textproduct: State College

WHAT HAS CHANGED

* Decreased fog potential slightly across northern Pennsylvania and retained fog chances south of the Turnpike. * Lowered temperatures through tomorrow morning given longevity of cloud cover this morning/early afternoon.

KEY MESSAGES

1) Locally dense fog across southern Pennsylvania tonight could lead to hazardous travel conditions into Tuesday morning.

2) Rain chances through mid-week with considerable cloudiness across much of the region tomorrow 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: Locally dense fog across southern Pennsylvania tonight could lead to hazardous travel conditions into Tuesday morning.

Current (as of 3:20 PM EDT) satellite outlines clearing south- to-north with cloud cover outside of the Lower Susquehanna Valley beginning to scatter out. Persistent cloud deck continues across far southeastern Pennsylvania with scattered showers which continues to be fairly well-resolved with recent model guidance. The bulk of model guidance keeps many of these returns to our south/east; however, cannot rule out some isolated showers for areas south of the Turnpike throughout the early evening hours. Drier air (causing skies to clear out across northwest Pennsylvania) will continue to encroach southeastward and will shut down these rain chances for the evening slightly ahead of sunset.

The main concern in the overnight period will be the potential for fog formation across central Pennsylvania in areas where dry air does not manage to make it further south/east. Recent HREF probabilities for visibility below one-half mile target much of the area south of the Turnpike overnight for some visibility restrictions. In comparing probabilities of visibilities between 4SM and 1/4SM, there seems to be very minimal difference which does hone in on the fact that if fog does manage to form, it will likely be dense with rapid drops in visibility. This is likely due to the wet ground from recent rainfall and clearing skies expected overnight; however, would like to see more rain hitting the ground this afternoon to see a slam dunk fog scenario. Given all of these factors, have opted for no HWO/DFA mentions this cycle and will give future shifts the opportunity to monitor these trends and determine this evening/overnight if we need to ramp up messaging for this potential.

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

The cold front that continues to move through the region today is still expected to stall along the Coalfields of West Virginia and Kentucky for the middle of the week. This closer proximity will retain some shower (and thunderstorm) chances in the forecast through Wednesday. This will also lead to an increase in cloud cover beginning early Tuesday with considerable cloudiness prevailing by the afternoon hours and continuing through Thursday morning for the region.

Models continue highlight the best chances for showers on Wednesday, mainly south of the Turnpike. Recent ensemble guidance has shifted slightly north, if at all, with an increase in rain chances up to the I-80 corridor with locations north of this corridor likely to experience dry conditions. The aforementioned cloud cover will lead to some uncertainty with respect to instability in play for thunderstorm potential so stuck with NBM model guidance with respect to that forecast element in this cycle.

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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 /19Z MONDAY THROUGH SATURDAY/

Gradually improving conditions this afternoon from northwest to southeast, with all sites likely becoming VFR by 22Z. Most guidance shows fairly widespread fog developing tonight across much of the region, but there is still a little uncertainty regarding how much increasing cirrus clouds will impact its development. That being said, IFR/LIFR visibility will be possible at all Central PA airfields tonight. Ceiling restrictions likely persist through the morning hours at JST/AOO as light SE flow reinforces cloud cover there.

Outlook...

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

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

CTP WATCHES/WARNINGS/ADVISORIES

None.