textproduct: State College

WHAT HAS CHANGED

* Added more detailed discussion regarding rainfall in the next 48 hours

KEY MESSAGES

1) Warm and windy conditions on Tuesday with gusts to 40 mph possible.

2) Heavy showers and thunderstorms are possible in NW PA Tue afternoon and evening.

3) More widespread stratiform rain expected across central PA on Wed.

4) Chillier to end the week with frost/freeze concerns returning Thursday night.

DISCUSSION

KEY MESSAGE 1: Warm and windy conditions on Tuesday with gusts to 40 mph possible.

Tuesday will be the warmest day of the week for most locations (exception may be NW PA where more clouds/convection on Tue could limit MaxTs). Across the south and east, highs will likely get into the lower 80s.

Model soundings show a nearly dry adiabatic lapse rate in the lowest 2-3 KM south/east of I-80/I-99. With SW flow of 35-45 kts in the 2-3 KM layer, wind gusts of 40 mph cant be ruled out at the sfc. Since minRH values are expected to range from 25-35 pct across south central PA, there could be an increased risk of wildfire spread, particularly in places that have not greened up yet (e.g. higher elevations).

Key Message 2: Heavy showers and thunderstorms are possible in NW PA Tue afternoon and evening.

Scattered showers and a few rumbles of thunder are possible across central PA tonight into early Tue AM, followed by a lull in the action from mid morning through early afternoon. By 16-18z, the approaching cold front and preexisting Erie lake breeze boundary should provide enough sfc convergence for convection initiation in NW PA. SPC outlook is just for general thunder, but gusty winds can't be ruled out given the strong ambient flow. HRRR suggests a few discrete cells east of the boundary, with some rotating right movers possible in the northern tier and up into NY State. Given the slow eastward translation of the cold front, convective precip will likely be confined to NW PA, but local amounts in excess of 1 inch are possible. Warren County is included in WPCs D2 MRGL risk for excessive rain.

Key Message 3: More widespread stratiform rain expected across central PA on Wed.

Best odds for widespread stratiform rain are Tue night into Wed as an upper shortwave trough moves overtop the cold front. Most of the rain will end prior to suppertime on Wednesday. This stratiform precip shield is forecast to drop between 0.25 and 0.75 inch of rain.

Key Message 4: Chillier to end the week with frost/freeze concerns returning Thursday night

Temperatures once again turn cooler behind the cold front. The first chilly night is Wed night, with minT in the 33-35 range across the NW. Some frost is possible, but it depends on how quickly clouds clear out behind the departing precip. Frost will be more likely Thursday night, with skies more likely to be clear with an axis of high pressure extending into PA.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Mostly VFR categories and LLWS persisting to daybreak Tuesday. Transient showers will pass through the region the rest of the night with any flight restrictions expected to be brief. Any remaining showers decrease in coverage after sunrise on Tuesday, giving way to mainly dry conditions for the rest of the morning. MVFR ceilings may develop at BFD, though the rest of Central PA should remain VFR. Expect southwesterly wind gusts to increase to 20 to 25 knots by 15Z, and as strong as 35 kts in the afternoon. Convective showers and thunderstorms will likely break out across the north and west Tue afternoon, with more widespread stratiform rain later Tue night into Wed. This will most likely impact flight categories in the northwest.

Model guidance is depicting a robust area of LLWS developing in E PA and impacting IPT, MDT, and LNS after 00Z Wednesday. Have kept magnitudes in 35-40kt range at this time; with nearer guidance in the next TAF package, more clarity regarding the ceiling of this LLWS will be present.

Outlook...

Wed...Widespread restrictions and stratiform rain early tapers to lingering showers.

Thu-Fri...-SHRA possible, but trending drier.

Sat...Restrictions possible in rain.

CLIMATE

Multiple low temperature records were set or tied across central Pennsylvania for May 3rd:

Altoona observed a low temperature of 31 degrees, breaking the previous record of 32 degrees set in 1957.

Johnstown observed a low temperature of 29 degrees, which ties the previous record of 29 degrees set in 1941.

CTP WATCHES/WARNINGS/ADVISORIES

None.