Weather Flashback: February 28, 2007

The threat of severe weather became even clearer on Wednesday, February 27, 2007.

During the early morning hours, the Storm Prediction Center in Norman, Oklahoma upgraded a good chunk of the state to a moderate risk for severe storms. At the time, forecasters were still having a hard time in deciding if the right components would come together for such a severe outbreak as computer models were predicting.

The weather team at ABC 33/40 was hard at working make sure that updates were made to their weather blog early and often just one day before the potential outbreak.

"This time around, unlike what happened on Saturday, there should be a plentiful surge of warm, moist, unstable air from the Gulf of Mexico starting early tomorrow morning. While there may be some showers or even a few thundershowers early Thursday as the warm air pushes in, the main event for strong to severe thunderstorms should begin in East Mississippi by late morning and spread across Alabama in the afternoon hours. With peak daytime heating pushing temperatures up to around 70 degrees tomorrow and a few sunny breaks in the clouds, the storms that develop will have a lot of fuel to work with.

The primary threats will be from wind & hail with the risk of a few tornadoes, too. That tornado threat increases greatly if storms start out isolated out ahead of a main line that will sweep through late Thursday evening. The small-scale (mesoscale) details will make all the difference in the world in the way the storms develop, and sometimes it's the last minute before we know for sure how it will work out, so be alert to changing weather over the next 24-48 hours."

ABC 33/40 Chief Meteorologist James Spann issued his first warning of the day several hours later in his morning weather post.

"MODERATE RISK: The Storm Prediction Center has a moderate risk of severe weather defined for tomorrow for most of Central Alabama, extending into the eastern part of Mississippi, and eastward into Georgia. Here are some severe weather parameters for late tomorrow afternoon from the NAM:

SB CAPE: 426 k/kg
Lifted Index: -3.4
0 to 3 km Helicity: 467 m2/s2
SWEAT Index: 414
Surface dewpoint: 63
850 mb winds: 57 knots
500 mb winds: 81 knots

The instability values, as always in early season events, are a bit questionable. But, most of the other elements are there. A strong, negative tilt upper trough providing a very diffluent flow across Alabama, an intense surface cyclone over the nation's bread basket (982 mb low near Des Moines), strong wind fields, and strong veering of the wind with altitude.

We should have round of rain and possible storms tomorrow morning with a warm front pushing northward across the state. That is one of the keys to the event; if the clouds and rain linger through much of the day, that would minimize the severe weather threat due a stable boundary layer. However, if the rain ends by mid-morning and the sun breaks out for a while, that would set the stage for numerous supercell storms tomorrow afternoon and tomorrow evening with the chance of significant tornadoes.

The greatest window for significant severe weather will be from about 2:00 p.m. until 9:00 p.m. Once again, every Alabamian will need to be close to a good source of weather information throughout the day and into tomorrow night."

At this point in the forecasting, the Wiregrass was just outside of the area considered for a moderate risk for severe weather. As the day moved forward the forecast would change for the entire state.

Longtime national weather service forecaster and Alabamawx.com blogger J.B. Elliott delivered the next warning to residents around the state that a serious potential for severe weather was on the way.

"The NWS/SPC (Storm Prediction Center) has upgraded the risk of severe weather tomorrow to moderate over a wide area, including virtually all of Alabama.

I have been in weather for eons and I do not ever remember seeing a moderate risk area cover such a large territory, especially on day two.

Generally, the moderate risk area covers from Northern Illinois, down through Central Missouri, to Western Arkansas and eastward to cover almost all of Alabama, Mississippi and Georgia as well as the west half of Tennessee, West Kentucky, south two-thirds of Illinois, SW Indiana, the east half of Missouri and almost all of Arkansas.

The portion of the SPC discussion that pertains to Alabama and Mississippi says that "maximized surface heating will coincide with optimal vertical shear and increasing low level moisture to maximize the risk for severe hail, wind, and in particular significant tornadoes. A few long-lived and long-track super cells are possible."

That is only part of the discussion. Do not be surprised if at some point tomorrow we are upgraded to a high risk area.

Let us hope not. Let us pray not.

This blog post is certainly not to scare you, but just to give you a heads up. James Spann will have a complete video discussion posted here by around 2:30 with all the graphics and detail."

As the models continued to roll in through the day, the threat only grew in the minds of forecasters around the state.

The Storm Prediction Center upgraded their graphic for a moderate risk for severe weather to include almost the entire state including the Wiregrass. Forecasters even began to hint that there might be a need to upgrade the moderate risk to a high risk...something that was rare at the time...especially so early in the year.

While forecasters in Alabama continued to fine tune their forecasts, a severe weather outbreak was underway in the Midwest with several tornadoes reported in Kansas.

As the evening moved on, people were beginning to take the warnings seriously. So much so that Spann had to explain what could be ahead.

"Lots of questions about the levels of severe weather risk from the Storm Prediction Center... here is what is all means:

A SLIGHT risk implies well-organized severe thunderstorms are expected but in small numbers and/or low coverage. Within a slight risk area, 5-29 reports of 1 inch of larger hail, and/or 3-5 tornadoes, and/or 5-29 wind events are forecast.

MODERATE risks imply a greater concentration of severe thunderstorms, and in most situations, greater magnitude of severe weather. Within a moderate risk area, at least 30 reports of hail 1 inch or larger, or 6-19 tornadoes, or numerous wind events (30 that might be associated with a squall line, bow echo or derecho) are forecast.

The HIGH risk area almost always means a major severe weather outbreak is expected, with great coverage of severe weather and enhanced likelihood of extreme severe (i.e., violent tornadoes or extreme convective wind events over a large area). Within a high risk area, expect at least 20 tornadoes with at least 2 of them rated F3+, or an extreme derecho causing 50+ widespread wind events (50+) with numerous higher end wind (80+ mph) and structural damage reports.

The report criteria for each of those risks is valid for an area the size of Oklahoma without the panhandle, or about 50,000 square miles. As the size of the risk area increases (decreases) from 50,000 square miles, those expected severe weather numbers would increase (decrease) proportionally."

As most people turned off their television sets for the evening, meteorologists around the state has sounded the warning that there indeed could be a severe weather outbreak the following day.