textproduct: State College

WHAT HAS CHANGED

* Collaborated with WFO LWX and SPC to increased POPs for pulse/multicell TSRA with the potential for gusty winds later this afternoon and evening across Scent PA and the West Br Susq Valley. SPC painted a MRGL Risk for SVR across that area of the CWA.

* Also slightly expanded the low pops for SHRA/TSRA Tuesday afternoon and evening and included the potential for gusty wind and hail.

KEY MESSAGES

1) Hottest temperatures of the year so far forecast this afternoon and Tuesday with highs pushing into the 80s and 90s.

2) A strong cold front to bring showers and thunderstorms with the potential for severe weather on Wednesday followed by colder temperatures.

DISCUSSION

KEY MESSAGE 1: Hottest temperatures of the year so far forecast this afternoon and Tuesday with highs pushing into the 80s and 90s.

An extensive, but rather thin veil of high clouds covering much of the CWA early today will help to create near optimal conditions for a surge in heat today, thanks in part to their blanketing effect to reduce radiational cooling overnight and their minimal impact on insolation today. Temps will start the daylight hours in the 60s in most locations.

Daytime high temperatures will be steadily rising today through Tuesday as an anomalous upper level ridge amplifies over the Eastern U.S. This will help to create very warm to hot, summerlike conditions centered on this afternoon and Tuesday afternoon.

500 mb heights per the GEFS rise about 120 dam from Sunday morning to late Monday with standardized anomalies of these heights reaching over +2 sigma along the Mid Atlantic Coast 18Z Monday through 18z Tuesday.

Collaborated with LWX and SPC to paint a MRGL risk for SVR TSRA from the Scent Mtns to the West Branch Valley of the Susq near the eastern edge of somewhat stronger (35-40 kt) swrly mid level winds with MU CAPE reaching near 2000 J/KG. Additionally, the eastern edge of an elevated mixed layer (currently over the Middle Ohio River Valley) will be tracking ENE at 15-20 kts and reach the western edge of the MRGL Risk area around 22-23Z today helping to enhance mid level lapse rates and updraft intensity.

Mentioned the potential for gusty winds associated with the the clearly high-based convection occurring within an inverted-V sounding.

High temperatures will peak in the mid 80s to mid 90s this afternoon based on elevation and proximity to the best llvl downslope and enhancement by adiabatic warming via the light southwesterly breeze today and moderately gusty WSW wind on Tuesday (with gusts in the 15 to 20 mph range during the late morning and afternoon hours).

Daily record highs could be challenged in some locations. See the Climate section for more details. Manual adjustments were made to lower NBM maxT by a few degrees today due to a known systematic bias correction issue identified during the shoulder seasons. This should also keep max heat indices under 100F, precluding any need for Heat Advisories. Still, heat risk impacts will continue to be monitored given the quick ramp-up in heat and limited acclimation time.

Dewpoints over 60F for many will also feel more humid relative the recent cool stretch we've had.

With a boundary just to our north and sufficient instability in the warm sector over PA, there will be a chance for additional stray afternoon and early evening showers or thunderstorms this afternoon, with a better chance for locally robust convection on Tuesday across the Northern half of PA. Most places stay dry though, but thunderstorms could drop a quick 0.10 to 0.25" of rain in any one location.

-------------------------------------------------------------

KEY MESSAGE 2: A strong cold front to bring showers and thunderstorms with the potential for severe weather on Wednesday followed by colder temperatures.

A cold front (accompanied by more widespread and frequent showers/t-storms) brings relief to the relatively short bout of heat and moderate humidity Wednesday into Thursday. DOD max temp drop from Tuesday to Wed will be 20 deg F or greater in most locations.

Some of the AI guidance paints an elevated risk of severe weather across the Lower Susquehanna Valley on Wednesday afternoon in the presence of peak heating and sufficient shear/CAPE profiles. The magnitude & location of the severe threat will be highly dependent on cold front passage timing and amount of cloud cover in advance of the frontal boundary. The eventual risk area will highlight locations along and downstream of the cold front between 12PM and 8PM on Wednesday.

In the wake of the cold front, high pressure will build in for a short time. Temperatures are forecast to cool down back to historical/climo averages for late May for the end of next week. Early indications show the aforementioned cold front stalling out south of the Mason-Dixon line late in the week and lifting back north across PA as a warm front into Memorial Day weekend. The current outlook favors a cooler/wetter stretch through the holiday weekend thanks to that warm front, but there is still a lot of time for the forecast to trend in a more favorable and optimistic direction for the holiday weekend that marks the unofficial start of summer.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Scattered cumulus clouds have been noted moving over the central Pennsylvania air space. Flight conditions are expected to remain VFR throughout the TAF period outside of a an isolated thundershower this afternoon. Confidence is overall low on thunderstorm development this afternoon. Forcing for storms is weak despite the available energy in the atmosphere. Latest CAM guidance would indicate a narrow window for convective storms to develop after 22Z this afternoon. These storms will be very isolated in nature, and PROB30 groups have been included at airfields that may see one of these storms.

Overnight, a shortwave tracking across the Great Lakes may result in a few showers/thundershowers across West-Central PA (mainly KBFD), though flight restrictions appear unlikely with this activity. After 12Z on Tuesday clouds will begin to scatter out again and clear, with wind gusts up to 25kts possible again on Tuesday throughout the afternoon.

Outlook...

Tue...Mainly VFR. Patchy A.M. fog possible. Isolated P.M. shower or t-storm possible.

Wed...Restrictions probable through Wednesday night with widespread showers/storms along CFROPA.

Thu...Lingering showers across S PA, restrictions possible.

Fri...Lingering showers across S PA, restrictions possible.

CLIMATE

Daily record max temperature for May 18-19:

5/18 5/19 Harrisburg 94 in 1962 95 in 1962 Williamsport 95 in 1962 96 in 1996 Altoona 91 in 1962/1996/2017 92 in 1996 Bradford 85 in 1962 85 in 1962 State College 92 in 1962 92 in 1934/1996

Overnight low temperatures on Monday night into Tuesday are also in jeopardy.

Please note: State College Co-operative observations are a 24-hour summary taken once per day around 7 AM (7AM-7AM). Therefore, a max temp occurring in the daylight or late in the day is usually reported in the _next_ day's observation. Also, the same min temp may be reported on two consecutive days if the min occurs at observation time.

CTP WATCHES/WARNINGS/ADVISORIES

Air Quality Alert until midnight EDT tonight for PAZ057-059- 063-065-066.