An upper-level low is forecast to move into the Midwest tomorrow before cutting off from the main flow, which will allow it to linger over the Midwest and Tennessee Valley regions through around Monday or Tuesday before it lifts out of the eastern U.S. This has a couple of different implications for the region…
The most pronounced threat with the cut-off low is the potential rainfall, with widespread totals of 1-3 inches or more in the Mid-Atlantic and Northeast. Normally 1-3 inches isn’t that critical, but when you add it to the recent record-breaking rainfall in these regions any larger rainfall potential becomes a significant event.
Here’s a look at the total rainfall and the percent of normal rainfall for the period starting August 1st and ending yesterday, September 19th:
With some areas with over 20 inches of rain in the last 45-50 days, anything over a couple of inches will cause some of the rain-soaked areas to flood once again. Right now it looks like the coastal areas are more at risk for heavy rain compared to the inland/mountain areas in the Mid-Atlantic.
In terms of severe weather, strong to severe storms will be possible Thursday through next Monday or Tuesday, depending on the position of the cut-off low. This complex cut-off will have a few pieces of energy floating around it (at least initially… some guidance suggests one of the pieces breaks away before it completely stalls):
Having 2-3 pieces of energy in this cut-off low will make the forecast very difficult as models struggle to resolve the complex mesoscale interactions between the different pieces of energy and what they’ll do in turn at the surface.
Also associated with this energy will be an upper-level jet streak out ahead of the trough, which will help enhance lift. The problems, at least initially, will be the fact that the energy is just a bit too far to the west to have that great of an impact on the Mid-Atlantic, and clouds and rain could inhibit heating and worsen the lapse rates. My main focus for severe is when the trough does finally push eastward over the region… hopefully the timing will be good and it could trigger some afternoon/evening storms over the Mid-Atlantic. Once it progresses into the region, the energy involved with it will cause greater lift and the lapse rates should improve.
Not getting my hopes up on severe yet, but at least it’s something to watch over the next several days.