Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Sat Apr 29 2017 Valid 292000Z - 301200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN TEXAS AND NORTHWEST LOUISIANA INTO CENTRAL ARKANSAS AND SOUTHEAST MISSOURI... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTH-CENTRAL TEXAS INTO THE LOWER MISSISSIPPI VALLEY AND INTO THE OHIO VALLEY... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK AND INCLUDING PARTS OF THE MIDDLE ATLANTIC STATES.... ...SUMMARY... Severe thunderstorms are expected from parts of south-central Texas northeastward to portions of the Ohio Valley and northern Middle Atlantic region, especially this afternoon and evening. The most likely region for severe weather is forecast from eastern Texas and northwest Louisiana across central Arkansas and into southeastern Missouri. Storms will be capable of damaging winds, large hail, and a few tornadoes. ...discussion... The only substantial change was to remove the 30% hail probabilities from the prior outlook and confine the 15% hail area to central AR southwest into TX where greater buoyancy resides. Elsewhere, removed severe probabilities from parts of TX/OK northeastward into the middle MS Valley where the front and/or convective complexes have substantially stabilized the boundary layer. ..Smith.. 04/29/2017 .PREV DISCUSSION... /ISSUED 1133 AM CDT Sat Apr 29 2017/ ...Central/Eastern Texas into southern Missouri... An upper low near the Four-Corners regions is expected to move eastward through the period reaching the Texas Panhandle and western Oklahoma late tonight. Strong mid-upper level winds associated with the low will translate across west Texas and over the southern Plains tonight, accompanied by 150-180 m height falls at 500 mb. At lower levels in advance of the upper low, a broad low-level jet is in place from eastern parts of Texas and Oklahoma into Louisiana and Arkansas with 50-60 kt winds in the 1-2 km agl level. These factors will provide strong low-level shear throughout the period, with strengthening deep-layer shear progressing eastward across the southern plains toward the lower Mississippi Valley tonight. At the surface, the primary low over eastern Oklahoma is forecast to move mainly northward into southeast Kansas/southwest Missouri tonight. A cold front currently extending southwestward from the low toward the Big Bend region will advance into central/south central Texas by this evening, and arc across central Arkansas into southwest Louisiana by the end of the period. A quasi-stationary front extending east-northeast from the low into southern Illinois will move little, and an outflow boundary persists south of the front across the Missouri/Arkansas border eastward into Kentucky may serve as the effective focus for storms. Ample low-level moisture is present over the warm sector with surface dew points of generally in the low 70s. Extensive cloud cover over the region will tend to inhibit stronger diabatic heating to occur, although breaks in overcast will promote local areas of more focused heating/destabilization this afternoon. A capping inversion evident in 12Z soundings at FWD, SHV and LZK is likely to limit convective development in advance of forced bands of storms, although storms currently near the Sabine River may persist as they move northeast this afternoon in association with a weaker perturbation evident in water vapor imagery. Otherwise, storms from southwest Missouri into extreme eastern Oklahoma are expected to spread eastward with time with intensification expected this afternoon. Some southward development along the cold front is also expected by mid-late afternoon as stronger heating appears likely over central into northeast Texas. NWP guidance including CAM forecasts suggests potential for several bands/lines of storms to progress eastward with some bowing segments developing. Large hail and damaging wind gusts will be possible with more intense cells. A few tornadoes will also be possible, especially with any discrete storms that can develop ahead of the cold front, as well as within QLCS mesovortices that may develop. The activity is likely to progress eastward during the overnight hours with a continued severe threat. ...Ohio Valley into the Mid-Atlantic States... Corridors of eastward-moving precipitation including heavy rainfall and a few strong storms will continue to reinforce a generally west/east-oriented frontal zone from the Ohio Valley to the coastal Northeast States. A gradually weakening low-level jet and moist conveyor, along with prevalent rising upper heights, may allow for some northward shift of the effective boundary and increasingly moist warm sector this afternoon. Regardless, one or more storm clusters ongoing across the upper Ohio Valley at this time may persist or reinvigorate in vicinity of the effective frontal zone toward PA/Delmarva vicinity with mainly a damaging wind risk. Other storms are expected to develop near the effective warm front from MO into IL and spread eastward with damaging winds and severe hail as the primary severe risks.Read more
from SPC Forecast Products http://ift.tt/u32qoI
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