Wisp Resort / McHenry

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McHenry, MD

Forecast Discussion



... One more dry day is forecast under high pressure, with temperatures near or just above 90 in many areas. An approaching weak front returns rain chances by Tuesday. Warm and humid weather will dominate the rest of the week, with daily rain chances, as the front stalls.


Weak surface high pressure will drift east of the CWA today in weak quasi-zonal flow aloft. Moisture will remain fairly restrained, especially in the mid levels. This will prevent the scant diurnal cumulus that are able to develop from obtaining too much vertical depth, and it will also prevent any diurnal convective precipitation from developing.

Above normal highs are expected right around or just below 90 at most locations.

SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... The run of dry, quiet weather will come to an end for the region during this period. Weak mid-level troughing will drop into the Ohio Valley later Monday night and on Tuesday. This will also push a frontal boundary into IN/OH and toward the western end of Lake Erie by 12Z tomorrow morning. With southwesterly flow bringing moisture northward ahead of the front, there may be enough support to produce a few showers in eastern Ohio towards sunrise.

The front will only make painfully slow progress south and east through Wednesday as it aligns itself to the still weak mid-level flow. On Tuesday, PWATs exceeding 1.5 inches and sufficient instability will allow scattered showers and storms to develop by the afternoon. PoPs will be highest in the northwest CWA, close to the boundary. Coverage will diurnally decrease Tuesday night, but then ramp up again Wednesday, with the southeast CWA getting the higher precip probabilities due to the progress of the boundary.

Soundings indicate that there should be enough warm air aloft to limit CAPE and thus tamp down the severe risk. However, the weak flow will promote slow storm motions, and the deep warm cloud depths will allow for some efficient rain-making cells. Localized heavy rain totals are possible, but the dry antecedent conditions will keep the flood risk low.

Temperatures will remain above normal through the period, with the front only providing marginally cooler air as it passes. Readings in the upper 80s to near 90 will remain common both days.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... The main belt of westerlies is expected to remain to our north through the extended period, with ridging across the southeast CONUS remaining in place. As a result, the frontal boundary is expected to stall in the general vicinity of the middle Ohio Valley into next weekend. This will keep daily chances of showers and thunderstorms in the forecast through Sunday, with coverage best during the afternoon and early evening thanks to diurnal influences. With plentiful moisture remaining in place, localized heavy rainfall may continue to be a concern, especially in areas near the quasi-stationary front. Temperatures will remain above normal, although 90 degree readings should be few and far between thanks to the front and precipitation.