Wisp Resort / McHenry

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McHenry, MD

Forecast Discussion



... An arctic cold front will provide scattered snow showers and much colder temperatures into Friday. Dry weather and a warming trend is then expected through the weekend under high pressure.

NEAR TERM /THROUGH TONIGHT/... The Arctic boundary has arrived into the forecast area as the line of moderate snowfall drops south through the overnight and into the morning. Influence from Lake Erie will support a bit heavier intensity initially. However, with main shortwave support/best DPVA remaining in Canada, the snow showers should decrease in intensity as they accompany the front further southward. In addition, with the rapid cold advection behind the boundary, the already meager moisture will find itself in a layer generally colder than -18C a few hours behind the front. Thus, the window for accumulating snow will be rather short, with the best chance of seeing overnight 0.5 to 1.0 inch accumulations remaining north of I-80, where lake influence plays a role, and in the Laurels/WV ridges where upslope flow may help.

During the coming day, snow showers will be isolated to scattered overall, and with the main layer of moisture now colder than the DGZ, accumulation in many cases will be quite minimal. Lake influences will be the main driver of any additional to overall totals, with the various hi-res models suggesting the possibility of one or more Lake Huron-connected bands. These should amount to less than 1 inch in most areas, with up to 2 near Lake Erie and any location that sees extended residence time within a lake band.

Subsidence and dry air will shut off snow potential later tonight while residual cold advection generally drops area temperature through the day. A residual streamer may keep a bit longer duration snow shower in place along/north of I-80 past 00Z tonight. But the longer duration should cease by 06Z tonight. The combination of cold air and gusty wind will create single digit to negative wind chill values by Friday morning and last through early Saturday morning, with the coldest likely in the higher terrain to northwest PA. A Wind Chill Advisory is already in effect for eastern Tucker County, where confidence in a range of minimum values of -10F to -20F is highest. An advisory or at least an SPS may be needed along the ridges in Preston/Fayette/Westmoreland counties to account for the colder temperatures and higher winds.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... After a chilly start to the day Saturday, high pressure will quickly reposition east of the region as shortwave ridging develops aloft. This with increased insolation will foster a fairly rapid rebound in temperature, with late day highs returning to only 5 degrees below seasonal averages.

Further warm advection will occur through Sunday as a weak shortwave approaches and SW flow increases ahead of this feature. Temperature will rise 5-10 degrees above seasonal averages, though clouds will increase through the day. Passage of the trough axis with a weak sfc cold front Sunday aftn/night could be enough to create light rain/snow showers, but forcing will be weak with meager moisture, thus keeping current chances low. The bulk of the better chance of precip will be to the north with the better lift and moisture.

LONG TERM /MONDAY THROUGH THURSDAY/... Residual cold advection and delayed onset of warm advection will cause temperature to drop a few degrees from Sunday to Monday, but high pressure will ensure dry weather.

Ensemble variation in the structure and path of the next system is notable but shows a high probability in strong warm advection Tuesday with SW flow ahead of a deepening Four Corners trough. This should promote well above normal temperature, with precipitation chances increasing late in the day with a northern stream trough cross the Great Lakes. The mid week period will then remain active with the eventual north to northeast path of the Four Corners trough, resulting in additional periods of widespread precipitation. Ensembles favor the region being within the warm sector through this time, thus precipitation is more likely to be rain. A mix with snow is possible during the overnight periods as well.