Twin States Weather Blog

Update from NWS Jackson

* Here's an excerpt from our Instant Messaging conference with NWS Jackson. Typing this is Jeff Craven, one of the brightest severe weather minds in the country. It's a discussion of positives and negatives about the severe weather potential:

NEGATIVES:

*Empirically, the 500 mb heights are pretty high. 18z was 583 dm at KJAN. Normally, to be in the core of the worst weather, we are in the 570 to 576 range.

*Surface pressures are rather high...currently around 1014 mb. Typically we are less than 1008 mb and it becomes quite favorable less than 1004 mb.

*500 mb temperature was -9. Our worst events are -12C or colder. However, we had values around -10 C for November 10th 2002, so this is only marginally weak on the parameter scale.

*Surface low is already moving into IL, which is pretty far north of us. The best pressure falls extend from MEM/TUP on north.

*500 mb winds are about 35 knots...though they are forecast to strengthen. We typically like to see 50-60 knots in the bigger severe weather events.


POSITIVES:

*0-1 km shear is running 25-30 knots...suggesting chance of strong tornadoes

*Sun was out today, so we have pretty high values of CAPE. 18z sounding from LCH had MLCAPE of 3000 j/kg, which is really high, with about 1500 j/kg at SHV.

*On water vapor...there seems to be a southern branch short wave trough moving northeastward from the TX coast toward our area.

*Showers and thunderstorms that developed ahead of cold front from Houston area toward west central MS have cellular character...which could evolve into supercells with somewhat higher chances for tornadoes.

*Overall pattern suggests that the worst threat for extreme damaging winds and tornadoes will be from Memphis County Warning area on north. We think that the high risk is too far south. Moderate risk seems a bit generous as well.

*I think we will see a few tornadoes and quite a few reports of damaging winds, especially along the cold front with the developing squall line. Just don't think this event, for Jackson County Warning Area, will be as big as some of the events we've seen in the past few years.

posted by WTOK Weather Staff @ 2:09 PM