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    Day 2 Outlook >
Sep 19, 2018 1300 UTC Day 1 Convective Outlook
Updated: Wed Sep 19 12:55:16 UTC 2018 (Print Version | 20180919 1300Z Day 1 shapefile | 20180919 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 191255

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Wed Sep 19 2018

   Valid 191300Z - 201200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTH-CENTRAL PLAINS TO UPPER MISSISSIPPI VALLEY...

   ...SUMMARY...
   A few severe storms, mainly with a threat for hail and damaging
   winds, are possible across parts of the north-central Plains to
   upper Mississippi Valley.

   ...Synopsis...
   In mid/upper levels, ridging is forecast to shift eastward from the
   southern Plains and Ozarks across the Mississippi Valley to the
   Tennessee and Ohio Valleys.  A synoptic-scale trough -- now evident
   in moisture-channel imagery over the Pacific Coast states -- is
   forecast to shift eastward to western MT, UT, and the AZ/NM border
   region by 12Z.  To its southeast, several minor shortwave troughs
   and vorticity lobes will eject northeastward across the central/
   southern Rockies and central/northern Plains.  

   At the surface, 11Z analysis showed a low over northeastern CO, with
   warm front roughly eastward across southern NE and northern MO.  A
   weaker, quasistationary frontal zone was drawn across southern MN,
   southeastern SD, and northwestern NE.  The low is expected to
   move/redevelop to central/southern NE by the end of the period as
   the mid/upper trough approaches, with the frontal zone consolidating
   toward the current position of the northern boundary, but with
   slight effective displacement southward by convective processes
   possible across the southern MN/northern IA and southern WI areas.  

   ...North-central Plains to upper Mississippi Valley...
   An extensive area of clouds, rain and embedded clusters of
   thunderstorms is present across portions of northern IA, southern
   MN, northern and eastern SD, and northern NE.  Being near the
   southern rim of the stronger mid/upper flow, but north of the
   surface front, a combination of elevated frontal lift and warm
   advection will support isolated strong-severe convection in roughly
   the southeastern half of this precip shield for a few more hours,
   with pulse hail and strong gusts possible. 

   The morning activity will reinforce antecedent baroclinicity
   accompanying the front, and another round of convection should
   develop later today, perhaps beginning late this afternoon but more
   likely evening, just poleward of the surface boundary.  Modified 12Z
   RAOBs, model forecast soundings and planar progs show the surface
   front and warm sector may remain diurnally capped, though an
   isolated surface-based storm with supercell characteristics, large
   hail and severe gusts cannot be ruled out over parts of central/
   northern NE.  That potential is very conditional, too uncertain and
   low in coverage to justify affixing a 15%/slight area to the broader
   marginal outlook at this time.

   The evening/overnight elevated convection will occur as large-scale
   ascent strengthens ahead of the synoptic trough -- primarily in the
   form of warm advection but also mesoscale enhancements to midlevel
   DCVA immediately preceding ejecting southern-stream perturbations. 
   Coverage may become scattered to numerous north of the boundary this
   evening over the corridor from southeastern SD to southern WI near
   the nose of a strengthening LLJ, with related intensification of
   moisture transport and isentropic lift.  Large hail will be the main
   concern, though a few strong-severe gusts are possible, especially
   with any convection that can access the warm-sector boundary layer
   before too much nocturnal stabilization occurs.  40-50 kt effective-
   shear magnitudes and 2000-2500 J/kg MLCAPE will support some hail
   risk wherever relatively discrete storms can mature before modes get
   too messy.

   ..Edwards/Peters.. 09/19/2018

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z

        
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Page last modified: September 19, 2018
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