Wisp Resort / McHenry

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McHenry, MD

Forecast Discussion



... A dry Thursday will give way to rain on Friday with the advance of strong low pressure.

NEAR TERM /UNTIL 6 AM THIS MORNING/... Low stratus will continue for most and keep temperature mild with subsidence aloft, but moisture at the surface. This is evident in the 00Z RAOB out of KPIT. Where clearing occurs to the northeast of Pittsburgh, some patchy frost is anticipated as temperature is allowed to fall to mid 30s, but this is not expected to be widespread enough to warrant an advisory at this late date.

SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY NIGHT/... Ridging in advance of an advancing Southern Plains low will maintain dry weather for Thursday, with temperature moderation about 5 to 10 degrees above the averages on the strength of insolation and ensuing warm advection.

The low is projected to cutoff as it digs over TN and KY on Thursday night and Friday. Strong warm, moist advection on its van will fuel rain for the Upr OH Valley Region probably beginning in the predawn of Friday over EC OH zones. Current indications are of totals 1 to 1.5 inches over the 24 hour period as mid level dry patch encroachment and low pressure progression are expected to alleviate a widespread flood threat. In addition, warm advection will cap low level moisture with heavier rain expected via upslope assistance east of the ridges. Otherwise, downslope wind will provide low level subsidence for eastern zones and mid level convergence areas are not model- sustained. That southeasterly downslope wind may be problematic though given potential gusts resulting from the inversion and low level jet converging with height upon ridge interaction. For now, have manually adjusted localized-gusts upward for Friday to begin an upward forecast trend.

By Friday night, rainfall will give way to scattered and light shower activity as the low digs over the Virginias and drops convective temperature via cooling mid levels.

LONG TERM /SATURDAY THROUGH WEDNESDAY/... Another deep low is forecast to across the Canadian Prairies this weekend, thus filling the Upper Ohio low on its van. Weekend shower potential is likely to be followed by a dry period to start the new work-week, but rain chance will quickly return with seasonable temperature throughout the period.