Forecast Discussion
Tuesday, August 13, 2024 11:58AM EDT
A dangerous day of tornadoes is already underway. Make sure you know where your safe place is in your home (basement or interior room in the lower floor of a house or apartment).
Arc of heavy rain and embedded supercells, some of which are tornadic, continues to lift north through the region and into northern/central MD with the warm front feature that has developed to the ENE of Joyce’s surface low center. With a potent shortwave trough swinging in and phasing with Joyce’s low pressure center, a mid-level dryslot has wrapped around the surface low to the east across Virginia and getting into Maryland along and south of the warm front. This is what’s allowing for some sunshine to continue to overspread the region. Dewpoints have risen into the upper 70s to around 80F south of the front and with the added sunshine temps will rise into the mid/upper 80s this afternoon. This combined with a modest cooling of mid-level temps associated with the approaching shortwave will allow for unusually large CAPE for a remnant tropical system (MLCAPE of around 2500 J/kg or so). The shortwave is also deepening the surface low so, as a result SE surface winds will strengthen across the region with 25-35 kt gusts commonplace. Hodographs will also be very large and curved with a strong 60+kt LLJ overhead resulting in effective SRH easily in excess of 400m2/s2. The sunshine combined with the ample low-level moisture will allow for large 0-3km CAPE of 250-300+ J/kg. All of this combining with 45-55kt effective bulk shear to make conditions highly favorable for a potentially significant tornado outbreak across the region.
Currently some supercells which have already caused a number of confirmed tornadoes continue to move NNE into northern and central MD. To the southwest across central and southern VA along and east of the mountains arcs of low-topped supercells, some of which have ongoing tornadoes, continue to mature and strengthen with the increasing instability. As the afternoon progresses bands of supercells will move quickly through the area from SW to NE. These supercells will likely produce several strong to intense tornadoes, some long-track. The Storm Prediction Center is considering an upgrade to a HIGH risk to account for the tornado threat. Due to the slight cooling and drying of the mid-levels, these storms could also produce severe hail as large as 1 to 1.5 inches in diameter. Even if there is no tornado with a particular storm, the 2.25”+ Pwats and large CAPE combining with strong low-level flow could aid in wet downbursts/microbursts bringing severe surface wind gusts. Storms will move to the northeast and exit the area by mid evening as Joyce’s center moves across the region.
By the late evening hours the cold front associated with the strong shortwave trough will move through from west to east bringing a 3 to 6 hour window of northwesterly winds gusting 40 to 50mph. A Wind Advisory is in effect for the region to account for this. Temperatures and humidity will fall sharply with this front. Winds will start to weaken towards dawn with temps bottoming out in the 50s in the Greater Metro regions with upper 40s in the far northwestern suburbs.
The bottom-line is that this is the beginning of one of the most dangerous tornado outbreaks to impact this area. Please be weather aware and ready to get to your safe places the moment a tornado warning is issued. Wearing a helmet and closed-toed shoes while in your safe place is essential as well to protect from flying debris during a tornado and debris in the aftermath of a tornado. Stay tuned to the NWS for the latest updates available during this event.
Forecaster Wannabe: George BM
