12/3-12/4 FCST: GULF COAST/TN VALLEY

[Brett Adair]

Wam front begins to move back towards the north as SFC low gets organized back into the SRN plains. NAM really screwed me last week, but the latest parameters from the MOS output are kind of scary for HSV...

Midnight Saturday Night

Dew Point 63.6
CAPE 1855
Helicity 508
PWAT 1.18"
LI -6.6
SWEAT 481
TT 57
Wet Bulb Z 9105
Hail Size 1 inch
Showalter Index -5.8

EHI is about 5.5
VGP .50

These two graphics indicate the warm frontal boundary very well as another meteorologist friend of mine pointed out to me...

http://www.wxcaster.com/CONUS_MESO-ETA_SFC...PTSBLI_36HR.gif

http://www.wxcaster.com/CONUS_MESO-ETA_0-1...KM_EHI_36HR.gif

This indicates that the directional/speed shear hangs out long enough for about an 8 hour period of tornadic supercells. I buy the latest weaker GFS solution myself....did I mention that the onset of the precip tonight will likely fall in the form of sleet in this region? What a difference 24 hours will make...

 

[nickgrillo]

Just browsed at a couple of forecast soundings for the area... NAM sounding for 03z Sun. at GWO shows very weak CINH atop moist / semi well-mixed boundary layer. Veering flow through the 0-1km layer yields favorable SRH in excess of 300m2/s2 -- with deep-layer vertical shear in excess of 45kts -- and strong sbCAPE of 2631j/kg (which is likely overdoing it). Looking at the sounding, mostly unidirectional flow appears to favor line segments -- but decent boundary layer veering along the warm front could yield a couple supercells afterdark across northern MS and likely into southern TN / northern AL.

 

[Angie Norris]

Talk about a well defined front...looks to be running along a Birmingham/Memphis/Little Rock axis as of 0052Z. Was working with this in our forecast lab at school this afternoon. The 850mb divergence was the first thing that caught my eye.
Think I'd be keeping an eye on the area between Tupelo/Memphis/GWD (not sure what station that identifier is). I like that bit of surface convergence in that area. Birmingham wouldn't be totally out of the question, but I don't like how they've cooled off. I'd think things should start with some isolated cells near the front and given the shear, I sure wouldn't rule out a tornado or two. Unfortunately, it's after dark again, typical for this time of year, so hopefully sirens are working and people are paying attention.
Angie