Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1123 AM CDT Sat Apr 22 2017 Valid 221630Z - 231200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN VIRGINA AND NORTHERN NORTH CAROLINA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM LOUISIANA TO THE VIRGINIA/NORTH CAROLINA BORDER REGION... ...SUMMARY... A few severe thunderstorms capable of damaging wind gusts and large hail will be possible this afternoon and evening from Louisiana to the southeastern Virginia/North Carolina Tidewater region. The best-organized potential appears to be from parts of Mississippi into western/northern Alabama and southern Tennessee, and over southern Virginia and extreme northern North Carolina. ...Mississippi and Tennessee Valleys... A well-defined vorticity maximum over Missouri is forecast by model guidance to move eastward over the Mississippi Valley tonight as the associated upper trough amplifies during the period. A strong band of mid/upper level winds is located on the southern periphery of the system with a 60-70 kt mid-level jet streak progressing toward the lower Mississippi Valley. At the surface, a low near the Mississippi Delta will move slowly eastward across northern parts of Mississippi and Alabama through tonight, as a trailing cold front moves southeastward across the lower Mississippi Valley. A quasistationary front extending eastward from the low is forecast to sag slowly southward with time. Earlier clouds over northern/central Mississippi into northern Alabama and southern middle Tennessee have diminished substantially permitting stronger diabatic heating to occur in advance of the approaching cold front. With surface temperature warming into the 70s and dew point values in the low-mid 60s, further destabilization is likely in the pre-frontal environment with MLCAPE reaching 1000-1500 J/kg this afternoon. CAM guidance indicates stronger storms will develop along/ahead of the cold front during the early afternoon with activity spreading eastward through the evening hours. Effective bulk shear of 35-40 kt will promote organized storm structures including isolated supercells. Stronger cells will be capable of producing mainly damaging wind gusts and severe hail. ...Southern Virginia/Northern North Carolina... The environment is undergoing strong diabatic heating over North Carolina where visible satellite imagery indicates few clouds, and low-level warming is spreading northward into far southern Virginia as cloud cover thins near an east-west frontal zone. Despite modest mid-level lapse rates, surface dew points in the low-mid 60s coupled with diurnal heating will result in further destabilization with MLCAPE near 1500 J/kg expected this afternoon. Storms are beginning to develop at this time over northwest North Carolina and southwest Virginia within a weakly-capped environment. Activity is expected to increase in coverage and intensity and spread/develop eastward during the afternoon with a few severe storms possible. See Mesoscale Discussion 545 for more details. ..Weiss/Cook.. 04/22/2017Read more
from SPC Forecast Products http://ift.tt/wWCv9s
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