Mid-Atlantic Discussion – September 27-28

Monday

Strong, twisting winds aloft ahead of a cold front will be the big player as the cold front approaches the Mid-Atlantic Monday and pushes through on Tuesday (from the SE no less!). Weak to moderate thermal instability on the order of 250-750 J/kg CAPE will provide the additional fuel to initiate storms. The strongest threat for severe storms is in CeVA/WeVA as helicity values max out in this area, which creates the greatest twisting motion needed for tornadic development. The upper-level jet is not in the most favorable position for storm initiation, but it could aid in sustaining long-lived cells.

Once these storms get going on Monday, they have the potential to continue well into the evening and overnight hours so long as the CAPE holds out ahead of the storms. Because of the initiation zone and potential life span with these storms, the threat for severe weather could extend NE/NNE following the storm motion into NoVA and MD. The northern extent of best CAPE values does not extend much further N than D.C., so the mesoscale evolution in this region will have to be closely monitored throughout the day for local severe weather potential.

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Chase potential: 85%

Chase target(s):
SoVA/CeVA
NoVA/MD

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Tuesday

The severe threat pushes north and east as we head into Tuesday. The chance for severe thunderstorms will diminish quickly in the region as the cold front pushes through the area, taking the good helicity values with it. Remnants from Monday and/or quick initiation Tuesday morning could spring up severe cells along the Coast. The HPC has the surface front progged to be just east of BWI in a N-S orientation at 12Z, so the front may be moving too quickly for severe storms to initiate locally on Tuesday. Other than that, the synoptic setup is the virtually the same. The upper-level support will be marginally better in NJ Tuesday compared to SoVA/CeVA on Monday, but lower-level speed and directional shear will not be quite as robust.

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Chase potential: 15%

Chase target(s):
DELMARVA/NJ


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