textproduct: State College

WHAT HAS CHANGED

* Freeze Watch issued for McKean, Potter, Elk, and Cameron Counties late Monday night through early Tuesday morning

KEY MESSAGES

1) Frost/freeze conditions are probable Monday night into early Tuesday morning over the western and central Alleghenies

2) Extended stretch of dry and seasonal Fall weather this week

DISCUSSION

KEY MESSAGE 1: Frost/freeze conditions are probable Monday night into early Tuesday morning over the western & central Alleghenies

As of mid evening, partial clearing into our western areas, but the cold front is lagging to the northwest over southern Ontario. A rather deep upper level trough over northern New York state will deepen overnight, with a tight 500 mb height gradient by morning. This will lead to bands of lower SC clouds and gusty winds early Monday, but 500 mb heights come up fast later in the day. The rising 500 mb heights will aid in a cold night Monday Night, as winds weaken, and clouds fall apart with warming aloft and much drier air being advected into central PA.

More detail below.

The coldest air of the early Autumn season will push southeast into Central PA early this week with frost/freeze conditions expected Monday night into early Tuesday morning over much of the western and central Alleghenies (northwest of I81). We issued a freeze watch for 4 counties in the NW Alleghenies leaning a bit colder vs. NBM/MOS blend. Placement of sfc high becomes somewhat less favorable for frost/freeze Tuesday night.

------------------------------------------------------------- KEY MESSAGE 2: Extended stretch of dry and seasonable Fall weather this week

Low clouds entrenched on the eastside of the Allegheny Front with embedded areas of light rain, drizzle and fog will gradually improve tonight into Monday as the mean low level flow shifts from the east/southeast to the west/northwest behind a secondary cold front. The colder WNW flow could bring a couple of rain showers downwind of Lake Erie tonight into early Monday.

Otherwise, we continue to have high confidence in a prolonged stretch of dry and seasonable Fall wx this week (Mon-Fri) as a large area of Canadian high pressure dominates the pattern.

The next chance of showers looks to be next Sunday. Sunday has often been the more active weather day this summer and early into the fall now.

AVIATION /01Z MONDAY THROUGH FRIDAY/

Widespread restrictions will continue tonight as southeasterly flow brings persistent moisture and low ceilings across the region. Light rain and mist will continue at MDT and LNS, with mainly dry conditions elsewhere.

A high pressure building from west to east across PA will bring improvements to cloud cover at BFD and JST, but allow for fog development at least in the vicinity as winds also calm across the area. East of the Alleghenies will see low level moisture trapped, resulting in areas of fog and low stratus overnight. These conditions will remain until a cold front moves through late tonight into Monday morning. Behind the cold front, widespread VFR will be accompanied by northwest winds gusting 15 to 30 mph.

Outlook...

Tue-Fri. VFR prevailing. Brief restrictions possible in late night and early morning fog.

CTP WATCHES/WARNINGS/ADVISORIES

Freeze Watch from late Monday night through Tuesday morning for PAZ005-006-010-011.