Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/07/20
Area Forecast Discussion
National Weather Service La Crosse WI
603 PM CST Fri Nov 6 2020
.SHORT TERM...(This evening through Sunday night)
Issued at 202 PM CST Fri Nov 6 2020
Another warm day was setting up across the region today, as early
afternoon temperatures had climbed into the upper 60s to lower
70s. Assuming these trends hold up through the afternoon, should
have no trouble setting some record high temperatures for the day.
Otherwise it was noticeably more breezy across the area today,
owing to tightening pressure gradient between high pressure over
the Ohio River Valley and low pressure over the western Dakotas.
More of the same is on tap through through the weekend as upper
level ridging and strong southerly surface flow keep warm air over
the area. While 925 mb temperatures will be a bit cooler than
past days, the aforementioned southerly flow should keep plenty
of warm air moving in, as temperatures continue to top out in the
60s and 70s. That said, will need to keep an eye on cloud cover
both days, as there`s good model agreement of 925 mb moisture
transport ramping up both tonight and Saturday night and leading
to some lower level clouds that could stick around through both
mornings. Should they stick around a bit longer than expected,
temperatures could be a fair amount cooler than currently
forecast, but still warm given the time of year.
.LONG TERM...(Monday through Friday)
Issued at 202 PM CST Fri Nov 6 2020
By Monday, an upper level trough will be firmly entrenched over
the western CONUS, as a low will have slid northeastward with the
upper level flow through the Dakotas and into southern Canada. An
associated cold front will be approaching the area on Monday, but
guidance has been pretty persistent in holding it just west of the
area through at least late afternoon. Therefore, continued strong
southerly flow ahead of the front will lead to yet another warmer
day, with highs in the 60s to lower 70s. In addition to the
continued warm air advection, plenty of moisture will be moving
into the area ahead of the front, which sets the stage for pretty
widespread precipitation as the front eventually passes through
Monday evening. Precipitable water values look to be in the 1 to
1.25" range, corresponding to the 90th+ percentile of climatology
per NAEFS guidance. In addition, should have at least a little
instability in the area as the front moves through, so could have
a few rumbles of thunder. While it`s still a little early to talk
exact amounts, looking like a fairly widespread 1" of rainfall is
a decent bet.
Models are then in good agreement of shortwave energy spinning up
a low over the southern Plains and tracking it northeastward
along the cold front. However, plenty of questions still remain
regarding strength and exact track of the low, both of which will
play a large part in location and amount of any potential snowfall
as colder air moves in behind the front. Just looking at various
GEFS members, you can get about any solution you want, ranging
from almost no snow anywhere in the region, to what would amount
to a Winter Storm Warning-criteria snow band, with a large spread
in where exactly it would fall. So bottom line, VERY low
confidence in how preciptiation plays out beyond Monday
night/early Tuesday morning. One thing that we do have higher
confidence in is that we will be cooling down quite a bit, as high
temperatures following the frontal passage look to be in the 40s
through the remainder of the week. Also, along those lines, even
if we don`t get much snow, with the amount of rain expected to
fall and likely linger on roadways, will need to watch out for
some slick spots developing as temperatures cool below freezing
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 558 PM CST Fri Nov 6 2020
VFR conditions through much of tonight. South to southwest winds
will remain elevated tonight 10-15kts with some gusts 20 to 25kts.
Some hint of stratus developing Saturday morning. The latest RAP
has these clouds somewhat patchy and possibly holding west or
north of KRST. Included low level wind shear tonight through
around 14-15Z. Continued gusty southwest winds Saturday 15 to
20kts with gusts 20 to 30kts.
Area Forecast Discussion
National Weather Service Bismarck ND
942 PM CST Fri Nov 6 2020
Issued at 923 PM CST Fri Nov 6 2020
No changes for the late evening update. There have been a few
instances of low stratus here and there this evening. Currently
Hazen has some low clouds. Some webcams may also show some hints
of lower clouds. Right now we don`think dense fog will be a
significant issue, but as we head towards Saturday morning we
could see some lowering of visibilities as stratus becomes more
widespread. RAP and HRRR are showing some splotches of fog. Will
continue to monitor but will hold off on adding any fog for now.
UPDATE Issued at 530 PM CST Fri Nov 6 2020
No significant updates late this afternoon. Low pressure continues
to push south across the state. Winds have now turned northeast
across the entire forecast area. It remains mostly cloudy with
abundant high clouds streaming over the area. The low stratus
around the Turtle Mountains has finally dissipated. Look for low
stratus to develop again late tonight or Saturday.
.SHORT TERM...(This evening through Saturday)
Issued at 343 PM CST Fri Nov 6 2020
Mid to high clouds are streaming across the region this afternoon in
anticyclonic flow aloft. At the surface, weak low pressure was
drifting along the North and South Dakota border. This setup has
resulted in weaker boundary layer mixing than the past several days,
with afternoon temperatures actually under-performing model
consensus in most areas.
A backdoor cold front is forecast to slide south across the region
tonight, possibly resulting in some low stratus. Cooler but dry
weather is expected for Saturday ahead of a deepening Pacific
trough. Think that skies will trend more towards mostly cloudy given
the presence of weak mid level PVA and a near-stationary low level
.LONG TERM...(Saturday night through Friday)
Issued at 343 PM CST Fri Nov 6 2020
A powerful low pressure system will cross the western half of the
region Sunday into Monday. The greatest expected hazard for western
and central North Dakota is strong winds. Impactful winter weather
is possible for the northwest corner of the state, especially along
and west of a line from Williston to Crosby.
By Saturday evening, a double-barrel upper level low is forecast to
be embedded in longwave troughing over the far western CONUS. As
these two lows begin to interact with and revolve around each other,
the southern low is forecast to quickly eject from the Mojave Desert
to the Northern High Plains on Sunday, with rapid surface
cyclogenesis near the Black Hills Sunday morning. There has been
decent consistency and clustering of the track and strength of the
surface low in multiple ensemble systems, with both the GEFS and
ECMWF ensemble showing a majority of members with a 980-990 mb MSLP
low tracking from southwest to north central North Dakota Sunday
morning through the evening.
Before the surface low develops, broad warm air advection and
isentropic ascent are expected to overspread the region Saturday
night. This may result in some drizzle or freezing drizzle across
far northwest and north central North Dakota, where deeper
saturation should be more easily achieved due to a cooler antecedent
boundary layer. We mostly accepted NBM surface temperatures through
the duration of the long term period, which gives us a slight chance
of freezing drizzle mainly across Divide and Burke Counties late
Saturday night through Sunday morning. A few hundredths of an inch
of ice accumulation may occur. Drizzle may expand across the state
and continue into the afternoon, where temperatures will remain well
above freezing. Only far western Divide County has the potential for
surface temperatures remaining below freezing through Sunday
afternoon, and that is not a guaranteed outcome. Therefore, any
impacts due to freezing drizzle are likely to be short in duration.
The greatest uncertainty regarding this system is the amount of snow
that will fall across northwest North Dakota. There are multiple
sources of uncertainty affecting snow accumulations, including exact
storm track, QPF amplitudes, and temperatures both at the surface
and aloft. A blended forecast of QPF determined by the WPC and NBM
temperatures both at the surface and aloft produces a storm total
snow accumulation around 2-4 inches across Divide, western Williams,
and northwest McKenzie Counties. This actually falls within the 25th
to 50th percentile of the WPC Super Ensemble, which we are okay with
given both the QPF and snow threshold probabilities of the 12Z GEFS
and ECMWF ensembles. It is worth noting that the full range of snow
amounts at Williston in the 12Z GEFS is zero to nearly 14 inches
(10:1 ratio), with weak clustering of members near both 2 and 5
The most certain, and perhaps most concerning hazard with this low
is the potential for very strong winds, both in the warm and cold
sectors. A 40-50 kt low level jet could get mixed down to the
surface Sunday morning along and west of the James River Valley.
Then, both the 12Z NAM and deterministic GFS are showing mean 900-
800 mb winds behind the cold front around 40-50 kts, with 3-hr
surface pressure rises anywhere from 7 to as high as 15 mb! The high-
end pressure rises are found in the GFS, which we suspect is a worst
case scenario (probabilistic pressure rise data are not readily
available). Nevertheless, the signal for strong winds has been
present in model data for several days and fits the conceptual model
well. Winds were trended toward the higher end of guidance in the
forecast Sunday afternoon through Monday morning. Warning criteria
winds cannot be ruled out, but there is not enough confidence for a
High Wind Watch at this time.
Finally, there is a slight chance of thunderstorms across much of
western and central North Dakota Sunday afternoon given the strong
dynamics of this system along with possibly a few hundred J/kg of
CAPE and negative theta-e lapse rates. Strong wind gusts would be
possible with any storm, and severe gusts cannot be completely ruled
out, though the overall probability of storms is low.
Light snow may linger across northwest North Dakota through Monday,
with elevated winds region wide. There will be an abrupt change in
temperatures, with most locations seeing highs go from the 50s and
60s on Sunday to 20s on Monday. An active pattern may continue
through next week, but precipitation potential appears lower due to
a drier air mass. Below normal temperatures are favored through the
remainder of the long term period.
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 923 PM CST Fri Nov 6 2020
UPDATE...There have been a few instances of MVFR stratus this
evening and may bump up the starting time of stratus with the 06Z
TAFS. Hard though to see much with so much high cloudiness
streaming by. Temp/dwpt spread are also getting closer. Don`t
think dense fog will be a significant issue but we may see some
vsbys lowering into the MVFR range Saturday morning.
MVFR to IFR stratus expected to develop late tonight through
Saturday morning, affecting all TAF Sites.
The main forecast issue will be stratus developing late tonight
into Saturday. All models depict an area of low stratus developing
over the northern TAF sites late tonight (after 06 UTC) and
spreading south into the southern TAF sites with All sites either
MVFR or IFR through much of the morning. Ceilings then quickly
lift around 18 UTC with VFR conditions prevailing Saturday
The NAM/RAP develop low stratus much quicker than the GFS or our
given NBM guidance. Generally followed the later solution bringing
everyone down around 12-18 UTC Saturday. For now we did keep the
IFR ceilings out of KBIS as there is a question on how far south
the stratus actually makes it.
A northeast surface flows around 10-15 kts across the forecast
area will gradually shift east to southeast through the 00Z TAF
period and increase Saturday afternoon.
Area Forecast Discussion
National Weather Service Charleston SC
1046 PM EST Fri Nov 6 2020
High pressure will persist north of the area through Monday
before shifting northeast. Waves of low pressure will
occasionally move in from the southeast through the middle of
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 1040 PM: Lightning detection and view out of the window
indicate that the cluster of showers off the lower SC coast
have recently produced occasional lightning strike. I will
update the forecast to indicated the potential for thunderstorms
into the late night hours.
As of 9 PM: Regional radar has indicated a decreasing trend in
shower coverage this evening. Recent runs of the HRRR show
another surge of showers across SE GA late tonight into early
Saturday morning. PoPs will remain between 30-40 percent across
coastal GA late tonight. Temperatures appear on track to range
in the 60s by daybreak Saturday.
As of 640 PM: KCLX detected clusters of showers over the marine
zones drifting west over portions of SE GA/SC. Generally,
showers were weakening as the showers pushed on shore. Based on
the limited instability and recent radar trends, the forecast
will be updated to remove the mention of thunderstorms for
This Evening: The coastal trough will move inland, bringing
with it increased moisture and convergence. The result will be
the main band of showers moving into our coastal counties, then
gradually dissipating as it moves inland.
Tonight: The coastal trough will gradually weaken from north to
south through the night. This will cause showers to diminish in
these same locations. Skies should be mostly cloudy, which will
lead to very mild temperatures. Lows will be in the low to mid
60s away from the coast and the upper 60s at the beaches.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
A deep layered ridge will remain north of the area Saturday
through Monday. A series of upper shortwaves will rotate around
the ridge and into the Southeast United States while a weak
surface trough remains just offshore. Isolated to scattered
showers will be possible Saturday, mainly over the marine area
and coastal sections. Increasing low-level moisture Sunday into
Monday should result in greater shower coverage. The best
coverage may be Monday afternoon across coastal southeast GA as
a stronger upper shortwave moves in.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
High pressure will be centered in the western Atlantic through
the middle of next week, while a tropical low likely meanders
over the eastern Gulf of Mexico. Later in the week, a cold front
is forecast to approach the region. Deeper moisture and passing
shortwave energy will result in a fairly unsettled period.
Temperatures will be above normal, especially overnight lows
which could be near record high minimums.
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
0Z TAFs: An inverted trough is forecast to ripple east from the
Atlantic to SE GA/SC. Rounds of light rain showers will be
possible tonight into early Saturday morning, especially across
coastal GA. Between the showers, MVFR ceilings may develop over
KCHS from time-to-time, highlighted with a TEMPO from 4-8Z. The
potential for MVFR ceilings appears greater at KSAV, primarily
from 9-14Z. Winds should remain steady from the ENE between 5-10
kts through the period.
Extended Aviation Outlook: Low ceilings likely each night
beginning Saturday night. Occasional visibility restrictions in
rain showers, especially Monday through Wednesday.
Tonight: The synoptic pattern will continue favor northeast to
east winds in the 15-20 kt range. Seas will be 4-6 ft within 20
nm and 6-8 ft for the GA waters beyond 20 nm. Small Craft
Advisories are in effect for all of the coastal waters outside
of the Charleston Harbor.
A persistent east to east-northeast flow continues Saturday
through early Tuesday before winds turn southeast mid to late
week. A fairly strong gradient will exist due to strong high
pressure to the north and low pressure to the south. Frequent 25
kt gusts, along with seas well in excess of 6 ft will continue
for all waters outside Charleston Harbor through at least
Wednesday or Wednesday night.
Conditions in Charleston Harbor could occasionally reach Small
Craft Advisory levels, especially Sunday into Monday.
MARINE...Small Craft Advisory until 5 AM EST Thursday for AMZ350-352-
Small Craft Advisory until 11 PM EST Wednesday for AMZ354.
Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
500 PM MST Fri Nov 6 2020
.UPDATE...Updated aviation discussion.
Well above normal temperatures will continue today, but a cooling
trend will also begin. A much more drastic cool down is then
expected Saturday as a low pressure system moves through the
region. It will also bring breezy to windy conditions and a chance
of rain with the best chances over the high terrain. Another
system will follow closely behind later on Sunday bringing a
better chance of precipitation. That second system is expected to
exit the region by Monday afternoon. Below normal temperatures
will continue through much of next week.
Latest water vapor imagery depicts the remnant moisture of
post-tropical cyclone Odalys advancing northeastward into the Desert
Southwest. Consequently, it is not entirely surprising the PWAT of
0.7 inches from this morning`s KPHX ACARS sounding is considerably
above normal. Mostly cloudy skies persist across the area today and
an isolated thunderstorm has even managed to develop near El Centro
in the Imperial Valley. Latest HREF indicates the threat for showers
and isolated thunderstorms will persist across southeastern
California and southwestern Arizona into this evening.
Elsewhere, latest runs of the HRRR suggest sprinkles and isolated
showers will also be possible further east across portions of central
Arizona. Despite the clouds and isolated precipitation, well-above
normal temperatures are expected again this afternoon after setting a
new high minimum of 72 degrees in Phoenix this morning. Forecast
high temperature of 93 degrees would fall only one degree shy of the
daily record of 94 degrees set in 2007.
The focus for precipitation will shift eastward tonight and Saturday
as an anomalously strong low pressure system dives into southern
California. The higher terrain north and east of Phoenix will be
favored for precipitation, given the widespread vorticity-forced
ascent and localized orographic lift due to the strong level-wind
fields. This will translate into generally breezy conditions, which
could result in areas of blowing dust, particularly across
WPC QPF will be utilized which indicates a few hundredths of an inch
of rain in the Valley, but up to an inch of rain in the Superstitions
through Sunday morning. Models then depict a discernible break in the
action before precipitation redevelops ahead of the next anomalous
Pacific closed low. Although PWATs will be considerably lower with
this system Sunday, it will also be colder and capable of producing
beneficial rainfall, given the well-defined jet-forced ascent,
particularly Sunday night and early Monday.
Highest rainfall totals are again expected across the higher terrain
north and east of Phoenix, however rainfall coverage will likely
extend further into the lower deserts. Precipitation is expected to
taper off Monday morning and with much cooler air behind the cold
front, very light snow accumulations will be possible across eastern
Gila County above 5500 ft in elevation. Across the lower elevations,
latest NBM guidance is exhibiting a tight spread and suggests
temperatures will likely struggle to reach the lower 60s.
Overall pattern next week will feature a longwave trough across the
western CONUS. This will result in a continuation of the below
normal temperatures, though a warming trend is likely as thicknesses
.AVIATION...Updated at 0000Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
There are several aviation issues over the next 24 hours as a series
of low pressure systems impact the central deserts: wind, wind
shear, CIGs and precip. First short wave to quickly move northeast
and across the area this evening will result in isolate high based
showers through about 07z. As such, have VCSH in the TAFs starting
around 02-03z. CIGS will be on the high side tonight, mostly 10k
feet or higher with this weaker wave. As another stronger wave
approaches Saturday, lower cloud decks develop with SCT-BKN decks 6k
or above develop during the morning. There will be a chance of
showers developing during the afternoon, confidence is not overly
high on when they will start but based on a variety of high res
models, will put PROB30 groups into the TAFs with precip starting by
around 21z Saturday. Do not expect any thunder, and precip amounts
should be rather light. May see CIGs lower a bit under the heavier
showers and down to around 5k feet at times.
Wind and wind shear will be the other issues. After a few hours of
rather light west/southwest wind early this evening, the wind will
start to back and then become stronger and locally gusty after
midnight. Wind shifts to southeast at KPHX likely to be starting
around 03z. Sustained speeds after midnight could exceed 10kt at
times with some gusts into the teens possible. During the evening,
after about 02z, we may still have some LLWS as south/southwest
winds from 2 to 5k feet pick up to 30kt or higher. Thus some TAFs
will see LLWS for several hours. After midnight, as winds increase
the shear should start to taper off. By late morning Saturday winds
should turn more to the south and become locally gusty, then
becoming southwest to west by 21z with gusts over 20kt possible.
Southeast California/Southwest Arizona including KIPL and KBLH:
For the most part, weather issues over the western deserts should
mainly be confined to winds, as precip should be minimal and mainly
impacting KIPL during the afternoon on Saturday. Look for elevated
southwest winds tonight at KBLH with gusts up to 20kt during the
evening. Stronger south/southwest winds expected Saturday afternoon
ahead of an approaching low pressure system; look for gusts over
25kt possible during the afternoon. At KIPL we will see southwest
winds develop and increase early this evening with gusts over 20kt
at times overnight and by noon Saturday they should continue to
increase with gusts over 30kt likely by 20z. Although there may be
some patchy blowing dust with stronger gusts, confidence in amount
of dust and effects on visibility are on the low side so no mention
of restricted vis made in the TAFs with the latest issuance. At KIPL
there may be a few showers developing in the afternoon with SCT-BKN
decks in the 8-12k range for the most part. No heavy rain expected.
Monday through Friday:
Valley rain and high-elevation snowfall associated with
a cold front will taper off Monday. In its wake, a gradual
warming trend is anticipated, however well-below normal temperatures
will persist through the week. Winds will also return to more
seasonable speeds, generally between 5 and 10 mph for most locations
through the week. Meanwhile, moist conditions Monday will give way
to min RHs in the 20s by Tuesday.
Record highs this week:
Date Phoenix Yuma El Centro
---- ------- ---- ---------
Nov 6 94 in 2007 96 in 1988 96 in 1988
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
CA...Wind Advisory until 7 PM PST Sunday for CAZ562.
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
429 PM MST Fri Nov 6 2020
.DISCUSSION...(This Evening Through Friday)
Issued at 142 PM MST Fri Nov 6 2020
With an upper low pushing over the Pacific Northwest, upper flow
is southwesterly over the northern plains, with clouds spreading
over the region. At the surface, low pressure over NW SD is
resulting in some gusty southwesterly winds across south central
SD. Adjusted highs down slightly for abundant cloud cover, but
temperatures have still managed to make it into the 60s across the
northwestern third, 70s across much of the western SD plains, and
lower 80s across the sunnier south central SD.
Mostly cloudy skies and southwesterly winds will keep lows tonight
in and around the 40s. With downslope winds expected again tonight,
the foothills may remain in the 50s. However, pressure gradient
across the Black Hills isn`t enough to warrant headlines.
Southwesterly flow will continue to advect warm air into the region
Saturday, while west coast low pressure system slowly approaches.
Highs will reach the 60s and 70s, with a few 80s possible.
Southwesterly winds will be breezy again, especially across
northeastern WY in the afternoon and south central SD overnight.
Initial wave will eject ahead of the main trough and swing through
the northern plains Sunday. The 700 mb low is progged to slide from
NW WY to NW ND, keeping most of the precip across MT. However, an
area of positive vorticity advecting over a band of low-to-mid-level
frontogenesis will help produce some light precipitation Sunday
morning, before forcing across our CWA diminishes in the afternoon.
Lingering warm air will allow most precip to fall as rain. Much
colder air will then move into the area behind the front on Sunday
afternoon, and so any precip that wraps around the low into
northeastern WY and northwestern SD will be snow. However, little if
any precip/snow accumulation is expected there. West-southwesterly
winds will be gusty ahead of the front on Sunday, and then gusty
west-northwesterly winds are expected behind the front Sunday
night, especially across NW SD. Bumped up forecast winds, as NAM
and GFS have 6-10 mb/3 hr pressure rises moving through. Highs
Sunday will reach the 40s and 50s before temperatures drop from
northwest to southeast in the afternoon. Lows Sunday night will
dip into the teens and 20s.
Beneath the cold airmass, Monday will be the coldest of the week,
with highs only in the 20s and 30s. Upper troughs/waves will cross
the region through the week, keeping temperatures cool, and allowing
for some small precip chances here and there.
.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 427 PM MST Fri Nov 6 2020
VFR conditions are expected through the forecast period. Gusty
south to southwest winds will return across northeastern WY, the
Black Hills area, and across southern SD on Saturday.
Issued At 142 PM MST Fri Nov 6 2020
Critical fire weather conditions continue over south
central South Dakota this afternoon, with Winner reporting RH below
15% and gusts over 30 mph. Breezy southwesterly winds are expected
again on Saturday, along with warm and dry conditions. The RAP and
HRRR are indicating a pocket of dry air pushing into
southwestern/south central SD, so lowered dewpoints there. That
placed min RH in the upper teens/lower 20s. Strongest winds will be
across northeastern WY, but RH there will be in the mid to upper
20s. Fire danger will be elevated, but not enough for headlines.
SD...Red Flag Warning until 6 PM CST this evening for SDZ334-335.