textproduct: State College

WHAT HAS CHANGED

* Frost Advisory expanded one row of counties eastward early Friday evening

KEY MESSAGES

1) Cool and unsettled pattern to start May with shower chances and a frost/freeze risk each night through the weekend, mainly across Central and Northern PA.

DISCUSSION

KEY MESSAGE 1: Cool and unsettled pattern to start May with shower chances and frost/freeze risk each night through the weekend, mainly across Central and Northern PA.

Several disturbances rotating around a broad, persistent upper level closed low centered over Ontario and Quebec will help to reinforce broadly deep troughing across the eastern U.S. through much of next week. This pattern will keep conditions cool and unsettled at times as multiple frontal systems move through. In addition to shower chances, the fronts will bring reinforcing surges of cool air, keeping temperatures near to below seasonal averages.

The first of these disturbances aloft and weak low pressure at the surface lift out of PA later tonight, bringing an end to the light to moderate showers we have seen over the past several hours. As drier air moves in and skies at least partially clear, light winds will likely allow for frost and freeze conditions to develop. We have issued Freeze Warnings and Frost Advisories for roughly the northwestern two-thirds of the forecast area that are in effect from midnight through 9 am Sunday. There could also be patchy fog given the wet ground.

The lowest temperatures of this current cool spell will be Saturday night and early Sunday with frost or freeze conditions across all of the CWA except for more patchy coverage in the Lower Susquehanna Valley and adjacent South-Central Counties of PA where low temps will be in the mid-upper 30s. There is still some uncertainty regarding the southeastward extent of frost as there will be a rather tight pressure gradient across the region due to a developing area of low pressure off of the coast.

Temperatures trend warmer for the beginning of next week, but all guidance indicates that unsettled weather will continue with multiple chances for rain next week, with the highest PoPs Wed- Thu. Latest guidance also suggests a potential return of frost/freeze conditions by Thursday and Friday nights.

AVIATION /02Z SATURDAY THROUGH WEDNESDAY/

Main area of light rain sliding eastward into the Susq Valley late this evening as an upper level wave and attendant weak surface frontal boundary slide across PA. Behind that, scattered showers persist with generally MVFR ceilings through the next several hours, dipping to IFR at BFD/JST. Then clouds begin to clear out toward sunrise, which may lead to patchy fog given wet ground and light winds.

Winds will shift from a prevailing southwesterly flow to a more northwesterly one across the state by daybreak. Prevailing winds will mostly be in the single digits (5-10 kts) with some scattered gusts in the teens possible (10-15 kts). After daybreak tomorrow across most TAF sites, VFR conditions are expected to prevail. JST may have the most trouble removing low level clouds into the morning.

Outlook...

Sat PM...Restrictions possible in SCT PM -SHRA.

Sun...SHRA moves in late; otherwise, VFR expected.

Mon...SHRA potential increases during PM hours, some TSRA possible across N/W PA. Restrictions possible.

Tue...SHRA becomes more widespread, TSRA chances expand across much of central PA. Restrictions possible.

Wed...Scattered SHRA remain. Restrictions possible.

CTP WATCHES/WARNINGS/ADVISORIES

Freeze Warning until 9 AM EDT Saturday for PAZ004>006-010>012- 017-018-024-033-037. Frost Advisory until 9 AM EDT Saturday for PAZ019-025>028- 034>036-041-042-045-046-049-050-056.