Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/18/21
Area Forecast Discussion
National Weather Service State College PA
1057 PM EST Fri Dec 17 2021
A storm system will bring a rainy start to the weekend, as it
tracks directly across Pennsylvania. Temperatures will likely be
cold enough over the northern Mountains for a period of snow,
sleet and freezing rain with a light accumulation late tonight
into Saturday morning. High pressure will build back in for
Sunday and Monday, leading to dry and seasonably chilly weather
which will last for the better part of next week.
.NEAR TERM /UNTIL 8 AM SATURDAY MORNING/...
All is on track. Rain (not measured yet) is falling in the SW
third of the area. Temp down to 36F in Somerset (K2G9) and
dewpoint up to 30F from near 10F earlier. So...there could be
some non-rain hitting the highest hill tops. No, it`s not
snowing in Bedford (KHMZ) per webcam. The AWOS there just tends
to report --RA/DZ as snow at times.
Clouds lowering over the SW, and radar returns aloft are getting
closer to the CWA. However, dewpoints in the teens in the SW
with a 9F Td at KAOO right now will make it difficult for
anything to reach the surface in the next 3 hrs. RAP soundings
show a slow moistening at the sfc with the temp profile still
well above freezing thru the night. However, the higher hill
tops may cool down to freezing with rain the dominant p-type
later tonight. Temps cooling off on the expected schedule over
most of the area. Only minor tweaks to grids. Wx grids are a
complex mix of everything across the N later tonight.
The leading edge of precip will spread NE across the SW half of
PA by about 06-08Z and likely start across the Laurel Highlands
shortly before midnight.
Deep layer of dry and chilly air should wet bulb down to the
28-32F range very late tonight through Sat morning across
northern PA and to a lesser degree across the Central Mtns.
Timing of the cloud cover is not favorable for the ground to
radiate a significant amount tonight across the north to support
widespread freezing rain. However, the elevated layer of sub-
freezing wet bulb temps will readily support at least a
several hour period of wet snow and/or sleet over the higher
terrain between I-80 and the PA/NY border.
We collaborated with WFOs BUF, BGM, CLE and PBZ to issue a
Winter Weather Advisory for the 09Z-18Z Sat period for the
Northern Mtns of PA. Minimal travel impacts are expected in most
places, thanks to the warm ground from the recent record
breaking temps and aforementioned lack of ideal radiational
cooling conditions to chill the ground tonight.
.SHORT TERM /8 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Similar conditions (as noted in the paragraph immediately above)
will continue through Sat morning with a good coating to one
inch of sleet/snow likely across the northern mtns, and even a
ground whitening of sleet possible throughout Central PA as 925
mb wet bulbs hover in the -1 to -2C range until around 17Z.
Again, the main system of consequence this period will be a
southern stream origin disturbance, with the surface reflection
expected to track from the Ohio Valley later tonight, across PA
on Saturday, then off the NJ coast Saturday night and early
Sunday. It does still appear from model solutions that this
system will tend to deepen as it passes on Saturday, with decent
jet dynamics at play. The best forced ascent looks to develop
from the Alleghenies up over the northern tier, where liquid
equivalent precipitation amounts will mostly range from
0.75-1.25" later tonight and Saturday. This is good news for
parts of the Laurel/Allegheny Highlands, where it has been
fairly dry the last several weeks.
Rain should begin to shift eastward and out of the region later
Saturday and Saturday evening. As the aforementioned storm
system departs to the east, it will begin to pull down enough
colder air so that rain tapers off to snow showers over the
Alleghenies and PA`s northern tier counties Saturday evening.
However, the overall lake response should be muted, with rapid
dry advection and low capping inversion heights foreseen.
We`ll close out the weekend Sunday with increasing sunshine, but
also with brisk, chilly conditions. Highs Sunday afternoon will
range from near 30 in the northern mountains, to the lower 40s
in the Lower Susquehanna Valley.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
High pressure builds over the area early in this period,
bringing fair and seasonably cool conditions. Zonal flow aloft
persists through midweek, and leads to a stalling cold front
extending from the central GLAKS to southern New England,
keeping most inclement weather to our north. Extended models
have diverged substantially on phasing of the northern and
southern stream over the latter half of next week, and latest
guidance continues to reflect this, leaving the end of the week
and Christmas Day highly uncertain, given the spread of
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions will transition to MVFR overnight (05z to 09z)
across the Laurels and northern mountains, along with the
arrival of light rain, mixed with sleet and FZRA in the northern
tier. Elsewhere, expect a gradually thickening cirrostratus
deck, followed by cigs lowering to around 6 kft with light
precip possible by sunrise for central and east central PA.
Conditions will gradually worsen on Saturday with widespread
IFR cigs expected by afternoon, and LIFR possible for BFD and
JST. Precip should switch to plain rain for all, with vsby
restricted in -RA and BR. Some LLWS is expected across mainly
the western half of the area as swrly flow increases to 40 kts
at 2kft, atop sfc winds that are southeasterly and less than 10
Sat night-Sun...Lingering reductions N/W, with scattered -SHSN.
Becoming VFR elsewhere.
Harrisburg set their daily max temp today/Friday (around 1AM).
Winter Weather Advisory from 4 AM to 1 PM EST Saturday for
Area Forecast Discussion
National Weather Service Lincoln IL
721 PM CST Fri Dec 17 2021
Issued at 721 PM CST Fri Dec 17 2021
Periods of rain will continue overnight into early Saturday across
central and southeast Illinois, with the steadiest rain south of
I-70. A mixture of sleet and rain is possible late this evening
north and west of Peoria, but this should change over to all rain
after midnight. After the rain moves out, dry weather is expected
for the remainder of the weekend.
Issued at 721 PM CST Fri Dec 17 2021
Initial area of rain continues to be most widespread south of
I-70, with regional radar mosaics showing an increase in shower
activity further north from central Missouri over to near
Danville. This northward expansion is expected to continue this
evening. Some of the high-res models suggest a rain/sleet mix in
the far northwest CWA, with HRRR soundings from Galesburg showing
a warm layer of 1-2C just above 800 mb. This layer was sampled by
our evening sounding, though warmer down here around 5C. A trend
toward all rain is indicated after midnight in that area.
Temperatures over most of the area shouldn`t change much
overnight, though the southeast CWA is expected to climb into the
40s as the front gets close to Lawrenceville.
.SHORT TERM...(This evening through Saturday)
ISSUED AT 252 PM CST Fri Dec 17 2021
A frontal system will continue to spread rain across eastern and
southeastern Illinois early this evening, but the rain will spread
north and northwestward during the evening hours and then continue
overnight. Will be keeping the highest pops east of the Illinois
river with chance pops around Galesburg where HiRes models keep
agree that the threat there will be limited. The rain should end
during the morning hours Saturday, but mostly cloudy skies will
remain through the afternoon hours. Cloud cover and precip will
hold temps and only expecting slowly falling or nearly steady
temperatures, reaching the lower 30s in the north to the upper
30s in the southeast. Sat afternoon highs will return to the upper
30s in the north to the mid 40s in the southeast.
.LONG TERM...(Saturday night through Friday)
ISSUED AT 252 PM CST Fri Dec 17 2021
Once the front moves east of the area, high pressure will build
into the region with dry weather. Even though another front is
expected to move through the state around mid week, it should come
through dry. Expect dry weather through the week with maybe a
chance of precip toward the weekend.
Temps through the period will range from the lower 30s to the
upper 40s, with Wednesday being the coolest with mid 30s in the
north to around 40 in the southeast. The warmest days will be Thur
and Fri when afternoon highs reach back into the middle to upper
40s...a return to above normal temps.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 519 PM CST Fri Dec 17 2021
Ceilings below 3000 feet have reached KSPI-KCMI early this evening
and will continue to push over the next few hours. Will continue
to see deteriorating conditions over central Illinois through the
evening, with IFR conditions likely from KSPI-KCMI before 06Z.
These lower ceilings likely will reach KPIA/KBMI by 09Z. A gradual
improvement is likely from west to east Saturday midday and
Rain showers are expected to spread across central Illinois this
evening. Some of the guidance hints at potential for some sleet
near KPIA later this evening, and will monitor that for any needed
amendments. Threat should lift north of there by 06Z.
Area Forecast Discussion
National Weather Service Sacramento CA
241 PM PST Fri Dec 17 2021
Dry weather into early next week. Cold nights with Valley fog and
frost possible into early next week. Rain and snow chances return
next week, with gusty winds at times. Mountain travel will likely
Visible satellite imagery depicts mostly clear skies across our
region this afternoon. Although, there are some lingering low
clouds still present in the San Joaquin Valley. Cool temperatures
are also being observed in areas in the Valley that saw low clouds
and fog today, with the Sacramento metro region running about 5
to 10 degrees cooler than this time 24 hours ago. Elsewhere,
areas under sunny skies are seeing temperatures 5 to 15 degrees
warmer than yesterday at this time.
Ensemble guidance is in good acquirement high pressure over
California will keep our region dry through the weekend. The cool
airmass in place in combination with light winds and mostly clear
skies this afternoon will lead to widespread near to below
freezing temperatures tonight in the Valley. Frost is likely to
develop as well as low clouds and fog overnight tonight into
tomorrow morning and will be possible in the overnight and morning
hours each day into early next week. HREF and HRRR guidance are
in agreement low clouds and valley fog will be more widespread
tomorrow morning than what was observed today with low clouds
potentially lingering for much of the day over the Sacramento
region and locations southward in the Valley. Mountain areas will
see a cool start to the day with partly cloudy skies.
Early next week a change in the weather pattern is anticipated
with wet weather returning to the region. ensemble guidance is in
agreement a low pressure system will likely deepen off the West
Coast. This feature is forecast to bring periods of valley rain
and mountain snow, however timing is still uncertain as the low
may stall off the west coast early next week. Current guidance
has precipitation chances gradually spreading south and eastward
as early as Monday. Snow levels could start below 3000 4500 feet.
Snow could begin to bring travel problems to the northern
mountains starting Monday, though higher potential for this will
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Ensemble guidance remains in agreement that longwave troughing
will develop off of the West Coast next week, producing multiple
rounds of widespread precipitation for Northern California into
next weekend. However, timing of when precipitation will begin
pushing into California is slowing down as the ensembles depict
the trough deepening off of the coast. Precipitation onset is now
slated for later Monday into Tuesday. Uncertainty remains in
timing and amounts as cluster analysis suggests some differences
regarding the progression and position of the trough. Overall, we
are forecasting around one to three inches of rain for the Valley
and multiple feet of snow over the mountains over a multi-day
period, which will likely cause holiday travel disruptions.
Periods of gusty winds are also possible with individual weather
systems, and temperatures will remain relatively mild. -HEC
MVFR/IFR/LIFR conditions due to BF/FG are forecast to return
across the Valley after 09-12Z Saturday and may remain through
most of the day Saturday for areas near and south of the
Sacramento area. Otherwise, VFR conditions expected next 24 hours
with winds generally below 10 kts.