As a shortwave lifts from the Southern Plains toward the Great Lakes today, its developing surface low should track from Arkansas toward Indiana. This will bring a cold front through Pine Belt, with a chance for strong to severe thunderstorms as the front moves through.
Instability is currently increasing in the developing warm sector. Latest RAP analysis fields show MLCAPE values of around 1000 J/kg over southeast LA. Expect instability and wind shear to increase through the morning, with the greatest contribution from instability being achieved during the after Noon today as the squall line reaches eastern Mississippi.
Deep layer wind shear of around 60 knots will support supercells, while 0- 1km shear of 30-40 km will support an isolated tornado threat especially with any bowing segments along the squall line which can become oriented perpendicular to the low-level shear vectors.
Strong winds just off the surface will make it easier for damaging wind gusts to be mixed down with stronger thunderstorms. A Marginal Risk for severe thunderstorms exists today for all but a small portion of the Delta region where storms will be less organized earlier this morning. A Slight Risk for severe thunderstorms has been expanded to cover a little more of northeast Mississippi, where the better overlap of instability and shear will develop during the afternoon hours. This area is roughly from Greenwood to Meridian and areas north and east from there.
The threat for showers or storms to impact New Year`s Eve celebrations will be very slim for the Pine Belt. The front and associated squall line should push through the area by early this evening, leaving only a chance for some lingering showers in far eastern Mississippi before midnight.
Apart from the severe weather threat across the area, tightening pressure and height gradients will result in the potential for gusty winds through early this afternoon ahead of the main thunderstorm threat. Sustained wind speeds of 20-25 mph and gusts of up to 35 mph will be possible ahead of the cold front passage. Elsewhere, gusts of up to 25 to 30 mph will still be possible apart from thunderstorms. Light winds out of the northwest will be in place behind the cold front. Patchy fog can`t be entirely ruled out for tonight though, and better chances will probably be in the vicinity of the frontal boundary through southeast Mississippi.
Hattiesburg Extended Weather Forecast:
Come Tuesday morning the cold front will continue shifting farther south in South Mississippi as a large 1040mb high drops south of the Northern Plains resulting in a cool dry northerly flow across the Pine Belt. Our winds aloft will remain southwesterly though as another closed low move over the Four Corners region.
Models have trended slower with the progression of this low but it will drop over the desert southwest Tuesday night into Wednesday and help send moisture back atop our cool and relatively dry airmass. Models are in good agreement that light rain will begin reaching the ground in our southwest Mississippi Counties after midnight Tuesday night and then spreading over the whole State of Mississippi Wednesday morning.
This model runs the Canadian is the fastest in moving the closed to the northeast while the GFS is the slowest. The low is expected to track east across the Southern Plains Thursday and across northern Mississippi Friday morning. Once the rain starts Tuesday night it likely will not end until Friday morning. Several inches of rain will be likely across most of the State Wednesday through Thursday with storm totals generally greatest across our northern part of Mississippi.
