SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1219 PM CDT Fri Aug 13 2021 Valid 141200Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SD AND WESTERN NE...OVER CENTRAL/SOUTHERN FL...PARTS OF THE MID-ATLANTIC...AND OVER PORTIONS OF ME... ...SUMMARY... Isolated strong to severe storms may produce strong wind gusts across parts of the Mid-Atlantic and portions of Maine Saturday afternoon and evening. Additional strong gusts and hail main also accompany storms across portions of western South Dakota and Nebraska. A couple of tornadoes associated with currently forecast Tropical Storm Fred will be possible over central and southern Florida. ...Florida... Tropical Depression Fred is currently forecast by the National Hurricane Center to emerge as a Tropical Storm Saturday morning near the Florida Keys. There continues to be quite a bit of uncertainty in forecast track at this time, but the system should generally lift north/northwest offshore from the western coast of the FL Peninsula. Stronger low level wind fields are expected to remain rather compact near the center. Enlarged low level hodographs and stronger SRH will mainly be confined to the FL Keys during the afternoon and evening. Nevertheless, a couple of tornadoes will be possible with convection across southern/central FL on Saturday. ...Mid-Atlantic... A very moist airmass will reside over the region ahead of south/southeastward sagging cold front. Strong heating will result in moderate destabilization during the afternoon. Effective shear magnitudes will remain poor over the region, along with modest midlevel lapse rates, limiting a more organized severe threat. However, a few strong clusters/line segments could produce strong gusts given steep low level lapse rates and water-loaded downdrafts driven by PW values near 2 inches. ...Maine... An upper trough and surface cold front will spread across New England during the day Saturday. The pre-frontal environment should become weakly to moderately unstable with 1000-1500 J/kg MLCAPE possible. However, stronger flow associated with the upper trough will remain post frontal, with weak winds forecast in the surface-700 mb layer. Nevertheless, up to 35 kt effective bulk shear could support some organization as storms develop along the front during the afternoon. Mid-level lapse rates will remain weak, but the boundary layer could destabilize sufficiently to support a few locally strong to severe wind gusts. ...Western SD/NE... A weak shortwave impulse is forecast to overspread the region in increasing northwesterly mid/upper level flow Saturday afternoon/evening. Modest low level warm advection will maintain adequate boundary layer moisture amid modestly steep midlevel lapse rates. Strong heating should result in isolated thunderstorms by late afternoon, mostly likely developing near the Black Hills. Forecast guidance is in good agreement that thunderstorms clusters will spread southward across western NE through the evening. While deep layer flow is forecast to be modest, southerly low level winds beneath northwesterly mid/upper winds will result in effective shear magnitudes around 30 kt. Coupled with moderate instability and midlevel lapse rates around 7-7.5 C/km, a few strong to severe storms capable of strong gusts and perhaps isolated hail will be possible. ..Leitman.. 08/13/2021 Read more LIVE: spc.noaa.gov
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