PBZ issues Area Forecast Discussion (AFD) at Nov 13, 7:34 PM EST286
FXUS61 KPBZ 140034 AAA
AFDPBZ
Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
734 PM EST Wed Nov 13 2024
.SYNOPSIS...
A front will approach late tonight bringing showers to the
region on Thursday. A drying trend begins Friday and continues
through Saturday.
&&
.NEAR TERM /THROUGH THURSDAY/...
KEY MESSAGES:
- Dry weather continues through this evening.
- Chances for showers increase late tonight over Ohio.
- Beneficial showers on Thursday.
------------------------------------------------------------------
A very dry 00Z sounding at PIT has prompted the slowing of PoPs
late tonight. This is also supported by a later onset of
measurable rainfall in the latest run of the hires models. Have
updated the overnight PoPs to reflect this. Overnight QPF has
also been trimmed back. Rest of the forecast is in good shape.
Previous discussion...
Low pressure will gradually approach from the west on Thursday
with precipitation (rain) ongoing across much of the region. In
terms of QPF amounts...most area basins will see between 0.25 to
0.50 of an inch, with up to 0.75 in spots. Otherwise...expect
breezy conditions with gusts up to 30 mph and temps in the 40s
to low 50s.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/...
KEY MESSAGES:
- Widespread showers taper off Thursday night.
- Drying trend begins Friday and last into this weekend.
-------------------------------------------------------------------
Lingering rain showers will persist into Thursday night as the mid-
level low moves overhead and eventually southeast of the area into
the Mid-Atlantic by Friday morning. 500mb height rises are expected
in the wake of this system Friday with drier weather expected as
surface high pressure builds across the Great Lakes and Ohio River
valley into Friday night. Temperatures Friday afternoon will recover
to slightly above normal for mid-November with highs mainly in the
50s. However, with northwest flow aloft and lingering low-level
moisture, could see a few lake showers remain across western PA
Friday night before drier air arrives. Little accumulation is
expected with latest NBM probability of exceeding a tenth of
accumulation remaining >5%.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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 THURSDAY THROUGH MONDAY/...
VFR prevails at all area terminals as cirrus continues to stream in
ahead of a disturbance moving in from the west. The nose of a LLJ
will poke through the region overnight and then slowly lose strength
as we move into the morning hours. At this time LLWS has been
included in the forecast for FKL and LBE. There could be marginal
LLWS conditions at other area terminals as well but due to lower
confidence and a shorter duration of these conditions, it has not
been included.
ZZV will be the first VFR domino to fall as a swath of rain riding
ahead of a dying warm front presses across the region from SW to NE
beginning Thursday morning in the west. Significant dry air in place
at low levels will act to initially slow CIG and VIS drops, but most
area terminals are expected to slip to MVFR within 2 hours of rain
beginning. IFR will follow quickly on the heels of MVFR but a slip
to LIFR is not guaranteed at this time. Latest guidance shows
between a 30-50% chance for CIGs to drop lower than 1000 feet by 18z
Thursday.
Outlook...
Our upper level trough begins to shift ESE and lose steam late
Thursday night into early Friday morning. Lingering cold air
advection and NW flow into Friday afternoon looks to favor prolonged
MVFR conditions. Latest guidance supports this and shows between a
60-70% chance for CIGs <3kft to still be in place Friday evening.
High pressure begins to filter back into the area Friday night into
Saturday morning. This will help to push any straggling area
terminals back to VFR conditions by Saturday afternoon.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...Red Flag Warning until 8 PM EST this evening for WVZ514.
&&
$$
SYNOPSIS...22
NEAR TERM...22/Shallenberger
SHORT TERM...Shallenberger
LONG TERM...Craven/Shallenberger
AVIATION...AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Nov 13, 7:34 PM EST---------------
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