PBZ issues Area Forecast Discussion (AFD) at Nov 29, 3:30 PM EST286
FXUS61 KPBZ 292030
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
330 PM EST Fri Nov 29 2024
.SYNOPSIS...
Snow showers will continue through the evening, with the
greatest chance for some accumulation north of I-80 and in the
ridges. A prolonged cold period sets in with occasional snow
shower chances likely through the beginning of December.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
KEY MESSAGES:
- Snow showers with brief visibility restrictions possible
through the evening.
- Minor accumulations with upslope snow in the ridges and lake
effect north of I-80.
-------------------------------------------------------------------
Snow showers will continue this afternoon as a shortwave pivots
through the upper trough. While lapse rates will be steepening
with strengthening cold advection, the lack of deep moisture due
to an unfavorable wind direction should temper efficient
snowfall. A few convective pulses are noted on radar, which is
supported by some marginal SBCape from ACARS soundings, but
generally expect accumulation to be quite minimal. This is also
the case in the terrain where upslope will support snow
generation but moisture in the DGZ is lacking. Still, models do
suggest a few inches of accumulation there through tonight.
Latest HREF still projects a 60% chance of >2" through midnight.
The prominent lake band off of Lake Erie will generally remain north
of the region through the period. There is a brief window this
evening with the departure of the aforementioned shortwave, that the
band could sink far enough south to reach the northern portions of
Mercer, Venango, and Forest. This is noted in some of the hi res
guidance this afternoon, but even if this does materialize, the
window is rather small, which should limit accumulation.
The more notable impact will be wind gusts and wind chill values
tonight into Saturday morning. Wind gusts of 30-35mph (and higher
gusts in the terrain to near 45mph) will bring wind chill values
into the single digits through Saturday morning. Latest ensemble
probabilities suggest >60% chance of wind chills below 0 in the
higher elevations, with the highest ridge tops potentially
approaching -10.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
- Well below-normal temperatures for the weekend, with near-zero
wind chills Saturday and Sunday morning.
- Clipper system will bring snow to the region south of
Pittsburgh Sunday
-------------------------------------------------------------------
Broad 500 mb trough will remain the in place through the rest of the
weekend, though height rises are expected Saturday with surface
ridge nudging into the upper Ohio valley. Even with the potential
for sunshine, the probability of highs above freezing is around
10- 40% (highest over east central Ohio).
The next system will approach on Sunday, which is a fast moving
clipper-type system moving through the base of the trough. At this
time, the best lift is progged south of Pittsburgh with upslope
continuing with the systems passage. While deep moisture through the
DGZ will be present, the fast track of the system should be a
limiter on accumulation. At this juncture, the NBM had the
probability of greater than 3.0" around 40% through Monday
morning. Will continue to monitor the trend in this system as
some guidance suggests a stronger system than others.
Kept the temperatures for the weekend period below the deterministic
NBM due to its warm bias as we enter the cold season. Steep lapse
rates will promote continued mixing of wind gusts with a 60-80%
chance of >30 mph gusts Saturday relaxing some on Sunday.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Much colder temperatures remain into next week.
- Rounds of shortwaves maintain snow chances.
-------------------------------------------------------------------
Eastern CONUS troughing will generally prevail during the long
term, with some flattening possible midweek before additional
shortwaves dig the trough across the NE for the end of the week.
With a more northwesterly component to the wind by late Monday,
some lake enhanced snows may be possible across the region
through Tuesday. This will be followed quickly on the heels of a
reinforcement in the trough by a low pressure system Wednesday
into Thursday. There are differences in the strength and timing
of the system during that time frame which could lead to some
precipitation type challenges. After that system, yet another
push of cold air is expected with lake enhanced snow showers to
end the week.
At this time, temperatures look to remain below seasonal
averages for the entire period, with the brief "warm up"
happening mid week before we once again struggle to go above
freezing.
&&
.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Persistent cold advection plus additional shortwave movement is
expected to promote isolated to scattered snow showers mainly
through 23z; confidence on heavier showers impacting terminals
is low but would have potential for brief reductions of
visibility to less than 2 miles. Best chances for accumulating
snow favor areas north of FKL/DUJ and the higher terrain east of
LBE/MGW. Little variation is expected in cloud heights through
this period, hovering around 4kft with occasional drops to 2kft
in snow showers. Steeper lapse rates and residual pressure
gradients will support gusty winds through 03z out of the west,
occasionally reaching 25-30kts.
Loss of deeper mixing and weak subsidence will erode snow
showers for most locations aft 00z while area wind lowers
slightly overnight. Dry advection and subsidence is expected to
erode stratocu though there is uncertainty in the timing of
said SW to NE erosion; TAFs lean toward climatology and slower
erosion but scenarios exist for scattering to occur as 02z
tonight.
Outlook...
VFR and breaks in clouds is favored Saturday before the next
shortwave within eastern CONUS troughing will support low VFR to
MVFR cigs and areas of light snow Sunday morning.
Periodic shortwave movement through the week may also provide
additional snowfall and restrictions chances to the region,
favoring northwest PA and the higher terrain.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...34
NEAR TERM...34
SHORT TERM...34
LONG TERM...34/MLB
AVIATION...Frazier
Source:
PBZ issues Area Forecast Discussion (AFD) at Nov 29, 3:30 PM EST---------------
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