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    Day 2 Outlook >
May 20, 2024 0600 UTC Day 1 Convective Outlook
Click to see valid 1Z - 12Z Day 1 Convective Outlook
Updated: Mon May 20 05:57:47 UTC 2024 (Print Version | 20240520 1200Z Day 1 shapefile | 20240520 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
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 Forecast Discussion
   SPC AC 200557

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CDT Mon May 20 2024

   Valid 201200Z - 211200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
   NORTHEAST COLORADO...SOUTHWEST NEBRASKA...AND FAR NORTHWEST
   KANSAS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   NORTHEAST ILLINOIS INTO SOUTHEAST WISCONSIN AND NORTHWEST INDIANA...

   ...SUMMARY...
   Severe thunderstorms are expected across parts of the central Plains
   this evening into the overnight hours. Other severe storms are
   possible from the Middle Mississippi Valley to Lower Michigan
   through early evening.

   ...Synopsis...
   The large-scale pattern on Monday will feature a positively tilted
   mid-level ridge across the eastern CONUS with a trough in the west.
   A shortwave trough currently across northeast Kansas early this
   morning will progress through the Midwest and into the Great Lakes
   by tonight. In addition, a closed upper low across the eastern
   Pacific will phase with the upper-level trough across the western
   CONUS and accelerate toward the Plains by the end of the period.

   A lee cyclone will deepen across the southern High Plains through
   the period as mid-level troughing amplifies across the western CONUS
   and mid-level flow strengthens across the Southwest. To the north of
   this surface low, a stationary front will become better defined from
   near the Palmer Divide to northwest Iowa with a dryline extending
   southward from this front. 

   ...Front Range into the central Plains and Upper Midwest...
   A significant void in low-level moisture is present across western
   Kansas and eastern Colorado early this morning in the wake of the
   MCS. By late morning, moisture should start to increase across
   Kansas in response to low-level moisture advection. This moisture
   advection will intensify during the afternoon as the primary lee
   cyclone develops across southeast Colorado and low-level flow
   strengthens. By late afternoon, low-level upslope flow will develop
   across northeast Colorado with dewpoints into the 50s. Within this
   region of upslope flow, supercells are expected to develop by late
   afternoon to early evening. Long hodographs will support the threat
   for large to very large hail initially. Any storms which are surface
   based, along or south of the frontal boundary, will pose some
   tornado threat, particularly after 00Z as the low-level hodograph
   enlarges and low-level moisture increases.

   Multiple rounds of supercells are possible within the Enhanced risk,
   as the initial supercells progress east, before additional
   supercells likely develop in a similar region as the primary trough
   ejects into the Plains. Eventually, supercells are expected to
   congeal into one or more bowing MCSs with an increasing severe-wind
   threat into south-central Nebraska. Some CAMs suggest the greater
   coverage severe-wind threat may persist into eastern Nebraska during
   the overnight period. Strong low-level moisture advection will
   maintain moderate to strong instability south of the frontal zone
   during the overnight period, and a strengthening low-level jet will
   also aid in MCS maintenance and intensity. However, the stable
   boundary layer during the overnight period casts doubt on how
   widespread the severe-wind threat will be after midnight. Therefore,
   the Enhanced risk is focused during the initial stages of
   supercell-to-bow transition where low-level thermodynamics will be
   more favorable during the evening hours.

   ...Northern Illinois vicinity into Wisconsin and Michigan...
   A compact mid-level shortwave trough over northeastern Kansas this
   morning will traverse the Midwest with ascent overspreading northern
   Illinois by mid-afternoon. Once the cap erodes, expect scattered
   thunderstorms to develop across central Illinois and move into
   northern Illinois, southeast Wisconsin and northwest Indiana.
   NAM/RAP forecast soundings show around 2000 to 2500 J/kg MLCAPE and
   around 30 knots of effective shear (in a confined region near the
   upper shortwave trough). This combination of instability, shear, and
   ascent with the passing wave should be sufficient for severe
   thunderstorms capable of primarily large hail and damaging wind
   gusts. These storms are expected to weaken as they move over the
   colder water of Lake Michigan and the boundary layer cools near
   sunset. 

   ...South Florida...
   Scattered thunderstorms are expected across south Florida during the
   afternoon and evening hours amid 1500 to 2000 J/kg MLCAPE. Shear
   will be relatively weak (20 to 25 knots) and lapse rates will be
   quite meager. Therefore, multicells with isolated large hail and
   damaging wind gusts will be the primary hazards.

   ..Bentley/Grams.. 05/20/2024

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z

        
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