Soggy, Humid, Tropical-like Along the East Coast (Photo Credits: CPC, WPC, Tropical Tidbits, College of DuPage)
If you’re like me and enjoyed the past few days of low humidity with plentiful sunshine in the northern Mid-Atlantic, you will not like this 2-week outlook. The Climate Prediction Center has issued their 6-10 (below) and 8-14 day precipitation probability outlook through the end of July into the beginning of August. It’s anything but sunshine and low humidity, but let’s dive into the setup and why the forecast calls for above normal precipitation along the East Coast.
The shortwave that is diving into the Ohio Valley shown below which was the lifting mechanism for the severe weather outbreak across Kentucky this afternoon and evening (July 20th) will be one of the keys to this upcoming wet forecast along the East Coast. This animation from GOES-16 Water Vapor shows this interaction between the shortwave moving into the Ohio Valley igniting the severe storms in Kentucky/Indiana, (satellite animation credited to College of DuPage).
Looking at the 500 mb pattern this weekend (July 21-22) an almost wintertime storm pattern develops. There is a substantial cut-off low pressure across the Ohio Valley, the same system that produced the severe weather mentioned above. The two ridges, one to the west across the High Plains region as well as the Bermuda high stretching and strengthening into portions of eastern Canada, keep will keep this pattern locked in.
The position of the cut-off low sits around the Ohio Valley will allow for a low pressure to develop and rotate around the counterclockwise circulation and up the East Coast. Shown below is an animation from the GFS depicting the coastal low’s location and intensity with the precipitation overlaid, courtesy of Tropical Tidbits. Notice the upper level low’s influence on the track of the coastal low in this animation.
As the shortwave drifts to the south while the high pressure continues to stay strong to the east, a stationary front develops and sits over the area Monday morning through mid-week (WPC photo below #1). Also notice the increase in moisture distinguished by the dew points surging back into the 70+ degree mark as Gulf of Mexico and Atlantic moisture is driven up the coast into early next week (photo below #2). With all the moisture in the area, CAPE values near 1000 J/kg in some places, the stationary front as the lifting mechanism along with upper level support from a jet streak to the north and northwest (jet stream photo below #3), periods of rain and thunderstorms will develop throughout much of next week.
Just to give a perspective on how much rainfall is possible, WPC paints a healthy amount of rain, up to 5 inches in areas from the interior Northeast down through portions of the Mid-Atlantic.
A wet and soggy weekend into next week is on tap for many along the East Coast especially from the Mid-Atlantic to the Northeast. Always be sure to look out for flooding and know the safety and precautions that come with it (click here to review flooding safety protocols from the NWS).
Stay tuned to GWCC and click here to view other potential flooding events!
©2018 Meteorologist Joe DeLizio