Marine Weather and Tide Forecast for Whitaker, PA

NEAR TERM /THROUGH TUESDAY/
KEY MESSAGES:

- Clouds increasing from south to north.
- Showers moving in and continuing through tonight.
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Evening update: Very few tweaks made to previous forecast. Mainly updating POPs and ingesting the latest NBM data for the current period. Our first precipitation is just crossing our southern border at this time and climbing on north. Latest ACARS soundings from PIT still show a very dry SFC-700 mb layer that will struggle to saturate from the top down as these first showers move through.
Areas may experience a period of high-based sprinkles before any kind of steadier showers arrive behind the initial push. Portions of the previous discussion below:

A closed upper low across the Mississippi Valley will slowly begin to meander northeast today overspreading height falls locally as a southeast to northwest oriented mid-level ridge slides off to the east.

Broad ascent with height falls, lobes of mid-level vorticity, and increased low level convergence on the nose of an 850 mb jet will eventually support a shield of rain this evening and continuing into the overnight hours. The best deep layer moisture through tonight is forecast to be across western Pennsylvania and northern West Virginia where the highest PoPs and amounts will lie while areas of eastern Ohio are favored to see more scattered showers and even some dry periods possible.

SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/
KEY MESSAGES:

- Rain continues with locally heavy amounts possible in the ridges.
- Moderating temperatures through mid-week.
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The upper low will cross through the Tennessee Valley on Tuesday with continued deep warm and moist southerly flow pumping precipitable water values locally up to 1.25-1.5" which is nearing or exceeding the 90th percentile climatology. Spokes of vorticity will support scattered showers in a very moist atmospheric setup, and the higher amounts and steadier rates will be favored to the east along the ridges on Tuesday in conjunction with the best jet support. That said, HRRR probability for >250 J/kg of CAPE reach up to 80% west of Pittsburgh aided by some slightly drier mid-level air. This could allow for convective enhancement in the afternoon hours and locally higher rainfall rates/totals, though severe weather is not expected given the saturated profiles and lacking instability.

WPC has maintained the Marginal Risk (1/4) across our entire area, but widespread flooding concerns are not expected and would only be tied to areas that see training heavier showers or thunderstorms as rainfall rates are not forecast to be much of a concern. Current flash flood guidance in a 1 hour period is ~1.25-1.75" and a 6 hour period >2.5" across most of the area. HRRR probs for these amounts are low (less than 10%), but forecast mbE vectors show values around 12 knots or lower which would point toward the potential for slow moving showers/storms.

Wednesday, as the core of the upper low is close overhead, we may see a decrease in overall rain totals and coverage given lack of stronger synoptic ascent. But, mid-level temps will cool some under the cold core low and allow for some better destabilization into the afternoon hours. NBM mean SBCAPE values are upwards of 1000 J/kg and could nudge even a bit higher if clouds can scatter at all, though that's a low probability solution. What we will be lacking is appreciable shear given the minimal flow as we're sitting very close to the core of the low. It's likely that we'll see a diurnally driven enhancement in showers and storms in the afternoon, but severe weather is low probability. Will have to continue watching for localized flooding threats, but if the CAPE profiles are deep enough, we may not capitalize on warm rain processes which could help mitigate heavy rainfall.

Most likely total QPF through Wednesday night is between half an inch to an inch of an inch outside of the ridges. Over that way, values are up toward the 1.5-3" range. The higher end of the goal posts could put 1-1.25" in the lowlands and up to 3.5" in the ridges tied to aforementioned convection. The lower end suggests at least a quarter inch areawide.

LONG TERM /THURSDAY THROUGH MONDAY/
KEY MESSAGES:

- Strong to severe thunderstorms possible Thursday night.
- Temperatures 15-20F above normal Thursday/Friday and cooling slightly into the weekend.
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Ridging building ahead of a strong trough in Upper Mississippi River Valley will allow for a drier and warmer setup on Thursday, though will maintain the mention of some residual showers across the ridges especially. 850 mb temperatures locally could warm into 14-17C range and a 30-50% chance of highs >85F. That chance ramps up even more on Friday to 60-80% with stronger warm advection in southerly flow, but confidence isn't quite there yet given the dampening effects of cloud coverage.

Models have remained relatively persistent at pushing strong warm advection across area late Thursday night and Friday morning.
That is when the strongest moisture transport is shown to push through Upper Ohio River Valley and a cold front drags through from the west. Still some timing differences among the ensembles with the upper pattern and progression of the cold front; current general consensus is pointing toward the overnight hours but solutions on the faster and slower end still exist with the slower one more suggestive of a higher severe weather chance. SPC post-processing GEFS based severe shows highest probabilities of severe staying west of the area on Thursday and then south and east of the area on Friday which appears reasonable given the most likely front timing.

An unsettled pattern is favored into the first half of the weekend with rain chances continuing, but heights begin to rise on Sunday as troughing exits suggesting a drier trend, although timing differences in the ensembles suggest showers are still possible into Sunday.

AVIATION /00Z TUESDAY THROUGH SATURDAY/
The initial wave rounding the eastern periphery of an upper level low will bring mainly light rain as it crosses the region through 06z, with the surface warm front stalling near I-80. A plume of moisture will continue to work NW from the Mid-Atlantic to create light rain through Tuesday morning, favoring western PA and the WV higher terrain. Uncertainty remains high on timing and coverage of cig reductions amid moist advection/convergence and likely will be predicated on areal coverage of rain to moisten the prior dry air mass. TAFs through 12z exhibit a blend of the less aggressive HRRR probabilities and more aggressive LAMP/MOS guidance.

Diurnal heating will be the primary driver of cig alterations Tuesday as the airmass remains moist, if somewhat stagnant. The expectation is greater heating/lift in OH will yield greater improvements than in northwest PA where IFR could linger most of the day. Broad ascent will favor scattered to numerous rain showers, but probabilities peak at 30-40% for afternoon thunderstorms at MGW/HLG/ZZV.

Outlook...
Restrictions and periods of showers with afternoon thunderstorms will continue into Wednesday before the upper level low shifts east of the region.

Brief VFR under ridging Thursday will give way to a fast-moving low pressure system Thursday night into Friday. An active weather pattern within turbulent upper flow should result in periodic rain and restrictions chances into the weekend.

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