SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0727 AM CDT Wed Sep 23 2020 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN LOUISIANA INTO SOUTHERN MISSISSIPPI...NORTHERN MINNESOTA INTO WISCONSIN AS WELL AS COASTAL WASHINGTON... ...SUMMARY... A few strong to severe storms with hail and gusty winds are possible this evening from northern Minnesota into Wisconsin. A brief tornado or two cannot be ruled out over parts of Louisiana and southwest Mississippi with the remnants of Beta. A few strong storms may affect coastal Washington this evening into tonight. ...Southern Louisiana and Mississippi... Remnants of Beta are being absorbed within southern periphery of a slow-moving shortwave trough centered over southwest MO. This will result in northeast advancement of the system currently situated over far southeast TX. By the end of the period, model consensus is that Beta will be located over central MS. A coastal/warm front will lift northward through southern LA into far southern MS today, and the inland advection of mid 70s F dewpoints will result in weak instability with 500-1000 J/kg MLCAPE in warm sector. Convection will continue developing within several convergence bands east of the center. The best threat for a brief tornado or two will be in a narrow corridor this afternoon and evening as storms move northward and interact with the warm front where 0-1 km hodograph size will be sufficient for a threat of low-level mesocyclones. ...Northern Minnesota into western Wisconsin... Steeper 7.5-8 C/km mid-level lapse rates will develop eastward through the upper MS Valley in advance of a low-amplitude shortwave trough. This will contribute to modest instability with 1000-1500 J/kg MUCAPE in vicinity of an east-west oriented baroclinic zone despite somewhat limited low-level moisture. It is likely that storms will develop this evening as deeper ascent accompanying the shortwave trough interacts with the boundary. Effective bulk shear might become sufficient for a few storms to develop modest mid-level updraft rotation which, in conjunction with the thermodynamic environment, will support some threat for hail. There may be some tendency for storms to congeal into a small MCS capable of producing a few strong wind gusts as well. ...Coastal Washington... Stronger height falls will occur later today with the strongest cooling aloft and destabilization after 00Z across western Washington. A leading band of precipitation associated with warm advection will give way to discrete cells moving rapidly east off the ocean. While only a few hundred J/kg MLCAPE will exist, strong large-scale lift as well as long hodographs may favor a few long-lived cells, possibly with rotation which will contribute to a threat for gusty winds and small hail. ..Dial.. 09/23/2020
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