textproduct: State College

WHAT HAS CHANGED

* Continue to trend afternoon highs below NBM guidance due to known warm bias * Changed wording for showers/storms Monday from probability (Slight Chance) to coverage (Isolated).

KEY MESSAGES

1) Hottest temperatures of the year so far forecast the next couple of days 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 the next couple of days with highs pushing into the 80s and 90s.

Daytime high temperatures will be steadily rising today through early week. An anomalous upper ridge amplifying over the east- central U.S. will help to create very warm to hot, summerlike conditions centered on Monday and Tuesday.

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.

High temperatures will peak in the mid 80s to lower 90s Monday and Tuesday and could challenge daily records in some locations. See the Climate section for more details. Manual adjustments were made to lower NBM maxT by a few degrees 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 quite 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 some stray afternoon and early evening showers or thunderstorms Monday and Tuesday. Most folks should stay dry, but thunderstorms could drop a quick 0.10 to 0.25" of rain in any one location.

New...

Rather strong cap noted on the 00Z Monday observed sounding over ILN Ohio, so might be hard to see much activity on Monday. Activity late this afternoon was isolated near the MD border, then a few showers formed just east of State College early this evening, most likely due to a weak lee-side trough.

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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 /01Z MONDAY THROUGH FRIDAY/

VFR conditions look to prevail throughout Monday. Light and variable winds are expected overnight. These gain strength in the late morning and early afternoon and become more out of the SSW with some gusts in the teens possible. Scattered daytime cumulus are expected tomorrow afternoon as well after a clear morning, ceilings are expected to remain VFR with this activity.

Convective showers and isolated thunderstorm activity is possible in southern PA at the tail end of the TAF period, may introduce -SHRA/-TSRA mentions in future TAFs.

Patchy fog remains a low (<30%), but nonzero, possibility tonight with light winds and clearer skies. Considered a 5SM visibility mention from 08Z-11Z in the BFD TAF but confidence is remains low in widespread visibility drops. Any activity would be after 06Z.

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

None.