New Tornado Watch Likely Soon for North/Central Alabama

Latest Mesoscale Discussion is out and the latest thinking has an issuance of a Tornado Watch likely for much of North/Central Alabama later this afternoon. Here is the text from the Storm Prediction Center…

Mesoscale Discussion 0442
NWS Storm Prediction Center Norman OK
0102 PM CDT Wed Apr 05 2017

Areas affected…Portions of central KY…middle
TN…northern/central AL…extreme northwest GA

Concerning…Severe potential…Tornado Watch likely

Valid 051802Z – 052030Z

Probability of Watch Issuance…95 percent

SUMMARY…The risk for significantly severe storms capable of
producing very large hail and tornadoes, along with damaging winds,
is expected to increase around and after 19Z. The issuance of a
Tornado Watch is expected soon.

DISCUSSION…Northward return of modest moisture continues in the
open warm sector of a deep cyclone — from parts of the TN Valley
region northward to the lower and middle Ohio Valley region. The
leading edge of towering cumulus fields is noted from far northwest
AL into western parts of middle TN and western KY, near a
pre-frontal confluence axis trailing south-southeast of deep low
pressure over eastern MO. Despite the modest moisture, with surface
dewpoints in the 50s to the lower 60s (highest south), moderately
steep midlevel lapse rates around 7.5 C/km will support 500-1500
J/kg of MLCAPE.

Weak capping and strengthening deep ascent ahead of an approaching
midlevel trough will allow convection to gradually increase in the
vicinity of the confluence axis. This activity will mature as it
moves off the confluence axis and into the destabilizing warm
sector — aided by an appreciable orthogonal component of deep flow
relative to the confluence axis. Strong deep shear and the
aforementioned midlevel lapse rates, encouraging enhanced
storm-scale upward accelerations, will support discrete and
semi-discrete cells capable of very large hail. Also, the
isallobaric response to the deepening surface low to the north will
maintain backed surface winds (pressure falls of 2-4 mb per 2 hours)
across the open warm sector, resulting in long/curved hodographs in
the low levels. Tornadoes are expected, and significant tornadoes
will be possible — especially as supercells mature within a
corridor from central KY to central/northern AL later this afternoon
into the evening. Damaging wind gusts are also expected.

Category: ALL POSTS