds will keep smoke out of eastern California and
western Nevada through tonight. However, increased fire activity
in northern California and a return to modest west winds are likely
to bring a return of haze and areas of smoke Tuesday. High pressure
over the region will produce warm afternoons, dry conditions, and
mainly light winds Tuesday through the weekend.
Remarkably steady-state conditions are expected Tuesday through
the weekend as high pressure parks itself overhead. Afternoon
temperatures near average today c/o light to moderate easterly
winds will warm to 10-15 degrees above average for the balance of
the week as the flow slackens and the ridge builds more directly
overhead. Given light winds, mainly clear skies, and the inexorably
lengthening fall nights, temperatures will fall substantially each
night with morning temperatures bottoming out in the 30s and 40s
for most valleys (exception: highly urbanized valley areas or
those with minimal vegetation may only fall into the low to mid
50s after tonight).
Smoke remains a concern for Tuesday into Wednesday morning as flow
briefly returns to westerly. HRRR smoke runs bring a substantial
increase in smoke particles for higher elevations of the Sierra
and far western NV by tomorrow morning as flow aloft turns to S-SW.
During the afternoon and evening Tuesday, lower level westerly
flow kicks in with the 18Z HRRR showing a major increase in
particulates (and a decrease in air quality) for valleys of eastern
CA and western NV as well as west-central NV near and south of
Hwy 50. Smoke and haze are likely to settle into the valleys
overnight into Wednesday as flow slackens. On Wednesday the flow,
albeit light, returns to northeast and east in the afternoon
which may stop additional smoke from working into the region.
However, with light flow the remaining smoke may take awhile to
thin out with air quality still a concern Wednesday morning. Note
that uncertainties have kept smoke and haze out of the forecast
beyond Tuesday evening; however, this does not mean there won`t be
any into Wednesday. -Snyder
Looking well beyond the 7-day forecast (October 8-15), long-term
ensembles are showing some preliminary indications of Pacific
moisture moving into the region around the October 10-15 timeframe
as the blocking pattern looks to break down and allow zonal flow
into northern California. In addition to the ridge breakdown,
there are signs in ensembles for increased winds which makes sense
given the tendency for zonal flow. -Snyder/Hoon
VFR conditions prevail through tonight with sustained northeast-east
winds around 10 kt this afternoon-early evening for most terminals.
A shift to west-southwest winds tomorrow is forecast to bring haze
and areas of smoke back to portions of eastern California and
western Nevada. Most visibility reductions will be of the slantwise
type, although KMMH could see low smoke layer ceilings and decreased
surface visibility later tomorrow if the Creek Fire continues to
show significant activity.
Mountain wave turbulence is likely along and west of the Sierra and
southern Cascade crests as gusty northeast winds persist into late
this afternoon. Light winds along with warm and dry conditions will
prevail this week, with areas of haze possibly lingering through mid-
late week. MJD/JCM
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Area Forecast Discussion...Updated Aviation section
National Weather Service San Diego CA
901 PM PDT Mon Sep 28 2020
Dry, offshore flow will continue through Tuesday, with areas of
gusty east to northeast winds, low relative humidity and increasing
heat. Critical fire weather conditions will occur through Tuesday
near the coastal foothills, where winds will be strongest. The
hottest and driest conditions will be felt on Wednesday as the ridge
aloft peaks, though winds will be weaker. Slow cooling will follow
later in the week as the upper high weakens.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
...Heat Advisories in effect Tuesday through Thursday west of the
...Red Flag Warning for the mounains and coastal foothill areas...
Low clouds were forming over the CA Bight this evening and were
remaining mostly just offshore through 8 PM PDT. The 00Z Miramar
sounding had a 7C inversion based near 1150 Ft MSL. winds aloft had
veered back to south or west below 7K FT. Surface dewpoints were up
along the coast, well into the 60s F. Winds were mostly light and
highly variable across the region.
The only potential forecast problem tonight involves the low clouds
and possible fog formation along the coast. Based on the sounding,
limited nearby observations and coastal cams, the IR satellite
signatures should be low clouds and not fog, at least at this point.
This could lower overnight and become fog, but it would most likely
be over the coastal waters and perhaps beach areas with a general
offshore drift forecast. The sfc pressure gradients had a slight
offshore trend as well. Orange County appears to have the greatest
probability of fog formation overnight based on repeated runs of the
HRRR model. Trends are not there yet though, so will not jump on the
fog train at this time. Tomorrow is shaping up to be quite hot
inland, based on observations today and continued heating. So the
current forecast may be a few degrees shy of the mark, especially
for those land-locked valley areas. No forecast updates are planned.
From previous discussion...
High pressure aloft will prevail this week over the far western US,
with a generally weak Santa Ana wind event through Tuesday. The
hottest weather will come Tuesday-Thursday, especially Wednesday,
with 850 MB temps reaching the 25-26 deg C range, combined with low
RH and very dry soils/vegetation to help maximize surface heating.
ECMWF ensemble solutions show temps likely reaching 105 or higher in
parts of the Inland Empire and possibly even hottest parts of inland
Orange County Tue and Wed. The lower deserts will reach 110 or
higher in hottest locations. One concern with the temperatures is
that parts of the San Diego County mesas could reach 100,
especially Wed when the hot airmass gets closest to the coast, so
the heat advisory has been extended to the San Diego County
coastal zone for Tue-Thu. Winds will increase Tue morning in places
normally prone to easterly winds in the San Diego and Riverside
County mountains and valleys, with some gusts around 45 MPH possible
Tuesday morning, based on output from the Cansac WRF and our local
San Diego NWS WRF.
When will the heat end? Cooling will be a gradual process as the
ridge will continue to prevail over the West, while a broad long-
wave trough prevails over the Midwest and northeastern US. However,
the upper high will gradually weaken late this week, so a cooling
trend should begin Thursday or, more likely, Friday and continue
through the weekend. Longer range progs show some disturbances off
the coast next week, and while they are unlikely to have much
moisture with them, some ensemble solutions suggest a small chance
of light precipitation the second half of next week, but nothing
that would have an impact on our vegetation or soils.
290355Z...Coast...Brief CIGs possible through 14Z Tuesday at
KSAN, KCRQ and KSNA with bases 005-010, but confidence is low.
Best chance will be at KCRQ. CIGS are most likely to stay over the
coastal waters and some sections of the coastline.
Valley/Mountains/Deserts...Clear with unrestricted vis through
Tuesday. East winds 15-20 kts gusting to 35 kts in the mountains and
foothills. There will be pockets of LLWS and MOD up/downdrafts west
of the mountains through Tuesday afternoon, strongest in San Diego
Northwest winds with occasional gusts around 20 kts in the outer
waters Tuesday afternoon and evening. Otherwise, no hazardous marine
conditions are expected through Friday.
On Tuesday and Wednesday, a southwesterly swell will be generate
above average surf of 3-6 ft at Orange County beaches, and 3-5 ft
surf at San Diego County beaches. Strong rip currents are likely.
The offshore flow will bring periods of gusty east-to-northeast
winds through Tuesday. Winds for northern areas, along and below the
slopes of the San Bernardino County mountains and below the Cajon
Pass are expected to be weaker, with peak gusts of 35 mph or less on
Tuesday. For the coastal slopes of the mountains into adjacent
valley areas in Riverside and San Diego Counties, and in the Inland
Empire below the San Gorgonio Pass, east winds will peak Tuesday
morning with gusts locally around 45 mph. Minimum RH for the
mountains into the inland valleys will fall to to 8-12% or even a
little lower Tuesday. Thus, Tuesday should have critical fire
weather conditions in San Diego and Riverside County mountains west
into the valleys, and the Red Flag Warning was extended there
through 5 PM Tue. Temperatures will peak, and RH will be lowest
Wednesday, though winds will be much lighter. Elevated fire weather
conditions will persist inland into the weekend.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Red Flag Warning until 5 PM PDT Tuesday for Riverside County
Mountains-Including The San Jacinto Ranger District Of The
San Bernardino National Forest-San Bernardino and Riverside
County Valleys -The Inland Empire-San Diego County Inland
Valleys-San Diego County Mountains-Including The Palomar
And Descanso Ranger Districts of the Cleveland National
Forest-San Gorgonio Pass Near Banning.
Heat Advisory from 10 AM Tuesday to 8 PM PDT Thursday for Orange
County Inland Areas-San Bernardino and Riverside County
Valleys-The Inland Empire-San Diego County Coastal Areas-
San Diego County Valleys.
Red Flag Warning until 5 PM PDT this afternoon for San
Bernardino County Mountains-Including The Mountain Top And
Front Country Ranger Districts Of The San Bernardino