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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 the morning of February 6th, an upper shortwave was lifting northeast from the southern Plains to the Lower Mississippi Valley. Our region was under SW flow aloft as several upper disturbances tracked across the region. At the surface, a broad area of ~996 mb low pressure was centered from eastern KY to northern AL, with a the associated (trailing) cold front extending southward into the Gulf of Mexico. A nearly stationary SW-NE oriented frontal boundary was draped from the northern NC Piedmont the Lower Eastern Shore. Temperatures were in the low-mid 60s across NE NC (in the warm sector), with upper 30s-mid 40s across the northwest two-thirds of the CWA. Strong southwesterly flow from 925-500 mb was advecting anomalous amounts of Gulf moisture into the region, and PWs were near record values throughout the CWA (especially SE).

Moderate (to occasionally heavy) rain was ongoing across the area as the frontal boundary struggled to lift northward, with a line of showers and thunderstorms just ahead of the trailing cold front (well to our southwest). Moderate to heavy rain continued across the NW two-thirds of the CWA through much of the day (as the aforementioned frontal boundary struggled to move NW of a Henderson (NC)-Emporia-Wakefield-Salisbury (MD) line). Temperatures did not get out of the 40s NW of the boundary. However, partial clearing occurred over far SE VA/NE NC, allowing temperatures to warm into the low 70s by early afternoon (with dew points in the mid-upper 60s). This happened at the same time as the aforementioned line of thunderstorms outpaced the trailing cold front, moving into the central Carolinas by early afternoon. The environment in the warm sector was characterized by a 60-75 knot southwesterly low-level jet from 925-850 mb, with 15-25 knot SSW winds at the surface. While low-level lapse rates were relatively modest, temperatures in the 70s/dew points in the mid-upper 60s were enough for mixed-layer CAPE of 500-1000 J/kg across NE NC Thursday afternoon. In addition, a meso-low had developed along the boundary (near AKQ) by 2-3 PM, with some (subtle) localized backing of the surface wind field just SE of the meso-low. This allowed effective SRH values to climb to 400-600 m2/s2 over parts of NC by mid afternoon. The line quickly moved across the area during the mid-late afternoon (w/ some elevated convection noted across central/eastern VA just north of the frontal boundary). This caused widespread 45-65 mph wind gusts across SE VA/NE NC, with one brief EF-0 tornado across Gates County, NC.

While rain continued across the area overnight (producing some minor flooding), no additional severe weather was observed through 7 AM Friday (2/7). However, the parent surface low rapidly deepened overnight as it moved northeast. By 7 AM Friday (2/7), the minimum central pressure of the low was ~980 mb and it was centered just near the Mason-Dixon Line. Southerly winds increased overnight, and temperatures/dew points were in the upper 50s-near 60° across much of Virginia/Maryland. A broken line of showers (ahead of the trailing cold front) was just to the west of the CWA by 7 AM Monday. This line of showers quickly crossed the area Friday morning before exiting to our north/east by midday. Despite temperatures/dew points only in the upper 50s, strong kinematic fields in the low and mid levels allowed these showers to produce wind gusts of 50-70 mph (mainly along and east of I-95). There were several reports of wind damage/trees down. At one point, 100,000 people were without power across our CWA Friday morning.

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