textproduct: State College

WHAT HAS CHANGED

* Lowered dewpoints on Tues and Wed * Increased wind gusts on Tues * Coordinated with WFOs PHI and LWX and bumped up the start of the growing season by several days due to the numerous days of well above normal temps the past few weeks, resulting in a Freeze Watch being posted for late Tuesday night into Wednesday morning across Scent PA and the Lower Susq Valley. Issued a Public Info Statement this morning with the details.

KEY MESSAGES

1) Light snow likely across the northern tier tonight into Tuesday morning with a coating to one inch in some spots.

2) Much colder for the first half of the week but warming up again at week's end.

DISCUSSION

KEY MESSAGE 1: Light snow likely across the northern tier tonight into Tuesday morning with a coating to one inch in some spots.

The moisture-challenged system moving in across the Great Lakes will generate numerous SHSN over the northern half of the state and in the Laurel Highlands.

Meager CAPE over the NW could generate a briefly heavier spot of precip/snow here and there. HREF members, GFS, and NAM all generate a heavier shower or two in the Laurels and perhaps into the central mountains. Temps should be a little milder than in the northern tier, but the very highest hill tops may get a thin coating tonight/Tues AM. Overall, the accums could be an inch or so in the nrn tier and perhaps a dusting in the Laurels and Alleghenies.

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KEY MESSAGE 2: Much colder the first half of the week but warming up again at week's end.

Tuesday morning mins will be cold enough for frost over all of the area, but wind of 10-15 G 20-25KT and sub-30F dewpoints should keep that from happening.

Still, a great portion of the CWA (not in the early stages of the newly adjusted growing season) will be <=32F Tues AM. Tues will be the coldest "Day" in this current cold spell as the cold front associated with the system passes before or around sunrise and a secondary front should move across during the daytime. Wind will also pick up as the dry, heavy air moves in. Model profiles show that we may be able to mix down gusts into the 30s on the ridge tops and in the downslope of the Lower Susq, and 20s elsewhere. RH will dip to 30-40pct.

Wednesday morning will be the coldest this week due to the center of the sfc high being right overhead. Morning mins will be well below freezing everywhere. Even the Lower Susq will get into the L-M20s. The start of the growing season (date of the normal last spring freeze) is not until the 11th there. So, we probably won't be issuing frost/freeze products for that morning. But, collaboration with our neighboring WFOs will weigh heavily on that decision.

It then warms up to about 5F below normal maxes on Wed as the sfc high slides to our E and S and the wind turns to come out of the S and we should be sunny. Dry air will still be in place, and the RH will certainly drop into the 20s for everyone as the temperatures warm but dewpoints don't keep up. Thursday looks much warmer, jumping 8-15F over Wed's numbers (greatest gains will be over the NW). PoPs stay pretty low as the sfc high noses back into the Deep South. That will help to keep moisture from the Gulf from getting to us. Temps rise another 10F on Friday. Moisture makes it all the way around the periphery of the high on Fri, and a front dropping in from Canada could make a couple of SHRA in the NW. But, these may dry up before reaching S of the Turnpike and I-81.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Scattered rain/snow showers continue to move across the Allegheny Plateau and Central Mountains as a shortwave trough crosses the Great Lakes. VFR prevails at most terminals with the exception of KBFD and KJST, where lake-enhanced moisture downwind of the Great Lakes (KBFD) and upslope WNW flow (KJST) are contributing to lower ceilings, with temporary IFR being observed in the heavier showers.

Winds will increase west to east through 12Z as the shortwave passes to our north and east, bringing northwesterly winds of 15-20 kts gusting to around 25 kts regionwide. Rain/snow shower coverage will gradually diminish through 18Z as a high pressure moves into the Northeast, accompanied by a drier air mass with PWATs around 1.5 SD below climo. For KBFD, recent mesoscale model guidance has been depicting an 850 mb vorticity maximum rounding the base of the shortwave trough later this morning (12Z-14Z), with a loosely organized area of snow showers being associated with this feature. For this reason, a PROB30 for -SHSN with visibility restrictions to at least MVFR was added at KBFD for that timeframe.

VFR is very likely (80% chance) across all terminals through 06Z as the shortwave moves off the coast of New England. After 06Z, the LAMP is signaling at a low-confidence chance (10-20%) of visibility restrictions as clearing skies and diminishing winds could provide favorable conditions for radiational fog, with the signal being primarily for KBFD given its proximity to the high pressure center overnight. No mentions of reduced visibilities were written into the TAF given the low probabilities, but this will be monitored in future TAF packages.

Outlook...

Wed-Thu...VFR.

Fri...Chance of rain showers especially in the western airspace.

Sat...Restrictions poss early N/W, then trending VFR.

CTP WATCHES/WARNINGS/ADVISORIES

Freeze Warning from midnight tonight to 9 AM EDT Wednesday for PAZ026>028-035-036-049>052-056-057-059-063>066. Freeze Watch from late Wednesday night through Thursday morning for PAZ026>028-035-036-049>052-056-057-059-063>066.