Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1127 AM CDT Sun Apr 02 2017 Valid 021630Z - 031200Z ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF FAR EAST TEXAS AND NORTHERN LOUISIANA... ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS SURROUNDING THE HIGH ACROSS PORTIONS OF EAST TEXAS...NORTHERN AND CENTRAL LOUISIANA...CENTRAL AND SOUTHERN MISSISSIPPI...AND EXTREME SOUTHERN ARKANSAS... ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE MODERATE FROM PORTIONS OF EAST TEXAS TO MISSISSIPPI... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED FROM PORTIONS OF EAST AND SOUTH TEXAS TO FAR WESTERN ALABAMA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT FROM EASTERN PORTIONS OF THE SOUTHERN PLAINS TO WESTERN ALABAMA... ...SUMMARY... Widespread severe thunderstorms capable of significant tornadoes, severe wind, and severe hail will spread across portions of east Texas to the lower Mississippi Valley through tonight. The greatest risk for tornadoes will exist from portions of far east Texas eastward across northern Louisiana this afternoon and evening. ...Portions of east Texas to the lower Mississippi Valley through tonight... A long-lived thunderstorm cluster that crossed central Texas through the overnight/morning hours is losing organization as it is advancing into east Texas. Convection continues to form ahead of the remnant outflow boundary related to the cluster -- from parts of the Upper TX Coast through the lower Sabine Valley region within a warm-advection plume. This plume of warm advection is associated with an amplifying midlevel shortwave trough, whose accompanying midlevel speed maximum is emerging over south Texas. As the shortwave trough continues to advance eastward, the low-level mass response will facilitate poleward return of rich boundary-layer moisture -- e.g., 15 g/kg mean mixing ratio per Lake Charles 12Z observed sounding. As such, an expansive warm sector associated with MLCAPE around 1500-3000 J/kg will become established through the afternoon from the western/central Gulf Coast northward to a precipitation-reinforced warm frontal zone forecast to extend from part of east-central TX eastward across northern Louisiana. With open-warm-sector convective development now becoming apparent ahead of the remnants of the convective cluster, it is expected that this activity will mature as it interacts with the northward-advancing warm frontal zone. This is where effective SRH around 300-400 m2/s2 amid strong deep shear and increasing buoyancy will exist. Given increasing confidence in semi-discrete supercells/supercell clusters interacting with this warm frontal zone around peak heating, confidence has increased in greater tornado potential -- including significant tornadoes -- across the now-upgraded High Risk area. The significant-tornado potential will spread toward the lower Mississippi Valley into the evening hours. Into the evening and overnight hours tonight, a band of warm advection/confluence will facilitate the development of a pre-frontal squall line that will advance eastward across parts of LA/MS and far southern AR. In addition to the potential for extensive wind damage, meso-vortices and embedded supercells capable of producing tornadoes are expected to spread eastward through the lower Mississippi Valley into the overnight hours. Increased confidence in this scenario warrants eastward extension of the Moderate Risk area. ..Cohen.. 04/02/2017Read more
from SPC Forecast Products http://ift.tt/wWCv9s
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