SPC AC 071957

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0257 PM CDT Tue Jul 07 2020

   Valid 072000Z - 081200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON AND EVENING ACROSS PARTS OF EASTERN MONTANA INTO WESTERN
   AND CENTRAL NORTH DAKOTA...

   ...SUMMARY...
   One or two clusters of severe thunderstorms may evolve across parts
   of the northern plains through this evening, posing a risk for
   strong wind gusts, in addition to large hail and perhaps a couple of
   tornadoes.

   ...20Z Outlook Update...
   Adjustments have been made to the categorical and probabilistic
   lines in an attempt to better account for the progression of the
   synoptic and sub-synoptic features, and trends concerning ongoing
   destabilization which will impact convective potential through the
   remainder of the period.

   Initiation of thunderstorm activity is already well underway across
   the northern Rockies.  This is occurring ahead of a vigorous short
   wave impulse now pivoting across western Montana, and forecast to
   continue east-northeastward across the North Dakota international
   border area by late tonight.  

   Upscale convective growth and organization sufficient to support
   potential for more widespread damaging wind gusts is probably still
   at least several hours away (toward or after 08/00Z), and severe
   probabilities across central Montana have been adjusted to account
   for this.

   Given surface ridging and associated stable air now present across
   much of northeastern North Dakota and northern Minnesota, the
   potential for severe convection to outrun supporting mid-level
   forcing overnight appears fairly low.  And there now appears a
   consistent signal in most of the latest model output that the
   leading edge of stronger mid-level forcing and possible low-level
   convective outflow will only reach portions of northwestern
   Minnesota by 12Z Wednesday.

   ..Kerr.. 07/07/2020

   .PREV DISCUSSION... /ISSUED 1112 AM CDT Tue Jul 07 2020/

   ...Northern Plains...
   Water vapor imagery shows a strong upper trough moving across parts
   of ID/NV toward the northern Plains.  This system will begin
   affecting the mountains over western MT/WY by early afternoon with
   showers and thunderstorm development likely.  Storms will develop
   eastward into the adjacent high Plains of central MT by
   mid-afternoon, where backed low-level winds will maintain 50s
   dewpoints and MLCAPE over 2000 J/kg.  Strong deep-layer shear and
   veering winds with height will promote supercell storms capable of
   very large hail, damaging winds, and isolated tornadoes.  As the
   storms spread eastward this evening, activity should become more
   widespread.  Multiple convective clusters are expected, with an
   increasing risk of corridors of enhanced wind damage.  Activity is
   expected to persist much of the night, tracking across ND and into
   northern MN by Wednesday morning.

   ...Western SD into NE/CO/NM...
   Scattered afternoon thunderstorms are expected to form along the
   instability axis from the Black Hills region southward into parts
   the NE panhandle, eastern CO and northeast NM.  Shear profiles on
   the northern end of this corridor will be sufficient for a few
   severe storms capable of hail and damaging winds.  However, weak
   flow aloft, warm mid-level temperatures, and lack of upper forcing
   suggest that the severe threat over the remainder of the area will
   be very isolated and chaotic.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z