Marine Weather and Tide Forecast for Prospect, PA

NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:

- A crossing front bring showers and thunderstorms south of Pittsburgh through this evening, while locations to the north remain dry.
- Higher rainfall rates and increasingly saturated grounds creates risk for flash flooding, mainly south of I-70.
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A surface front cuts across eastern Ohio/southwest Pennsylvania this afternoon, extending from low pressure over the St.
Lawrence River Valley and spurred on by an associated shortwave trough. Deep mixing over the region has allowed for 20 to 30 MPH wind gusts at the surface as a low-level jet crosses; these gusts will subside this evening. Temperatures have reached seasonable levels in the lower to mid 80s.

To the north of the boundary, dry conditions continue to be favored, with seasonable temperature and lower dewpoints.
Convective development ahead of the front remained isolated through 18Z, much of it confined to areas south of the PA/WV border, although some cells are now forming in the Laurels.
This is in agreement with CAMs, which overall are fairly muted regarding afternoon/evening activity. A decent environment supporting efficient rainfall still exists south of the boundary, particularly in the ongoing Flood Watch area.
Precipitable water values of 1.6 to 1.8 inches are in place south of I-70, along with MLCAPE of 1000-2000 J/kg and warm cloud depths of 10-12 thousand feet. Still cannot rule out the potential of waves of east-to-west moving storms containing 1-2" per hour rainfall rates. A training setup would be supported by the boundary eventually becoming parallel to the zonal mid- level flow as it moves south of Pittsburgh. Given the antecedent saturated ground, maintenance of the ongoing watch seems prudent, with any extension of said watch being deferred until overnight trends become more clear. A secondary threat will be the potential for isolated strong to damaging wind gusts over the same general area, with pockets of 600-900 J/kg of downdraft CAPE through the afternoon.

The surface boundary is still expected to stall near the I-68 corridor tonight. Convection will largely dissipate by 06Z with the loss of heating and upper support. That said, isolated showers may continue into Friday morning along the stalled boundary given the warm, moist environment.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
KEY MESSAGES:

- Diurnally driven convection is expected Friday along and south of the stalled boundary, favoring mainly northern WV, with dry conditions to the north.
- The front likely returns north on Saturday, bringing a risk of heavy rain and flooding to a wider area.

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The front is likely to remain stuck to the south of Pittsburgh on Friday, with weak mid-level ripples traversing from west to east to the south of the boundary. This keeps rain/thunderstorm chances to the south of Pittsburgh, mainly over northern West Virginia. To the north, surface high pressure will favor dry weather and temperatures even falling a touch below seasonable levels. Any risk of flooding/severe wind gusts will remain confined to areas south of the Mason-Dixon Line, where precipitable water values remain above the 90th percentile and where there is a 40 percent chance or greater chance of 1000 J/kg of surface-based CAPE. Deep shear remains near or below 20 knots in this area as well, meaning lower end downburst/storm training risks.

A slightly more potent shortwave traveling across the Middle Ohio Valley on Saturday could waver the boundary back north again, bringing the 90th percentile precipitable water air mass back northward. There remains a bit of question as to the northern extent of the boundary and deeper moisture, as well as the possible influence of some sort of remnant MCS, crossing the western Great Lakes during the morning. However, the moisture level and the better potential for general support of lift leads to high rain chances areawide. There remains decent confidence that flash flooding risks will extend further north and east as compared to Saturday, encompassing more of eastern Ohio, northern West Virginia, and perhaps extreme southwest Pennsylvania at least, with the potential for a larger area.
Further refinement in the threat area is likely once CAMs encompass the Saturday period. For its part, WPC encircles the entire CWA with a slight risk of excessive rainfall. Another Flash Flood Watch for this period is certainly possible, covering the afternoon and evening hours. Isolated instances of damaging wind may be possible as well with possible dry air aloft, supported by machine- learning guidance.

More scattered activity could linger into Saturday night although intensity is likely to decrease with the diurnal loss of instability. Another soupy night is forecast, with lows of 70 or higher south of I-80.

LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/
KEY MESSAGES:

- Monday may feature a break from the rainfall and humidity as high pressure crosses.
- Occasional rain chances exist from Tuesday through Thursday as the overall weather pattern remains active.
- Flood and severe potential remain highly uncertain and is likely largely predicated on prior days outcomes.
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Ensembles are in decent agreement that the boundary will once again sink south across the region on Sunday in response to increasing northwest flow aloft on the periphery of building lower Mississippi Valley ridging. Another round of showers and storms is likely, with coverage peaking diurnally. With precipitable water remaining high, a threat of at least isolated flash flooding issues remains, perhaps with a tilt towards areas south of Pittsburgh depending on the position of the front during the peak heating period. A severe risk cannot be ruled out as well, with potential dry air aloft feeding a downburst threat.

The best chance for a break in the rainfall (as well as the humidity) appears to be Monday, as surface high pressure traverses the Great Lakes, keeping the boundary to the south. Thereafter, the ridging expands northward into the lower/middle Ohio Valley, leading to a slow build in 500mb heights over our region. Thus, a warming trend back to above-normal temperatures expected - probabilities for 90 degrees or higher rise into the 50 to 80 percent range by Thursday. Shortwave movement in the ongoing northwest flow aloft will continue to provide shower and storm chances from Tuesday on, and flooding/severe risks cannot be ruled out during the period.

AVIATION /17Z THURSDAY THROUGH MONDAY/
Scattered to broken cumulus clouds will continue through late afternoon as convective temperature have been reached.

A surface boundary will drift south across the Upper Ohio Valley region this afternoon and evening, and will be the focus for showers and thunderstorms. Maintained a prob30 mention for thunder for airports generally from ZZV to LBE, where timing of convective development along the boundary is in question. MGW has a higher chance of seeing thunder, so maintained a Tempo with a subsequent prob30 to account for convection along and ahead of the boundary. Expect MVFR to IFR stratus and patchy fog to develop overnight with low level moisture in place.

Outlook...
After any morning for or stratus, shower and thunderstorm chances are expected mainly south of a ZZV-LBE on Friday as the surface boundary drifts southward. The front will return north as a warm front on Saturday, with more numerous showers and thunderstorms across the area. Additional showers/storms are expected Sunday as the front returns south as a cold front.
There will also be a potential for overnight/early morning fog and stratus through Sunday night. Mainly dry weather is expected for Monday as high pressure begins to build in. A chance of showers/storms returns Tuesday with approaching low pressure.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...None.
OH...None.
WV...Flood Watch until midnight EDT tonight for WVZ012-021-509>514.