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FXUS61 KPBZ 111640 AFDPBZ

Area Forecast Discussion National Weather Service Pittsburgh PA 1240 PM EDT Sat May 11 2024

SYNOPSIS
Rain showers and scattered thunderstorms are likely through tonight with passage of a cold front. Dry and more seasonable weather will develop through Monday before the next round of upper level disturbances increase precipitation chances midweek.

NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:

- Showers and thunderstorms expected through tonight, favoring NW PA - Low probability for small hail and gusty wind through this evening -------------------------------------------------------------------

A warm front, centered on the 700mb layer, will continue to push a swath of light to moderate rain showers through the region during the afternoon period. Dry slotting will promote quick precipitation dissipation after passing of that warm front. The surface cold front will quickly cross the region thereafter as the 500mb trough axis drifts over the Great Lakes.
Scattered convection will develop ahead of this boundary (with light showers lingering with trough axis) through the evening before tapering off overnight.

Cold advection aloft will increase lapse rates over the region and create a low probability potential for small hail/gusty wind dependent upon degree of heating that occurs behind the warm frontal band. Latest HRRR modeling suggests instability/shear will be best aligned along/south of I-70, but drier air and weaker forcing should limit much in the way of convective development. Stronger convection is more likely over northwest PA given greater cooling aloft and stronger forcing, but weak shear and more limited instability development is likely to keep convection sub-severe.

High pressure and subsidence will slowly clear out showers and area cloud cover from SW to NE overnight, though NW flow may persist such conditions longest over northwest PA. Low temperature will be near the seasonal average.



SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
KEY MESSAGES:

- Dry weather likely, saving for passing disturbances near far northwest PA.
- Above normal temperature likely by Monday.
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Shortwave ridging ahead of a deepening central CONUS upper trough will promote dry weather and rising temperature through Monday. Residual NW flow Sunday with the surface high just to the west will limit the degree of temperature rebound. But as heights further increase Monday and the surface high positions along the eastern coast, warm advection in southwest flow will drive temperature to about 5 degrees above the daily average.

Any precipitation chances during this period will be tied to shortwave movement well to the north and the positioning of a developing warm front near the region. Latest trends lift the warm front and upper wave north of the region, but will maintain low probability chances in northwest PA in case those trends change.

LONG TERM /TUESDAY THROUGH FRIDAY/
KEY MESSAGES:

- Midweek showers and thunderstorms likely, with limited severe and flooding threats.
- Dry conditions likely to end the week.
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The sagging central plains trough will meander eastward across the TN River Valley Tuesday into Wednesday, with weak shortwaves likely traversing the Upper Ohio River Valley ahead of the wave.
Showers and thunderstorms are likely through the afternoon/evening Tuesday, though positioning of forcing and potential influence of shortwave ridging in the mid-Atlantic could alter the areal coverage/probabilities. Early analysis suggests that the instability/shear parameters are unlikely to promote much severe threat, while forcing/deep moisture should remain south of region and limit a flooding threat (only 20% probability of seeing greater than 1" of rain over 24 hours at any location).

The trough will progress towards the eastern coast Wednesday, with low positioning and depth dictating how long precipitation will linger in the Upper Ohio River Valley. Ensembles are confident in ridging developing over the lower Ohio River Valley late week that should promote a few day period of dry weather and above normal temperature.

AVIATION /18Z SATURDAY THROUGH WEDNESDAY/
After the exit of a mid-level warm frontal rain band, dry advection aloft may create a window of drier weather at TAF onset before scattered to numerous showers and thunderstorms develop along the cold front. Upper level support and greater moisture depth will favor northwest PA for this convective activity, with decreasing probabilities moving towards KZZV.
Sufficient wind flow aloft, and a low freezing level, should result in gusty wind and small hail in some of the storms.

Shower activity will slowly dissipate overnight (ending later in NW PA) with the exit of the surface cold front and upper level trough axis. Cold advection by Sunday morning should return MVFR to localized IFR stratocu to most terminals before high pressure and subsidence lift area cigs to VFR levels.

Outlook
VFR favoring through Monday under the influence of high pressure. Slow progression of the next upper level trough system means increases precipitation and restriction potential Monday night through Wednesday night, peaking Tuesday night into Wednesday.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...None.
OH...None.
WV...None.

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