Multi-Day Severe Weather Setup Leads to Tornadoes, Flash Flooding in Oklahoma

Early May is typically when the severe weather season really ramps up in the US Plains and this week has certainly lived up to that. The region has seen severe weather every day since Wednesday and is expected to see more today. A western troughing pattern has been dominant the past few days, allowing a strong southerly flow to take place in the lower levels of the atmosphere – advecting in plenty of moisture from the Gulf of Mexico located nearby. High levels of instability, coupled with enough shear to support supercells was in place.

[map autofit=”1″ disable_scrollwheel=”1″] [pin tooltip=”Bridge Creek”]Bridge Creek, ok[/pin] [pin]Norman[/pin] [/map]

The worst day of the outbreak tornado-wise occurred on Wednesday where 48 tornadoes touched down from Nebraska, all the way down to Texas. A particularly dangerous situation unfolded in Oklahoma as a supercell with a history of producing tornadoes moved northeast along I-44 and through the large city of Norman where it dropped a tornado, later rated EF-1. The same supercell also produced an EF-2 tornado near Bridge Creek, shortly before it dropped the Norman tornado. Tornadoes were not the only threat on Wednesday; significant rains fell across Oklahoma, including Oklahoma City, which saw trailing supercells hit the city and as a result severe flash flooding. One person died from the storms, while a few dozen were injured. Ditches became raging creeks that spilled their banks onto highways and residential areas. It’s not uncommon to see supercells drop 100mm of rain or more in an hour. Radar indicated that some areas just southwest of Oklahoma City saw over 250mm on Wednesday. Numerous stations in the area broke their daily rainfall records from this event. A state of emergency was issued in 12 counties as a result of the storms.

Chickasha Supercell
The tornadic supercell that hit Norman in its early stages, showing an obvious hook. (Source: Radarscope)
Oklahoma Flooding Rains
Storm total accumulation for Wednesday through 9pm shows areas of over 250mm (pink areas). (Source: Radarscope)

More severe weather is expected today as the trough shifts slightly eastwards. There’s a chance that today could be the second significant tornado day in less than a week in the Plains – Kansas, southeast Colorado and northern Oklahoma regions are under the gun. However, there are still a few uncertainties due to the models showing some mid-day convection possibly limiting the heating. The Storm Prediction Center had issued a moderate risk for the region as of Friday night. Regardless of what happens in the first half of the day, there will be severe storms; residents in the region will have to keep an eye on the sky for large hail, severe winds, torrential rains and even tornadoes!

Elsewhere in Weather News: April 11th, 2015

Severe Weather Outbreak Strikes Plains and Midwest

As April rolls around the severe weather season in the United States is on an uptick, and with that comes a higher threat for tornadoes. The latest severe weather outbreak occurred Wednesday and Thursday of this past week and hit hardest a few small communities of northern Illinois.

[map autofit=”1″ disable_scrollwheel=”1″] [pin]Medicine Lodge, Kansas[/pin] [pin]Fairdale, Illinois[/pin] [/map]

The setup on Wednesday was a fairly typical setup that you would see for a Southern Plains outbreak – surface low in central Kansas with sharp warm front extending eastwards and dryline extending southwards. This, combined with an upper-level trough moving in aloft, destabilized the environment sufficiently for supercells. Only a few tornadoes were observed on Wednesday, with most spotted just west of Wichita (including a large cone tornado near Medicine Lodge) and one unconfirmed in western Oklahoma. No damage was reported as tornadoes mainly touched down in open areas.

Thursday was a different story however, as the system progressed eastwards. The main risk for the day zeroed in to an area near the triple point where both CAPE and shear values were high and surface winds were slightly more backed compared to further south along the cold front. Once again, supercells were triggered in the early evening hours – this time in northern Illinois. One supercell near the triple point stood out from the others however; there no other cells to its southeast to inhibit growth and it latched along the warm front. What came of this supercell was a long tracked tornado that was on the ground for an estimated 25-35km and measured just less than a kilometre in width. It tore through mostly rural area and outskirts of two other towns before striking the town of Fairdale, Ill, which sustained heavy damage from the twister. On Friday, National Weather Service teams were out to examine the damage and gave it a preliminary rating of EF-4 (winds of about 315km/h). Two people were killed and a dozen more injured by the tornado. Cleanup is currently underway in the town as calmer weather sets in for the weekend.

Note: there is some strong language near the end of the video clip

Elsewhere in Weather News: November 29th, 2014

Widespread Floods Affect Southern France

A low pressure system advecting plenty of moisture Poleward from the Mediterranean Sea was in place over south-central France on Monday making for a good setup of long lasting heavy rains. The rains, enhanced by scattered thunderstorms prompted Météo France to issue various warnings, from strong wind warnings to severe thunderstorm warnings in addition to the rainfall warnings. A few areas along France’s southern coast were particularly hard hit with rainfall totals between 180-210mm in six hours on Monday. In addition to that another general 40-50mm (some amounts higher locally) fell as the system was moving off on Tuesday. On Wednesday, another low pressure system quickly moved into the region, again bringing with it rain and more storms. There was also a report of a weak tornado accompanying the one of the storms.

With already saturated soils from earlier in the week, conditions were primed for overland flooding as the second system moved in. Helicopters and rescue workers were hard at work towards the end of this week as people got trapped in their vehicles and houses from the flooding in southeastern France. There were five deaths related to the flooding events and 6,000 households were without power. The damage from the unconfirmed tornado comprised of roofs blown off and trees uprooted.

Precipitation map (in millimeters) of the rainfall in Southern France on Monday only. (Source: Météo France)
Precipitation map (in millimeters) of the rainfall in Southern France on Monday only. (Source: Météo France)

Unfortunately the soggy weather is expected to stick around the region this weekend. The upper-level cutoff low located over Southern Spain will drift ever so slowly to the east but will bring with it more showers and rain to southern France.

In other news, a supercell hit Brisbane, Australia this past week and knocked out power to 90,000 residents. The storm brought just about everything with it; golf ball size hail, strong winds and flash flooding – damages are in the hundreds of millions.

Radar image at the time the supercell was passing over Brisbane. (Source: BoM)
Radar image at the time the supercell was passing over Brisbane. (Source: BoM)

Elsewhere in Weather News: June 7th, 2014

Large Hailstorm causes Millions in Damages

This past week featured severe thunderstorms that tore through the Nebraska countryside producing extremely large hail in the region. Conditions were primed for a severe weather outbreak this past Tuesday; moisture streamed up from the Gulf of Mexico, a strong jet streak was in place overhead and the environment was relatively uncapped. Convective Available Potential Energy (CAPE) was quite high that day which was a significant contributor to the large hail sizes observed. Generally the higher the CAPE, the faster the updraft velocity which means that the updraft can support larger hailstones. Supercell thunderstorms were triggered Tuesday afternoon and persisted through the evening, trailing along the warm front that bisected the region.

In total over 200 hail reports were submitted on Tuesday and of these 38 were considered large hail reports (hail of 5cm in diameter or larger). The most damage caused that day appeared to come out of the town of Blair, Nebraska where hail caused major damage. Windows were blown out and car windshields smashed by the baseball size hail that fell – damage totaled in the hundreds of millions. Other storms along the warm front, the weather feature that triggered the severe weather, moved into the Omaha area not only bringing hail, but also torrential downpours. 13.5mm of rain was recorded in 3 minutes at the Omaha airport!

Hail damage in Hoover, NE shows the strength of baseball size hail, completely shredding the siding and breaking the windows. (Source: Kevin Krohn)
Hail damage in Hoover, NE shows the strength of baseball size hail, completely shredding the siding and breaking the windows. (Source: Kevin Krohn)

There is a possibility for more severe storms this weekend in Texas and New Mexico, but the parameters are not as as favourable for severe weather as seen this past Tuesday in Nebraska. Models show the active pattern continuing in the US Plains into next week, and rightfully so as severe weather season nears its peak.