SPC Mar 19, 2018 0600 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 19 Mar 2018

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Mon Mar 19 2018 Valid 191200Z - 201200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PARTS OF TN...NORTHEAST MS...NORTHERN AL...AND NORTHWEST GA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK FROM THE TENNESSEE VALLEY TO THE SOUTHEAST STATES... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK FROM THE MID-SOUTH AND SOUTHERN KY TO NORTHERN FL... ...SUMMARY... Tornadoes (some strong), very large hail, and damaging winds are expected across parts of middle Tennessee into northeast Mississippi, northern and central Alabama to western Georgia. Severe storms will be possible into southern Georgia and northern Florida. ...Synopsis... A compact closed cyclone and attendant shortwave trough will weaken this forecast period as this system remains progressive, reaching the lower Ohio and Tennessee Valleys by 20/00Z and into the upper Ohio Valley by 12Z Tuesday. Meanwhile, a pair of shortwave troughs and accompanying midlevel jets is expected to phase across the southern Plains this afternoon into the evening, with further amplification of this trough into the middle Mississippi Valley to the northwest Gulf Coast region. A surface low, attendant to the lead trough, will track from northeast OK to western middle Tennessee by late this afternoon (by 21Z), with a cold front extending southwest through northeast MS to southern LA. At 12Z today, a warm front should extend through central AR and MS into southern AL/GA. An increase in southwesterly winds across the lower Mississippi and Tennessee Valleys to the Southeast States will result in a moistening warm sector as the warm front advances to the northeast. This boundary should extend from the surface low in middle TN south-southeast through northern and central AL to south-central GA by mid-late afternoon, before advancing farther northeast tonight. ...TN/northeast MS/AL/northern and western GA... Elevated showers and thunderstorms are expected to be ongoing at the start of D1 within a zone of warm advection and strong forcing for ascent attendant to a strong southwesterly low-level jet and the lead compact shortwave trough moving through southern MO and AR. As the deep-layer ascent spreads east into the lower Tennessee Valley this morning to early afternoon, the early day convection will shift into the Mid-South, likely delineating the northwest extent of stronger destabilization. Surface dew points in the 60s and steepening lapse rates will result in moderate instability across the warm sector. New storm development is expected by mid afternoon in western middle TN into northeast MS as the surface low and cold front reach these areas. This will coincide with strong forcing for ascent spreading across the western extent of moderate instability. Strengthening deep-layer winds (westerly at 50-70 kt in the 500-700-mb layer and southwesterly at 40-50 kt at 850 mb shifting across MS into AL) this afternoon will prove favorable for supercells. Given effective SRH will exceed 300-400 m2/s2, a strong tornado or two will be possible from parts of middle TN into northeast MS, northern AL and northwest GA late this afternoon into the early evening, as the cold front advances east. The favor thermodynamics and strong bulk shear will support very large hail, as well. Farther south across central into southeast AL, organized storms including supercells will prove favorable for all severe hazards as activity forms along the warm front this afternoon. ...Southern and eastern GA into northern FL... Weak height falls across this region where the environment should become moderately unstable may prove favorable for thunderstorm development. Strengthening deep-layer westerlies across this region will result in favorable shear for organized storms producing all severe hazards into the early evening. ..Peters/Gleason.. 03/19/2018 Read more



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