Extreme Flooding in Alabama and Florida; 1 EF-4 and 5 EF-3 Tornadoes Rated

After two wild days of tornado devastation across the U.S. on Sunday and Monday, an unexpected break occurred on Tuesday, when only nine tornadoes touched down. NOAA’s Storm Prediction Center (SPC) had issued a forecast for a “Moderate Risk” of severe weather over much of Alabama and Mississippi, but none of Tuesday’s tornadoes hit those states. Instead, North Carolina saw the bulk of the activity, with eight preliminary reports of tornadoes. The welcome forecast bust was caused by a very difficult to predict scenario—a cluster of intense thunderstorms called a Mesoscale Convective System (MCS) remained strong Monday night over a large portion of the Southeast coast, creating a large pool of cool, stable air. This cool air formed its own high pressure system that reduced instability and cut off the flow of moist, unstable air into the Southeast from the Gulf of Mexico on Tuesday afternoon. However, the moisture that was cut off from flowing northwards instead fell to the ground over coastal Alabama and the Florida Panhandle in the form of torrential rains on Tuesday. A flash flood emergency has been declared this morning in Pensacola, Florida and Mobile, Alabama. Record daily rainfall amounts were set on Tuesday in both cities, with 11.13” and 11.24”, respectively. Pensacola Airport recorded a remarkable 5.68 inches of rain in just one hour ending at 10 pm Tuesday night. Flood waters closed a 30-mile stretch of I-10 near the Alabama/Florida border Tuesday night, and a 5-mile stretch remained closed this morning. Numerous high-water rescues have been performed Tuesday night and Wednesday morning, and one drowning has occurred, in a vehicle that tried to cross flooded Highway 29. Two deaths were also reported this morning in Athens, Georgia , where severe thunderstorm winds toppled a tree onto a car.


Figure 1. Storm chaser Jim Edds is trapped in the Florida Panhandle by extreme flooding, but was able to tweet out this photo this morning. The Pensacola News Journal has also been tweeting some remarkable photos of the flooding.


Figure 2. Radar-estimated rainfall for the Florida Panhandle for April 29 and 30, 2014. Precipitation amounts in excess of 12” were indicated just west of Pensacola. The spectacular rains were reminiscent of what happened June 7 - 11 2012. Torrential rains in excess of 20” flooded portions of southern Alabama and the Florida Panhandle when a large plume of moisture from the Gulf of Mexico interacted with an upper-level disturbance over the region. Flooding was particularly severe in Pensacola, FL, where 13.13 inches of rain fell on June 9.

Tornado outbreak death toll rises to 35
Sunday and Monday’s tornado rampage across the Midwest and Southeast U.S. brought at least five EF-3 tornadoes and one EF-4 tornado, and has claimed 35 lives. For the 24-hour period beginning at 8 am Monday, SPC logged 72 preliminary tornado reports from five states. An additional 35 preliminary tornado reports came on Sunday, bringing the two-day preliminary tornado total to 107. The deadliest tornado was an EF-3 that killed 14 people in Arkansas, ravaging the towns of Mayflower and Vilonia. Damage surveys are not yet complete, but the strongest tornado rated so far was an EF-4 with 185 mph winds that hit Louisville, Mississippi on April 28. The tornado killed nine people, carved a damage path 35 miles long and up to 3/4 mile wide, and stayed on the ground for 56 minutes. The NWS survey noted:

“THIS TORNADO PRODUCED A LARGE AREA OF EF2 TO EF4 DAMAGE ALONG ITS PATH. HUNDREDS OF STRUCTURES WERE HEAVILY DAMAGED AND THOUSANDS OF TREES WERE SNAPPED AND UPROOTED. THE EF4 DAMAGE CONSISTED OF SEVERAL HOMES AND APARTMENTS THAT WERE REDUCED TO SLABS...INDUSTRIAL BUILDINGS THAT WERE COLLAPSED...CHICKEN HOUSES THAT WERE COMPLETELY DESTROYED WITH LITTLE TRACE LEFT OF THEM...DEBARKED AND DENUDED TREES AND A COLLAPSED CELL TOWER.”


Figure 3. Severe weather outlook for Wednesday, April 30, 2014, as issued on Wednesday by NOAA's Storm Prediction Center. For the first time this week, the severe threat is below the “Moderate Risk” level.

Wednesday the final day of this week’s severe weather outbreak
The strong, slow-moving low pressure system that brought this week’s deadly tornadoes will continue to spawn a few more supercell thunderstorms capable of generating large hail, damaging winds, and tornadoes on Wednesday. NOAA's Storm Prediction Center (SPC) has issued their “Slight Risk" forecast of severe weather over a region stretching from Maryland southwest to north Florida. Rainfall amounts of 1 - 3 inches can be expected in much of the severe weather risk area, with some 3+ inch totals in Florida and Eastern Pennsylvania.

Disaster Relief Donations Needed
The devastation from this week’s tornadoes have brought a need for donations for disaster relief. The Portlight.org disaster relief charity, founded by members of the wunderground community, is supporting the efforts of a group of local volunteers in Arkansas doing search and rescue, and needs donations. Portlight volunteers are working in tornado-hit towns to clear debris and help with other clean-up efforts. This team will also be visiting shelters and reaching out to survivors with disabilities to determine their immediate needs, whether for replacement of durable medical equipment and ramps, or for assistance with shelter and transportation issues. The Red Cross is also a great place to send your donation dollars.

Jeff Masters