SPC AC 270041

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0741 PM CDT Wed Aug 26 2020

   Valid 270100Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHERN AND CENTRAL LOUISIANA...

   ...SUMMARY...
   Hurricane Laura will pose an increasing threat for several tornadoes
   this evening and continuing overnight across much of Louisiana and
   far east Texas. Elsewhere, marginally severe wind gusts and hail
   will be possible in parts of the Great Lakes, northern Plains and
   northwestern states.

   ...Sabine and Lower Mississippi Valleys...
   Hurricane Laura will approach the coast of southwest Louisiana this
   evening as rainbands associated with Laura spread inland. As the
   center of Laura approaches land late this evening, low-level shear
   will dramatically increase across southern and central Louisiana
   into far east Texas. From 06Z to 09Z across much of southern and
   central Louisiana, hodographs become large and looped with 0-1 km
   shear increasing into the 45 to 60 kt range. This will be favorable
   for tornadoes with rotating cells embedded in the rainbands of
   Laura. Tornadoes will be most likely from the track of Hurricane
   Laura eastward about 100 statute miles, where an Enhanced Risk is
   maintained. The tornado threat should gradually increase with
   northward extent as the hurricane moves inland after midnight.

   ...Great Lakes...
   A anticyclonic flow pattern is in place across the Great Lakes
   region with water vapor imagery showing a shortwave ridge moving
   east-southeastward through the flow. At the surface, a moist airmass
   is in place from the upper Mississippi Valley extending eastward
   across much of the Great Lakes region. RAP analysis shows moderate
   instability across much of the region. Thunderstorms are ongoing on
   the northern edge of the stronger instability across northern
   Wisconsin and western upper Michigan. This activity will likely move
   eastward across the remainder of upper Michigan this evening and
   could be accompanied by a marginal wind damage threat. As low-level
   flow increases tonight, additional thunderstorms should develop
   across parts of northern lower Michigan where a few strong wind
   gusts will also be possible.

   ...Northern Plains...
   The latest water vapor imagery shows a zonal flow pattern in place
   across the northern Plains. A moist and unstable airmass is located
   in much of South Dakota where scattered thunderstorms are ongoing.
   The largest cluster of thunderstorms is in the south-central part of
   South Dakota where the RAP is estimating MLCAPE in the 2000 to 2500
   J/kg range. In addition, regional WSR-88D VWPs have 0-6 km shear
   near 40 kt. This combined with steep low to mid-level lapse rates
   should be enough for a marginal wind damage and hail threat for a
   few more hours this evening.

   ...Northern Rockies...
   Southwest mid-level flow is evident on water vapor imagery across
   the northwestern U.S. According to the RAP, moisture and instability
   is analyzed across much of Idaho and southwest Montana. Scattered
   thunderstorms are ongoing near the strongest instability in southern
   Idaho. Additional storms are located in the higher terrain of
   southwest Montana. In addition to the instability, moderate
   deep-layer shear is present and lapse rate are steep in the low to
   mid-levels. This environment should be enough to continue a marginal
   wind damage and hail threat for a couple more hours.

   ..Broyles.. 08/27/2020

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