Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/19/23
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
505 PM CST Mon Dec 18 2023
...New AVIATION...
.SHORT TERM...
(Tonight through Tuesday night)
Issued at 128 PM CST Mon Dec 18 2023
Sunny skies are prevailing across south central Texas with a few
high clouds pushing along the Rio Grande and southern Edwards
Plateau early this afternoon. A weak and shallow frontal boundary
pushed across most of the local area this morning, however, the tail
end of it looks to be seating to the east of Del Rio per latest
surface observations and RAP analysis map. Today`s highs are on
track with mid 60s expected across the Hill Country and upper 60s to
low 70s along the I-35 corridor, coastal plains and Rio Grande.
Upper level moisture continues to push eastward across the local
area as upper level flow stays from the west through the overnight
and then shifts to the southwest on Tuesday. Overnight lows are
forecast to be around the low to mid 40s, however, can not rule out
a few spots over the Hill Country reaching the upper 30s.
Tuesday is forecast to be a bit cooler with cloud coverage taking
place over most areas. Therefore, high temperatures are forecast to
range from the low to mid 60s across the Hill Country, southern
Edwards Plateau and the northern part of the Rio Grande while the
rest of south central Texas gets into the upper 60s to low 70s.
Increased moisture continues on Tuesday night with low level
moisture taking place as southerly flow dominates the local area.
Low clouds are forecast to develop on Tuesday evening and spread
across south central Texas overnight into early Wednesday morning.
Can not rule out patches of fog and even drizzle overnight/late
Tuesday night especially across the coastal plains and portions of
the I-35 corridor including the San Antonio metro area. Overnight
lows are forecast to range from the upper 40s to low 50s.
&&
.LONG TERM...
(Wednesday through Monday)
Issued at 128 PM CST Mon Dec 18 2023
On Wednesday morning, broad surface high pressure over the eastern
CONUS will be driving continued onshore flow, with dew points
already in the lower 50s at 12Z. Patchy to areas of fog will be
possible, as well as some drizzle and perhaps even a streamer shower
or two in the morning. Given the difficulties of nailing down a
location at this lead time, I`ve broad-brushed a 10% chance of
showers into the forecast for the morning hours. By the afternoon,
temperatures are forecast to reach the upper 60s to mid 70s despite
mostly cloudy skies. Models are in slightly better agreement in the
potential for a ribbon of isentropically-generated showers over the
eastern Coastal Plains in the afternoon and evening, so I`ve added
20% POPs there.
Upper pattern on Wednesday and Wednesday night will consist of a
closed upper low off the coast of CA and a weak ridge axis over the
mid-south to southeastern US. The surface high will move very
little, and onshore flow will continue off the Gulf. Fog and drizzle
potential could be even higher on Thursday and Friday mornings as
dew points rise into the upper 50s and lower 60s. The combination of
onshore/upslope surface flow and weak shortwaves embedded in the WSW
flow aloft could begin to allow for isolated shower development over
mainly northern portions of the region as early as Thursday morning,
but rain chances will increase Thursday night into Friday. A bit of
a break from the more better rain chances is expected on Friday
night into Saturday morning, but over the weekend the primary upper
level low spinning off the west coast will finally begin to open and
progress eastward. It`s timing and placement are in question, as
well as it`s interactions with another trough entering the Pacific
NW on Friday night. Regardless, some rain chances will continue off
and on locally through Christmas Eve. There is even a low-end
potential for a stronger thunderstorm or two as the Pacific cold
front traverses the region (probably on Sunday), but this would be
highly dependent on a lot of factors that cannot be accurately
predicted at this lead time.
Chances for rain decrease by Christmas Day. Rain chances throughout
the Thursday PM through Christmas Eve period will be highest across
northeastern portions of our region, where we`ll be crossing our
fingers for the higher end potential of 1-2" of rain. The best
chances for these more notable rainfall totals will be NE of Austin,
where both the GEFS and EPS suggest 60-70+% chances for >1" by 00Z
on the 25th. No guarantees just yet though.
&&
.AVIATION...
(00Z TAFS)
Issued at 505 PM CST Mon Dec 18 2023
VFR conditions will continue through the period as upper level cloud
cover continues to move in from the west. Light winds generally at
or below 5 kts are expected overnight before increasing to around 10
kts out of the southeast during the day tomorrow (slightly higher
winds for KDRT). The southeasterly winds will bring increasing low-
level moisture, which will likely result in fairly widespread MVFR
cigs for Wednesday morning just beyond the current TAF period.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 42 65 50 70 / 0 0 0 10
Austin Bergstrom Intl Airport 40 67 50 71 / 0 0 0 10
New Braunfels Muni Airport 43 68 51 73 / 0 0 10 10
Burnet Muni Airport 40 64 50 68 / 0 0 0 0
Del Rio Intl Airport 46 68 51 70 / 0 0 0 10
Georgetown Muni Airport 39 65 49 70 / 0 0 0 10
Hondo Muni Airport 44 67 50 71 / 0 0 0 10
San Marcos Muni Airport 41 67 50 72 / 0 0 0 10
La Grange - Fayette Regional 41 66 50 70 / 0 0 0 20
San Antonio Intl Airport 45 67 53 72 / 0 0 10 10
Stinson Muni Airport 45 69 53 74 / 0 0 10 10
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Short-Term...17
Long-Term...KCW
Aviation...Gale
Area Forecast Discussion
National Weather Service Hastings NE
540 PM CST Mon Dec 18 2023
.KEY MESSAGES...
- Mainly (if not completely for most places) dry through at
least Fri night:
Although there is still a slight (20%) chance of some light rain
perhaps catching mainly our extreme southeast coverage area
(CWA) Thursday, the remainder of this time maintains a high-
confidence dry forecast.
- Seasonably-mild conditions persist:
While we are not talking "shorts weather", highs well into the
40s/50s will prevail at least Tues-Sun. With each passing day of
this, we just keep getting more "spoiled" given that
average/"normal" highs are upper 30s-low 40s and average/normal
lows teens (Grand Island has only dropped into the teens TWICE
this month!)
- Breezy Tuesday, but unusually-light (for this time of year)
winds Wed-Fri, adding to the seasonably-mild feel.
- A multi-day (but also still VERY uncertain/somewhat complex)
precipitation event) Sat-Tues, POSSIBLY disrupting mainly
post-Christmas travel:
We have a LONG way to go to pin down finer details, but our
official forecast is littered with precip chances (PoPs)
Saturday-Monday (and later forecasts will likely continue PoPs
into at least Tues Dec. 26). This system currently looks to
bring widespread RAIN during the Sat-Mon AM time frame, but then
with a transition to POSSIBLE snow Monday afternoon/Christmas
Day into Mon night/Christmas night. At least the majority of our
CWA appears on track to pick up at least 0.50" of total precip
from this system.
&&
.DISCUSSION...
Issued at 406 PM CST Mon Dec 18 2023
-- PRIMARY CHANGES IN THIS 7-DAY "FORECAST PACKAGE" VERSUS THE
PREVIOUS (EARLY-AM) ONE:
Honestly, nothing truly major, but the main ones include:
1) The previous, slight (20%) chances for rain within several
of our east-southeast counties for Thurs-Thurs night have been
almost completely removed from our CWA, as confidence continues
growing that at least the vast majority of rain potential with
this system will focus at least slightly off to our south-
through-east. In fact, only parts of Thayer County are still
holding on to any mentionable (20+%) chance of rain at all.
2) PoPs were nudged upward (roughly 10% higher) for much of the
Sat-Mon time frame, with the highest (for now) chances at 60-70%
Sat night-Sunday.
3) High temps for Sunday (Christmas Eve) were nudged up 2-4
degrees...now more coverage of low 50s vs. upper 40s. Although
not a significant change in the grand scheme, this bolsters
confidence that precip type should stay RAIN through at least
Sunday.
-- PRIMARY FORECAST CHALLENGES/UNCERTAINTIES (almost entirely
focused on the Sat-Tues system):
Needless to day, the vast majority of forecast uncertainties
(not to mention the primary focus of the forecast overall) lie
with the Saturday-Monday (and eventually beyond) precip chances.
With the Christmas holiday and related-travel concerns obviously
of concern (for good reason), we`ll be paying particularly close
attention to this system and its trends with each passing day
this week. That being said, we are simply TOO FAR OUT IN TIME
(5-7 days out) to confidently drone on with any particular
degree of great detail. That being said, here are at least the
"latest basics" for now:
1) Timing-wise (and is is oh-so-typical several days out), the
latest GFS is roughly 12 hours sooner than the typically-
preferred ECMWF regarding the initial onset of rain, with the
GFS already bringing in rain Saturday daytime, while the ECMWF
holds off until later Sat night into Sunday. If trends
eventually come around to the ECMWF solution, look for our
Saturday daytime PoPs to be on the decrease.
2) While fairly widespread RAIN is likely especially Sunday into
much of Monday (Christmas), exactly how much and how persistent
(vs. off-and-on) is still fairly uncertain. Among various other
complicating factors, is the uncertainty regarding the exact
manner in which the parent upper level low pressure system
ultimately evolves/tracks into the Central Plains. It will be a
complex evolution for sure, with the main upper low over our
region evolving form the expected phasing/merger of initially-
separate systems (one over the southwestern continental
US/CONUS) and another over the northwest CONUS). Depending on
how this evolves, we could see anything from a fairly modest
(and almost entirely rain-only) event with dry-slotting cutting
down our precip totals (per GFS), or perhaps a more
widespread/significant system with at least 0.50" of rain
followed by roughly a couple of inches of snow favoring Monday
afternoon-Tues AM (which would obviously affect mainly post-
Christmas travel).
3) Focusing solely on ensemble precipitation/snowfall data
regarding this system, and specifically the latest 12Z ECMWF:
- Our CWA stands a 50-70% chance of receiving AT LEAST 0.50" of
total precipitation (generally highest south).
- Most of our CWA is currently only pegged for a 20-40% chance
of receiving AT LEAST 1" of snow (again mainly
Monday/Christmas afternoon into Tuesday), with much higher
(50-70%) chances for at least 1" focused to our west over the
Panhandle and points west. For our CWA, chances for receiving
higher snow totals of 3+" are quite low (only 10-20%, and
mainly just in our west).
4) IF accumulating snow does become an issue especially
Christmas afternoon into the following day (Tues)...as suggested
by the latest 12Z deterministic ECMWF but far from a "sure
thing"...fortunately winds do not appear overly-strong, with
even gusts only topping out around 25 MPH per latest ECMWF
ensemble. In other words, this does not look like a
"powerhouse" system with 50+ MPH gust potential.
With the above points stated, this forecaster is going to call
it "good enough" for now with what can be usefully said
regarding this Sat-Tues system. As always, keep in mind there
is still a LOT of time for things to evolve change, but from a
purely hazardous weather/travel perspective our attention is
currently mainly drawn to Monday (Christmas) afternoon-Tues AM
for POSSIBLE snow issues.
-- SHORTER TERM FORECAST DETAILS FOCUSED SOLELY ON THESE NEXT 36
HOURS (through late Tues night/sunrise Wed):
- Current/recent weather situation as of 3 PM:
Kudos to preceding night shifter for handing over an on-the-
mark high temperature forecast for today, as most of the CWA is
clearly on track to top out in the 39-46 range (warmest far
west-southwest), but with slightly-cooler highs only 36-38
prevailing over some of our mainly far northeast counties. In
the big- picture of the mid-upper levels, water vapor satellite
imagery and short-term model data clearly reveal and expansive
upper ridge (high pressure) dominating much of the CONUS, with
its axis centered roughly north-south through the Rockies. As a
a result, our CWA is on the downstream side of this ridge under
broad northwesterly flow, and well removed from primary low
pressure systems over the: 1) Great Lakes...2) off the Pacific
coast. At the surface, a ridge axis has shifted across our CWA
over the course of the day, with its axis currently centered
over eastern parts of NE/KS. As a result, breezes have made the
gradual switch from north-northwesterly to start the day, to
southerly to end the day. Although our eastern zones (closest to
the ridge axis) still haven`t quite made the transition to
southerly breezes), our western zones are seeing sustained
speeds around 10 MPH with slightly higher gusts. Cloud-wise,
what was largely pristinely-clear skies to to start the day is
steadily giving way to a veil of relatively-thin high cirrus
pushing in from the west.
- This evening-overnight:
For sure, it`s guaranteed dry, with only a fair amount of
passing mid-high level cloud cover drifting over (generally
partly cloudy). At the surface, by far the main feature will be
slightly-breezy southerly winds, with a gradually-tightening
pressure gradient driving sustained speeds 10-15 MPH and some
occasional gusts to around 20 MPH (especially post-midnight).
The combo of the increasing breezes, along with at least thin
higher clouds overhead, makes the temperature forecast a bit
tricky, as this setup often yields lows occurring before or
around midnight, with steady-to-slightly rising temps
thereafter. At any rate, made minimal change to official lows,
with most of the CWA aimed into the 26-30 range. If there is
anything remotely concerning with the late night forecast, it`s
that there is probably a non-zero chance for patchy fog near the
far western fringes of our CWA where winds will become lightest
(5-10 MPH) toward and shortly after sunrise. However, with
latest higher-res visibility forecast from HRRR keeping any
possible fog slightly west of our CWA, have opted against a
formal forecast inclusion at this time.
- Tuesday daytime:
Although not overly-windy by any means, this will nonetheless be
the breeziest day of the week within our CWA (especially our
eastern half). However, it will also be warmer than today, with
most places climbing a good 10+ degrees higher. In the mid-
upper levels, we`ll transition to a flatter/zonal (west-to-east)
flow regime, as the big ridge axis weakens somewhat. Sky-cover
wise, we`ll continue to see passing mid-high level clouds, but
skies still no worse than mostly sunny/partly cloudy. At the
surface, a northeast-southwest oriented trough axis will set up
from north central NE into northwest KS during the day, with its
close proximity to our western zones (especially
Dawson/Gosper/Furnas) allowing south-southwesterly winds to be
lightest there (only 5-15 MPH at most). However, the farther
east one goes (especially east of Highway 281), it will be a
noticeably breezier day within the tighter pressure gradient
out ahead of the trough axis, with sustained south-southwesterly
speeds commonly 15-20 MPH/gusts 20-30 MPH. Temp-wise, kept
highs very similar to previous, ranging from near-50 far east,
low 50s central and mid 50s far west, with extreme western
places (such as Cambridge/Gothenburg) perhaps flirting with 60.
- Tuesday evening-overnight:
Another dry and likely uneventful night. At the surface, winds
will be lighter than tonight, with only a subtle/weak trough
axis sliding through and promoting a shift from mainly
southwesterly breezes pre-midnight to more northerly post-
midnight. Like tonight, there are again subtle hints of at least
patchy fog development, but this time within our east-southeast
zones along the trough axis. However, with the model signal
rather weak and this still 30+ hours away have refrained from a
formal forecast inclusion. Despite the warmer preceding day
(compared to today/tonight) and presence of continued passing
high clouds, the lighter winds (versus tonight) should actually
allow low temps to fall to similar readings as tonight, and have
most of the CWA again aimed 25-30, with any possible lower 20s
most favored in typically-cooler spots (such as Ord).
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 509 PM CST Mon Dec 18 2023
High confidence VFR conditions expected through the period with
just some passing high clouds and good visibilities.
Otherwise...expect southerly winds to increase across the area
overnight...as the departing area of surface high pressure
shifts further southeast and the pressure gradient increases in
its wake. While this will result in steady southerly winds near
12KTS later this evening...winds aloft will increase further,
and expect LLWS to develop from about 19/04Z-19/13Z. Surface
winds will increase further once the sun rises and some mixing
is realized Tuesday morning...with LLWS coming to and end and
those surface winds eventually gusting to near or just above 20
KTS from late morning and into the afternoon hours.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&
$$
DISCUSSION...Pfannkuch
AVIATION...Rossi
Area Forecast Discussion
National Weather Service Morristown TN
815 PM EST Mon Dec 18 2023
...New UPDATE...
.UPDATE...
Issued at 809 PM EST Mon Dec 18 2023
Current radar shows bands of snow showers primarily NE counties,
but some lighter returns further south. Have a few reports of
light accumulations so far in and near SW VA. Will beef up PoPs
across much of the advisory area based on latest trends, but no
changes to amounts. Will also add flurries further south into
portions of the northern Plateau and central Valley. Otherwise,
just some tweaks to temps and dew points with this update.
&&
.SHORT TERM...
(This evening through Tuesday)
Issued at 128 PM EST Mon Dec 18 2023
Key Messages:
1. Still expecting snow in the higher elevations starting late
this afternoon continuing overnight. Snow totals have come down a
bit, but 1-3" totals could be seen in the higher elevations of
the East Tennessee Mountains and SW Virginia. Up to 4 inches
possible on the highest peaks.
2. In the lower elevations of SW Virginia and NE Tennessee, a
rain/snow mix turning to snow is likely late this afternoon and
evening. However, temps will be above freezing when this starts
so the best window for accumulation will be when temps drop around
sunset. A dusting to half an inch is possible.
3. Gusty winds are expected late this afternoon through the
evening, especially in the higher elevations. This could lead to
blowing snow that reduces visibility significantly in the
mountains where gusts of 35 to 45 mph will be possible.
4. Mountain snow will begin to taper off after midnight but some
light accumulations will be possible in the mountains until
daybreak.
Discussion:
This Afternoon through Tonight
A potent shortwave trough is diving into the region this
afternoon. Snow showers or a rain/snow mix is starting to move
into SW Virginia as of 2pm as the trough approaches. Latest
guidance is suggesting that the northwesterly flow at 850 mb won`t
be quite as strong as originally thought. 850 mb winds will begin
to decrease after sunset. This means that the window for snowfall
accumulation may be shorter than originally thought. However,
HRRR has showers moving through SW Virginia and NE Tennessee this
afternoon and evening as temps are dropping below freezing. HRRR
activity drops off around sunset. So snow showers are still
possible but accumulation will be light (0.5 inch or less) in the
lower elevations where temps will be above freezing this
afternoon, so the window for accumulation will be around sunset.
In the higher elevation`s of the East Tennessee and SW Virginia
mountains snow totals have come down a bit due to the shorter
window for snow but 1 to 3 inches can generally be expected above
2500 feet. The highest peaks could see 4 inches. After midnight
snow will begin to taper off as the 850mb jet weakens but some
light accumulations may continue until sunrise. Strong
northwesterly winds are still expected through this evening,
mainly in the higher elevations with gusts up to 40 or 45 mph
possible late this afternoon through midnight. After midnight
winds will begin to decrease. Blowing snow in the higher
elevations may reduce visibility significantly, making driving
dangerous at times. Wind chills will be very cold tonight in the
teens throughout the Tennessee Valley.
Tomorrow
All precip will be over by tomorrow morning as the 850 flow
decreases and the trough makes its way eastward. Highs will be in
the upper 30s and lower 40s but there will be plenty of sunshine
and winds will be light tomorrow.
&&
.LONG TERM...
(Tuesday night through next Monday)
Issued at 128 PM EST Mon Dec 18 2023
Key Messages:
1. Dry weather and moderating temperatures Wednesday through
Saturday.
2. For the Christmas Eve to Christmas Day timeframe, above normal
temperatures are expected, along with increasing rain chances.
Discussion:
Quiet weather is expected from Wednesday through at least the first
half of the weekend. Surface ridging will be in control beginning
Wednesday and continuing through Friday as high pressure anchors
over the Appalachians keeping conditions dry with moderating
temperatures. Temperatures on Wednesday will be just slightly below
normal, but by Thursday we should be back to normal.
Friday and into Saturday, upper level troughing develops out west as
a weak shortwave propagates through the midwest. Conditions are
expected to remain dry, although an increase in cloud cover may
accompany this wave. For the latter part of the weekend and
Christmas Day, guidance favors a more active pattern with the low
out west moving into the plains increasing chances across the entire
area. Temperatures will also be on the increase within the warm air
advection regime with above normal temperatures expected.
&&
.AVIATION...
(00Z TAFS)
Issued at 540 PM EST Mon Dec 18 2023
Scattered snow showers around at TRI briefly to start, with some
brief MVFR conditions likely. Otherwise, there will be low VFR
cigs for a period early in the period at TYS and TRI, but these
will clear out later tonight and CHA will be mostly clear and VFR
for the period. Gusty west and northwest winds to start will
gradually diminish overnight.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 25 43 27 51 / 0 0 0 0
Knoxville McGhee Tyson Airport, TN 23 39 24 49 / 10 0 0 0
Oak Ridge, TN 22 41 23 48 / 10 0 0 0
Tri Cities Airport, TN 21 37 21 49 / 30 0 0 0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Winter Weather Advisory until 7 AM EST Tuesday for Blount Smoky
Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky
Mountains-Southeast Carter-Southeast Greene-Southeast
Monroe-Unicoi.
VA...Winter Weather Advisory until 7 AM EST Tuesday for Lee-Russell-
Washington VA-Wise.
&&
$$
SHORT TERM...McD
LONG TERM....Diegan
AVIATION...
Area Forecast Discussion
National Weather Service Pittsburgh PA
936 PM EST Mon Dec 18 2023
.SYNOPSIS...
Upper level low pressure and cold northwest flow will produce
widespread snow showers through tonight. A few snow squalls are
also possible during the late afternoon and evening. The
heaviest accumulation is expected across the higher terrain of
Pennsylvania and West Virginia. Snow showers will taper off late
tonight and Tuesday as high pressure begins to build across the
region.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Current conditions show the last of another round of snow
showers exiting the area to the east. This will bring a reprieve
to the snow showers and squall potential. Upstream into NE OH,
another round is slowly pushing southeast from CLE`s area. This
area is causing some vis to drop below a mile and even a half
mile in some spots. Expect this to move into the area within the
next hour or so. Concerns then turn to around the 04Z - 06Z
time frame when a strong band is expected to develop and dive
southeast across Mercer/Venango areas. This band will need
watched for the potential of warning level snows. So far, road
temperatures have not been a concern and have only recently
begun dropping below freezing.
Previous discussion...Key Messages:
* Convective snow showers will continue through the night, with
greatest accumulations north of I-80 and in the Laurel
Highlands/WV ridges.
* A few snow squalls possible later tonight.
* Wind gusts of 30-40 MPH through tonight may contribute to
visibility and blowing snow concerns.
The main shortwave trough is currently centered over the lower
Michigan peninsula, taking on a negative tilt. Convective
showers are ongoing across the region in the cold advection
pattern. The changeover to snow will complete across the region
over the next couple of hours, coincident with the arrival of
850mb temperatures of -7C to -8C and sufficient moisture in the
dendritic growth zone. Snow showers will continue to increase
in coverage over the next few hours as the shortwave arrives and
as low-level flow veers to a more northwesterly direction. All
locations in the CWA will be impacted by snow tonight, but
coverage, intensity, and accumulation will be best in location
subject to lake enhancement (north of I-80) and upslope
enhancement (Laurel Highlands/WV ridges). A reinforcing cold
front/surface trough will bring 850mb temperatures solidly down
into the -10 to 12C range tonight.
The potential for heavy snow showers and even snow squalls
remains for the overnight. The main limiting factor to this
being more of a classic setup will be the relatively slow cold
advection tonight, as opposed to a true arctic frontal passage
with its burst of low-level frontogenesis. Also, without that
rapid coalton, flash freeze potential is low for this event.
Nevertheless, model soundings continue to show a period this
evening with saturation and steep lapse rates right through the
DGZ. The potential for 30 to 40 MPH gusts will remain as well
with the excellent mixing and tight surface pressure gradient,
perhaps as high as 45 MPH or so in the most extreme cases. Thus,
there is the potential for numerous snow showers that will
reduce visibility to less than one-half mile at times, producing
brief 1+ inch snow rates. The relatively warm ground/road
temperatures at the start will limit accumulation where snow
rates remain lower, but impacts to roads this evening are
expected. If a more concentrated area of high- impact heavier
snow showers develops, Snow Squall Warnings may be needed, with
Special Weather Statements otherwise used. Will also add blowing
snow wording to the warned ridge zones where strong winds will
be most persistent.
The storm total accumulation forecast has not changed
appreciably from the previous forecast, and the current headline
structure will remain unchanged for now. Still have expectations
of 6-12 inches in the Winter Storm Warning area. One area to
monitor will be portions of Venango and especially Mercer
Counties. Hi-res models like the HRRR and NamNest have been
hinting at a main lake effect band in this general vicinity that
could locally enhance snow totals. NBM probabilities of 6+
inches have increased into the 50 to 80 percent range for both
counties. Did sharpen the accumulation gradient in response,
with up to 7 inches possible in the "most likely" deterministic
forecast. Confidence is not quite high enough for an upgrade to
a warning here yet, but will alert future shift to consider this
if a persistent band does in fact set up.
After 06Z, snow shower coverage will begin to wane in eastern
Ohio as the shortwave departs this region, but numerous snow
showers will keep going during the predawn hours otherwise,
especially in the lake-effect/upslope areas. With temperatures
dipping into the lower and mid 20s and the wind, wind chill
values will dip into the single digits in the ridges and into
the teens in most other areas.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY NIGHT/...
Key Messages:
* Snow showers end Tuesday
* Quiet weather under high pressure thereafter
The shortwave trough axis will have swung across the ridges by 12Z
Tuesday. Still, scattered to numerous snow showers will continue
during the morning with ongoing NW flow and sufficient moisture, so
impacts to the Tuesday morning commute will likely occur.
Coverage will taper off through the daytime hours as moisture in the
dendritic growth zone decreases and as the subsidence inversion
lowers. Increasing surface ridging will also help to back low-level
flow to more of a westerly direction, cutting off access to Lake
Erie. At this time, expectations are that most, if not all, snow
will cut off by sunset. Temperatures will remain some 10 degrees
below normal for daytime highs.
The surface high will then park itself across the Upper Ohio Valley
through Wednesday night, leading to dry weather from Tuesday night
on. Rising 500mb heights in the wake of the departing trough will
allow temperature moderation towards climatology on Wednesday.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
Key Messages:
* No major storms through the period
* Near to above average temperatures expected
Quasi-zonal flow aloft holds on through Friday as the surface high
lingers across New England. Dry weather and seasonable temperature
remain in the forecast for our region. A weak crossing shortwave in
the flow should result in limited light rain or snow chances Friday
night into early Saturday. Flat ridging is then expected to build
across the much of the Eastern CONUS through Christmas Day, with
more dry weather and a return to above-normal temperature. Chances
of a white Christmas look rather dim at this distance.
&&
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Ongoing snow shower activity will continue through the remainder
of this evening. Area terminals will bounce between VFR/MVFR
conditions outside of showers to IFR/LIFR in showers. Winds
remain breezy and out of the west, around 10-15 knots gusting to
20-25 knots.
Cold advection will persist overnight within NW flow while
subsidence aloft develops west of the region. Expect a downtrend
in areal coverage of snow showers, but development of enhanced
lake bands that could feature periods of 1"/hr snowfall
accumulations near FKL (roughly 30 percent probability of
occurrence between 04z-09z). Otherwise, cold advection and
subsidence inversion will foster widespread MVFR cigs overnight.
Rising pressure heights and building surface high pressure will
erode remaining snow showers and clear MVFR restrictions from
west to east on Tuesday.
.OUTLOOK...
There is a high probability for VFR conditions and dry weather
starting Tuesday night through Friday before the next potential
low pressure system approaches the region.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 10 AM EST Tuesday for PAZ007>009-
015-016-078.
Winter Storm Warning until 10 AM EST Tuesday for PAZ074-076.
OH...None.
WV...Winter Weather Advisory until 10 AM EST Tuesday for WVZ510-511.
Winter Storm Warning until 10 AM EST Tuesday for WVZ512>514.
&&
$$
SYNOPSIS...CL
NEAR TERM...CL/Shallenberger
SHORT TERM...CL
LONG TERM...CL
AVIATION...Cermak/Frazier