SPC AC 021730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Sun Aug 02 2020

   Valid 031200Z - 041200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   EASTERN NC/SC...

   ...SUMMARY...
   A few tornadoes in association with Isaias appear possible across
   the eastern Carolinas, mainly Monday evening into Monday night.
   Other isolated strong to severe thunderstorms may occur Monday
   afternoon and evening from portions of the Appalachians to the
   Mid-Atlantic, and also across parts of Montana to the
   central/southern High Plains.

   ...Coastal Carolinas into the Southern/Central Appalachians and
   Mid-Atlantic...
   Tropical Storm Isaias is forecast to move north-northeastward by the
   National Hurricane on Monday as it begins to interact with
   large-scale upper trough centered over much of the central/eastern
   CONUS. The enhanced low-level flow associated with Isaias should
   overspread the coastal Carolinas beginning Monday evening, and
   continuing through the end of the period. A substantial increase in
   the 850 mb flow is expected across this area, with some guidance
   suggesting the potential for 50-60+ kt south-southeasterly winds in
   the low levels. A corresponding increase in low-level shear and
   effective SRH is also anticipated. Mid to potentially upper 70s
   surface dewpoints are forecast to spread northward in tandem with
   Isaias, and instability may modestly increase overnight as low-level
   moisture increases and the boundary layer remains well mixed. Any
   storms that can form in the outer rain bands of Isaias will be
   located in this very favorable kinematic environment. A few
   tornadoes with low-topped cells appear possible Monday
   evening/night, and the strength of the low-level wind field suggests
   an increase in tornado probabilities is warranted.

   Other strong to severe thunderstorms may occur from parts of the
   southern/central Appalachians northward into the Mid-Atlantic. Here,
   modestly enhanced southwesterly mid-level flow associated with the
   upper trough may promote modest storm organization through Monday
   afternoon/early evening. Strong to locally damaging winds should be
   the main threat with this activity given steepening low-level lapse
   rates through the day owing to diurnal heating. Marginal deep-layer
   shear should tend to limit a more organized severe risk.

   ...Northern Rockies to the Central/Southern High Plains...
   A shortwave trough is forecast to move across the northern Rockies
   and adjacent High Plains Monday, suppressing an upper ridge over the
   High Plains. Low-level moisture should tend to remain fairly limited
   ahead of the shortwave trough across MT, although deep-layer shear
   should strengthen through the day. Opted to expand the Marginal Risk
   for large hail and severe wind gusts eastward into more of
   central/eastern MT to account for latest trends in guidance. If
   confidence increases in greater low-level moisture and related
   instability across this region Monday afternoon, then an upgrade to
   Slight Risk may be needed.

   Farther south across the central/southern High Plains, isolated to
   widely scattered storms should form once again in a persistent
   northwesterly mid-level flow regime. Weak to locally moderate
   instability coupled with sufficient deep-layer shear should support
   widely spaced storms capable of producing isolated large hail and
   severe wind gusts through Monday evening.

   ..Gleason.. 08/02/2020

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