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Aug 20, 2017 1730 UTC Day 2 Convective Outlook
Updated: Sun Aug 20 17:22:24 UTC 2017 (Print Version | 20170820 1730Z Day 2 shapefile | 20170820 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 201722

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1222 PM CDT Sun Aug 20 2017

   Valid 211200Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MID MISSOURI VALLEY AND MID TO UPPER MISSISSIPPI VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL PLAINS...LOWER TO MID MISSOURI VALLEY...MID TO UPPER
   MISSISSIPPI VALLEY AND WESTERN GREAT LAKES...

   ...SUMMARY...
   Severe thunderstorms associated with wind damage and hail are
   forecast to impact parts of the mid Missouri Valley
   east-northeastward into the mid to upper Mississippi Valley on
   Monday afternoon and evening.

   ...Mid Missouri Valley/Mid to Upper Mississippi Valley/Central
   Plains/Western Great Lakes...
   A low amplitude cyclonic flow pattern will be in place across the
   north-central United States on Monday as an upper-level trough moves
   into the central Plains. At low-levels, a jet maxima is forecast
   across Iowa during the morning. A cluster of elevated storms may be
   ongoing near the exit region of the low-level jet in north-central
   Iowa and southern Minnesota at the start of the period. This
   convection is forecast to move eastward into the western Great Lakes
   region by midday and could be associated with a marginal severe
   threat. An outflow boundary may be left behind across parts of
   northeast Nebraska and Iowa which could be a focus for surface-based
   convective development during the mid to late afternoon. A cold
   front is also forecast to move southeastward into the mid Missouri
   Valley by late afternoon which will also be a focus for convection.
   Depending upon where the morning outflow boundary sets up, a moist
   and unstable airmass should be in place by afternoon. Model
   forecasts suggest that MLCAPE values may reach 2000 J/kg across
   parts of the slight risk area by late afternoon. Forecast soundings
   along this corridor at 21Z/Monday show moderate deep-layer shear and
   steep low-level lapse rates. Surface winds may be locally backed
   just to the south of the cold front helping to enhance shear and
   making conditions more favorable for severe storms. The wind profile
   may support the development of isolated supercells in areas where
   moderate instability is realized. Large hail and wind damage will be
   possible with supercells. However, multicells should be the more
   common storm mode. Wind damage and hail will be possible with the
   multicell line segments. The severe threat should gradually develop
   east-southeastward into parts of southern Wisconsin, northwest
   Illinois, southern Iowa and far northern Missouri during the early
   to mid evening.

   Further to the west in the central Plains, an upper-level trough is
   forecast to move across the region during the mid to late afternoon.
   Thunderstorms that form along the front to the west of the trough,
   mainly in central and northern Nebraska, should have a less
   favorable shear environment due to veered low-level winds. In spite
   of this factor, steep low-level lapse rates and moderate instability
   may be enough for a marginal wind damage threat.

   ..Broyles.. 08/20/2017

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z

        
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Page last modified: August 20, 2017
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