textproduct: State College

WHAT HAS CHANGED

* Minor adjustments to forecast snow accumulation for tonight

KEY MESSAGES

1) Rain and wet snow later today into tonight with limited minor accumulation most likely (C-1") over east-central PA

2) Mid-February thaw continues next week with temperatures remaining above the historical average

DISCUSSION

KEY MESSAGE 1: Rain and wet snow later today into tonight with limited minor accumulation most likely (C-1") over east-central PA

The majority of the 15/00Z and overnight guidance favors somewhat less to later (timing) interaction between the northern and southern stream shortwaves as they translate eastward from the Great Lakes/Deep South this afternoon to the NJ/DE and Carolina coast by 12Z Monday. That said, the model envelope (global to regional to hires CAMs) has been very sensitive to fluctuations in the strength of the northern stream wave and therefore would not rule out ongoing shifts in projected snow placement and amounts even as the event begins to unfold later today. In this type of scenario where uncertainty remains elevated even inside of 24 hours, we have to lean on the probability signal and hedge to the most likely outcome - which remains a wet/slushy (low SLR) minor impact snowfall range between a coating and 1 inch focused over the eastern periphery of the forecast area. Other factors to consider are elevation and temperature profile uncertainty in an environment where the boundary layer will start off rather warm ~40F with snow rates <0.5 in/hr not likely to achieve maximum wet bulb cooling. KEY MESSAGE 2: Mid-February thaw continues for most of next week with temperatures remaining above the historical average

Stretch of above average warmth for mid February continues through most of next week with highs in the 40s to lower 50s. A seasonable cool down is likely by next weekend.

After mainly dry start to the week, rounds of precip are likely Wednesday and again Friday into the weekend. Rain is the dominant ptype with some mixed precip potential primarily over the northern tier.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Main changes to the 06Z TAF package was to add some fog to MDT and LNS, as these areas are already cold. Further west the temperatures are warmer. Some clouds at BFD as well. These factors may limit fog formation to the west overnight.

Other change was to extend fcst out to 06Z Monday. Still expect some snow and rain to linger overnight Sunday night.

Earlier discussion below.

VFR conditions will continue throughout the night for most sites as high clouds begin to build in over the region ahead of the upper level trough and surface low expected to arrive Sunday afternoon. The only airfield expected to see flight restrictions will be BFD overnight tonight. Little to no winds and increased surface moisture could result in early morning fog or very low stratus by daybreak. Everywhere else should see VFR through Sunday morning with ~90% confidence.

Precipitation arrives late Sunday afternoon beginning in the Laurel Highlands as a very cold rain. Expect visibility reductions throughout the afternoon as this stratiform shield of precip spreads from west to east. Most everywhere will see MVFR conditions or worse by 00Z Monday due to low clouds and precip. Mixing of rain and snow could occur where cooling is most efficient, the greatest possibility to see rain mixed with snow will be at LNS and MDT.

Outlook...

Mon...Low clouds linger much of the day. IFR expected NW.

Tue...Mainly VFR.

Wed-Thu...IFR -RA/cigs N, MVFR -RA/cigs elsewhere.

CTP WATCHES/WARNINGS/ADVISORIES

Air Quality Alert until midnight EST tonight for PAZ057-059- 063-065-066.