textproduct: State College

WHAT HAS CHANGED

* Minor upward adjustment in POPs and QPF/Ice Accum across the Laurel Highlands for the period of light, mixed precip (totaling generally less than 0.20 of an inch) that will be focused later Mon night and Tuesday morning.

* Potential for a lingering light freezing rain threat for the Northcentral Mtns and Western Poconos into tuesday afternoon, with a changeover to periods of rain elsewhere.

KEY MESSAGES

1) A light wintry mix with light freezing rain accumulations likely late Monday night into Tuesday morning.

2) Periods of rain with temperatures very much above normal Wed onward.

DISCUSSION

KEY MESSAGE 1: A light wintry mix with light freezing rain accumulations likely late Monday night into Tuesday morning.

Moderately strong low-level cold/dry advection this afternoon will compete with the increasing, early March sun angle to greatly flatten the typical daytime temp curve. Even with almost cloud free skies by the early to mid afternoon, max temps today will range from the low-mid 20s across the Northern Tier Counties to the upper 30s and low 40s in the Lower Susq Valley.

An expansive 1040 hPa sfc high pressure dome slides over the NErn US Monday, pressing very dry air into the state. The W-E frontal boundary will be very far to the south of the state Monday, but warm/moist air will overrun the dome. Precip is expected to get right up to the Mason-Dixon Line on Monday, and bubble north into the CWA later Monday night.

There could be a small patch of --SN slide thru the Laurels and South-Central Mtns on Monday per the latest HREF. Anything that does fall would barely be enough to dust the ground.

NAM having troubles staying with the pack; as it is bringing light precip up well north/faster then any other model on Mon night. We'll follow with the bigger group for now, and expect precip to arrive in the S between -6-09Z Tuesday and around sunrise Tues across the NE half of the CWA.

Temps will be very close to freezing at that time in the S and a few degs colder over the central and northern 2/3rds of the CWA (where max wet bulbs aloft should only be +1-2C and in quite a shallow layer a few to svrl KFT AGL0. While current wind dir progs have it mainly srly on Tuesday, the big high may keep the dry/cooler air wedged up against the mtns, and keep the wind light and more from the E/SE. That would result in cold air damming and raise the risk of temps staying below freezing longer into the day, esp for the NErn third of the CWA. With the strong WAA aloft, the light mix of precip will turn to all liquid fairly quickly (before noon) in the SW half of the CWA, with the rest of the CWA becoming all liquid by 21Z. With the sfc temps cold to start, there is a 3-6hr window of possible ZR and ice accretions. Again, the current QPF thru noon Tues is pretty light (0.10-0.20"). So, any ice accretions should be below warning criteria (0.25" S, 0.50" N). As it looks now, this could eventually necessitate an advy for the ZR, and all of the CWA is at risk for a thin glaze. But, at this range, we'll just advertise it here in the discussion. Sfc temps are the most challenging thing for this situation, and will be the most likely thing to bust/change the forecast. Without a high certainty in the temps and the changing timing of the precip onset, confidence is too low to do more than just mention it here in the discussion and in the HWO (which we have been for a couple of days). It should turn to all plain rain before sunset Tues, even in the NE. Those areas that do get ice in the AM won't have any left in the aftn as temps rise and melt it.

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KEY MESSAGE 2: Periods of rain with temperatures very much above normal Wed onward

An amplifying mid/upper level ridge off the SE U.S. coast for Wed-Friday will support a big sfc high parked off the East Coast. These features will direct plenty of warm and moist air at the surface and aloft north and into the state for the rest of the week and weekend.

Temps are slated to be well above normal with sfc dewpoints climbing in to the 40s and possibly lower 50s in some areas later in the week. The W-E frontal boundary does become pretty stationary, but wavy, over the CWA for that time frame, though. There is a possibility of a small surge of cooler air sliding down from the NE (backdoor cold front) Friday-ish. But, by then, the temps will be so warm that no threat exists for any wintry precip. It should all be plain rain. The wavy front will be the pathway for repeated shot of forcing and consistent lift. So...it should be a wet time. But, that's not so bad, considering some of the area is still in drought.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

VFR for the rest of today through most or all of Monday (though an extensive layer of mid and high clouds will race east across the region very late tonight and Monday, with a few flakes of snow possible south of the KJST and KAOO areas.

Northerly winds will be sustained between 6-10 knots for the rest of the daylight hours today ocnl gusts into the mid and upper teens (KTS). Decreasing northerly wind this evening will veer to light easterly then southeasterly on Monday.

Outlook...

Mon...VFR likely.

Monday Night/Tue...Restrictions likely in a light wintry mix developing late Monday night, changing to rain later Tuesday morning and Tues Night. A high probability for Low Level Wind Shear late Monday night through Tuesday morning. A second round of LLWS expected later Tuesday afternoon and Tuesday night.

Wed-Thu...Restrictions possible in periods of rain.

CTP WATCHES/WARNINGS/ADVISORIES

None.