textproduct: State College

WHAT HAS CHANGED

* Minor modifications

KEY MESSAGES

1) Hottest temperatures of the year so far forecast early next week 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 will occur Monday and Tuesday.

Daytime high temperatures will be steadily rising today through early in the upcoming 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 between this morning and 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.

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 for the most part.

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.

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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/optimistic direction for the holiday weekend that marks the unofficial start of summer.

AVIATION /07Z SUNDAY THROUGH THURSDAY/

Low-level moisture from yesterday's showers + upslope southwesterly flow will contribute to IFR/LIFR restrictions across portions of the Northern Tier (KBFD), with intermittent MVFR/VFR across the Central Mountains (KJST/KAOO/KUNV). Patchy fog may develop overnight given antecedent moisture & pockets of clear skies, though no fog mentions were added in the TAF outside from KBFD. After daybreak, boundary layer mixing will raise ceilings and scatter the low cloud deck, with regionwide VFR expected by the afternoon.

VFR will prevail on Sunday as a ridge continues to build along the East Coast on Sunday. With that said, weak shortwaves embedded within the northern periphery of this ridge may initiate spotty convection. Instability will grow supportive of convection as the day progresses, with HREF mean SBCAPE around 1000 J/kg & negligible CIN in place, though synoptic-scale suppression will temper activity overall. Coverage and timing of convection is inconsistent across CAMs given the nebulous forcing, with shower/thunderstorm coverage expected to be below 30% across the region. Any cells that do develop will dissipate during the evening as daylight ends and ridging becomes further entrenched across the East Coast.

Patchy fog will be possible once again Sunday night (mainly after 06Z Monday) given light/variable winds, mainly clear skies, and surface dew points around 60 degrees.

Outlook...

Mon-Tue...Mainly VFR. Patchy A.M. fog. 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.

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

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.