SPC AC 200500

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1200 AM CDT Mon Jul 20 2020

   Valid 201200Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   NORTHERN PLAINS...

   ...SUMMARY...
   Scattered strong to severe storms capable of large hail and damaging
   winds are expected over parts of the northern Plains, with a few
   severe storms over the central Plains. Sporadic strong wind gusts
   are also possible from the middle Mississippi and Tennessee Valleys
   into the Middle Atlantic region.

   ...Synopsis...
   A band of moderate westerlies aloft will extend from the northern
   Plains into the Northeast, with various embedded waves. The
   strongest shortwave trough will proceed east across Quebec, with
   height falls grazing parts of New England. Behind this feature,
   other fast-moving shortwave troughs will move across the Upper MS
   Valley and Great Lakes, with little fanfare due to high pressure.

   To the west of the Great Lakes surface high, southerly surface winds
   will allow for meager moisture return across the northern Plains, in
   advance of another shortwave trough moving out of MT and into the
   Dakotas late in the day and overnight. A cold front will be near the
   MT/Dakota border at 00Z, and will proceed into the central Dakotas
   and NE during the evening. This boundary, as well as sufficient
   destabilization beneath 40 kt midlevel winds, will aid storm
   development and severity.

   Elsewhere, a stalled front will extend roughly from NE/KS into
   southern IL/IN/OH and northeastward across southern New England
   during the day, with ample moisture to support daytime
   thunderstorms. However, winds aloft will be weak across most of
   these areas.

   ...Northern Plains...
   Steep lapse rates will develop via heating near and ahead of the
   wind shift which will move into the western Dakota after 18Z. Early
   day, elevated storms will be possible across parts of southern SD
   and NE, and this may affect moisture return. Storms are likely to
   initiate along the cold front across far eastern MT and western ND,
   and will develop southward into western and central SD by early
   evening. An axis of 2000 J/kg MUCAPE is forecast generally west of a
   BIS to PIR line, with over 40 kt effective bulk shear. This will
   support cells, including a few supercells, capable of large hail
   initially before mergers enhance outflow and gusty wind potential.
   While elevated storms may continue overnight into the eastern
   Dakotas, the environment does not appear to support severe hail.

   ...Central Plains/Mid MO Valley...
   Diurnal storms are again likely across eastern CO and NM, but
   instability and shear both appear marginal for any severe threat for
   much of the area. However, one area of potential will be from
   northeast CO into southern NE and northwest KS, where backed surface
   winds near the stalled front will maintain 60s F dewpoints and
   stronger instability and shear. Little large-scale lift will be
   present with only 25 kt northwesterly midlevel winds, but at least
   isolated severe storms are expected from eastern CO into southern
   NE. Large hail and strong wind gusts will conditionally be possible,
   and a Slight Risk cannot be ruled out for parts of the area. This
   will depend on how the early day storms affect the air mass and
   boundary positions.

   ...Mid MS Valley to the Mid Atlantic and New England...
   An expansive area of moderate instability will develop with heating
   south of the stationary front, but shear will remain weak. Still, a
   few areas may favor clustering and thus gusty winds. Lapse rates
   aloft will be poor in most areas, further suggesting only a minor
   severe wind threat.

   A cell or two over southern New England along the cold front may
   briefly become strong by midday, with marginal hail or wind, but
   winds aloft will continue to veer during the day as the upper trough
   over Quebec lift northeast.

   ..Jewell/Cook.. 07/20/2020

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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