textproduct: State College

WHAT HAS CHANGED

* No new updates

KEY MESSAGES

1) A nice end to the Labor Day weekend.

2) Uptick in heat and humidity for mid midweek.

3) Showers, storms, and gusty winds Wednesday night into Thursday.

DISCUSSION

KEY MESSAGE 1: A nice end to the Labor Day weekend.

A refreshingly low dewpoint airmass has settled in across Pennsylvania and will ensure pleasant conditions for Labor Day outdoor activities. With high pressure over the region, clear skies, calm wind and quite cool temperatures have led to widespread fog development in the deepest river valleys across northern PA this morning.

After morning valley fog mixes out, Labor Day will feature weather conditions be about as good as it gets. A few wispy cirrus clouds will accentuate bright blue skies with abundant sunshine, passing fair weather cumulus clouds, and seasonable temperatures. High temperatures will range from near 70 in the northern tier to near 80 across the south central mountains.

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KEY MESSAGE 2: Uptick in heat and humidity for midweek.

As the center of high pressure drifts southeast of PA on Tuesday and Wednesday, return southwesterly flow will usher in an uptick and heat and humidity. The never ending ridge of high pressure centered over the Central US will also begin to nudge into the Mid Atlantic as upper troughing over the Northeast retreats and the amplified upper level pattern begins to flatten out a bit. Highs on Tuesday will range from the mid 70s to mid 80s and Wednesday will trend about 5 degrees warmer areawide. Combined with dewpoints back in the mid to upper 60s, heat index values may crest the 90F mark in the south central mountains on Wednesday. Dry conditions will prevail and we'll continue to enjoy a break from very active stretch of severe weather we've dealt with this summer.

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KEY MESSAGE 3: Showers, storms, and gusty winds Wednesday night into Thursday.

By Wednesday night, a low pressure system will be moving across northern Ontario with a cold front extending south through the Great Lakes and Ohio Valley region. The pressure gradient will support a notable uptick in synoptic scale winds Wednesday afternoon into Thursday. It's been awhile since we've had widespread gusty winds, but we're getting into the time of year where such a weather pattern becomes more common.

Gusty winds will ramp up Wednesday during the day out of the southwest ahead of an approaching cold front, and continue through Thursday afternoon shifting to a westerly direction after the front passes. Wind gusts of 25 to 35 mph seem realistic at this point, with the highest readings occurring at higher elevations in the Laurel Highlands.

The cold front will also bring a chance for showers and storms ahead of and along the front. The risk for severe weather will depend on the magnitude of a shortwave trough racing through the region and any associated jet dynamics in play. AI NWP guidance highlights the potential for severe weather in southeast PA at this time, but percentages remain low (the equivalent of a Marginal, level 1 out of 5, Risk) due to lingering uncertainty. Vertical wind profiles look unidirectional, so the primary hazard would be from damaging winds. Rain arrives in northwest PA late Wednesday night and will sag south across the Commonwealth during the day on Thursday.

High pressure builds behind the cold front, giving way to a dry and sunny Friday. There could be a few isolated PM showers and a storm or two on Saturday or Sunday, but most locations will stay dry.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Areas of valley fog will persist thorough 14-15Z this morning, though impacts to TAF sites appear to be unlikely. VFR conditions are expected once the fog dissipates with mainly clear skies and light winds. Another round of patchy fog will be possible into Tuesday morning, though it may not be as extensive as it is this morning. BFD and IPT will be most likely to see visibility restrictions develop.

Outlook...

Tue...AM valley fog possible; otherwise predominantly VFR.

Wed...Primarily VFR, although late-day SHRA/TSRA possible across the northern tier.

Thu...Cold FROPA could bring scattered SHRA/TSRA areawide.

Fri...Primarily VFR conditions, some potential for afternoon SHRA/TSRA but uncertainty remains high.

CTP WATCHES/WARNINGS/ADVISORIES

None.