textproduct: State College

WHAT HAS CHANGED

Welcome to Spring!

Minimal changes from previous forecast cycle.

KEY MESSAGES

1) A couple of strong to locally severe thunderstorms are possible across parts of southwest Pennsylvania mainly late today into the evening

2) First weekend of Spring warmup precedes rain later on Sunday into Sunday night followed by breezy and much cooler conditions for Monday

DISCUSSION

KEY MESSAGE 1: A couple of strong to locally severe thunderstorms are possible across parts of southwest Pennsylvania mainly late today into the evening

Convection moving into Someset Co is sub-severe at the moment, but bears watching. It is riding a boundary and developing into a line. However, the risk for flooding is rather low since PWATs are rather low and individual cell movements are pretty fast. This continues to look like the last hurrah for convection for the night. Once this passes through, our only trouble will be the advection fog starting to show up across the N and at IPT already. Some radiational fog is possible S of I-80, but most of the fog will be low clouds hitting the terrain. Will also keep watch over the visibilities for a possible dense fog advy.

Prev... No change to the SPC outlook for Day 1 which still shows a level 1 out of 5 (marginal) severe t-storm risk across the Upper Ohio Valley into southwest PA.

Widespread layered clouds have advected ESE and now blanket practically all of the CWA late this afternoon at the nose of a theta-E ridge - associated with the Swrly LLJ to the South of an approaching cold front (Southern Lake Huron to the South Shore of Lake Ontario) and warm front (across Central and Eastern NY).

LLVL dewpoints within this moist axis range through the 40s, but low to mid level directional and speed shear will be increasing as we head through the afternoon/evening hours with enhanced deep layer UVVEL associated with the thermally indirect branch (and left exit region) of a 140+ kt nwrly upper level jet approaching our western zones later this afternoon.

There will be a few to several hour gap with clearing skies across eastern OH and Western PA late today and early this evening that will allow the boundary layer to destabilize with a few to svrl hundred J/KG of CAPE developing and supporting a bkn line of +SHRA/low-topped TSRA.

Details noted below w/respect to the type of convection and somewhat limited severe weather threat are still valid.

Hires models depict rain expanding from NW to SE this through the rest of the afternoon and evening along/ahead of a cold front. Instability (MUCAPE <500 J/kg) will be limited and confined mainly to locations near and south of I-80. However, strong deep layer shear profiles and steep low level lapse rates will pose an isolated risk of locally strong/severe wind gusts. Rain should exit most of CPA by 06Z with conditions drying out to start the weekend.

KEY MESSAGE 2: First weekend of Spring warmup precedes rain later on Sunday into Sunday night followed by breezy and much cooler conditions for Monday

Max temps fcst to rise +10-20 degrees day/day to kickoff the first official weekend of Spring. Highs on Sunday should reach the upper 50s to lower 70s before a period of rain arrives late in the day and lasts through Sunday night. A few t-storms will be possible, with the primary severe risk located in the Ohio Valley. Colder temps bleeding southward behind a cold front could mix/turn rain to snow across the northern tier late Sunday night into early Monday morning. High temps on Monday are projected to be 15 to 25 degrees colder than Sunday and 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 chance for snow showers next week (mainly across the Northern and Western Mtns of PA) will be Monday and again Tuesday night and Wed, followed by another round of rain showers, mixing with or changing to snow showers late Thursday into Friday.

AVIATION /02Z SATURDAY THROUGH WEDNESDAY/

Rain and a few heavier showers will move into the southeast this evening along the leading edge of warm advection. Generally MVFR conditions will follow the rain just in time for a cold fron to pass through the area later in the evening. This feature may develop additional showers and a few thunderstorms, with the best chance for thunder (around 30 percent) at JST. A 40 to 50 knot low-level jet crossing the region ahead of the frontal boundary will lead to LLWS into the late evening.

Typical northwest flow pattern is expected behind the front with MVFR ceilings developing at all TAF sites except MDT and LNS. Recent model guidance also suggests some fog may form, with the HREF showing a 50 percent chance of visibility dropping below 1 mile at BFD. Patchy fog may also form near MDT and LNS as skies gradually clear out. Expect a return to VFR conditions area-wide Saturday morning.

Outlook...

Sat...VFR.

Sun...Rain overspreads north to south, restrictions possible.

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...Rain and snow showers across northern PA with restrictions possible.

CLIMATE

Astronomical Spring (Vernal Equinox) officially kicked off today March 20th at 10:46 a.m.

CTP WATCHES/WARNINGS/ADVISORIES

None.