textproduct: Pittsburgh

SYNOPSIS

Dry weather is expected through Friday afternoon with temperature rising around 10 degrees above the daily average. A series of low pressure systems will promote widespread Friday night through Monday while temperature remains above normal.

NEAR TERM /THROUGH TONIGHT/

KEY MESSAGES:

- Probabilities favor some amount of sunshine Thursday afternoon, with longer duration of sunshine to the southeast. - Expect high temperature around 5-10 degrees above the daily average. --------------------------------------------------------------------

Weak height rises as an embedded shortwave over Ohio lifts northward will allow subsidence to slowly erode area clouds through the day Thursday. By 3pm, ensembles suggest high probabilities (60-80%) for enough cloud breaks to enjoy some sun before it sets, with highest confidence around/east of Pittsburgh. Enjoy it before another multi-day run of cloudiness develops! Modest warm advection and some insolation will continue the prior temperature rises to aid highs reaching 5-10 degrees above the daily average.

Above normal low temperature is favored Thursday night as warm advection aloft increases mid-high level cloud decks ahead of the first in a series of lows lifting NE out of the southern Great Plains.

SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/

KEY MESSAGES:

- Back to back low pressure systems will generate widespread rain, with higher QPF amounts likely with second system. - Associated warm air will drive temperature 15 to 20 degrees above the daily average. --------------------------------------------------------------------

Southerly flow is expected to increase through the day Friday as low pressure beings to lift out of Texarkana toward the western Great Lakes. Influence from surface high pressure over New England and subsidence ahead of the upper shortwave favors dry weather holding out for most of the daylight hours. The main influence will be increased cloud cover at temperature rising 10 to 15 degrees above the daily average.

Rain is favored to overspread the region Friday night into Saturday morning as the upper shortwave lifts NW of the region. Upper jet positioning and terrain convergence will favor a corridor of higher QPF to the south and east of Pittsburgh, where probabilities of >0.25" are generally above 60% (probabilities fall to the NW). Overnight temperatures are likely to fall most notably after precipitation onset due to wet-bulbing before steadying as those effects are countered by warm advection. Ensembles favor a downward trend in precipitation chances Saturday amid weak shortwave ridging between systems, with the occasional light rain/sprinkle occurring as a result of warm, moist air being in place. Models suggest that locations along and south of I-70 will have a 40-70% probability of 60+ degree highs for Saturday afternoon.

The next low pressure system and upper trough will quickly follow late Saturday through Sunday, taking more of an eastward jaunt as its lifts northward than the first system. Confidence is high for another round of widespread rain that likely will have a better Gulf of Mexico moisture fetch leading to higher QPF totals. Uncertainty increases in the timing and depth of the lifting trough feature, which will likely impact the positioning and high-end potential of the QPF axis. Mean 24-hour totals at this time suggest an additional 0.75"-1.5" of rain on top of Saturday morning's total, but large model QPF spread highlights that uncertainty in the system positioning/dynamics. AT this time, flooding isn't a concern though higher-end totals may cause some river locations (most likely along the Monongahela River) to reach action stages. Sunday night likely features a transitional period is the system begins to move northeast, with dry advection behind the surface cold front eroding at precipitation chances and offer some temperature reduction.

LONG TERM /MONDAY THROUGH WEDNESDAY/

KEY MESSAGES:

- Temperatures well above-average for the weekend. - Rain returns Saturday and lingers into the start of next week. --------------------------------------------------------------------

Early model consensus favors dwindling of precipitation chances Monday in the wake of Sunday's system, with weak vorticity advection in NW flow. However, if that system more quickly transits to the NE and allows for zonal flow to develop, current precipitation chances may end up overstate. This will also dictate the degree of cooling seen Monday, though confidence is very high that temperature will remain at least 5-10 degrees above normal.

Ensembles currently favor another upper level trough passage around Tuesday that may presage a pattern shift (longwave eastern CONUS trough) ahead of the New Year. This scenario will result in periodic precipitation chances that lends to more lake-favored areas (northwest PA and the higher terrain) and temperature dropping below the daily averages. A lower probability scenario does exist where Caribbean ridging remains more stubborn and limits height falls over the Upper Ohio River Valley; this would likely delay temperature falls and keep more widespread precipitation chances in play.

AVIATION /07Z THURSDAY THROUGH MONDAY/

Guidance indicates improvement to VFR is likely overnight as the stratocu deck erodes northward. Will likely see MVFR fog develop at the fog prone ports as moisture near the surface remains elevated. The low clouds will continue to decay northward and FKL and DUJ should see these clouds scattering out by late afternoon or early evening.

Outlook...

VFR is expected through Friday under high pressure. Restrictions and rain are likely Friday night and Saturday with a crossing warm front. More widespread restrictions and rain are expected again Saturday night through Monday with low pressure.

PBZ WATCHES/WARNINGS/ADVISORIES

PA...None. OH...None. WV...None.