5/1/02 nontornadic supercell environment over Arkansas and Oklahoma (warm sector "elevated" storms)

On this evening, supercell thunderstorms developed over northwest Arkansas and east central Oklahoma, prompting several tornado warnings, although no tornadoes were reported.

This severe weather epsisode was associated with a postive tilt upper trough over the northern plains and strong west-southwest flow at 500 mb.  The storms fired just ahead of a stalled cold front over south-central Missouri into central Oklahoma, including a tornado-warned supercell (radar indicated) near Fayetteville near 02 UTC:
< Eta analysis 500 mb winds and height contours 00 UTC 5/2/02   < surface map 01UTC

< INX radar base refl. 0159 UTC

Parameters at 02 UTC from the SPC mesoscale analysis page showed significant shear-CAPE combinations (EHI) ahead of the front from eastern Oklahoma to southern Illinois and Kentucky, with the largest values near the junction of the Mississippi and Ohio River valleys.  The strongest deep layer shear was across the Ohio River valley, but BL-6 km shear of 50 knots or more was also present across Oklahoma nosing into Arkansas.  However, mean-layer CIN was 200-400 J/kg across Arkansas and Oklahoma along the front, and LFC heights were high (2800-3200 m), indicating that the storms firing ahead of the front were "elevated", despite fairly low LCL heights and being located in the warm sector.  This in turn suggested that the main threat would be large hail, with low potential for signficant tornadoes, even with sizable values of the signifcant tornado parameter guideline (Thompson 2002):
< 02 UTC 0-1 km EHI   < 02 UTC BL-6 km
< 02 UTC LCL height   < 02 UTC CIN & Sig Tor Parameter   < 02 UTC LFC height

The RUC-2 analysis profile at Fayetteville for 02 UTC also suggested an elevated environment, with mean-layer CIN approaching 300 J/kg and an LFC height above 3 km:
< Fayettevile (FYV) AR RUC-2 analysis sounding 02 UTC

Other storms developed back into eastern Oklahoma, including a supercell northeast of Muskogee:
< INX radar base refl. 0227 UTC

None of the supercells over Arkansas and Oklahoma produced confirmed tornadoes.  This may have been partially due to the "elevated" environment, resulting from a temperature inversion and elevated mixed layer centered around 750mb in the warm sector.

Below is a summary of the evening environment near Fayetteville based on relative parameter categories:  .  The favorable shear characteristics appear to be negated by poor low-level thermodynamic conditions (CIN and LFC):

Further east, over the westerrn Ohio River Valley where shear-CAPE combinations were larger, few storms were able to develop or persist (see radars below).   Later SPC graphics (below) continued to indicate a generally "elevated" environment where storms were occurring, with most LFC heights > 3000m, suggesting an unfavorable environment for signficant tornadoes:
< 0230 and 0600 UTC radar base refl. composites central Mississippi River Valley
< 05 UTC 0-1 km EHI    < 05 UTC LFC heights

The overnight SPC log shows that no tornadoes occurred over Oklahoma/Arkansas/Missouri and the western Ohio Valley area:
<SPC log for night of 5/1/02

A few days earlier in the same area (western Ohio River Valley) on the night of 4/27/02 into 4/28/02, large shear-CAPE combinations accompanied more favorable low-level thermodyanic conditions (much lower LFC heights and smaller CIN over the same area) when an overnight tornado episode claimed 3 lives in southeast Missouri, southern Illinois, and northern Kentucky.

- Jon Davies 7/1/02

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