textproduct: State College

WHAT HAS CHANGED

* Dense fog advisory until 10 AM for Schuylkill Co. * Added mention of isolated rain chances along the cold front this afternoon from I-80 southward

KEY MESSAGES

1) Rain drifts southeast this morning with decreasing clouds in time for Memorial Day afternoon/evening activities.

2) Stalled boundary south of the Mason-Dixon Line will keep clouds/rain in the forecast along and south of the Turnpike through midweek.

3) High pressure builds in later this week, ushering in a seasonably cool and beautiful end of May.

DISCUSSION

KEY MESSAGE 1: Rain drifts southeast this morning with decreasing clouds in time for Memorial Day afternoon/evening activities.

A surface low will drift across the Southern Great Lakes today and drag a cold front through Pennsylvania. Widespread steady showers ahead of this system should move south of the I-80 corridor this morning as the cold front sags south toward Maryland. Rain will likely linger in the southeast into the mid afternoon, but a drying/brightening trend can be expected in the northwest with mainly dry conditions north of I-80 through the day. There could be a few isolated showers along the actual cold front, but coverage should be isolated.

With building surface high pressure behind the front, stubborn cloud cover will finally mix out/collapse this afternoon across the area. There will be some high clouds overhead, but filtered sunshine is a good bet for locations north of I-80 by dinner time. Highs trend much warmer today, generally in the 70s everywhere. Afternoon/evening cookouts should be largely rain- free northwest of I-81.

Clearing skies across the north tonight in the presence of wet ground could lead to fog formation in valley locations by Tuesday morning. Additionally, fog will also be possible along/south of the stalling front if it hangs up in Pennsylvania tonight.

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KEY MESSAGE 2: Stalled boundary south of the Mason-Dixon Line will keep clouds/rain in the forecast along and south of the Turnpike through midweek.

The cold front that moves through PA today will stall out across KY/WV/VA for the middle of the week. This could keep some daily shower/thunderstorm chances in place across the southern tier of PA along with more widespread cloud cover there. Showers and storms are likely along and south of the boundary, while locations north of the boundary will see fewer clouds, more sunshine, and warmer temperatures.

Models continue to depict some fairly large disagreement in the northward extent of showers, especially on Wednesday. At this point, we have the highest confidence in periods of rain (and perhaps some storms) south of the PA Turnpike. A few models, including the European suite, bring rainfall all the way up to the I-80 corridor on Wednesday. Bottom line: I-80 and north looks mostly dry, folks between I-80 and I-76 are in the zone of uncertainty, and locations south of I-76 will definitely see lingering rain. Sufficient instability without much shear will lead to some scattered thunderstorms on Wednesday afternoon as well. The latest SPC outlook brings the general thunder area up to I-80.

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KEY MESSAGE 3: High pressure builds in later this week, ushering in a seasonably cool and beautiful end of May. A reinforcing ridge of high pressure will push another cold front through the Commonwealth on Thursday. Behind it, cooler temperatures and brighter skies will follow. High pressure should ensure a much more pleasant last weekend of May than we've had this Memorial Day weekend. Lows in the 40s to 50s and highs in the 60s to 70s will be within a few degrees of average conditions this time of year. Dewpoints will also drop back to spring-like ranges and will feel quite comfortable. It will be a great weekend for planting flowers if you haven't gotten anything in the ground yet. In fact, it will be an ideal weekend for about any outdoor activity you can think of.

AVIATION /07Z MONDAY THROUGH FRIDAY/

Light rain continues to push eastward across Central PA, with the back edge of the steady precipitation approaching BFD and JST as of 06Z. A wide range of conditions have been reported as the rain moves through ranging from VFR to LIFR. While most guidance would suggest that IFR will be most likely through the rest of the night, continued fluctuations in ceilings and visibility are expected.

Dense fog has started developing over Ohio and western Pennsylvania behind the rain, and this will likely expand into at least some of the forecast area over the next few hours as the rain begins to exit to the east. The best chance for fog appears to be at BFD and JST, though it is certainly possible that visibility could drop lower than what is currently shown in the TAFs for the other sites as well.

Expect gradual improvement from northwest to southeast during the late morning and afternoon as flow becomes northwesterly, ushering in a drier airmass. VFR conditions should return area- wide by 20Z. A few showers are possible during the afternoon, but we will keep any mentions of rain out of the TAFs for now.

There is some signal for fog to develop across parts of the area Monday night, but confidence is low on restrictions at any TAF sites. There is also a low chance (around 30 percent) that low clouds move into southeastern PA as a quasi-stationary boundary attempts to lift northward. This would most likely impact MDT and LNS.

Outlook...

Tue...Possible morning fog, then VFR.

Wed...Mainly VFR, some scattered SHRA could bring restrictions.

Thu-Fri...Mainly VFR, skies mostly clear

CTP WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 10 AM EDT this morning for PAZ058.