SPC AC 011712

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1212 PM CDT Sun Aug 01 2021

   Valid 021200Z - 031200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk of severe thunderstorm appears negligible across the U.S.,
   Monday through Monday night.

   ...Discussion...
   The most prominent short wave trough impacting the U.S. during this
   period appears likely to accelerate east-northeast of New England by
   early Monday.  This is expected to occur as an even stronger
   upstream perturbation digs southeast of Hudson/James Bays, before
   turning eastward across northern Quebec by Monday night.

   While the stronger westerlies may begin to trend at least a bit more
   zonal across eastern Canada, models indicate that larger-scale
   mid/upper troughing will persist east of the Rockies through the
   Atlantic Seaboard, within a much weaker flow regime across the
   southern mid- and subtropical latitudes.  Some further amplification
   of the troughing is possible across the Gulf Coast region, in
   response to digging smaller-scale perturbations to the east of
   large-scale ridging initially encompassing much of western North
   America.

   Downstream of quasi-stationary troughing off the Pacific coast,
   strongest mid-level level ridging appears likely to persist across
   the lower Colorado Valley into the Great Basin.  To the north and
   east of this axis, at least a couple of weak perturbations will
   contribute to suppression of the ridging, while very slowly
   continuing to progress through the broader anticyclonic regime.

   ...Rockies and areas to the west...
   A plume of monsoonal moisture along and east of these perturbations
   appears likely to provide the primary focus for diurnal thunderstorm
   development across the Intermountain West and Rockies.  However,
   there may be sufficient residual low-level moisture to the east of
   the Oregon Cascades to support a few thunderstorms, and perhaps a
   developing cluster of storms late Monday, aided by large-scale
   forcing for ascent downstream of the offshore troughing.  While (as
   is typically the case) there is potential for thermodynamic profiles
   across each of these areas to become at least locally supportive of
   isolated downbursts and/or perhaps marginally severe hail, the risk
   for organized severe weather appears low and severe probabilities,
   in general, still less than 5 percent.

   ...East of Rockies...
   The leading edge of substantive low-level cooling and/or drying
   appears likely to reach the Gulf and south Atlantic Coast states by
   early Monday.  Some continuing southward progression toward the
   northwest Gulf coast appears probable through early Tuesday, with
   some northward return possible across the Carolinas.  

   While daytime heating may contribute to sufficient CAPE to support
   scattered vigorous thunderstorm development within the moist air
   mass during the day, this heating is forecast to be more modest than
   prior days.  With modest to weak lower/mid tropospheric lapse rates
   a limiting factor, coupled with the generally weak flow and shear,
   severe weather probabilities associated with the risk for downbursts
   and damaging surface gusts still appears less than 5 percent at the
   present time.

   ..Kerr.. 08/01/2021

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