Moderate Risk: 4/12/20

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

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

To summarize the SPC:  An ongoing Mesoscale Convective System (MCS) that produced tornadoes overnight continues on its path east.  It is entering an area of ample moisture, with dewpoints in the lower 70s F, and strong low-level shear, increasing the likelihood of tornadoes.  Embedded supercells are possible in the MCS, but discrete convection may occur ahead of the MCS.

The 12 Z upper air sounding from New Orleans, LA, shows some fat Convective Available Potential Energy (CAPE) of 1888 J/kg, and a supercell parameter of 17.3.  There is more than enough low-level (33 kts) and deep-layer shear (47 kts).  With this air mass moving to the northeast, things could be intense for Mississippi today.

The visible satellite imagery shows the cold front as a line of clouds extending to the southwest from Louisiana into eastern Texas.  Also, notice the spotty clearing in Mississippi and Alabama.  To the west of each clear spot is developing cumulus clouds.

The surface observations show moisture advecting into the threat area from the Gulf of Mexico.  Notice the moderate surface winds moving from the Gulf into the southern states.  The temperatures are mild and the dewpoints are high.  The whole region is under cloudy skies.  The cold front extending from Louisiana southwest into eastern Texas, and that only shows up as a shift in wind direction.

The surface pressure chart shows a deep low pressure system over northeastern Texas.  The RAP has the low pressure system deepening and moving to the northeast over the next six hours.  The cold front extends from this low pressure system.

The HRRR simulated reflectivity is showing a nasty squall line with perhaps a few embedded cells (based on the helicity swaths).  Ahead of the squall line, a line of discrete cells begins forming by 23 Z.

The HRRR is showing only a weak, diffuse dryline behind the cold front.  It won’t be as big of a factor today.  There is plenty of moisture available.

The HRRR CAPE/CINH plot is showing CAPE rising to 4000 J/kg just ahead of the cold front this afternoon in central Louisiana and eastern Mississippi.

The HRRR shows that the supercell parameter will be consistently high, all day, over the threat area.

The HRRR also shows that the SigTor parameter is high, particularly in a few stripes through Alabama.

The HRRR shows a few strong helicity swaths cutting through Mississippi and northern Alabama through this evening.

If I were targeting and chasing today, I would probably head towards southern Mississippi near the Louisiana border.  My three targets would be:
1.  Columbia, MS
2.  Franklinton, LA
3.  Poplarville, MS
Somewhere in that triangle.  I’m thinking farther south is better- getting away from the mess a bit, based on the satellite imagery.

This would still be a very difficult chase.  This terrain is awful- you’re basically chasing in the bayou.  At best, you are in the woods and hills of Mississippi with only a few hundred yards of visibility at best.  It is going to be a drone-chase day, as getting above that treeline is going to be imperative.

Storm Prediction Center
College of Dupage – SATRAD



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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