textproduct: State College

WHAT HAS CHANGED

* Slight increase in rainfall amounts, mainly across northwestern Pennsylvania overnight into Monday morning. * Slight decrease in eastward extent of the thunderstorm potential this evening. * Dense fog advisory until 10 AM for Schuylkill Co.

KEY MESSAGES

1) Widespread rain across central Pennsylvania later Sunday evening through Memorial Day morning.

2) Warmer midweek with scattered showers before a cooler and brighter end of May.

3) Areas of low clouds and fog overnight.

DISCUSSION

KEY MESSAGE 1: Widespread rain across central Pennsylvania later Sunday evening through Memorial Day morning.

Current radar outlines some showers across southwestern Pennsylvania this (Sunday) afternoon, which are expected to continue tracking northeast, with more robust rainfall stationed across the Mid-to-Lower Ohio River Valley. An upper-level disturbance will continue to swing through the area tonight, with an additional round of showers expected overnight and into Monday morning. Current forecast does bring this initial round of showers with a two-three hour lull before the more widespread rainfall starts for the evening. Recent HREF model guidance brought a signal for locally heavier rainfall northwest of the Pittsburgh metro area) and does touch our some of our western zones in Elk/Cameron counties, where a swath of 2-3" PMMs has been observed in the 12Z HREF run. These areas have avoided much of the heavier rainfall over the past couple of days, thus not a lot of large- scale flooding concerns. WPC did maintain a Marginal Risk for Excessive Rainfall across Cambria/Somerset counties this evening, mainly due to some convective elements; however, generally expect the flooding concern here to be very isolated with no large-scale concerns. Further southeast, ongoing drought conditions and lower rainfall totals provide zero flooding threat with this rainfall.

Guidance continues to depicts a cold front dropping southeast through the Commonwealth on Memorial Day with dry air behind the frontal passage bringing an end to the showers. Rain will likely linger in the southeast into the mid afternoon, but a drying/brightening trend can be expected in the northwest. Building surface high pressure also means the stubborn cloud cover will finally mix out/collapse Monday evening across the north. A few peeks of sun could even make an appearance at Memorial Day cookouts across the northern tier. Highs trend much warmer on Monday, generally in the 70s everywhere.

-----------------------------------------------------------------

KEY MESSAGE 2: Warmer midweek with scattered showers before a cooler and brighter end of May.

Clearing skies across the north on Monday night in the presence of wet ground will likely to fairly widespread fog formation into Tuesday morning. Many models depict high probabilities in reduced visibility, especially north and west of the I-81 corridor. Dense Fog Advisories may be needed; however confidence remains low at this juncture.

Monday's warming trend will continues into the middle of the week, with highs expected to be in the upper 70s and low 80s by Wednesday. The cold front that moves through PA on Monday 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. Wednesday looks like the best chance for storms at this point.

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. It will be a great weekend for planting flowers if you haven't gotten anything in the ground yet!

___

KEY MESSAGE 3: Areas of low clouds and fog overnight.

Unlike the last 2 nights, lower clouds down to top of the hilltops in spots, especially northeast of MDT, along interstate 81. Not seeing much change in conditions across Schuylkill Co. before morning, so issued a dense fog advisory until 10 AM.

AVIATION /22Z SUNDAY THROUGH FRIDAY/

Mostly MVFR being observed in the early afternoon except for BFD at IFR. Guidance appears to have been too pessimistic this morning for many sites as the widespread IFR flight conditions haven't manifested quite yet. The rest of the afternoon, up until around 23Z-01Z, has conditions straddling the line between low MVFR and high IFR with ceilings around 1000ft at all sites except BFD which is expected to stay mostly IFR. JST, UNV, and IPT are the sites where MVFR has the highest signal to persist before the evening rain comes in. Pre-rain IFR developing seems more likely at AOO, MDT, and LNS.

As another round of showers moves through this evening into the overnight as a small upper level disturbance moves through. Signal remains high for widespread IFR/LIFR to develop. The shower activity will start in the western sites around 23Z or so and spread eastward in the hours after. IFR ceilings are expected to accompany this activity into the morning. IFR visibilities and LIFR ceilings are currently expected in some capacity overnight at each site. As the rain moves out, any remaining LIFR will give way to IFR in the morning with MVFR looking to develop around the end of the TAF period. As a weak surface low passes to the northwest and a high builds in behind it, winds will shift from an easterly/southeasterly pattern to a more northerly one towards the end of the TAF period

Outlook...

Tue...Possible morning fog/low visibility, then VFR.

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

Fri...Mainly VFR, skies mostly clear

CLIMATE

Several daily record low maximum temperatures were set or tied on Saturday May 23:

LOCATION OBSERVED HIGH PREVIOUS RECORD (YEAR) Harrisburg 54 54 (1982) Williamsport 54 57 (1982) Altoona 50 52 (2005) State College 51 53 (1968)

CTP WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 10 AM EDT Monday for PAZ058.