textproduct: State College

WHAT HAS CHANGED

Severe thunderstorm risk level increased from 1 to 2 for Sunday over south central PA.

KEY MESSAGES

1) First weekend of Spring warmup precedes rain and severe thunderstorm risk Sunday afternoon into Sunday night.

DISCUSSION

KEY MESSAGE 1: First weekend of Spring warmup precedes rain and severe thunderstorm risk Sunday afternoon into Sunday night.

A nice start to Spring this weekend with fcst highs ramping 15 to 30F above the historical average by Sunday. This surge of warmth will be brief and followed by a noticeable cooldown on Monday with max temps 20-30 degrees lower than Sunday.

Main factor for strong storms on Sunday will be rather warm temperatures across the south. Limiting factor will be that dewpoints not all that high, less than what we had back on Monday. More of an inverted V profile, where this in combination with fast cell movement can support strong wind gust.

Some indications that some spots could get some higher QPF amts. However, this may be limited by fast cell movement and if any cells can train over the same area. Also not real wet across the south.

Other thing to watch is another round of snow possible later Sunday night into Monday morning. Last 2 events resulted in snow either in our area or nearby CWA areas.

Earlier discussion below.

SPC expanded the level 2/slight risk outlook from the Upper Ohio Valley into south central PA (south of I-80) for Sunday afternoon and evening. CAPE and 0-6km shear profiles appear rather favorable for organized severe storms ahead of a southeastward advancing cold front. Large hail probs are relatively high with 700-500mb lapse rates 7-7.5 C/km and essentially match the damaging wind probs.

Secondary frontal wave development near the Delmarva/srn NJ should hold up the cold front and allow colder temps to bleed/creep southward late Sunday night into Monday morning.

This should result in a rain/snow mix or changeover to wet snow along the northern edge of the frontal precip band as it exits the area. A coating of snow up to 0.5" is most likely on non- paved sfcs across the northern tier by 12Z Monday. High temps on Monday are projected to be 20 to 30 degrees colder than Sunday, punctuated by a chilly and brisk/gusty NW wind.

The rest of next week should feature more temperature swings up and down with occasional light precip. The best precip signal in the 21/00Z model cycle is in the late Thursday/Thursday night timeframe.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

VFR conditions are expected through the evening with increasing mid and high cloud cover. Low-level flow becomes southeasterly as high pressure exits the region to the east, which will allow for low clouds to work their way into eastern PA after 06Z. This should bring a period of MVFR or IFR conditions to IPT, MDT, and LNS into Sunday morning, but VFR conditions likely continue elsewhere. A 40 to 55 knot low-level jet will lead to LLWS concerns overnight for BFD, JST, AOO, and possibly UNV.

Clouds lower across northern PA through the morning, with ceilings at BFD likely becoming MVFR by 16Z as a few showers move into the area. VFR conditions will return across eastern PA, though, as the low clouds dissipate.. Numerous thunderstorms should develop ahead of a cold front after 18Z on Sunday, particularly for areas south of Interstate 80. These storms will be capable of producing strong wind gusts and large hail.

Outlook...

Mon...Rain gradually tapers off north to south, transition to snow possible mainly north of I-80 (BFD/IPT). Restrictions possible within rain/snow showers.

Tue...Mainly dry with VFR conditions. Slight chance of snow shower across northern PA late which could bring some restrictions.

Wed...A few rain showers across northern PA.

Thu...Rain with restrictions possible.

CLIMATE

Daily record high temperatures for March 22:

Harrisburg 80 in 1938 Williamsport 82 in 1938 Altoona 81 in 1966 State College 80 in 1938

CTP WATCHES/WARNINGS/ADVISORIES

None.