textproduct: State College

WHAT HAS CHANGED

* SPC has continued to extend/expand the risk of severe thunderstorms to the east another tier or more of counties for both the SLGT and MRGL areas. * Updated near term sky/temps/PoPs to match current trends.

KEY MESSAGES

1) Upper level low pressure swinging SE from the upper Glakes to southern Ontario will lead to high temps trending cooler by a few to several degrees each day through Monday along with periods of showers and isolated to scattered gusty thunderstorms.

DISCUSSION

KEY MESSAGE 1: Upper level low pressure swinging SE from the upper Glakes to southern Ontario will lead to high temps trending cooler by a few to several degrees each day through Monday along with periods of showers and isolated to scattered gusty thunderstorms.

11 AM Update... The fog has burned off, but cu has started to expand a bit across the S. Temps pleasant and dewpoints climbing with M60s in the Lower Susq. TSRA over Erie are sliding N of the CWA, but certainly a bit of lift remains and could flare up.

Previous... Significant amplification of a longwave trough will occur over the next several days across the Glakes, Mid Atlantic region and Central Appalachian with 500 mb height falls of 60-100 meters and mean 850-700 mb layer temps of around 6 deg C from this evening to Monday morning.

Abundant sunshine expected across the CWA North and West of the Lower Susq Valley with max temps this afternoon generally between 75-80F.

The initial lead shortwave and right entrance region of a 65 kt upper level jet trailing a zone of very sharp upper diffluence over the western 1/3 of PA late today/early tonight will support development of scattered strong to severe TSRA across the western 1/3 to 1/2 of our CWA with the likely evolution/upscale growth of multicell clusters into a bkn line of TSRA with its axis near the RT 219 corridor between 00Z and 03Z Sunday where 0-1KM EHI will be in the 1-1.5 M2/S2 range and 0-3 KM Bulk shear will be average 20-25 KTS with some pockets just above 30 kts across the NW Mtns near KBFD at 03Z Sunday.

HREF MU CAPE Values do drop off fairly quickly from their late afternoon/early evening peak of 1200-1500 J/KG across western PA, and the severe threat will be diminished by 02z across the Mtns of Western PA. The eastern half of PA will get the gradually weakening convection later this evening/overnight.

For Sunday, the best larger scale/deep layer cooling aloft will occur across the eastern half of the state and that will be the focus for the SVR threat. MU CAPE will be lower by around 500 J/KG but deep layer swrly shear will be 35-40 kts across our eastern CWA. Therefore, SPC's MRGL risk covers the better threat for gusty winds with the storms across the eastern half of PA on Sunday with some isolated occurrences of pea to marble size hail in the taller storms Sunday.

The cyclonic flow may keep showers downwind of Lake Erie into Monday. Daytime highs will be near to slightly below the historical average for late August, making it feel more like mid September especially Sunday into Monday. SPC trimmed the MRGL back a bit to the west on Saturday, which should feature early day clouds and a few showers spreading from SE to NW during the day. Drier/less humid conditions are likely to prevail during the first half of next week.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Much of the area is VFR as of early aft. Still a bit of lower conditions across the far east.

Timing of showers and storms in the 12Z TAF package looks good, so will use it. Best chance for a strong storm is near the across the far northwest part of PA, where higher dewpts are and also closer to the low pressure system.

Also a coastal low will keep a chance of shower or perhaps a brief storm over the southeast.

For Sunday, went with VCSH at BFD, but dry otherwise, as wind shift line is past our area.

Outlook...

Mon-Wed...Patchy morning fog, otherwise mainly VFR conditions return early next week.

Thu...Chance of showers and storms again.

CTP WATCHES/WARNINGS/ADVISORIES

None.