textproduct: State College

WHAT HAS CHANGED

* Isolated/Marginal (level 1/5) risk for gusty to locally severe thunderstorms expanded for Wednesday afternoon

KEY MESSAGES

1) Midweek moisture with potential for gusty to locally severe thunderstorms precedes unseasonably cool/very chilly Thursday

2) Significant summerlike weekend warmup ramps into early next week with the highest temperatures of the year so far

DISCUSSION

KEY MESSAGE 1: Midweek moisture with potential for gusty t-storms precedes unseasonably cool/very chilly Thursday

A seasonably strong upper level trough will carve out over Great Lakes Wed-Thu and eventually close off over northern Mid Atlantic before ejecting off the New England coast by the end of the week. The upper trough and its associated sfc low and trailing cold front will bring wet weather to CPA for midweek with periods of rain/showers and perhaps a few gusty t-storms focused over the southwestern quadrant of the CWA Wednesday afternoon.

SPC has expanded a level 1/5 marginal severe t-storm risk over this area with the 1730UTC D2 update. Increasing low-level convergence near the front will lead to scattered thunderstorm development, with additional storms forming due to topographic forcing over the Allegheny Mtns. Ahead of the front, low to mid-level lapse rates are forecast to steepen by midday/early afternoon, lending the potential for several stronger storms capable of an isolated risk for wind damage and localized severe gusts.

While all of CPA will get wet, rainfall amounts will remain on the light side with fcst QPF through 8AM Friday ranging between 0.10-0.50 inch. This won't even put a dent in the moderate/D1 to severe/D2 drought conditions across far south central PA.

Scattered showers linger into Thursday which will be the coldest day of the week. Max temps will be unseasonably cool and quite chilly for mid May with highs in the 45-60F range or 10 to 20 degrees below the historical average (frequent 20-25 mph wind gusts will only add to the chill).

Conditions will dry out on Friday with daytime highs rebounding +10-20 degrees vs. Thursday.

KEY MESSAGE 2: Significant summerlike weekend warmup ramps into early next week with the highest temperatures of the year so far

After a cool start to May, guidance continues to signal a significant warmup on the horizon for this weekend into early next week. This large scale pattern shift should deliver a rather sudden and perhaps long-awaited midsummer warm surge with max temps projected to reach into the 80s and even low 90s.

There may be some potential heatrisk considerations not only with the forecast high temperatures - but also from an acclimation perspective after coming off a pretty cool stretch of weather over the past 10-15 days. Probabilistic heat risk shows >50% odds for moderate or higher across south central PA Monday and Tuesday.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

18z update... High confidence (90+%) in the maintenance of VFR conditions through the pre-dawn hours Wednesday. Clouds will be slowly lowering and thickening in the meantime, but restrictive ceiling bases/visibilities are not expected.

Early Wednesday, an area of showers and lower ceilings is expected to enter northwest PA and impact KBFD. At this point, IFR restrictions seem probable (60-70%) as early as 09z, perhaps lasting into mid-morning, before cloud bases begin to elevate.

Elsewhere across central PA, isolated-scattered showers are anticipated Wednesday morning after 12-15z. At this early vantage point, coverage seems isolated enough and showers brief enough to preclude any restrictions in the terminal forecasts. After 18z, a few thunderstorms may develop, and these could bring at least brief restrictions beyond the end of the valid TAF period.

Another aspect to be cognizant of early Wednesday morning is low-level wind shear, as the flow out of the SW increases to 35-45 kt just above the boundary layer.

Closer to the surface, W-SW winds this afternoon, will turn southerly this evening, then increase by late Wednesday morning from the SW (gusts into the 22-25 kt range).

Outlook...

Thu...Lingering clouds and showers with restrictions north/west and improvement southeast.

Fri...VFR likely.

Sat and Sun...VFR is likely much of the time, although brief restrictions are possible with isolated afternoon/evening showers and thunderstorms.

CTP WATCHES/WARNINGS/ADVISORIES

None.