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Sep 20, 2019 1730 UTC Day 2 Convective Outlook
Updated: Fri Sep 20 17:28:24 UTC 2019 (Print Version | 20190920 1730Z Day 2 shapefile | 20190920 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 201728

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1228 PM CDT Fri Sep 20 2019

   Valid 211200Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
   KANSAS INTO IOWA AND OVER NORTHWEST MINNESOTA...

   ...SUMMARY...
   Severe storms are possible across parts of the Plains on Saturday,
   most concentrated from Kansas into Iowa. Severe storms are also
   expected across northwest Minnesota. Other more isolated activity is
   possible over parts of the southern High Plains.

   ...Synopsis...
   Progressive shortwave trough embedded within a broad upper trough
   will move northeastward across the Dakotas and into southern
   Manitoba on Saturday. Its parent upper trough will also gradually
   move eastward as a second shortwave trough rotates through its base
   across the Four Corners region. Overall evolution of these features
   will result in strong mid/upper-level southwesterly flow spreading
   across the northern/central Plains into the mid/upper MS Valley and
   Upper Great Lakes.

   The surface pattern early Saturday will feature a cold front
   extending from a low centered over the central Manitoba/Ontario
   border south-southwestward to another low over the southern CO/KS
   border. Northern portion of this front is expected to progress
   quickly eastward/southeastward throughout the day, likely reaching
   the Upper Great Lakes by early Sunday morning. Southern portion of
   front is also expected to move southeastward, but more slowly than
   portions farther north. Expectation is for this portion of this
   front to extend from southwest KS into northern MO by early Sunday
   morning. Thunderstorms are expected along the length of the front as
   it interacts with the moist and unstable air mass ahead of it.

   ...Central Plains into the Mid MS Valley...
   Highest thunderstorm coverage is expected along the front from KS
   northeastward into northwest MO/southern IA. In this region, several
   mechanisms for ascent will overlap, including convergence along
   front, persistent warm-air advection, and large-scale lift provided
   within the entrance region of the upper jet. This ascent combined
   with the moist low-level air mass and moderate vertical shear will
   support some more organized updrafts and potentially a few
   supercells. Given the sagging cold front and persistent warm-air
   advection, storms may have trouble remaining surface based,
   potentially limiting a more widespread severe threat. Even so, the
   more organized storms will be capable of large hail, with some
   instances of very large hail (i.e. greater than 2" in diameter)
   possible. 

   ...Far Eastern Dakotas across MN into WI...
   Showers and thunderstorms will likely be ongoing at the beginning of
   the period, supported by a strong low-level jet. A few of these
   storms may be strong enough to produce hail. These showers and
   thunderstorms will drift eastward/northeastward and weaken during
   the morning as the low-level also shifts eastward.

   Moisture advection ahead of the approaching front is expected to
   result in mid to upper 60s across the region by mid-afternoon. Lapse
   rates are also expected to steepen as cooler mid/upper-level
   temperatures gradually move into the area while low-level
   temperatures remain relatively warm from antecedent convection.
   These thermodynamic conditions coupled with strong mid-level flow
   aloft result in an environment conditionally supportive of strong to
   severe thunderstorms. Main deterrents for storm initiation are the
   warm low-level temperatures (i.e. between 850-700 mb) and the lack
   of stronger convergence along the front. As such, much of the region
   will likely struggle to produce deep convection. Most probable
   location for thunderstorms is across northern MN where the frontal
   ascent is well correlated with ascent provided by the shortwave
   trough. Here, a few supercells capable of large hail and strong wind
   gusts are possible.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   5%     - Slight
   Wind:     15%     - Slight
   Hail:     15% SIG - Slight

   ..Mosier.. 09/20/2019

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

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

        
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Page last modified: September 20, 2019
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