textproduct: State College

WHAT HAS CHANGED

* No significant changes at this time.

KEY MESSAGES

1) Frost Advisory/Freeze Warning for the NW Mtns through early today and a Freeze Watch for the Laurels, Central and Northern Mtns Monday night/early Tuesday.

2) Potent/amplifying, northern stream upper level trough moves through for the Wed-Thu period with more widespread clouds occasional showers and maybe even a few wet snow flakes on the higher ridge tops of the Laurels and Northern Mtns.

3) Warmup beginning this weekend into next week.

DISCUSSION

KEY MESSAGE 1: Frost Advisory/Freeze Warning for the NW Mtns through early today and a Freeze Watch for the Laurels, Central and Northern Mtns Monday night/early Tuesday.

A several hour period of high clouds streaming NE across the NW half of PA have moved into upstate NY and New England as of 08Z and the combination of this clearing, light wind and low dewpoints (in the wake of yesterday's Cfropa) has caused temps to dip into the 30-32F range in numerous locations across the NW Mtns with the lowest reading (so far) coming in at 29F in Northern McKean Cty. This agrees well with the current Freeze Warning, while counties within this morning's frost advisory are seeing predawn temps in the mid-upper 30s.

There will be a higher frost/freeze risk for tonight/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 allow the current Freeze Warning/Frost Advis to expire at 12Z before following shortly afterward with headline transitions/upgrades.

KEY MESSAGE 2: Potent/amplifying, northern stream upper level trough moves through for the Wed-Thu period with more widespread clouds, occasional showers/isolated low topped TSRA and maybe even a few wet snow flakes on the higher ridge tops of the Laurels and Northern Mtns (Thurs Morning and Night). Showers move into the NW Mtns Tuesday night with the bulk of the rain starting across the Central Mtns and Susq Valley around or after 12Z Wed.

A digging/compact upper low with colder temps aloft (and lower 500 mb heights by 40-60 dam at its base at 12Z Thu) than the one moving across the CWA today will drop across the Upper Great Lakes Tuesday and bring SHRA into western PA by Wednesday AM.

Probabilities for greater than 0.50 inch/24 hr exceed 60 Percent across the far NW part of the CWA while QPF elsewhere (and centered on Wed) will be between 0.25-0.40.

WAA and MU CAPE doesn't look particularly strong in advance of the system, so any TSRA should remain quite isolated and low- topped with CAPE of 500 J/KG or less.

Lastly, the wet bulb zero level descends to under 2 KFT AGL across the NW Mtns later Wed night into Thurs night (but is a tad higher the a few model cycles back). It's likely that some wet snow flakes will be flying at that time (mainly 06-15Z Thu and after 00Z Friday).

KEY MESSAGE 3: Warmup beginning this weekend into next week.

Northern stream relaxes/becomes more zonal and thicknesses/heights rebound for the weekend and become about 1 sigma above normal (standard anomaly-wise at 500 mb) by 12z Monday.

As this transition occurs over the weekend, moisture/energy flows over the flattening western/central U.S. upper ridge bringing the chance for a few bouts of light QPF from isolated to sctd SHRA/TSRA.

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 /08Z MONDAY THROUGH FRIDAY/

After many cloudy and wet days, high pressure building into the area will bring mainly dry weather to central PA into Tue, along with plenty of sunshine.

While there could be a brief shower this afternoon across the north and east, the airmass is on the dry side. Thus mainly looking at high base clouds at times this afternoon, as strong May sun and abnormally cold air aloft results in some clouds.

Winds will pick up a bit after late morning, but will weaken by early this evening.

Outlook...

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

Wed...Restrictions possible with showers.

Thu...Lingering clouds and showers.

Fri...Clearing.

CTP WATCHES/WARNINGS/ADVISORIES

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