Severe Thunderstorms Possible Saturday

Saturday is shaping up to be an interesting day across the Washington Region with temperatures soaring into the upper 90s, dew points just shy of 80 degrees, an upper level (500-mb) disturbance slated to cross our region, high surface CAPE (convective available potential energy) and very strong wind shear (some models forecasting values approaching 50 knots)! An area of low pressure will also be passing just to our north and east as a cold front approaches from the northwest.  If these trends continue and timing of the features is accurate, our region could be under the gun for damaging winds, hail and possibly even some tornadoes.

Dew points will be Oppressive and this saturated air mass will be fuel for deep moist convection:

Temperatures will be in the middle to upper 90s with some locations possibly approaching the 100 degree mark (depending upon how much sunshine we have during the afternoon hours).  Convective Available Potential Energy (CAPE) values will be running very high (CAPE is simply the potential energy available for convection).  Mixed-Layer CAPE will also be adequate for storms to fire (image below shows surface-based CAPE but mixed-layer is a more realistic value to consider as convective eddies in the atmosphere typically mix with cooler air aloft being mixed down with warm air in the first 100-mb of the atmosphere).

Wind Shear values will be favorable for some storms to rotate.  Shear values above 30 knots is a pretty standard threshold for thunderstorms to rotate and values on Saturday afternoon could be approaching 50 knots across much of the Washington Region.

A 500-mb disturbance (upper-level spin or vorticity) will be passing over our region on Saturday.  This added spin should also help to aid all the surface heat and humidity rising to their level of free convection (LFC).

The next two images show super-cell composite and significant tornado composite (two model algorithms from the latest North American Model (NAM):

The ingredients for at least the potential for scattered strong to severe thunderstorms will definitely be present on Saturday afternoon across our region.  The devil is always in the details when it comes to weather outcomes as the slightest changes in surface conditions (potential cloud cover in the morning hours, potential mid-level capping) can quickly diminish the initiation of thunderstorm development.

Forecast soundings on Saturday will be key as will be the exact timing of the features that I mentioned above.

Bottom Line: Saturday afternoon could be interesting with scattered super cell thunderstorms capable of producing damaging winds, hail, and possibly even some tornadoes.



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