SPC AC 171954

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0254 PM CDT Sun May 17 2020

   Valid 172000Z - 181200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MIDWEST...

   ...SUMMARY...
   Isolated to scattered wind damage and perhaps a few tornadoes will
   remain possible through about 9 PM CDT for portions of the Midwest,
   centered on eastern Illinois and western/central Indiana. Isolated
   severe hail and/or wind are also possible this afternoon into early
   evening across parts of the Northwest/northern Rockies, southern
   Rockies, and Mid to Deep South.

   ...20Z Update...
   Earlier thoughts remain unchanged regarding the potential for strong
   to severe thunderstorms across portions of the Midwest this
   afternoon and evening. A 15% severe wind area has been added within
   the existing Slight Risk, with the expectation that storms form into
   one or more linear segments posing mainly a damaging wind risk. For
   more information on the near-term severe threat for this region, see
   recently issued Mesoscale Discussion 620.

   Elsewhere, no changes have been made to the Marginal Risk areas for
   parts of the Northwest/northern Rockies vicinity, southern/central
   High Plains, or Mid/Deep South.

   ..Gleason.. 05/17/2020

   .PREV DISCUSSION... /ISSUED 1142 AM CDT Sun May 17 2020/

   ...Midwest...
   Broken cloud cover and scattered precipitation remain semi-prevalent
   at late morning within the warm/moist conveyor preceding an
   eastward-moving cold front, although cloud breaks are noted across
   southern Illinois. Lingering clouds/precipitation may still tend to
   somewhat curb the overall severe potential particularly where
   deep-layer/low-level shear is strongest near the warm front.
   However, gradual destabilization coincident with cloud breaks in the
   presence of 60s F surface dewpoints will support an increase and
   intensification of surface-based storms initially across
   northeast/central/southern Illinois this afternoon. Aided by a belt
   of moderately strong low-level southerly winds, transient low-level
   mesocyclones and organizing small bowing segments will be capable of
   producing brief tornadoes/isolated wind damage. 

   ...Mississippi/western Tennessee...
   Deep-layer/low-level winds will tend to weaken today ahead of the
   upper low approaching the Lower Mississippi Valley. Moderate
   destabilization will otherwise occur within a moist air mass ahead
   of an eastward-moving cold front. While an overly
   organized/sustained severe risk is not expected, some severe storms
   are possible this afternoon through early evening.

   ...Northwest/Northern Intermountain West...
   Forcing for ascent and moderately strong wind profiles will be
   influenced by the exit region of a strong mid/upper-level jet.
   Clouds will tend to thin/scatter into the afternoon, with subsequent
   storm development/intensification expected toward peak heating, with
   this initially occurring across eastern Oregon into southeast
   Washington through late afternoon. Isolated severe hail/wind will be
   possible.

   ...South-central Colorado/northeast New Mexico...
   Mid-level heights will rise today, although weak low-level upslope
   flow/differential heating should contribute to isolated thunderstorm
   development this afternoon near the Sangre de Cristos and Raton Mesa
   vicinity. Steep lapse rates and adequate deep-layer shear should
   exist for a brief supercell or two capable of marginally severe hail
   and gusty winds.

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