textproduct: State College

SYNOPSIS

* Slightly milder with an 8 to 10 hour period of steady rain today followed by even milder conditions Wednesday with a few showers, along and ahead of a strong cold front * Becoming windy and much colder Wednesday night through Friday * Lake effect snow may result in significant Thanksgiving holiday travel disruptions across northwest Pennsylvania, while scattered snow showers and a few squalls impact the weather across the Central Mtns, Laurel Highlands and possibly the Middle Susquehanna Valley

NEAR TERM /UNTIL 6 PM THIS EVENING/

Overcast skies resulting in a mild night/early morning relative to normals for late November with temps ranging from the mid and upper 30s across the NE CWA to the low and mid 40s over the Western Mtns and Southern Valleys where a 5-10 kt SSE breeze developed. Radar returns we're seeing on MRMS were almost exclusively virga falling from uniform mid level cloud bases around 11 KFT AGL.

Temps will be nearly steady through the mid morning hours and highest on the southwest ridgetops where a SSEly breeze may increase another 5 kts toward daybreak. The leading edge of a large area of stratiform rain is likely to be pushing into the Laurel Highlands right around sunrise Tuesday.

HREF and the consensus of deterministic models show the rain beginning near a KELZ to KUNV and KMRB line around 16Z, then early this afternoon across the Susq Valley - supported by a surge of low level warm/moisture advection via 30-40kt Sswrly 850mb LLJ.

Periods of moderate intensity rainfall are possible through this afternoon (especially across the eastern portions of the CWA), which could slow holiday travel.

Rainfall amounts by late this evening will average between 4 and 7 tenths of an inch with locally higher amounts possible in the 8 hour period from 1pm to 9pm as the axis of the LLJ crosses the Central Mtns and Susq Valley.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/

Steadier rain tapers to intermittent light rain/showers or drizzle from west to east late this evening into Wednesday morning as milder air continues to advect into the area and the main WAA and UVVEL pushes east of the region with the LLJ.

Tonight will be very mild relative to climo with min temps +15-20F above normal, ranging from the 40s to near 50.

The current, rather short-lived mild trend peaks Wednesday with afternoon high temps in the 50s to low 60s range, which equate to 10 to 20 degrees above the normal for late November.

Its worth noting that there is some uncertainty in the max temps due to the timing of the cold front; if the front passes earlier, temps will be lower and the 60s temps will be confined farther southeast. Rain coverage on Wed continues to look more limited/sparse compared to Tuesday, and likely confined right along/ahead of the cold front sweeping eastward through CPA during the afternoon and evening hours. Conditions turn breezy by Wednesday afternoon with gusts 20-30 mph.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Gusty winds continue to ramp up Wednesday night, possibly approaching wind advisory criteria with gusts nearing 45 mph. The strong wind will direct much colder air into the area sending temperatures plummeting Wednesday night through Thanksgiving Day.

Blustery post-frontal flow is expected through late week with peak gusts 35-45 mph range Thursday and Friday. Wind chills Thanksgiving morning are fcst in the low teens to mid 20s and will be even colder in the +single digits and upper teens for Black Friday morning shoppers.

The low level wind trajectory will shift from WSW to WNW Wednesday night through Friday - triggering lake effect snow downwind of Lake Erie. Several inches of snow accumulation and significant travel disruptions are possible - particularly across the NW snowbelts. A winter storm watch for heavy lake effect snow (6" or more) was issued for Warren and McKean counties where confidence in warning criteria snow is 50-80% per WPC WSO (in collaboration with CLE and BUF). The combination of heavy snow and blustery winds could also result in blowing and drifting snow. The heaviest snow looks to be from late Thursday afternoon into Friday afternoon.

Some heavier snow showers/squalls are possible farther inland reaching Interstates 80/99 on Friday as the flow aligns from the WNW. Some localized hazardous travel conditions are possible in sudden bursts of snow causing quick reductions in visibility and snow accumulation on roadways.

The lake effect snow pattern should end Friday night thanks to backing llvl flow and 1030mb high pressure sliding eastward from the Ohio Valley, producing a lowering subsidence inversion. Gusty winds should also relax by Saturday morning. A short break or lull in precip is most likely Saturday/Saturday night based on the NBM and GFS/EC models.

There is still some uncertainty with speed/timing, but overall guidance agrees in returning precip to the area on Sunday. Thermal profiles appear to be cold enough to initially support a mixed ptype transitioning to rain for the last day of November. Unsettled weather will continue into early next week as cold air in the middle of the country sets up a strong baroclinic zone over the eastern US.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Looking at VFR conditions early this morning with mid and high clouds.

Earlier discussion below.

Main change was to bump winds up overnight and on Tuesday, given that the winds are already gusty across the west, and the pressure gradient tightens today.

Winds likely to weaken some after dark this evening, as the pressure gradient weakens.

Showers will overspread the area after sunrise today, with MVFR to IFR restrictions later this afternoon and into the evening hours, as rain cools the airmass. Borderline for LLWS. Left LLWS out for now.

The rain will remain widespread through Tuesday night before tapering off into scattered rain on Wednesday. A cold front will come through Wednesday night bringing gusty winds and the possibility of lake effect snow across the NW through Friday.

The lake effect and upslope snow could become more widespread into the Laurel Highlands (i.e. JST) as one heads further out in time, i.e. on Friday. UNV and AOO could see some flurries and snow showers as well. This based on winds shifting more to west to northwest, from the west southwest direction. Often this takes some time, as the warm lakes tend to modify the wind fields.

Outlook...

Wed...Breezy with intermittent rain showers; becoming windy with sharp CFROPA Wed night with gusts >30kt from 240-270 deg.

Thu-Fri...Windy with gusts 30-35kt from 270-300 degrees. Frequent snow showers over the NW 1/2 of the airspace.

Sat...Improving conditions/lighter winds with snow showers ending downwind of Lake Erie.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Storm Watch from late Wednesday night through Friday evening for PAZ004-005.