Areas affected...eastern Ohio...much of Pennsylvania and into parts of New Jersey...Maryland...northern and eastern West Virginia...and northern Virginia Concerning...Severe potential...Watch unlikely Valid 282151Z - 282345Z Probability of Watch Issuance...5 percent SUMMARY...Local risk for gusty/damaging winds and marginal hail is evident early this evening across portions of the central Appalachians/mid Atlantic region. Threat will likely remain isolated and temporally limited however, likely precluding the need for a WW. DISCUSSION...Latest surface analysis shows a cold front arcing from eastern New York into central Pennsylvania, and then westward into central portions of Ohio and Indiana. Near and ahead of this boundary, diurnal heating has pushed surface temperatures well into the 80s. This, in conjunction with a moist warm sector (dewpoints into the mid 60s) is resulting in 1000 to 1500 J/kg mixed-layer CAPE across the discussion area. Storms have formed in two distinct areas -- across parts of eastern Ohio near the front, and into central Pennsylvania over the higher ridges of the Appalachian front. This is loosely in line with some CAM guidance -- particularly the HRRR that suggests both of these areas of development should continue to blossom over the next couple of hours, possibly evolving into loosely organized clusters. Area VWP data confirms model forecasts of a strengthening westerly flow field with height, and the resulting speed shear may enhance the potential for storm organization. As such, locally gusty/damaging winds may occur with stronger updrafts, and marginal hail also appears possible (particularly with the eastern Ohio storms where some updraft rotation has been indicated by radar in the past half hour). Given the overall isolated nature of the convection that is expected, and the sub-optimal time of day, risk should remain limited in both duration and intensity. As such, WW issuance is not anticipated. STEVEN'S THOUGHTS: A few of these thunderstorms will be capable of producing heavy downpours and wind gusts over 50 mph through 9 PM this evening. Most of the showers will collapse before reaching the coast. However, the Delawere River Valley has the best chance for thunderstorms.
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