Sunrise 6:24 AM   Sunset 8:11 PM Moonrise 9:21 PM   Moonset 6:02 AM

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FXUS61 KPBZ 252143 AFDPBZ

Area Forecast Discussion National Weather Service Pittsburgh PA 543 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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Made some minor adjustments to sky cover and hourly temps/dewpoints for the next several hours, but there have been no major changes to the forecast thinking. Clouds have become more cellular and have started to dissipate as diurnal heating and mixing start to decrease. The overnight temperature forecast remains the same for now, and will reevaluate over the next few hours whether frost/freeze headlines need any adjustments.

Previous discussion...

Mundane weather will persist as the area sits underneath a subsidence inversion in a weak pressure gradient. For this reason, winds are expected to remain calm to light through the near term.

A weak 850mb meso-low has been observed across southwest Pennsylvania, allowing weak low-level convergence and moisture pooling in the area just south of I-80. This has allowed stratocumulus decks to persist for much of the day as mixing has attempted to erode them. The current thinking is that most cumulus will dissolve with sunset, but patches of stratocumulus may linger in the aforementioned area overnight. Low- probability clouds are also possible in the Laurels with upsloping.

Areas that are clear at this point will likely remain clear and there is a high probability that low temperatures tonight will under-perform guidance, thus, adjusted towards the NBM 10th percentile with calm winds. Should clouds linger a bit longer, temperature will likely run higher than the forecast.

Frost advisories were hoisted based on the areal extent of 36 degrees or lower across a forecast zone after adjusting nocturnal temperatures down. The same goes for freeze warnings; there is a high probability of a freeze for Forest, and a moderate probability of a freeze for Venango, Clarion, and Jefferson PA. In these zones, calm winds and clear skies are high probability.

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 /22Z THURSDAY THROUGH TUESDAY/
Stratocumulus continues across a significant portion of the forecast area early this afternoon while ceilings have generally lifted to low-end VFR (3-5kft). Some erosion is beginning to take place along the southern border of this cloud deck per latest visible satellite imagery as MGW/ZZV have scattered out to mostly sunny skies. This trend should continue through the rest of the day with most of these clouds clearing by late evening, though some patches of scattered/broken coverage may linger into overnight hours. Winds are light across the area and should remain that way through the night before a strengthening and better established southeast flow sets up after 12Z Friday.

Outlook
VFR conditions are expected Thursday and Friday.

The probability of showers and isolated thunderstorms increases Friday night into Saturday which will come with increasing probabilities for restrictions as well.

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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