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FXUS61 KCTP 260308 AFDCTP

Area Forecast Discussion National Weather Service State College PA 1108 PM EDT Thu Apr 25 2024

SYNOPSIS
High pressure will provide dry cool and dry conditions with widespread frost and freeze conditions expected Friday morning.
Clouds will increase late Friday leading to a chance of showers Friday night and into the weekend before it turns much warmer for Sunday and even warmer still for most of next week.

NEAR TERM /UNTIL 7 AM FRIDAY MORNING/
The thicker of the high clouds are slipping to the SE and revealing only a small patch of lower clouds in Somerset/Bedford. However, lots of guidance expands this patch of clouds through the night with help from the gently upsloping SSE flow. Overall, the current forecast covers this. Now, the temps are trailing the forecast dip by a few degs. The dewpoints are still very low across the nrn half of the CWA
That should allow them to catch up. The main trouble with temps right now is the SE where temps are the clouds have just dissipated/left and there was recently a 20KT gust at LNS.
Dewpoints there are still in the u30s. But, we expect the temps in the SE to get back on track shortly as the pressure gradient relaxes. Will continue to hold all the frost/freeze flags as is.
There is the potential for some AM fog in the SE, too, with those higher dewpoints. Lack of recent rainfall is a negative for fog, though.

SHORT TERM /7 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
Friday will be another fair day under the influence of retreating high pressure, with return flow freshening over western areas, and especially the Laurel Highlands. Rain free wx conditions will continue with morning sun mixing with high clouds throughout the day and max temps trending warmer into the upper 50s to lower 60s. Showers along a warm front are likely to move into the western Alleghenies very late Fri night or early Saturday morning based on the latest operational model/ens consensus.

LONG TERM /SATURDAY THROUGH THURSDAY/
An approaching warm front will result in a cloudy and relatively cool Saturday, with a chance of showers accompanying the passage of a weakening low level jet. Weak large scale forcing under an upper level ridge should result in minimal rainfall. Most likely rainfall by Sat PM based on ensemble plumes ranges from around 0.2 inches over the N Mtns, to just a few hundreths over the southeast counties. Brightening skies and markedly warmer conditions appear likely Sunday, as the warm front lifts north of the region. However, ensemble plumes indicate scattered PM convection is possible, especially over the N Mtns, where progged pwats are highest and temps aloft coolest.

Fair and unseasonably warm weather is likely Monday, as anomalous upper level ridge crests over the state. Mean 850mb temps near 15C supports max temps in the low to mid 80s. All medium range guidance points to a good chance of PM convection Tuesday associated with the passage of a mid level shortwave.

Diverging model solutions and greater uncertainty then creep into the forecast the second half of next week. Upper level ridging and above average temperatures look very likely.
However, timing differences exist with regard to an upstream trough and associated cold front late next week. Expect a widespread round of convection to accompany the front either Thu PM or Friday.

AVIATION /03Z FRIDAY THROUGH TUESDAY/
High pressure passing north of PA will provide most of Central PA with VFR conditions and light winds tonight. However, lingering low level moisture could potentially result in a period of low cigs/fog across parts of Southern PA around dawn. Current model guidance indicates the odds of reductions are relatively low (<25pct) at AOO, MDT and LNS. However, model soundings and ensemble prob charts support a >50pct chance of MVFR cigs at JST and even ~25pct chance of IFR cigs around dawn.

The threat of low clouds/fog will diminish Friday, as drier air mixes to ground level. However, ensemble prob charts suggest an upsloping southeast flow could potentially result in lingering MVFR cigs across the high terrain of Somerset County through the afternoon.

Outlook...

Sat...Scattered shra. IFR cigs possible Central Mtns.

Sun...AM low cigs possible, mainly N Mtns. Isold PM tsra possible.

Mon...No sig wx expected.

Tue...Sct PM tsra impacts possible.

FIRE WEATHER
Fuel moisture may fall below 10% over the next two days. With light winds today, the risk of fire spread remains very low.
However, return flow around departing high pressure on Friday may increase the potential for spread on Friday afternoon.

MinRH this afternoon (Thu) is forecast to drop to 15-25% over the northern half of the area with potential downside to 10%.
MinRH over the southern tier districts along the MD line is forecast between 30-40%. The wind will <10 mph from the north/northeast.

MinRH is forecast to recover a bit Friday afternoon bottoming in the 25-40% range. However, the wind will increase from the south southeast with gusts to 20 mph at times over the higher terrain along the southern Allegheny Plateau.

Increasing low level moisture/dewpoints along with some rain will limit fire weather concerns this weekend.

CTP WATCHES/WARNINGS/ADVISORIES
Freeze Warning from 2 AM to 8 AM EDT Friday for PAZ004-005-010- 011-017-018.
Frost Advisory from 2 AM to 8 AM EDT Friday for PAZ019-024>028- 045-046-049>053-056-057-059-063-065-066.

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