The Storm Prediction Center has issued a particularly dangerous situation warning today for strong EF2+ tornadoes for the Mississippi River Valley region from northern Mississippi to southern Illinois.
TORNADO WATCH FOR PORTIONS OF SOUTHEAST ARKANSAS FAR NORTHEAST LOUISIANA
NORTHERN AND WESTERN MISSISSIPPI & WESTERN TENNESSEE
* EFFECTIVE THIS WEDNESDAY MORNING AND EVENING FROM 1155 AM UNTIL 800 PM CST.
...THIS IS A PARTICULARLY DANGEROUS SITUATION...
Warm air from the Gulf of Mexico humid enough to produce a tornado has pushed northwards towards the border of Illinois and Wisconsin. The weather service has now issued tornado watches from Iowa city, through central Illinois and central Indiana in addition to the particularly dangerous situation area further south. Tornadoes are fairly common in the deep south in December and January, but in late December Iowa, Illinois and Indiana it's too cold for tornadoes (the dew point is too low). People living in the central midwest should prepare for a tornado today as if the calendar said April.
Strong winds at the jet stream level from the southsouthwest over strong southerly to southeasterly winds near the surface will create strong wind shear over an area from the Gulf coast to the northern midwest. The northern boundary of severe weather will be limited by the how far the warm front moves the very warm humid gulf air into the upper Mississippi River and Ohio River valleys. Storms will track from SSW to NNE along the track of the strong winds aloft. Strong lift and spin will be provided to storms by a short wave moving from SSW to NNE on the jet stream.
The sector of warm Gulf air, that is humid enough to support severe thunderstorms (dewpoint of 55ºF or higher) will push as far north as the Great Lakes by late afternoon central time.
Wind Shear will be very high over the midcontinent region late this afternoon. I have reviewed the wind shear forecast maps and other severe storm indices and have noticed that conditions favoring severe storms get worse over central Tennessee and Kentucky after dark. Please watch out.
There have been reports of tornadoes on the ground issued by the Memphis NWS office. The tornadic storms are moving at a high speed 50mph to 65mph according to the NWS reports. The high speed of these severe thunderstorms makes it harder to get to shelter in time, so be prepared.
Here’s the official public statement by the NWS
PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0147 PM CST WED DEC 23 2015
Severe thunderstorms expected over parts of the Lower/Middle Mississippi Valley and Tennessee Valley this afternoon and tonight.
* LOCATIONS
Kentucky
Tennessee
Far southern Indiana
Far southern Illinois
Southeast Missouri
Northern Mississippi
Eastern Arkansas
Northwest Alabama
* HAZARDS
Widespread damaging winds, some hurricane force
Several tornadoes, a few intense
Isolated large hail
* SUMMARY
An outbreak of severe thunderstorms and tornadoes is forecast
today into tonight from the Ohio Valley into the Tennessee and
lower Mississippi Valleys. The greatest risk for a few intense,
long-tracked tornadoes will exist over western Tennessee into
northern Mississippi and eastern Arkansas this afternoon into
tonight.
Preparedness actions...
Review your severe weather safety procedures for the possibility
of dangerous weather today. Stay tuned to NOAA Weather Radio,
weather.gov, or other media for watches and warnings. A watch
means that conditions are favorable for severe thunderstorms
over the next several hours. If a severe thunderstorm warning is
issued for your area, move to a place of safety, ideally in an
interior room on the lowest floor of a sturdy building.
There’s also a low but significant risk of tornadoes in the Carolinas, where I live. The air mass here more humid than I have ever seen it near Christmas. We certainly have had many warm days in mid December in the past but the humidity is extraordinary today as is the risk of tornadoes. We had a tornado warning this morning in the county I live in now, but fortunately, the severe storm was south of us. This is not normal weather here even for an El Nino year.
Reports are coming in of devastation in Holly Springs, Mississippi from a wedge tornado.