Wisp Resort / McHenry

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McHenry, MD

Forecast Discussion



... Upper-level high pressure will govern the weather in the upper Ohio Valley for much of the next week. Low chances for showers and storms will develop as moisture increases through the coming week. A gradual warming trend can be expected, with temperature approaching 80 by Thursday.

NEAR TERM /THROUGH TONIGHT/... A slow-moving Rex block structure advancing ewd into the wrn Atlantic and a wrn-CONUS ridge will maintain modest nwly mid-level flow across the Midwest and upper Ohio Valley. The first in a series of shortwave troughs will advance through this flow today.

A lack of low-level moisture (dewpoint depression of 20-30F) and assertive sfc high pressure likely will yield mainly increasing cloud cover, with any showers remaining very light and focused in the ridges, where light upslope flow may aid in updraft development.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... Weak cutoff low pressure over the Four Corners region is projected to split flow over the CONUS early next week with deeper moisture focused in a stalled frontal zone across srn OH/WV and far-removed from the forecast area.

Nevertheless, a second trough will advance across the region on Sun, with stronger forcing for ascent available owing to the passage of the left-exit region of a jet streak. Precipitation once again will be focused primarily along the ridges, and in the I-80 corridor where sfc convergence may be enhanced in a weak sfc trough.

As the upstream ridge advances ewd and amplifies, mid-level flow across the upper Ohio Valley will veer to more nly. As sfc high pressure reorients the stalled frontal zone on Mon, the combination of a modest moisture increase and ample heating could yield a few showers/storms primarily Mon afternoon, although forcing for ascent appears lacking at this time.

A warming trend is set to begin early next week, and temperature Sun and Mon will hover around seasonal average in the lower 70s.

LONG TERM /TUESDAY THROUGH FRIDAY/... Strong low pressure approaching the nwrn CONUS and a closed low exiting ewd from the Four Corners region will lead to amplification of an ern-CONUS ridge.

Despite increasing moisture and abundant insolation, convective coverage will be limited by an absence of forcing for ascent as the ridge axis will be ensconced along the Appalachians from the Gulf Coast to the Great Lakes and will limit ewd progression of shortwave troughs ejecting from the Four Corners low.

Any shortwave troughs that are able to traverse the periphery of the ridge could help increase coverage of showers and storms on a given day, but such waves will not be discernible at this time scale as they will depend on the effects of upstream storm systems.

The primary change to NBM data made during this time range was an increase in maxima/minima owing to bias-correction issues related to the prolonged cool period recently experienced. Although the strength and amplification details of the forecasted H5 ridge are inconsistent among models, temperature into the 80s late next week is a high- confidence forecast.