Central Plains tornado outbreak today, then storms march east towards the Mid-South

Tornado Alley will be given a chance to live up to it's name today as the Storm Prediction Center has placed a very large area from Nebraska to Oklahoma under a High Risk for severe thunderstorms, predicting a "significant outbreak of strong to violent, long-track tornadoes" for the region (see first graphic below).

Several notable actions were taken in preparation for this event, including a very rare Day 3 Moderate Risk issued Thursday, a Day 2 High Risk issued yesterday (only once has this ever been done before), a Public Severe Weather Outlook from SPC (issued only when an outbreak is expected), and a 45% tornado risk area for parts of NE and KS (see second graphic below), meaning there is nearly a 1-in-2 chance of a tornado within 25 miles of any point within that area.  The greatest tornado risk is this afternoon and evening, followed by the formation of a squall line over eastern KS and into OK this evening into the overnight hours.

A very large high risk area has been issued for the Plains in advance of an expected outbreak of violent tornadoes

Tornado risk for today - percent chance of a tornado within 25 miles of a point

On Sunday, a slow-moving squall line is expected to move east from the Plains as a Pacific cold front begins pushing east.  Low pressure moving out of the Central Rockies that is providing the necessary low-level wind shear across the Plains for tornadoes today will move northeast into the western Great Lakes Sunday, so a significant tornado threat is not expected further south, thus wind and possibly some hail will be the primary threats during the day from the Mid-Mississippi Valley into northeast Texas (see Day 2 severe risk graphic below).

You'll notice that Sunday's slight risk area extends to just west of the metro.  This is because the line of storms is expected to move east of the slight risk after midnight, when atmospheric conditions are least conducive for severe weather.  I expect the line to weaken as it approaches the river after dark Sunday night and move through the metro before dawn Monday morning as a "general" line of thunderstorms.  A remnant wind threat is still possible with the line, but the chance of severe weather is relatively low.

The bottom line: while tornadic storms are likely in the Plains today, the storms become more of a wind producer as they approach the Mid-South Sunday and will weaken further as they enter the metro area early Sunday.  Until then, we'll experience warm, humid, and windy springtime conditions, followed by more typical springlike weather in the wake of the front and for the first half of next week.

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Recap of Mid-South severe weather on Friday, 3/2/12

For the second time in 3 days, the city of Memphis and immediate suburbs were largely spared from possible severe weather. As forecast, the vast majority of the severe weather, including multiple tornadoes and 27 reported fatalities as of this writing, occurred east of the metro, although storms along the cold front fired over Fayette and Marshall Counties. Large hail was reported in Grand Junction, Fayette County, from that storm.  Below are the preliminary storm reports received by NWS-Memphis today.

NWS-Memphis preliminary storm reports. Red = tornadoes; purple = hail; yellow = wind. 

Heading into today, a widespread and potentially devastating setup prompted the issuance of a rare high risk outlook for central KY and TN and a very large moderate risk surrounding the high risk. The 8:00am outlook from the Storm Prediction Center (shown below) depicts the area of concern.

8:00am severe weather outlook from SPC.

The result (as of 6:30pm CST) is shown below in terms of the number of severe weather warnings issued.  The warnings were, as expected, largely within the moderate and high risk zones shown above, indicating that the SPC forecasters had a good handle on the area most likely to be affected.

NWS-issued warnings through 6:30pm. Tornado = red; T'storm = blue; Flood = green.

With the passage of the cold front through the Mid-South at mid-afternoon, a drier and stable airmass was ushered in.  High pressure will continue to build in bringing cooler, though not unseasonably cool, weather for the next few days.  Certainly much cooler than the record high of 83 degrees that was set at Memphis today!

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For weather information for Memphis and the Mid-South, where and when you need it, visit MemphisWeather.net on the web, m.memphisweather.net on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.