SPC May 18, 2017 0100 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 17 May 21:01

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 PM CDT Wed May 17 2017 Valid 180100Z - 181200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF WISCONSIN...NORTHWEST ILLINOIS AND FAR EASTERN IOWA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID TO UPPER MISSISSIPPI VALLEY IN THE WESTERN GREAT LAKES... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE SLIGHT RISK AREA ACROSS PARTS OF THE MID TO UPPER MISSISSIPPI VALLEY...WESTERN GREAT LAKES AND OZARKS... ...SUMMARY... Severe storms will continue to impact parts of the mid to upper Mississippi Valley this evening into tonight. The threat for damaging wind gusts will be greatest across eastern Iowa, northwest Illinois and southwest Wisconsin. Large hail and a couple brief tornadoes will also be possible across the mid to upper Mississippi this evening. ...Mid to Upper Mississippi Valley... Water vapor imagery shows a negatively tilted upper-level trough over the mid Missouri Valley with a band of large-scale ascent moving northeastward across the upper Mississippi Valley. At the surface, a 993 mb low is moving northeastward across northwest Iowa with a corridor of low-level moisture ahead of the low extending northward from Illinois into Wisconsin and southeastern Minnesota. Several line segments are ongoing along this corridor with one line in north-central Wisconsin and another near the Mississippi River in far eastern Iowa. The latest RAP shows moderate instability ahead of this activity with MLCAPE values across much of Iowa and northern Illinois estimated in the 1200 to 1800 J/kg range. In addition, the RAP shows a 65 to 80 kt mid-level jet over the mid Mississippi Valley with the left exit region of this feature located across eastern parts of the upper Mississippi Valley. The exit region of the jet is enhancing lift and deep-layer shear across the Upper Mississippi Valley where 0-6 km shear values are estimated in the 45 to 55 kt range. This will be enough to maintain a wind damage threat with line segments that can persist this evening and into the early overnight period. Large hail will also be possible with the stronger embedded cells. A couple brief QLCS type tornadoes will also be possible. ...Arkansas/Missouri and central Illinois... Southwest flow will remain in place across the Ozarks and mid Mississippi Valley this evening into tonight. An axis of moderate instability is currently analyzed by the RAP from the Arklatex northeastward into eastern Missouri where MLCAPE values are estimated in the 1500 to 2000 J/kg range. Moderate instability should remain in place across the region as warm advection is maintained due to veering winds in the low-levels. This may allow for isolated convective initiation along the instability axis during the late evening or in the early overnight period. NAM forecast soundings in the Ozarks around midnight show 0-6 km shear in the 50 to 60 kt range and show potential for surface-based convection. This could be enough for a marginal wind damage or hail threat. ..Broyles.. 05/18/2017 Read more



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