textproduct: State College

WHAT HAS CHANGED

*A new flash flood watch has been issued for much of west- central Pennsylvania valid 12 pm through 10 pm Friday

KEY MESSAGES

1) Unsettled pattern continues through the first half of the weekend, with some flash flooding and severe potential.

2) Trending warmer into the upcoming work week, with above average temperatures expected by Tuesday.

DISCUSSION

KEY MESSAGE 1: Unsettled pattern continues through the first half of the weekend, with some flash flooding and severe potential.

Given the expectation for convection to develop over portions of west-central PA where flash flood guidance is quite low (less than 1 inch in 1 hr / 1.5 inches in 3 hours) we issued a Flash Flood Watch valid from 12pm through 10 pm. A slow moving cold front near the PA-NY border will sag across the northern tier through the day today. On the warm side, clusters of thunderstorms and heavy downpours will move from west to east through the day. With the mean cloud layer motion roughly parallel to the cold front and SBCAPE around 1500 J/kg, training lines of convection may develop. Sfc dewpoints in the upper 60s to low 70s and PWAT around 1.60 inch indicate moist profiles with efficient rainfall processes likely. The 00z HREF PMM 3-hr QPF does paint some 1-2 inch bullseyes in the Laurel Highlands through the western Alleghenies, which would be enough for flash flooding in vulnerable basins that have seen several inches of rainfall over the past week or so. The main question is eastward extent of the heavy rainfall potential, as some of the CAMs keep most of the heavy rain farther west across the Allegheny Plateau.

With the cold front still across the southern tier early Saturday, scattered showers and afternoon thunderstorms remain possible on Saturday across the southern half of the area. Sunday looks like a much drier day as the front finally moves off to the south and high pressure builds in.

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KEY MESSAGE 2: Trending warmer into the upcoming work week, with above average temperatures expected by Tuesday.

Drier conditions are expected to prevail for the first half of the week with a strong ridge expected to develop over the middle of the country. Increasing heat is progged by LREF ensemble guidance across central Pennsylvania although there remains some uncertainty with respect to how warm temperatures and/or humidity get across the region. Current forecast of the latter half of the week outlines above average temperatures Tuesday and into the end of our forecast timeframe (highs in the mid 80s to mid 90s). Chances of rain begin to increase into the latter half of the week as temperatures and humidity increase; however, quite a bit of time to hone in on exact placement of showers/storms that will likely change as we approach that timeframe.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Lingering MVFR ceilings are noted this morning across the west with most prevailing conditions moving to more VFR ceilings by noon as mixing helps increase cloud ceilings. Restrictions, particularly from visibility in heavy rain and thunder are possible this afternoon as scattered prefrontal convection will impact PA this afternoon. This looks most likely at BFD, JST, and AOO but the other sites may see some brief restrictions from convection as well. Sites such as IPT, MDT, and LNS are moreso VFR through the day but still may see some afternoon showers cause restrictions.

Patchy fog looks to develop overnight in the wake of this convective activity. The areas that see more precipitation during the day and clear out in the wake of it (BFD, JST, and AOO) are the TAF sites to watch for these restrictions during the overnight. Depending on more than expected precipitation at other sites, that may help with visibility restrictions there too.

Outlook...

Sat...Reduced chance and more limited coverage of PM showers/t-storm.

Sun-Tue...Mainly VFR/no sig wx.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch from noon EDT today through this evening for PAZ010-011-017>019-024>026-033-034.