textproduct: State College

WHAT HAS CHANGED

* Fog has begun to form across the area, especially south of I-80. However, there is a medium uncertainty on just how dense and widespread the fog will get before morning.

KEY MESSAGES

1) Fog may be dense this morning. Advisory possible-likely.

2) Rain chances through mid-week with considerable cloudiness across much of the region today and Wednesday.

3) Tranquil weather conditions emerge in the latter stages of the week and continue into the final weekend of May.

DISCUSSION

KEY MESSAGE 1: Fog may be dense this morning. Advisory possible- likely.

Early morning nighttime microphysics sat loop shows a rapidly expanding area of fog filling in the valleys first. Visby bouncing somewhat at observation sites. But, the general trend is that the fog is becoming more widespread. The high clouds are less of an issue for forecasting the fog than the mid-low clouds which are expanding NE from southwestern PA into the Laurels and south-central mtns. This cloud deck will be a big player in just how widespread the fog will get. However, the northern tier is also filling in with river valley fog, too, and they have virtually no impediments toward fog stopping. BFD and N38 have already seen their Td go down by 5F in the last 1-3 hrs. Despite the drier air up there, the temps have cooled off to meet their cross-over temps. Overall, the widespread fog is likely to be most impactful between UNV-SEG-MDT, but even there, the low- ish clouds could thwart the best efforts of fog to get <=1/4SM. Also, the nrn tier valleys have nothing stopping them from getting worse. Will continue to monitor fog for the need for an Advisory. Thinking is that we will eventually need one, but for what area(s)?

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KEY MESSAGE 2: Rain chances through mid-week with considerable cloudiness across much of the region tomorrow and Wednesday.

Front stalling just to the south of PA will keep a focusing mechanism close and force the mention of SHRA today, tonight and Wednesday across the southern half of the CWA. After the fog starts to burn off, the moisture and ridgetops may combine to pop the first SHRA of the day. A sfc wave rolling along the stalled front will help make numerous showers (and a couple of thunderstorms) tonight and Wednesday. A mainly-dry cold front then drops down from the N and brings drier, cooler air for Thursday. Despite the current lack of moisture along this feature, models continue to pop sct SHRA over NErn PA Wed aftn/evening. So, we can't get rid of the PoPs there.

The greatest liklihood for showers is still S of I-80, esp S of US Rte 22 on Wednesday. Cloud cover yields a low confidence in TS formation, as the temps may stay too chilly to allow for deep convection both today and Wed.

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KEY MESSAGE 3: Tranquil weather conditions emerge in the latter stages of the week and continue into the final weekend 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 /06Z TUESDAY THROUGH SATURDAY/

High clouds have largely cleared out across Pennsylvania and areas of valley fog are beginning to develop. The fog may be locally dense, with visibility potentially dropping to as low as 1/4SM. There is significant uncertainty regarding the extent and magnitude of visibility restrictions, but there is at least some chance that all TAF sites see IFR/LIFR visibility at some point through the rest of the night as the fog continues to expand.

VFR conditions will return by mid morning as the fog mixes out, giving way to scattered clouds between 3500 and 5000 feet for much of the day. A few showers will likely develop near JST and AOO during the afternoon, potentially bringing brief periods of MVFR ceilings to those sites.

Southerly flow will usher in increasing low-level moisture Tuesday night, likely resulting in increasing low clouds. MVFR ceilings will develop from south to north after 00Z, with IFR possible after 06Z.

Outlook...

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

Thu-Sat...VFR with no significant weather expected.

CTP WATCHES/WARNINGS/ADVISORIES

None.