PBZ issues Area Forecast Discussion (AFD) at Nov 12, 7:35 PM EST086
FXUS61 KPBZ 130035
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
735 PM EST Tue Nov 12 2024
.SYNOPSIS...
Large polar high pressure will push across Quebec tonight bringing a
clear and seasonably cold night to the Upper Ohio River Valley. Low
pressure over the northern Plains will push into the middle
Mississippi Valley late Wednesday and the Ohio River Valley
Thursday, bringing another period of rain to the region.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
KEY MESSAGES:
- Clear and cold tonight.
------------------------------------------------------------------
Forecast remains on track. Dew points are currently lower than
the prior forecast package. The new update tracks this change
and nudged temperatures down accordingly tonight with greater
potential to cool. Low temperatures tonight may vary a good bit
with terrain, but lows in the mid 20s to low 30s are still a
good bet for most.
.. Previous Discussion..
Winds should drop off quickly around sunset and wind sheltered
spots should crater pretty fast. Good shot at 20s in most
locations, with lower 30s in the Pittsburgh urban heat island.
Lower 20s and perhaps even some upper teens may be seen in the
northern third of forecast area.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
KEY MESSAGES:
- Dry and seasonable Wednesday.
- Rain likely Thursday, potentially lingering through Friday.
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Sharp upper ridge moves overhead Wednesday with a dry airmass.
Despite a cold start temperatures should climb into the 50s with a
decent amount of morning sun before the high clouds start to spread
in late in the day.
Surface low heads into MO by Wednesday evening and heads for the
Chicago area by early Thursday before crossing IN and OH Thursday.
500 mb height falls are shown to fall Wednesday night by about 100
meters and then another 100 meters during the day Thursday.
Confidence on the evolution of this upper trough is fairly high,
though there are some minor timing differences shown in the global
ensembles that could impact the precipitation type over the ridges
early Thursday (see next paragraph). Decent warm advection appears
likely along with moisture transport from the Gulf of Mexico,
resulting in another period of welcome rains. Probability of 48 hour
QPF exceeding 0.10" is nearly 100%. The 25th to 75th percentile 48
hour QPF ranges from about 0.30 to 0.60" in the Pittsburgh area.
While most of the precipitation is likely to fall during the day
Thursday, lingering light rains are possible Thursday night into
Friday.
While most of this event will be rain, there is a window
especially for eastern Preston and eastern Tucker County WV
where the precipitation may arrive as freezing rain or snow late
Wednesday night or Thursday morning. Tds are likely to be in the
teens and 20s with temperatures near freezing, resulting in wet
bulb cooling as the precipitation arrives. NBM Probability of
freezing rain is in the 20-50% range from roughly 4-10 am
Thursday morning especially in far eastern Tucker County.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
KEY MESSAGES:
- Highs a few degrees above normal for the weekend.
-------------------------------------------------------------------
A high amplitude pattern is shown to continue over the weekend
into early next week. Ensemble cluster analysis indicates that
the primary issue will be timing of the upper ridge spreading
east into Great Lakes and Ohio Valley Saturday due to a low
moving and deep low near Nova Scotia. Readings may well be near
normal on Saturday if the trough hangs on a bit longer to the
east.
Most of the ensemble guidance has the upper ridge overhead by
Sunday, suggesting highs about 5F above normal. Primary
uncertainty is related to the details of a trough lifting
northeast out of the northern Plains towards the Great Lakes,
and a potential short wave trough digging into base of western
Atlantic trough near New England. Neither of these features
would impact our area much other then minor differences in
temperatures.
Uncertainty begins to increase significantly by Monday and
Tuesday. While many of the global ensemble members keep a
somewhat flattened ridge overhead with mild weather continuing,
a significant number of ECMWFE members dig the Great Lakes
trough southeast and lower the heights across area. The NBM 10th
to 90th percentiles show this range of possibilities well,
ranging from middle 60s/10F above normal with the ridge
remaining in place, and near normal and lower 50s if the trough
digs southeast per subset of ECMWFE members.
Potential exits for a short wave trough to eject out of the
central US long wave trough position on Monday and potentially
be in the Middle Mississippi River Valley. Ensembles have
tendency to build the ridge downstream of this feature into the
Great Lakes and Ohio River Valley, which would keep readings
above normal (per the NBM 90th percentile MaxT in the mid to upper
60s Monday and Tuesday). While the ejecting and weakening trough
could bring showers around Tuesday to the area, it appears that
significant rain chances will be slow to move east from the
central US as the ensembles hint at a blocking pattern with long
wave trough remaining anchored somewhere near NM to TX area.
&&
.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
High-confidence VFR forecast over the next 24 hours. A 500mb
ridge axis will cross the Great Lakes tonight and the Upper Ohio
Valley tomorrow, leading to generally quiet weather. High clouds
will begin to thicken tomorrow afternoon in the southwest flow
behind the ridge axis and ahead of the next Upper Midwest
shortwave.
After light wind tonight, surface high pressure crossing across
Quebec will create an east or southeast wind at the surface once
the morning inversion breaks. A slowly tightening pressure
gradient and sufficient mixing may yield some 15 to 20 knot
gusts during the afternoon.
.Outlook...
Cloud bases will gradually lower Wednesday night. Rain then
overspreads the region Thursday morning ahead of a warm front.
Restriction potential likewise begins to increase, with
probabilities for MVFR ceilings exceeding 50% at ZZV by 13Z
Thursday and at DUJ/MGW by 16Z. Guidance suggests high
confidence (70-90% chance) in areawide MVFR ceilings from around
16Z Thursday through at least Friday morning. Probabilities for
IFR through that time are generally lower but still notable, at
around 40-60% with the greatest focus near and north of PIT.
The low exits to the east Friday morning, though residual cold
advection in NW flow may maintain restriction potential
through the day Friday as guidance still indicates a 40-60%
chance for MVFR ceilings lasting through at least 19Z. Expect
VFR to return by Saturday under building high pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Craven
NEAR TERM...Craven/Milcarek
SHORT TERM...Craven
LONG TERM...Craven
AVIATION...Cermak
Source:
PBZ issues Area Forecast Discussion (AFD) at Nov 12, 7:35 PM EST---------------
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