textproduct: State College

WHAT HAS CHANGED

* Wind and Winter Weather Advisory extended until Tuesday morning/afternoon

KEY MESSAGES

1) Severe t-storm risk confined to southeast quadrant of CPA through early evening

2) Quick burst of moderate to heavy snow and sharply falling temperatures to bring slippery travel across the Alleghenies this evening into early tonight

3) Much colder with a couple of locally heavy snow showers possible Tuesday

DISCUSSION

KEY MESSAGE 1: Severe t-storm risk confined to southeast quadrant of CPA through early evening

Focus for severe t-storms appears confined to the southeast quadrant of the CWA over the Lower Susquehanna Valley. This area is on the northern end of linear convective line evolving eastward from DCA/BWI. Within a deeply meridional wind profile, damaging winds and embedded tornadoes will be the main hazards. Latest WOFS is more bullish on severe risk (both wind and tor probs) to the south of the MD line toward Chesapeake Bay. We plan to trim the Tornado Watch #68 based on the latest SPC watch status report.

KEY MESSAGE 2: Quick burst of moderate to heavy snow and sharply falling temperatures to bring slippery travel across the Alleghenies this evening into early tonight

Well-defined surface/arctic cold front is on the western doorstep at 18-19Z. Observed 1hr temp drops are on the order of 10-15 degrees along with wind shift to the west. In wake of this FROPA, temperatures will continue to plummet due to strong CAA, while mid and upper level flow remains southerly in response to the strongly tilted and digging upper trough. Combined with upslope enhancement, this will cause precipitation to rapidly transition to snow from the Laurel Highlands across the western and central Alleghenies through the evening commute.

While some snow accumulation may be initially limited to non- paved surfaces particularly at lower elevations, the higher elevations will see a two-part winter wx event consisting of front-end "thump" followed by lake-enhanced upslope flow. A brief period of snowfall rates surpassing 1"/hr (>60% chance) is expected btwn roughly 00-04UTC where a quick 1-4" of snow is fcst. Typically favored locations +2,000ft elevation should continue to see additional minor accums into Tuesday with local amounts 4+ possible.

Pressure rises and steeper lapse rates/colder air aloft will maintain gusty winds with max gusts approaching advisory levels.

KEY MESSAGE 3: Much colder with a couple of locally heavy snow showers possible Tuesday

As the trailing vorticity maxima and secondary shortwave embedded within the trough over the OH Valley moves east Tuesday afternoon, convective cellular snow showers and isolated snow squalls could develop across the area. Additional snowfall accumulations will be light with any of these convective elements, but briefly heavy snow rates and gusty winds could cause local travel impacts due to rapid reductions in visibility. A SPS may be needed due to the broad coverage of locally heavy snow showers.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Expect quick drop to MVFR/IFR across the western terminals late this afternoon behind sharp cold front pushing eastward across the airspace. Rain will transition to a brief period of mdt to heavy snow with highest confidence in LIFR at KJST and KBFD. Showers/severe storm risk shifts eastward from KMDT/KLNS vcnty by 23Z. VFR showers in the central airfields KAOO-KUNV-KIPT transitions to MVFR or IFR as colder air mixes rain to snow by this evening. Pattern transitions to brisk westerly flow late tonight with scattered to frequent snow showers expected through Tuesday afternoon.

Outlook...

Tue...Blustery. Sct +SHSN and brief IFR.

Wed-Sat...VFR to MVFR with ocnl light rain or snow.

CTP WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 8 AM EDT Tuesday for PAZ004>006-010>012- 037-041. Winter Weather Advisory until 5 PM EDT Tuesday for PAZ004>006- 010>012-017-018-024-033. Wind Advisory until 11 PM EDT this evening for PAZ042-051>053- 057>059-065-066.