textproduct: State College

WHAT HAS CHANGED

* No significant changes.

KEY MESSAGES

1) Beneficial rainfall through midweek

2) Cool pattern shift late week into the first weekend of May

DISCUSSION

KEY MESSAGE 1: Beneficial rainfall through midweek

Occasional light rain showers are expected to expand from west to east through the afternoon into the evening. 24hr QPF amounts ending 12Z Wednesday are less than 0.25" focused over the western Alleghenies.

Increased cloud cover along with a gusty wind from the south southeast will result in a noticeably cooler day vs. late April climo (5-10F below normal) and yesterday's maxT (5-15F lower) with highs this afternoon in the mid 50s to lower 60s.

More widespread soaking rainfall is forecast across CPA Wednesday afternoon through Wednesday night as a more robust frontal wave tracking northeast from the Central Appalachians transitions to a coastal low. 24hr QPF amounts ending 12Z Thursday range from 0.50-1.25" with max totals focused over the NW Alleghenies adding to 30-90 day precip surpluses.

SPC did expand the D2 MRGL risk SWO a bit farther to the north along US-22 covering more the Laurel Highlands and south central mtns. However, there is substantial uncertainty concerning the convective potential with cloud cover and rain overspreading the region early in the day.

Total rainfall forecast through midweek is 0.75-1.50" and will continue to be of the non-flooding and overwhelmingly beneficial variety particularly over D1-D2 drought areas across southeast PA.

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KEY MESSAGE 2: Cool pattern shift late week into the first weekend of May

Mean troughing/cool cyclonic flow pattern aloft sets up over the eastern U.S. by late week with closed 500mb low rotating over the northern Great Lakes into southeastern Canada. This results in high confidence in temperatures 5-15 degrees below the historical average Thu-Sun. Breezy conditions on Thursday with wind gusts 25-35 mph will add to the relative chill factor.

Precip will be showery and episodic tied to shortwave impulses rotating around the upper low. Frost risk is non zero given the colder nighttime temperatures especially later in the weekend, but it appears more likely to see an advective freeze or nothing scenario given the persistent cloud cover and sustained NW wind.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

VFR conditions continue through the mid morning hours today across the Western Mtns of PA, until the early afternoon hours throughout the Central Mountains and likely through the mid afternoon hours over the Lower Susq Valley.

In the meantime, Central and Western PA airfields will feel the impact of a southerly Low-Level Jet leading to Low-Level Wind Shear. The longest periods of LLWS will be at KBFD, KJST, KAOO and KUNV - through 18-20Z today. Peak southerly winds around the 2000 FT AGL level will be between 45-50 kt at KBFD during the mid to late morning, and in the low 40 KT range from KJST to KAOO and KUNV with values between 35-40 kts over the Susq Valley.

Cigs drop to IFR by 20-21Z over the airfields of KJST and KBFD and around dusk (01Z Wed) at KUNV. The airfields of KAOO, KIPT, KMDT and KLNS should only drop to MVFR - CIG-wise.

The probability for showers today will vary from 60-75 percent over the Central and Western Mtns to 40-55 percent over the Lower and Mid Susq Valley respectively.

Outlook...

Wed...MVFR/IFR favored due to low cloud ceilings & rain overspreading the region.

Thu...VFR/MVFR overnight as rain ends west to east, becoming VFR in the afternoon.

Fri-Sat...Mainly VFR with brief restrictions possible in showers.

CTP WATCHES/WARNINGS/ADVISORIES

None.