Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Sun Apr 30 2017 Valid 302000Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN ALABAMA INTO NORTHWEST GEORGIA AND EAST-CENTRAL TENNESSEE... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL GULF COAST NORTH INTO THE OHIO VALLEY AND INTO PARTS OF THE CENTRAL APPALACHIANS... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A SMALL PORTION OF THE MIDDLE MISSISSIPPI VALLEY... ...SUMMARY... Scattered damaging winds and a few tornadoes are possible across parts of the Deep South late this afternoon and evening. Isolated severe thunderstorms are possible across parts of the Ohio Valley east into parts of Maryland and over portions of the middle Mississippi Valley. ...discussion... The substantial changes to the previous outlook are listed below. 1) Removed low severe probabilities over parts of the Corn Belt owing to limited destabilization prior to the loss of heating this evening. 2) Extended 15% wind and 5% tornado probabilities downstream over the TN Valley QLCS which included parts of northwestern GA and more of east-central TN. 3) Removed probabilities west of the convective line along the central Gulf Coast due to stabilization influences of the line itself. Early afternoon HRRR runs appear to depict a low probability scenario of regeneration of a severe threat along the AL/FL Panhandle coast later tonight. ..Smith.. 04/30/2017 .PREV DISCUSSION... /ISSUED 1129 AM CDT Sun Apr 30 2017/ ...Deep South... A QLCS is ongoing across MS into southeast LA, with a decaying comma-head MCV over north-central MS. This line should be the primary focus for a continuing severe threat this afternoon. Although high-level winds are weak per regional 12Z soundings, strong low-level shear will continue to support embedded mesovortices capable of a few tornadoes and damaging winds. The instability axis will occlude as the eastward surge of the QLCS outpaces Gulf boundary-layer moisture return, limiting a more substantial risk farther north in the TN Valley. ...Midwest... Low confidence persists regarding the likelihood of appreciable destabilization in a scenario that appears otherwise favorable for severe storms given ample deep-layer/low-level shear. This low confidence is related to extensive convection ongoing from the Mid-MS Valley into the Mid/Deep South. A couple clusters of severe storms may develop downstream of this midday activity across parts of IN/KY/OH where diabatic heating should be more pronounced amid middle 60s surface dew points. Farther west over the Mid-MS Valley in the wake of the midday convection, widely scattered storms should attempt to form late afternoon along/near the cold front/surface cyclone track. Instability will probably remain rather weak and deep-layer winds meridional, suggesting overall severe coverage should be isolated.Read more
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