After two weeks of seemingly nonstop heavy rain for parts of the Mid-Atlantic, a break from the wet weather is finally in store. The Bermuda High will shift off shore as a parade of shortwaves weaken its western flank and push it southeastward enough to keep the plume of moisture away from the Mid-Atlantic and New England. Over the weekend it will expand across the Southeast, where the flow of moisture will continue but result in fewer storms given the presence of high pressure aloft.
To say it has been wet would be an understatement. Parts of Pennsylvania, Maryland, and New York have received between 10 and 15 inches of rain over the last two weeks. Baltimore and Harrisburg both recorded their wettest July on record, with many other cities recording this July as a top five wettest month. The upcoming few days of dry weather has been long expected.
The arrival of the reprieve will come at a hefty cost. A shift of the Bermuda High in the peak of summer is no simple feat. The force required to achieve that may be sufficiently powerful enough to generate yet another flooding rain event for the same areas that have already been targeted by the tropical fire hose. The stalled frontal boundary, which served as tracks for a slow-moving trough to ride along and press against the tropical moisture since Monday, will finally garner enough momentum to push eastward. The intense dynamics of the front and jet stream will pull a vast swath of air upward, enough to generate a northeastward trekking cyclone along the frontal boundary Friday night. The rain will clear the inland Mid-Atlantic by noon Saturday, but could remain in eastern New England until the evening. Western New York, Southern New Jersey, Long Island, and southeastern New England are expected to be spared from the heaviest rain.
Behind a douse of heavy rain, clearing skies will be met with a warm welcome. “Warm” here is implied in a literal sense. The shortwave trailing the one responsible for Friday and Saturday’s flooding rains will flatten in the approach of a shortwave ridge over the Great Lakes. This will be enough to maintain dry weather for an additional two days through Monday night, but it will not be enough to keep the heat and humidity from the tropical high pressure over the Atlantic Ocean and the Southeast from intruding northward.
A brief heat wave will be the second cost incurred by the eviction of the Bermuda High’s moisture. Three days of temperatures in the low to mid 90s will bake the eastern Mid-Atlantic, southern New England, and the Hudson and Champlain valleys. The antecedent moist soils from the heavy rains will keep dew points in the low 70s, making it feel as hot as 100 degrees. It may be uncomfortable, but at least the heat will evaporate some of the floodwaters.
The heat wave will be broken Tuesday by a series of slow-moving shortwaves. Three days will not be enough to heal flooded areas, but it could be enough to buffer the effects from more heavy rain. While rain chances will return, it will not be an all-week washout. It could be dry throughout the region by Friday.