March 26, 2011 Chase Report – Alabama and Mississippi

by on Mar.27, 2011, under Other

Originally posted: here

We initially targeted the Grenada, MS area on Saturday morning, but decided to head further east into the Golden Triangle region of eastern Mississippi after later convective trends indicated that initiation of the first round of convection would commence late morning or early afternoon across that region. The region was upgraded to a MOD risk by SPC in the morning outlook, with a 15% probabilistic TOR region across the risk area.

An early afternoon surface analysis (see above) shows a quasi-stationary frontal boundary stretched across the region, with the main forcing associated with the primary surface low approaching SW AR.  A TOR watch had been issued for the first round of convection across the warm sector that would impact mostly central AL and GA.

The morning upper air analysis at 300 mb (see above) indicates that the Gulf-Atlantic Coastal Plain region lies between two jet cores, with the main zonal flow promulgating an impulse across the High Plains, which would reach the mid-Mississippi Valley towards evening.  A subtropical jet over TX was nosing into the northern Gulf region, but the area would remain largely entrenched within slightly drier air between the bi-flow patten.

The mid-level upper air analysis indicated temps of -14C over the region at 12z (see above), though the region doesn’t lie proximal to any substantial mid-level jet core as is common in some more notable severe WX setups.

Special 17z (BMX) and 18z (JAN) soundings (see above) indicate favorable deep layer shear, yet a worrisome 0-1 km shear profile, with relatively weak surface winds and rather unidirectional flow > 800 mb.  Mid-level lapse rates of 6-7 C/km indicated the presence of conditional instability, but could have been more magnanimous given the lack of stronger upper-level dynamics.

Nevertheless, instability and SRH values (see graphics above) across the warm sector by late afternoon were indicating an appreciable severe weather threat, with an enhanced TOR thread associated with an cell that could become rooted in the boundary layer INVO of the quasi-stationary frontal zone across the region.  I’ve included various CAPE parameters, as well as the 0-1 km SRH and EHI profiles from the 21z RUC feed ingested into the Mesoanalysis profile.  Obviously this wasn’t the archetypal 2011 early season case where EML spoiled the show until after sunset.

We intercepted a TOR warned cell across the border near Fayette, AL that moved along the I-22 corridor north of the warm front and later dissipated.  After heading back to Birmingham and not being satisfied with the storms in that region, we decided to backtrack to Columbus, MS and monitor convective trends as the atmosphere across the Hwy 82 corridor had become quite unstable due to afternoon heating in advance of the surface cold front that was gradually pushing SSE ahead of the low.

Shortly after 6 PM, we noticed a cell with decent towers going up north of Columbus AFB in eastern MS, so we headed north with the intention of intercepting near Vernon, AL as the cell crossed the border heading ESE in the vicinity of the warm front. A radar loop from the region appears above.  This is the cell in the EC part of MS that treks towards Birmingham.

Radar Loop for the first 1.5 hrs after initiation 

Radar loop of the cell as it headed towards Birmingham 

While mid-level lapse rates were mediocre, what probably also hurt the tornado potential on this event was the presence of relatively weak surface winds with abysmal 0-1km turning courtesy of almost easterly storm motions of roughly 30 kts against directional shear in the lowest 1 km that was largely parallel to MSMs (see the aforementioned 17z and 18z soundings and compare to the 22z surface profile below).

We saw some good structure, along with some great hail fog, decent wall clouds with a few possible (brief) funnels, and an awesome lightning show, though we were not able to confirm any tornado touchdowns from our vantage point.  There were unconfirmed sightings of tornadoes NW of Birmingham, and numerous spotter reports of funnel clouds, but overall this was a good starter chase for the season.  The time lapse video at the top of this entry captures the best moments of this supercell, with most of the time lapses during the day shot near Beaverton, AL, with the nightime hail fog shot just east of Eldridge, AL, and the final lightning time lapses taken between Eldridge, AL and Jasper, AL.

Written By (Jesse Risley)

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