SPC AC 271250

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0750 AM CDT Mon Jul 27 2020

   Valid 271300Z - 281200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE OHIO
   VALLEY AND NORTHERN NEW ENGLAND...

   ...SUMMARY...
   Scattered to isolated strong thunderstorms are expected across
   northern New England and portions of the Ohio Valley Monday
   afternoon and evening, accompanied by a local risk for
   gusty/potentially damaging winds.

   ...Overview...

   A mid-upper low and attendant trough will move east across southern
   Canada today, with glancing effects impacting areas from the lower
   Great Lakes into northern New England. Farther west, a weak
   mid-upper trough located across southern California will begin to
   lift north-northeast today. 

   At the surface, a cold front associated with the Canadian low
   stretches from southwest Kansas northeast into southeast Iowa
   northeast into northern Michigan. This cold front will slowly move
   south and east today. The precise location of this diffuse front may
   be somewhat irrelevant for convective initiation as previous days'
   convection has congealed into an effective cold front located ahead
   of the synoptic boundary. 

   ...Northern New England...

   Thunderstorms should develop across portions of Quebec later this
   morning into the afternoon and move into/across the area. Deep-layer
   shear on the order of 20-30 knots and most-unstable CAPE on the
   order of 500-1000 J/kg will support multicell clusters capable of
   locally gusty winds and isolated tree damage.

   ...Ohio Valley...

   Showers and thunderstorms will develop in the vicinity of the
   aforementioned cold front during the late morning and afternoon.
   Poor mid-level lapse rates should limit the overall vigor of
   thunderstorm updrafts, despite CAPE values approaching 2000-2500
   J/kg. Although mid-level flow should be on the order of 30-40 knots,
   westerly low-level low will act to reduce effective shear to around
   20 knots. limiting the overall thunderstorm organization and severe
   potential. However, multicell thunderstorm clusters capable of
   producing locally gusty winds and isolated tree damage will be
   possible. Thunderstorm intensity will lessen with the loss of
   diurnal heating. 

   ...Oklahoma and Kansas...

   A mesoscale convective vortex (MCV) developed this morning across
   southwest Kansas out of the overnight convection. This MCV should
   continue to continue moving east-southeast today. By this afternoon,
   the airmass ahead of the MCV will be largely uncapped and strongly
   unstable, resulting in numerous showers and thunderstorms. Despite
   poor mid-level lapse rates, high precipitable water values and
   modest sub-cloud-layer lapse rates in rain-free areas may support a
   couple of isolated damaging wind gusts. 

   ...Intermountain West...

   Large-scale ascent associated with aforementioned California trough
   will support an increase in thunderstorm coverage as compared to
   previous days. Precipitable water values around 0.75 inches and
   strong diurnal heating should yield maximum mixed-layer CAPE values
   between 500-1000 J/kg during the afternoon. Inverted-V soundings,
   characterized by steep low-level lapse rates (approaching 9 C/km)
   and a dry sub-cloud layer, will support a few dry microbursts,
   especially early in a thunderstorm's life cycle. Weak mid-level flow
   and slow storm motions should limit momentum transfer and a more
   widespread convective wind threat.

   ..Marsh/Edwards.. 07/27/2020

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