Monday 25 April 2011

Tornadoes likely today in the southern USA

Several days of severe weather are likely across the USA, starting today. A deep upper trough will approach the central Plains states, with one short-wave trough moving through later today, before the main trough approaches tomorrow.

Strong southerly winds will develop ahead of these features, transporting Gulf moisture into the region, whilst a front will be draped in a general east-west fashion through the southern Plains and Mississippi river valley.

A dryline will mix eastwards this afternoon whilst a surface low develops and moves north-east. These will likely be foci for severe thunderstorms this afternoon, once morning convection across the area tends to shift away.

The image below is my analysis of the current situation - the purple box is where I think the best chance of tornadoes will be this afternoon/evening. NE Texas maybe a favoured location for mid-late afternoon supercells and tornadoes ahead of a dryline bulge. These storms will then likely propagate north-eastwards across Arkansas, but will likely grow upscale into one or more cluster(s) of storms, including supercells, as the upper trough moves in.

For a (virtual) chase target, I initially pick Clarksville, TX.


Wednesday 20 April 2011

Tornadoes in the US - results


A fair amount of severe weather occurred last evening and night across portions of the Central Plains and Midwest of the USA.

A number of tornadoes developed, including this one, caught by Reed Timmer et al:

http://www.youtube.com/watch?v=MwL1Hy4A1TE


As per my post yesterday evening, this and several other tornadoes developed ahead of the surface low, close to the warm front.

Tuesday 19 April 2011

Tornado warning in Missouri

Streaming TV coverage

Tornado warning in Missouri

Tornado warning now in Missouri - this is a confirmed tornado.

...A TORNADO WARNING REMAINS IN EFFECT FOR SOUTH CENTRAL PIKE COUNTY
IN WEST CENTRAL ILLINOIS...AND CENTRAL PIKE COUNTY IN NORTHEAST
MISSOURI UNTIL 445 PM CDT...

AT 401 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
CONFIRMED TORNADO ON THE GROUND HEADED TOWARD BOWLING GREEN. THIS
TORNADO WAS LOCATED NEAR CURRYVILLE...OR 5 MILES WEST OF BOWLING
GREEN...MOVING NORTHEAST AT 30 MPH.

LOCATIONS IMPACTED INCLUDE...
BOWLING GREEN...LOUISIANA...PIKE...ATLAS AND ST. CLEMENT.

Tornadoes soon in the Midwest


Another day, another outbreak of severe weather is expected in the USA. This time it's portions of the Central Plains and Midwest, especially Missouri and Illinois.

This chart shows the latest SPC mesoanalysis for sea level pressure and surface dewpoint. There is a well-marked warm front to the east of surface low, which is currently in central Missouri. Latest satellite imagery shows a deepening cumulus field around the low, the warm front, and down the trailing cold front to the south-west of the low.

Scattered thunderstorms should develop very shortly, especially INVOF the low and warm front. The low will move in the direction shown by the arrow, and low-level shear/helicity will be maximised just ahead of the low. The red polygon shows my interpretation of the highest risk of tornadoes in the next several hours, along the path and just ahead of the surface low.

Storms should develop down the cold front too, eventually turning into a line of severe storms, although initially some supercells are possible. Large hail, severe winds, and isolated tornadoes likely with these.

Thus, in short, another outbreak of severe thunderstorms will develop shortly, and the highest tornado risk, at least in the short term, in my opinion, is central Illinois.