Moderate Risk: 2/23/19

The Storm Prediction Center (SPC) has issued a Moderate Risk in Dixie Alley for this afternoon.

Associated with the Moderate Risk is a hatched 15% tornado threat ring.

The 18 Z upper air sounding from Jackson, MS, shows a rich storm environment, though there is no capping inversion.  There is plenty of moisture available, given the 67 F surface dewpoint and 1.46 inches of precipitable water.  This environment shows 1812 J/kg of Convective Available Potential Energy (CAPE) and no Convective Inhibition (CINH).  The LCL is 895 m.  The hodograph shows that the shear is strong, with 27 kts of low-level shear, and 72 kts of deep-layer shear.  Because of all of this, the supercell parameter is 7.8.

The visible satellite imagery shows cloudy skies over the entire southeast, with pockets of convection along the western edge of the clouds, representing the approaching cold front.

The surface observations show southeasterly winds under cloudy skies.  Conditions are humid throughout the whole southeast, with dewpoints in the upper 50s to upper 60s.

The surface pressure chart shows that there is a mid-latitude cyclone (low) pressure over the eastern Great Plains, headed northeast, with slightly higher pressure over the Carolinas.  This has set up a pressure gradient that is helping to advect more moisture into the warm sector of this system.

The HRRR simulated reflectivity is showing a powerful squall line moving through the deep south by this afternoon.  There are a few storms expected to form in front of the squall line that may remain discrete for a little longer.

The HRRR is showing a diffuse dryline that will tighten up in the evening.  The sharpest part of this dryline will be over central Mississippi this afternoon.

The HRRR shows that the supercell parameter will be high throughout all of Mississippi and parts of Alabama.

The HRRR also shows that the SigTor parameter is high through northwestern Mississippi.

The HRRR shows helicity tracks moving to the northeast, with the strongest helicity being over north central Mississippi.

This would still be a very difficult chase.  This chase terrain is hilly and full of trees, and roads are often small, slow and windy.  Under these cloudy skies and low LCLs, tornadoes will be difficult to see.  Also, this system is moving quickly.

There is too much lift from the cold front for discrete supercells.  Everything today will quickly go linear and exist as embedded supercells in a long, quick-moving squall line.

If I were going to chase, I might hang out near (one of) my alma mater, Mississippi State, in Starkville, MS.   The trick today will be finding the strongest helicity, as this will be the part of the squall line that is most likely to go supercellular.

Sources:
Storm Prediction Center
College of Dupage – SATRAD

 

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About highplainschasing

This blog is about my tales in storm chasing. My name is Seth Price and I am an instrumentation instructor at New Mexico Tech. My amateur radio call sign is N3MRA.
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