Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/10/22
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
943 PM CST Fri Dec 9 2022
Issued at 926 PM CST Fri Dec 9 2022
Western edge of the stratus deck is stalled just east of the
Missouri. Under the stratus we are seeing light (also patchy
dense) fog, along with scattered flurries and patchy freezing
drizzle. Evidence of this on web cams and an mping report near
Watertown. Added mention of flurries/freezing drizzle to the
forecast earlier to account for this. Will monitor for increasing
areal coverage of dense fog, which some guidance suggests. May
need a headline if that`s the case. Otherwise, visibility at
reporting stations remains above 1SM as of 03Z. Should start to
see eastward movement of the stratus deck closer to morning as the
surface trough/wind shift line continues advancing eastward,
bringing with it drier air. Don`t expect much change in
temperatures through the night under the stratus deck either.
Also issued a Winter Storm Watch for central SD to better match up
with surrounding offices. Left it along the Missouri River for now
as this is where ensemble means continue to show the highest probs
for 6+ inches of snow. Some of these higher probs do show up
further northeast to between Aberdeen and Jamestown, but will let
later shifts sort through those details.
UPDATE Issued at 533 PM CST Fri Dec 9 2022
Aviation discussion updated below for the 00Z TAFs. Also updated
the forecast for the overnight hours into Saturday to increase the
mention of fog, as most models keep us in lowered visibility into
Saturday. Should see the fog/low clouds dissipate from west to
east with the passage of the surface trough/wind shift on
.SHORT TERM...(This Evening through Saturday Night)
Issued at 215 PM CST Fri Dec 9 2022
A persistent stratus layer with some embedded freezing fog will
remain a forecast challenge through Saturday morning. Even with high
clouds streaming in, the stratus is not eroding but expanding west.
The hi-res models all exit it to the east Saturday afternoon as high
pressure and northwest flow briefly move in.
The NBM (and most of the other models) continue to struggle (a lot)
with temperatures, staying too warm in clear areas overnight and too
warm over snow covered or cloud covered areas during the day. A mix
of HRRR, RAP and HREF proved to be the best contenders today so
stuck with that blend for tonight through tomorrow night. Saturday
does appear to have the potential to be much warmer with dry mid
levels and an upper ridge transitioning in. The ridge will stick
around into Saturday night, but high clouds may increase with
shortwave flow through the ridge. Southerly winds will increase
Saturday night ahead of low pressure along the lee of the Rockies.
.LONG TERM...(Sunday through Friday)
Issued at 215 PM CST Fri Dec 9 2022
When the period opens on Sunday, conditions are quiet over the CWA.
The biggest forecast challenge remains nailing down precipitation
timing, type and amounts between Monday night (6PM CST) and Thursday
morning (6AM CST), along with what, if any, impacts breezy to windy
northerly winds that develop on Wednesday could have on visibility
and travel from falling/blowing/drifting snow.
By 18Z Tuesday, the whole CWA (except perhaps the I-29 corridor
eastward) should be into snow p-type, heavy at times, with the
highest amounts likely piling up along and west of a line from Leola
to Murdo. That far eastern portion of the CWA may have a hard time
switching over to snow prior to 6PM CST Tuesday, and probably end up
receiving the least amount of snow from this event (potentially less
than 6 inches). It`s likely that precipitation starts off as drizzle
by Monday afternoon. Not really seeing data that supports snow p-
type until closer to 12Z Tuesday. The drizzle (or freezing drizzle
if there is some portion of the CWA at or below freezing on Monday)
will likely become heavier heading into Monday night, until
saturation aloft catches up to the deep lower stratus deck to
produce plain rain or snow, probably by 6AM CST. Still looks like
breezy to windy easterly component winds will be setting up as the
event unfolds, before gradually switching around to a more northerly
direction on Wednesday. NBM4/1 ensemble-based guidance +
deterministic poor man`s ensemble of low level wind progs and what`s
available in the S.A. Ensemble table suggests that the strongest
winds on Wednesday will be developing/spilling over from western
SoDak, potentially creating a situation where visibility could be
considerably reduced (especially in open/rural areas) in
falling/blowing snow, complete with hazardous drifting snow
potential. By Thursday afternoon, the system and it`s wintry
precipitation/wind should be dwindling/moving away from the region,
leaving the remainder of the extended dry and cold, as a rather
blocky upper level pattern could be setting up across the central
portion of the CONUS.
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 533 PM CST Fri Dec 9 2022
IFR CIGs/VSBY expected overnight across KABR/KATY. Currently, the
fog/low cloud line is just east of the Missouri River. Guidance
suggests this line creeps westward to perhaps affect KMBG with
lower CIGs, but not KPIR. Will certainly watch this trend and
adjust TAFs as needed. Otherwise, anticipate a gradual improvement
in conditions from west to east on Saturday as a surface trough
moves east across the area and shifts surface winds to a
SD...Winter Storm Watch from late Monday night through late Wednesday
night for SDZ003-004-009-015-016-033>035-045-048.
Area Forecast Discussion
National Weather Service Denver/Boulder CO
806 PM MST Fri Dec 9 2022
Issued at 758 PM MST Fri Dec 9 2022
Short wave trough is passing across WY this evening, with
increasing mid/upper level subsidence developing from west to east
across our area. Gusty downslope winds will develop as the
airmass be becomes increasingly stable overnight. Berthoud Pass
ASOS has been gusting to around 60 mph so far this evening, with
gusts of 40-50 mph possible in the foothills. The latest RAP
keeps the idea of isolated-scattered snow showers mainly over the
higher west facing mountain slope of Jackson and Larimer counties
tonight. Most of this is depicted well in the current forecast so
only minor adjustments planned at this time.
.SHORT TERM...(This evening through Saturday)
Issued at 241 PM MST Fri Dec 9 2022
Winds are starting to blow over the higher foothills as the
mid level speed max associated with the passing shortwave
approaches. The wave has nosed down into Boulder over the past
hour or so. Speeds are mostly 30-40 mph gusts. We expect the
downslope winds to become more widespread but mainly stay in the
foothills and the spots where it usually leaks out onto the
plains...Rocky Flats/Broomfield, Carter Lake, Cheyenne Ridge.
Speeds will likely come up a bit more but the 50 mph gusts should
be limited to the normally windier areas. There`s still a shallow
moisture layer upstream of the Park Range, but it`s pretty
limited, so the low PoPs we have over the northernmost mountains
through this evening look sufficient.
Skies will clear over the plains pretty quickly, allowing for
another cool night. That upstream cloud layer will be slower to
dissipate, though it should vanish late tonight or Saturday
morning. We`re showing warmer lows around zero in the mountain
valleys based on the clouds, it could drop much colder if they
clear early. A warming and subsident air mass will bring slightly
warmer highs tomorrow. Winds drop off pretty quickly, though there
will still be some over the ridges. Breezy conditions will also
develop over the area south of I-76 in the afternoon, which
combined with low humidities will produce elevated fire danger,
but we`re not expecting Red Flag conditions.
.LONG TERM...(Saturday night through Friday)
Issued at 241 PM MST Fri Dec 9 2022
1) Large winter storm expected across portions of the region late
Monday through late Tuesday
2) Still ample uncertainty in the track of the developing low
pressure over the plains - track dictates more/less heavier snows
and therefore impacts in tandem with stronger winds
3) Elevated fire danger concerns Sunday across portions of the plains
4) Well below mid-December temperature averages expected through the
Sunday...Short-wave ridging moves overhead and the upper level jet
max pulls farther east across the mid-west allowing surface winds to
relax a bit more. Winds veer more towards the south-southwest on
bumping up daytime temperatures back to 7-10 degrees above climo
averages. With the warmer temperatures and some breezy conditions in
place, elevated fire danger conditions will likely be present across
the Palmer Divide and eastern plains.
Monday...We`ll call this the `Deep Breath Before the Plunge` in a
few ways - big pattern swing, potential high impact winter storm,
and cold temperatures after Monday. Large scale troughing starts to
enter into the Great Basin sending stronger southwest flow aloft
into the region. This will help to keep temperatures above average
for much of the day, drawing up warmer and somewhat moister air from
the south-southeast. The Denver cyclone stands out Monday afternoon
which could help to pull down an encroaching cold front later
Monday...temperatures start to crash behind the front.
Tuesday...The main event. Though modeling has been consistent in the
general placement of the surface low pressure on Tuesday, there are
still small juxtapositions that will greatly affect the overall
impacts from this system. The trends in ensemble guidance have
shifted the position of the surface low a few miles farther north
meaning, winds are a pretty solid lock, and a little bit less snow
outside of the northern mountains and far northeastern plains. We
drop the low`s placement a few more miles south, more snow for a lot
more places. As of now the positive tilt of the mid-level troughing
should transfer the energy from west to east across the state faster
on Tuesday morning meaning a more limited shot of snow across the
Front Range is expected. If we`re able to slow down the troughs
movement a bit more, with stronger downstream blocking, we may be
able to have the trough axis go neutral or negative allowing for a
slightly longer snowfall event overall.
Though details are rather thin at this time we should note that
stronger northerly winds will be in place for much of the day
Tuesday. The colder nature of the system overall could produce snow
ratios into the 12-16:1 ratios, a bit more airy, which would allow
for more blowing of the snow to occur. There is still a lot in play
with both a snow boom or bust that could occur. Ah, forecasting
winter weather with a lee-cyclogenesis in your backyard, it`s rather
"fun" at times.
Wednesday - Friday...Though there may be some lingering wrap around
snow showers on Wednesday as the main trough continues to deepen and
pull away to the east-northeast. A much colder airmass then settles
in place with highs around 5-10 degrees below climo averages and
still rather breezy out east and along the foothills.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 455 PM MST Fri Dec 9 2022
VFR through Saturday. Typical light winds except maybe some brief
gusts to 20 kts at KBJC from 03-09z. Not confident enough to put
it in the taf at this time however.
Area Forecast Discussion
National Weather Service State College PA
731 PM EST Fri Dec 9 2022
1046 MB high pressure centered just east of James Bay Canada
will extend its ridge into Central PA and bring us dry weather
into Saturday evening.
A shortwave trough will move across the state from the west
later in the weekend. A period of light precipitation should
result for Saturday night and Sunday, with snow over the north
and a mixed bag turning to rain over the south. Upper level
ridging is then expected to move in with fair weather for the
first half of next week.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Lingering low and shallow strato cu based around 1 KFT AGL were
noted across the n-central mountains where a light sfc-925 mean
NNE flow was transporting moisture off Lake Ontario and the
Finger Lakes beneath the strong, 6-7 deg C/kft subsidence
inversion. Elsewhere, skies were clear with a very light nerly
Mid and high clouds slide east and overhead late this evening
through the overnight, ahead of the weak sfc low over southern
Ohio and supporting 500 MB trough near South Bend, Indiana.
That wave moves toward us tonight probably makes some very
light precip over the southern part of Somerset Co late tonight
and very early Sat AM.
The big high pressure overhead will continue to suppress the
moisture with this system tonight to our S.
HRRR and RAP forecasts and HREF precip mean barely makes any
precip fall over the Laurels. Thus, the bulk, or even all, of
the precip should miss us to the south.
There is a better chance for a coating of ZL/ZR over the
counties immediately adjacent (S&W) to Somerset Co. This part of
the forecast is highly consistent. Whether or not there is an
accumulation of any bit is a question which remains slightly
below the 50/50 yea/nay line. Without a more-definite threat of
a coating of ZL over a majority of Somerset Co, we`ll hold off
on issuing a winter wx advy for them at this point.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Ridging remains overhead Sat with any precip ending by mid
morning over the Laurels, followed by another fair day with
sun in the AM for much of the area. The return/srly flow over
the Ohio Valley will allow clouds to form and ride northeast
into the CWA. The clouds should cover about half of the CWA by
sunset. Maxes will be cooler than Friday over the Laurels, and
maybe just a deg or two lower over the rest of the far wrn tier
of counties depending on how fast the clouds encroach/overspread
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Upper level ridging should support fair and mild conditions
into early Saturday night. Forecast focus then shifts to a
potent shortwave approaching from the lower Grt Lks. Strong warm
advection at the nose of low level jet, combined with upper
level divergence ahead of the shortwave, could support a light
to moderate precip event across upstate NY/northern Pa late Sat
night into part of Sunday. Borderline model soundings indicate
ptype could be either rain or snow, with the best chance of
accumulating snow over the northern mountains, where the NBM
indicates a 50-60pct chance of at least 1 inch.
All medium range guidance supports fair and seasonable
conditions for the early and middle part of next week,
associated with upper level ridging and strong subsidence
between slow moving cutoff upper lows over the central US and
the Canadian Maritimes. Guidance has slowed down with the
arrival of precip later in the week, now holding off until Wed
night or Thu most likely. A surface high and pool of relatively
cold air poised north of New England could potentially result in
an initial wintry mix before a change to rain.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
A weak wave aloft will cross OH tonight and Sat morning and
bring a small amount of very light precip to SWrn PA. Most, if
not all, of it will remain to the W and S of JST. Thus, we`ve
kept the fcst dry there with only an MVFR deck of clouds
Elsewhere, expect VFR conditions with only high/mid clouds
overspreading the western half of PA tonight.
After the morning clouds slide south, plenty of sunshine can be
expected for the Central and Eastern terminals. If there is
clearing at JST, clouds (MVFR) should move back in from the SW
to JST in late morning, and by late in the day to BFD, AOO, and
The next weather system is a more significant long-wave trough
which will deepen some as it moves across the Great Lakes. That
will develop light precip over wrn PA and slide it over Central
PA Sat night and Sunday. Expect IFR for almost every terminal
for 12-24 hrs, and perhaps a period of LIFR, with less impact
for MDT and LNS than other terminals. Mainly snow will far N of
I-80, and snow/mixed precip may turn to rain before ending in
the S. Little or no lake effect is expected after this main
batch of precip.
Mon...MVFR west, VFR east.
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
535 PM CST Fri Dec 9 2022
.DISCUSSION...(This evening through Friday)
Issued at 310 PM CST Fri Dec 9 2022
* Fog and Stratus will plague the eastern portions of the forecast
area through tonight.
* A seasonal weekend with highs back up into the 40s and 50s
before the next storm system.
* Strong upper low will impact the area next week: Monday night
through Wednesday. Stronger winds through much of the work week. Liquid
precip expected for the most part with some snow as it exits.
* Cold temperatures filter in after the system next week. Below
normal temperatures will persist through approximately Christmas.
The main forecast concern tonight is Fog and Stratus. The Stratus
on the back side of the upper low has been stubborn to erode and
model guidance is struggling with it at best. Have trended towards
the HRRR with the afternoon and overnight forecast as it seems to
have the better handle on the stratus. Have kept Fog in the
forecast for much of the area along and east of Hwy 281 where
clouds will be the most prevalent. Additionally due to the
persistent cloud cover, have increased overnight lows to account
for the lack of sufficient radiational cooling.
Areas today that have been able to see some sun have warmed
nicely...and even those areas with persistent cloud cover have
reached to 32 degrees and hopefully this will mitigate the icing
on roadways for most areas.
A disturbance will move overhead tonight, but remain dry. As this
system exits Saturday evening, the region will be under
southwesterly upper level flow as a deep trough digs into the
western CONUS on Sunday. This is the next big weather maker. Ahead
of this system, lee troughing will develop and southerly wind will
persist. South winds may be breezy during the daytime hours Sunday
and even stronger on Monday as the surface low deepens over the
High Plains. These winds will help mix the BL causing temps to
increase, however, even 50+ degrees won`t feel great with 30+mph
Storm system Monday night - Wednesday:
The models and ensembles have been in fairly good agreement for
quite a few days already about the evolution and track of this
system. This system looks to track across Nebraska on its way
northeast, which should keep us in the warmer sector for the most
part. Rain and thunderstorms look to be the primary threat. As the
system moves overhead we could get some snow on the back side, but
it doesn`t look to be a large amount.
Thursday - Friday and beyond:
This system will bring in cold air that will likely persist
through the next couple of weeks - until near Christmas. Highs
will be below normal which is in the 30s for this time of year.
Highs in the 20s and lows in the single digits look to be on tap
for the end of the next work week.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday)
Issued at 528 PM CST Fri Dec 9 2022
Rather tricky forecast with main concerns being fog and low cigs
for KGRI. MVFR conditions at KGRI will deteriorate as we get
closer to midnight local time. Cigs are expected to come back down
to IFR around 800 ft as the stratus deck back builds to the west.
Then the stratus will erode back east slightly and will leave us
with clearing and when coupled with lighter winds gives us the
potential for fog to develop. Several models show a corridor of
fog forming over the eastern half of the area.
Closer to morning a trof will be moving in and will gradually
switch winds around to the west and then the northwest. This
should help clear out the fog and the remaining stratus.
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
901 PM EST Fri Dec 9 2022
A series of weather disturbances will bring occasional chances
for rain through Saturday. Temperatures will remain a few
degrees above normal into next week, with the next chance for
widespread steady rain arriving by midweek.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
With rain now clear from the area, leaving just some patchy
drizzle behind, the main concern going into the rest of the
night is the potential for fog. GLAMP data has been more
aggressive than HRRR projections in terms of visibility
reductions in the southern / southwestern sections of the ILN
CWA tonight, but given the very light winds and the visibilities
already being observed just outside of the forecast area, the
more pessimistic forecast is looking more likely for now.
A Special Weather Statement was issued for the fog based on
where it is expected to be at its worst, with an eye toward
upgrading to a Dense Fog Advisory in the next hour or two as it
continues to develop.
Temperatures in the far northern CWA have been trending a little
cooler than the previous forecast, so some downward adjustments
were made there.
Previous discussion >
An axis of light rain showers, associated with a weakening mid
level short wave, will continue to shift east across our area
through early evening. On the back side of this, a weakening
surface trough and some deeper low moisture could lead to a
lingering chance of drizzle as we head into this evening. This
could also lead to some areas of fog, especially later tonight,
with the most favored area for this appearing to be across Tri-
State area. Lows tonight will be in the upper 30s to lower 40s.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Mid level ridging will shift quickly east across the area
through Saturday morning before another weak mid level short
wave moves quickly east across the area Saturday afternoon into
Saturday night. Deeper moisture is fairly limited with this
system though so expect mainly just some lower chances for light
showers or sprinkles. Temperatures will remain a few degrees
above normal with highs on Saturday in the mid 40s to lower 50s
and lows Saturday night in the 35 to 40 degree range.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Surface high pressure builds in from the upper Midwest Sunday as
northwest flow aloft persists behind the trough over the northeast
United States. The surface high then shifts east across the upper
Great Lakes on Monday, then holds across region Tuesday, providing
cool dry days over the Ohio Valley.
Well-developed troughing moves from the Rockies on Tuesday into the
Plains by mid-week. Guidance suggests an amplified low pressure
system increases the chance of rain Wednesday into Thursday
associated with height falls and a strong cold front ahead of the
trough. Likely the best instability (and thunder chances) will be
located to the south of the region, with showers occurring across
the Ohio Valley.
By week`s end, a large upper low will likely cause a few rain/snow
showers as weak energy pivots around the low in the cold post-
frontal air mass.
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Steady rain will be exiting the Columbus area after 01Z, but
some drizzle will be possible for the next few hours at all TAF
sites. MVFR visibilities are fairly common around the area right
now, but drizzle could briefly drop visibilities to IFR.
Ceilings are also generally MVFR, but some IFR ceilings are
expected to move into the Cincinnati area in the next few hours.
IFR visibilities are also possible later in the overnight hours,
mainly at Cincinnati and Wilmington.
Tomorrow, visibilities are expected to improve to VFR, but MVFR
ceilings are likely through the day. Winds are expected to
remain very light through the forecast period. Some light rain
could make its way into the Cincinnati area late tomorrow
afternoon, but so far the chances appear too low to include in
OUTLOOK...Occasional MVFR/IFR conditions are possible through