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FXUS61 KPBZ 260046 AFDPBZ

Area Forecast Discussion National Weather Service Pittsburgh PA 846 PM EDT Thu Apr 25 2024

SYNOPSIS
Mostly dry weather and a warming trend is expected through Monday save chances of isolates showers or storms Saturday and Sunday afternoon.

NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
KEY MESSAGES:

- Freeze warnings and frost advisories are in effect for portions of the area, beginning at midnight.

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Surface ridging remains in control, but high pressure will slowly drift into New England tonight, maintaining a weak pressure gradient over the Upper Ohio Valley. Most of the cumulus/stratocumulus from earlier has dissipated, but high clouds associated with a 500mb shortwave are traversing the region this evening. These clouds are progged to largely vacate the region overnight. Upstream cirrus will largely remain off to the west according to the HRRR, and a mostly clear overnight period is anticipated.

No changes to frost/freeze headlines for now. If anything, potential looks a touch lower, as 19Z NBM dropped the probabilities of 32/36 degrees slightly, and temperatures were running a touch warmer than anticipated during the evening.
Temp/dewpoint spreads also remain fairly wide and wind has yet to decouple, bringing chances of dew formation a little bit more into doubt. Nevertheless, low temperatures will end up some 5 to 10 degrees below climatology.

SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/
KEY MESSAGES:

- Dry and warmer through Friday - Showers and possible thunderstorms return Friday night into Saturday with a warm front

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The surface high pressure will migrate to the east for Friday, with mostly clear skies for much of the daytime hours. As surface southeast flow accelerates with pressure gradient increases, temperatures will bounce above normal once again.

Friday evening and overnight, clouds will increase as cirrus decks advect overhead. Thereafter, a warm front will progress through. Precipitation timing and amounts have trended slower and lower since the last update. Fumes of elevated instability are possible, thus a rumble of thunder could not be ruled out as it passes through Saturday morning. Even the 90th percentile is only around 0.25 inches of QPF.

A moisture and temperature push is expected behind the warm front, with a chance of isolated afternoon showers and/or thunderstorms. Precipitation chances taper overnight. Because of the passing warm front from the west, daytime highs will range from above average in eastern Ohio to near/below average in central Pennsylvania.

LONG TERM /SUNDAY THROUGH THURSDAY/
KEY MESSAGES:

- Warm with minimal chances of afternoon thunderstorms Sunday and Monday.
- More widespread showers and possible thunderstorms with a Tuesday cold front.
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Model ensembles continue to indicate the strongest riding across the Upper Ohio Valley region Sunday and Monday. Sunday should be mainly dry under the ridge, with warm air aloft limiting convective potential. Still, an isolated afternoon storm or two is possible, mainly north of Pittsburgh, where another vort max moves across southern Ontario on the northern periphery of the ridge.

Similar conditions are expected Monday. The ridge axis is expected to shift slowly eastward later Monday, with slightly better chances for afternoon showers and thunderstorms late in the day as a shortwave trough and associated surface cold front begin to approach from the Midwest.

Temperatures mainly in the 80-85 degree range (outside of the higher terrain) are expected Sunday and Monday with a 1000-500 mb height of 582 dm, and 850 mb temperatures ranging from 12-14 deg C. Cooler, but still above average, temperatures should return Tuesday behind the front.

Showers are likely, along with a few thunderstorms, on Tuesday as the trough and cold front cross the region. The precipitation should end Tuesday night as the front exits.

By Wednesday, one thing is more certain; the ridge amplitude will decrease. Clustered variability of the 500mb pattern sits anywhere between a weak 500mb trough to a weak 500mb ridge. This ridge breakdown may lean towards more unsettled weather.

Late next week, a central CONUS ridge may develop (shown in 3 out of 4 clusters). Should it develop, it is favored to move east (as shown in 2 out of 3 clusters) and allow warmer-than- normal temperatures to continue through next weekend. Some alternate scenarios include 1) the ridge not developing, whereby temperature would remain closer to normal in zonal flow and 2) the ridge develops but does not move east and enforces eastern troughing, which would keep temperatures below normal.

AVIATION /01Z FRIDAY THROUGH TUESDAY/
Daytime stratocu/cu development has mostly dissipated this evening with loss of daytime heating and intrusion of drier low level air. The rest of the night should feature just a few cirrus but otherwise SKC with decoupling allowing wind to remain 5 mph or less generally out of the northeast.

VFR continues with high confidence on Friday, though wind will pick up to around 10 knots as a building gradient veers direction more to the southeast through the afternoon. A few diurnal cumulus may dot the sky as convective temperatures are achieved. Upper cloud cover will increase late Friday afternoon as moisture advects in ahead of an approaching warm front that will bring showers into the area beginning overnight Friday night.

Outlook
The probability of showers and isolated thunderstorms increases Friday night into Saturday which will come with increasing probabilities for restrictions as well. Latest ensemble guidance increases MVFR CIG probabilities to 50-60% by Saturday afternoon.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...Frost Advisory from midnight tonight to 9 AM EDT Friday for PAZ007-013-014-020-022-077-078.
Freeze Warning from midnight tonight to 9 AM EDT Friday for PAZ008-009-015-016.
OH...Frost Advisory from midnight tonight to 9 AM EDT Friday for OHZ039>041-048>050-057>059-068-069.
WV...Frost Advisory from midnight tonight to 9 AM EDT Friday for WVZ001.

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