textproduct: State College

WHAT HAS CHANGED

* Increasing confidence in widespread frost and freezing temperatures for Tuesday morning.

KEY MESSAGES

1) Periods of light rain/showers through Mother's Day weekend

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

3) Cool/unsettled pattern through much of next week; sizable warmup on the horizon? into third week of May

DISCUSSION

KEY MESSAGE 1: Periods of light rain/showers through Mother's Day weekend

A very weak sfc low continues to slide over the Mid- Atlantic today, bringing light rain over most of the state for the beginning of the afternoon. Some instability could develop SE of I-81. However, the amount of cloud cover could limit the CAPE. Rain will diminish into the early evening hours where light drizzle and fog will take over mainly over southeastern Pennsylvania.

Shear is in the 35-45KT range, so it's not too shabby. The CAPE is the uncertain part of the forecast today...not only in the aftn in the SE, but then a few hours later (likely after sunset) over the far NW, too. SPC has placed both the far SE and far NW into MRGL risks of svr wind and hail, acknowledging the potential limiting stability. While worth mentioning, it affects only a small portion of the area and there should only be isolated cells in our CWA that could approach svr thresholds. The incoming frontal system will be poor in the way of moisture. The low will pass well to our north and the cold front will pass slowly tonight and Sunday. The upper heights will be rising tonight even as the front is moving through. SHRA and any TSRA that enter the NW in the evening/early night will probably break apart and dry up by 2 or 3 AM as they would be arriving in JST- UNV-IPT. There should then be a break in precip until after noon on Sunday when precip is generated north of the front as the base of the long-wave trough/low swings across the Great Lakes. Models differ on the poleward extent of precip that should be generated Sunday night and Monday. For now, we'll keep with middle of the road PoPs for the whole SE half of the area Sun night, and shrink them southward Monday morning.

It won't be a total washout with total rainfall hard-pressed to exceed 0.50 inch over the next 48 hrs. Rain ends/shifts to the east by Monday evening.

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

Confidence is increasing for another frost/freeze situation Monday night into early Tuesday morning over the western and central Alleghenies (to the northwest of I-81).

But first...Clouds may slow cooling Sunday night over the NW. But, there is certainly a low (20-40%) chc for frost/freeze in the nrn tier Monday morning. The possibility is highest then/there if no additional clouds move across LE into PA and the high stuff clearing to the SE does as expected. Will continue to mention frost for the nrn tier Monday AM.

The almost-certain time for a frost and freeze to happen next is Monday night/Tuesday morning. Forecast min temps for Tuesday morning have been dropping slowly and consistently over the past few days. Clearing should be near-total. A light wind in the SE and generally warmer temps should limit the frost potential SE of Blue Mountain to a minimum. There is a medium to high (60-80%) confidence in a freeze for the nrn Alleghenies, even at this range (Day 3.5), given the constant downward trend in all guidance minTs and favorable sky and wind. Frost is expected (90-100%) NW of AOO-UNV-IPT. Even AOO and UNV and the higher valleys S/SW of IPT should frost up Tuesday morning. As we get closer to the event, we'll likely be issuing frost advisories and freeze warnings should the set up/pattern look as it does right now.

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KEY MESSAGE 3: Cool/unsettled pattern through much of next week; sizable warmup on the horizon? into the 3rd week of May

Mean troughing keeps cool/unsettled pattern in place through much of next week with below normal temperatures and several opportunities for rain next Wednesday-Friday.

There are signs of a pattern shift starting next weekend (~May 15-16) that returns more typical/warmer late Spring conditions to central PA heading into Memorial Day or the "unofficial" start of Summer.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Conditions are holding in the MVFR to even VFR in a light rain across most sites this afternoon. Expect things to improve as the day rolls along as we see the weak upper level system move east.

A break in the lower cloud and precipitation is expected between systems until the next shortwave moves into the northwest early this evening. With very cold air aloft, there could be a gusty shower or even a thunderstorm after sunset, mainly at KBFD. Areas across central PA and points south should continue with MVFR to VFR conditions.

VFR conditions will hold on Sunday until another in a series of weak upper level storms systems brings another chance for showers and lower conditions again late in the day on Sunday. Winds remain generally less than 10KTS through the period except in a gusty shower across the northwest later today.

Outlook...

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

Wed...Restrictions possible with rain.

CTP WATCHES/WARNINGS/ADVISORIES

None.