Wisp Resort / McHenry

Summary

SYNOPSIS

... High pressure will move offshore through Wednesday. A cold front will approach from the Midwest late Wednesday, then cross the northern Mid-Atlantic Thursday. The front will stall to the north across Pennsylvania keeping the local area in a warm and humid air mass through early next week.

NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... A weak shortwave will move through western parts of the area this afternoon. This, along with slightly increased instability will allow for an isolated shower or thunderstorm to pop up this afternoon across areas along and west of the I-81 corridor. With weak flow in place, the storm motion will be stagnant and could drop 1 to 2 inches in isolated areas for any storms that form. Also cannot rule out some small hail with slightly elevated lapse rates in place. Highs for today will continue to climb into the low to mid 80s for most areas aside from the mountains where upper 70s will be more common. By tonight, mid and high level clouds will build in with some patchy fog possible, especially in areas that receive rainfall. Overnight lows will fall into the low 60s.

SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... High pressure will continue to slide further east on Wednesday, with approaching low pressure system centered just west of the Great Lakes. This low and its associated cold front will continue to slide further east Wednesday into Thursday. Unsettled weather will be possible both Wednesday and Thursday.

For Wednesday, isolated to widely scattered showers and thunderstorms will be possible during the afternoon and evening hours. Cannot rule out a strong to severe thunderstorm, especially along and west of the Blue Ridge where areas will be most separated from the lingering subsidence as a result of the departing ridge. Highs on Wednesday will rise into the mid to upper 80s. Cannot completely rule out a few localized sites hitting 90 degrees.

A more potent setup on Thursday will be possible across the Mid- Atlantic as a result of the approaching cold front. Timing continues to be favorable for peak heating with moving through the area. Increased instability parameters will allow for increasing showers and thunderstorms. Some of these storms may be strong to severe in nature. The main hazards for these storms will be damaging winds and large hail. The best chances for any severe storms will be along and south of I-66. Highs will be in the upper 70s to mid 80s for most areas. The storms should begin dissipate by Thursday night with lows tracking into the upper 50s in the mountains to the low to mid 60s further east across the lower elevations.

LONG TERM /FRIDAY THROUGH TUESDAY/... On Friday, shortwave energy aloft will be approaching the area before traversing to our north Saturday afternoon. At the surface, a frontal boundary will be draped south of the Great Lakes will be pushed southward towards our area. This will leave the region in the warm sector, leading to a prolonged period of unsettled weather. The frontal boundary is set to sink over the area on Saturday before stalling over the region throughout the long term. Daily thunderstorms driven by diurnal heating and the nearby frontal boundary are expected with warm and humid conditions leading to the possibility of some storms being severe. Daily CAPE values greater than 1000 J/kg and lapse rates greater than 6 C/Km are expected each afternoon. While conditions are the most favorable on Sunday with the highest levels of CAPE and steepest lapse rates,

Low pressure to our south will provide the area with plenty of moisture on Friday. WPC has the southwestern portions of the forecast area in a marginal risk for excessive rainfall on Friday with locally heavy rain possible during storms.

High temperatures will be in the upper 70s to low 80s each day with overnight low temperatures dipping into the mid 50s to mid 60s each night. Temperatures cool slightly in the wake of the cold front early next week.