textproduct: State College

WHAT HAS CHANGED

* McKean/Potter upgraded to Freeze Warning & Frost Advisory expanded to Northern Centre County tonight based on updated forecast with slight decrease in expected temperatures.

KEY MESSAGES

1) Collaborated with surrounding WFOs to post a Frost Advisory/Freeze Warning for the NW Mtns late tonight/early Monday and a Freeze Watch for the Laurels, Central and Northern Mtns Monday night/early Tuesday.

2) Energetic, northern stream system moves through mid-week with more widespread clouds occasional showers 9maybe even a few wet snow flakes on the higher ridge tops of the Laurels and Northern Mtns.

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

DISCUSSION

KEY MESSAGE 1: Collaborated with surrounding WFOs to post a Frost Advisory/Freeze Warning for the NW Mtns late tonight/early Monday and a Freeze Watch for the Laurels, Central and Northern Mtns Monday night/early Tuesday.

A cold front will clear southeast PA overnight ushering in clearing skies. Some mid- high clouds will stream over the southern half or more of the area for tonight, but mostly clear skies are expected farther north. There could be a few patches of lower, strato cu clouds sliding into the nrn tier (at the leading edge of anomalously cooler air aloft) around daybreak, which may be just enough to limit widespread/thick frost from forming in the nrn tier tonight/Mon AM. However, it's too close of a call to not hoist a Frost Advisory/Freeze Warning and caution growers to protect sensitive crops and flowering vegetation.

Temps will cool into the low-mid 30s in the north, but only the mid 40s in the south. Some of the latest guidance indicates upper 20s lows are possible along and north of US-6 in McKean and Potter Counties. As such, we upgraded to a Freeze Warning for those counties tonight.

There will be a higher frost/freeze risk for Monday night/Tuesday morning over the western and central Alleghenies. 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 will make upgrade decisions in the next couple forecast cycles.

------------------------------------------------------ KEY MESSAGE 2: Energetic, northern stream system moves through mid-week with more widespread clouds occasional showers 9maybe even a few wet snow flakes on the higher ridge tops of the Laurels and Northern Mtns.

A digging/compact upper low with colder temps aloft that Sunday night/Monday's trough will drop across the Upper Great Lakes Tuesday and bring SHRA into western PA by Wednesday AM.

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 broad- brushed 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.

Lastly, the wet bulb zero level descends to under 2 KFT AGL across the Central and Western Mtns later Wed night and Thurs, and its not out of the question to have some wet snow flakes flying at that time (mainly 06-15Z Thu).

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KEY MESSAGE 3: 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 /01Z MONDAY THROUGH FRIDAY/

A cold front exiting the area to the southeast still has just a few lingering -RA over southeast PA. All forecast location are VFR and should remain so through the forecast period.

Gusty winds over the southeast will diminish through sunset.

High resolution short term models do indicate an isolated -SHRA possible Monday afternoon but probabilities too low (<20%) to feel confident placing this in any specific location.

Winds will increase Monday afternoon with a few gusts to 15-20KTS.

Outlook...

Tue...VFR conditions expected with generally clear skies.

Wed...Restrictions possible with rain.

Thu...Lingering clouds and showers.

CTP WATCHES/WARNINGS/ADVISORIES

Frost Advisory until 8 AM EDT Monday for PAZ004-010>012-017- 018-037-041-042. Freeze Watch from late Monday night through Tuesday morning for PAZ004>006-010>012-017>019-024-033-037-041-042. Freeze Warning until 8 AM EDT Monday for PAZ005-006.