textproduct: State College

SYNOPSIS

* Impactful Boxing Day snow, sleet, and ice lasting into the middle of Friday night. * Rain Sunday then turning colder and windy with lake effect snow to start next week

NEAR TERM /UNTIL 8 AM FRIDAY MORNING/

All is well. Sky fairly clear but there is still some wind. We shouldn't have trouble holding onto the going min temps for tonight (teens and 20s). Precip also on track for late morning arrival in the west per the preponderance of model output. Might be a brief flurry across the northern mountains before noon on a small wave of lift/WAA. But the airmass is pretty dry, so it would be coming down from on high, and should make any accumulation or impact.

SHORT TERM /8 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/

WHAT HAS CHANGED...

Ice storm warnings and winter weather advisories issued. HWO updated.

Earlier discussion below.

Main changes was to lower snowfall amts some. Slightly more freezing rain across the northwest.

Sfc ridge axis extending south from 1030mb high centered over Quebec migrates through CPA tonight - bringing some clearing and colder min temps in the 15-25F range. The sfc ridge and shallow cold air wedge channels down the east side of the Appalachians by Friday morning - setting the stage for a classic CAD "overrunning" post-Christmas wintry mix event.

As was noted on the overnight shift, there was a slight shift to the north/northeast with the WAA which nudged QPF/snow/ice amounts a tad lower. The NAM was a notable leader?/outlier? with this trend.

This trend continued on the day shift here. The NAM tracks to primary low more to the northwest now, before transferring the energy off the coast late Friday. This resulted in warmer temperatures and less snow for Friday. For temperatures and snowfall, I ended blending the official and NBM by 50 percent each. Thus most areas still remain below freezing Friday, with a tight temperature gradient west side of the Laurels, with a mix of snow, sleet, and freezing rain across the CWA.

Most of the precipitation falls after 15Z west, and the heaviest pulls east of the area around early evening. Most of Friday night into Saturday will feature low clouds and some light freezing drizzle into Saturday morning. Most of the rest of Saturday should be dry.

More information below.

Strong warm air advection, isentropic lift, and healthy mid-to- upper level ascent will send anomalous moisture plume into a cold and dry boundary layer (sub-freezing wet bulb temperatures at the surface). This will allow for potential significant freezing rain over the southwest 1/3 of the CWA. The best and most consistent ZR signal (40-60% probs of at least 0.25" icing) remains over the Laurel Highlands and NW Alleghenies.

Looking into the interior and eastern portions of the CWA where the cold layer is gradually deeper with northeast extent, a snow/sleet to sleet/zr transition is forecast. Model output continues to flash a moderate to heavy sleet signal (0.5-1.0") over this area which essentially encompasses the central 1/3 of the CWA. Precip should stay snow the longest over the far north/eastern periphery of the CWA.

LONG TERM /SUNDAY THROUGH THURSDAY/

Another low pressure system is expected to track west of the area on Sunday will result in very warm temperatures again west of the Laurels. Most of our area should be just rain, but some light freezing rain could occur early on, especially to the north and east. Temperatures early Sunday will depend on how much clearing takes place ahead of the system Saturday night.

More information below.

A strong cold front plows southeastward across the region on Monday. A rain/snow transition may occur along the front with falling temperatures Monday afternoon. Windy conditions are expected behind the front Monday afternoon through Monday night with gusts over 40 mph possible. A blustery NW flow will also generate several inches of lake enhanced snow over the NW mtns later Monday into midweek. Min wind chills Monday night into Tuesday morning are fcst in the -5 to 10F range. Below normal temps are projected Tuesday and Wednesday.

AVIATION /03Z FRIDAY THROUGH TUESDAY/

VFR expected through mid morning Friday. High clouds will increase from NW to SE overnight.

Mid to later morning Friday, attention shifts to the arrival of frozen precipitation. Expect -FZRA to develop over the far west around 15-16Z. This will transition eastward through the afternoon but for this forecast package, the only airfields affecting toward the tail end of the forecast will be KBFD, KJST and KAOO. However, this will continue to move across all locations through the afternoon and evening with -FZRA mixing with -PL. Freezing rain results in low level moderate to severe icing in and out of clouds.

Some improvement for Saturday, but a strong cold front on Sunday will bring more adverse weather to the area.

Outlook...

Sat...Spotty precipitation tapering off.

Sun...Rain with -FZRA possible across higher elevations early, then becoming windy. Restrictions possible.

Mon and Tue...Windy and cold/er with snow showers across the mountains.

CTP WATCHES/WARNINGS/ADVISORIES

Ice Storm Warning from 10 AM Friday to 7 AM EST Saturday for PAZ004-005-010-017-024-033. Winter Weather Advisory from noon Friday to 7 AM EST Saturday for PAZ006-011-012-018-019-025>028-034>037-041-042-045-046- 049>053-056>059-063>066.