textproduct: State College

WHAT HAS CHANGED

* Continued increasing confidence in widespread frost and freezing temperatures for Tuesday AM, but decreased confidence in frost for the north tonight/Mon AM.

KEY MESSAGES

1) Rain will sink to the south this morning, and leave a mostly dry late morning and afternoon. Frost is possible, but not likely tonight/Monday morning.

2) Frost/freeze risk Monday night/Tuesday morning over the western and central Alleghenies

3) Energetic system moves through mid-week

4) Warmup for the weekend? More certain is warmer temps for beyond day 7.

DISCUSSION

KEY MESSAGE 1: Rain will sink to the south this morning, and leave a mostly dry late morning and afternoon. Frost is possible, but not likely tonight/Monday morning.

Showers moving through the CWA this morning will continue to fragment further. Weak cold front will push the showers off to the south this morning. Showers will probably redevelop in the afternoon with the fropa over the SE third of the area. TS is still possible in the far SE this aftn, but a 20 PoP might be overdoing it due to limited CAPE. By noon, the dewpoints will be into the 30s in the NW and this drying will continue to expand SE in the aftn as the new airmass moves in.

Clearing will occur behind the front, but mid-high clouds will stream over the southern half or more of the area for tonight. There should also be a patch of lower clouds sliding into the nrn tier for the second half of the night. That patch of clouds may be just enough to keep frost from forming in the nrn tier tonight/Mon AM. The other checkboxes will be filled in on the frost checklist with wind diminishing/calming by morning and the colder/drier airmass settling in. Confidence in frost forming in the north tonight is only about 60pct. So, we'll hold off on issuing a frost advisory for the time being and allow further evaluation by later shifts. In any case, temps will cool into the mid 30s in the north, but only the mid 40s in the south.

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KEY MESSAGE 2: Frost/freeze risk Monday night/Tuesday morning over the western and central Alleghenies

Almost a slam dunk for a widespread frost for more than half the CWA tomorrow night (N and W) - and a freeze in the nrn mtns. Dewpoints will be 25-30F - just low enough to allow the temps to be able to drop, but not too dry to keep frost away. Confidence in frost is near 100 pct, but for freeze is about 49 pct. Due to increasing confidence, frost advy and freeze warnings seem likely, but the consensus among the regional offices on this (midnight) shift was to allow at least one more forecast cycle for that to happen.

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KEY MESSAGE 3: Energetic system moves through mid-week

A digging/compact upper low will drop across the Upper Great Lakes Tuesday and bring SHRA into western PA Tuesday night. There is a wide range of possible paths for the sfc low to take. Current guidance moves a triple point through the state sometime between Wed aftn and Thursday morning. However, model spread is high and confidence is low for details. Using a broadbrushed approach, we'll paint categorical 80+ PoPs during the daylight Wed for everyone and lower them somewhat and slide them east for Wed night and Thursday. At this point, the WAA doesn't look particularly strong in advance of the system. So, we'll keep max temps rather similar (60s) for Tues-Wed-Thurs. TS returns to the forecast Wed-Wed night. However, the coolness could/should negate worries for widespread severe wx. Moisture feed is questionable with high pressure cutting off much of the potential feed from the Gulf. QPF through the mid-week period looks less than an inch total, and closer to half of an inch average area-wide. No threat for flooding.

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KEY MESSAGE 4: Warmup for the weekend? More certain is warmer temps for beyond day 7.

Thicknesses/heights seem to rebound for the weekend. But, moisture/energy continues to come over the western/central U.S. upper ridge. Uncertainty in details (esp precip possibilities) is high as the spread in the mass fields over the weekend is rather high. Eventually, a sfc high is expected to park over Bermuda and direct warm/summery air in for next week (days 7+).

AVIATION /09Z SUNDAY THROUGH THURSDAY/

Just a few more hours of showers, then clearing with lots of sun today. Conditions should trend up today, as the showers move out of the area.

LNS had dense fog and low CIGS early on, then the winds shifted more to the west and the fog went away. Now the winds are nearly calm, with some fog, but also a mid deck. Also IPT has some lower CIGS but a mid deck as well.

Anyway, expect conditions to improve quickly today.

Wet by Wednesday with lower conditions again.

Outlook...

Mon-Tue...VFR conditions expected to prevail.

Wed...Restrictions possible with rain.

Thu...Lingering clouds and showers.

CTP WATCHES/WARNINGS/ADVISORIES

None.