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Hazardous Heat Across the Western U.S.; Heavy Rain and Flooding in the Southwest and Western Gulf Coast

Dangerous heat will persist over portions of interior California, the Great Basin, and the northern Rockies through Thursday. Heat will gradually spread into the northern Plains today. Across the western Gulf Coast, heavy to excessive rainfall will persist through mid-week. Additionally, the Southwest Monsoon will continue to bring a flash flooding threat to the Four Corners Region this week. Read More >

Overview

On October 7th, Michael formed into a tropical storm just southeast of the Yucatan Peninsula. It then moved northward into the Gulf of Mexico toward the Florida Panhandle. 24-36 hours before making landfall near Panama City, FL, Michael rapidly strengthened into a Category 4 hurricane. After making landfall, Michael weakened into a tropical storm and started to accelerate as it turned to the northeast (in response to a large scale trough moving east from the Rockies). Michael started to transition into an extratropical system as it was moving through the Carolinas when it began to interact with a cold front moving toward the southeast. Michael continued its transition into an extratropical storm as it moved into southeastern Virginia as the cold front was entering northern/western portions of the Wakefield CWA. It was the combination of Michael and cool, dry air wrapping in from the NW that helped create the conditions for damaging wind gusts over a large part of our CWA. Michael completed its transition by early Friday morning as it moved offshore and continued to accelerate to the east-northeast.   

The main area of rain started to enter the western part of the Wakefield CWA during the early afternoon hours on 10/11. With rainfall rates well in excess of 1”/hour, flash flooding quickly developed across the area. The rain had overspread much of Virginia by the early evening hours on Thursday before entering the Lower Eastern Shore by 9-10 PM. The rain rapidly ended across the area early Friday morning as Michael moved well offshore. A widespread 3-8 inches of rain was observed across much of Virginia (in addition to the Lower MD Eastern Shore). Areas in/around Farmville, Nottoway County, Lunenburg County, and the Northern Neck were especially hard hit with flash flooding. This prompted Flash Flood Emergencies to be issued for these areas during the height of the storm. Areas in SE Virginia/NE North Carolina received only 1-2 inches of rain on average.

In addition to the widespread flash flooding, conditions set up favorably for tornadoes to form on the eastern edge of the rain (during the late afternoon/evening hours).   Temperatures warming into the 80s (coupled with dew points in the mid-70s) lead to moderate instability (SBCAPE values of ~1500 J/kg). The moderate instability, coupled with more than enough low-level speed and directional shear (sfc-1 km SRH values were ~300 m2/s2 in spots), was more than enough for the formation of brief spin-up tornadoes. See the Environment section for a NAM Analysis Sounding from the Middle Peninsula, where multiple tornadoes were confirmed during the evening of 10/11. While all of the tornadoes were EF-1 (or weaker) in magnitude, significant impacts were still felt.

Despite the fact that Michael had weakened to low-end tropical storm strength, winds at 925hPa were still 60+ MPH  on the back side of the storm. The cool/dry air coming in from the north and northwest helped the stronger winds from aloft mix down to the surface. As a result, wind gusts of 45-75 MPH were observed across much of our inland areas on the leading edge of the cool/dry air. Water temperatures ~2 standard deviations above average on the Chesapeake Bay enhanced the mixing of stronger winds from aloft. As a result, hurricane force wind gusts were observed at many sites on the bay in addition to land areas immediately to the south and east. See the Environment section for a more detailed depiction of this wind event. These damaging wind gusts caused widespread power outages and downed numerous trees across the area. At one point, ~600,000 people were without power in the state of Virginia! Due to the combination of major flash flooding, tornadoes, and damaging winds, Michael will certainly be remembered across the area.  

Radar/Photo Radar/Photo
Storm Total Rainfall  Maximum Wind Gusts
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