SPC AC 011704

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1204 PM CDT Mon Nov 01 2021

   Valid 021200Z - 031200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk for severe thunderstorms appears negligible across the U.S.
   Tuesday through Tuesday night.

   ...Synopsis...
   Models suggest that mid/upper flow will remain amplified and split
   inland of the Pacific coast, across and east of the Rockies, through
   this period.  However, an initially prominent mid-level ridge in the
   northern stream is forecast to weaken while shifting across the
   Canadian Prairies vicinity, as a short wave trough to its west
   progresses northward across and north of the Canadian Rockies.  In
   the wake of the short wave trough, models indicate that mid-level
   ridging will build in the southern stream, across much of the
   Pacific Coast states and Intermountain West, while downstream
   troughing digs to the lee of the southern Rockies, to the southwest
   of significant northern stream troughing across the Great Lakes into
   Northeast.

   The primary frontal zone associated with the northern branch
   troughing appears likely to extend across the southern Mid Atlantic
   coast vicinity into the Tennessee Valley, lower Mississippi Valley
   and Texas South Plains at 12Z Tuesday, with at least some further
   southward advancement forecast through daybreak Wednesday.  This
   front has been preceded by a weaker cold intrusion now
   stalling/weakening south of the Florida Peninsula into the
   southeastern Gulf of Mexico.  However, modest boundary-layer
   moisture return is ongoing off the western Gulf of Mexico into parts
   of southern Texas and lower portions of the Rio Grande Valley, with
   some of the moisture also returning northward above the front across
   the Edwards Plateau/South Plains into portions of the central Great
   Plains.

   ...Texas Davis Mountains adjacent Rio Grande Valley vicinity...
   Moistening near-surface upslope flow may contribute to weak to
   modest boundary-layer destabilization by late Tuesday afternoon.  It
   appears that this will occur beneath 30+ kt westerly flow around 500
   mb, which may contribute to moderately strong shear, aided by
   pronounced veering of low to mid-level wind fields with height. 
   Various model output, including the latest HREF, is suggestive that
   the environment may become conducive to isolated supercell
   development for a period during the afternoon and evening.  However,
   aside from orographic forcing, large-scale forcing for ascent to
   support thunderstorm initiation remains a bit unclear.  Due to
   uncertainties concerning mid-level inhibition and limited CAPE,
   severe probabilities are being maintained at less than 5 percent,
   but it is possible that this could change in later outlooks for this
   period.

   ...Red River Valley vicinity...
   Lift above the frontal zone, supported by low-level warm advection
   ahead of one progressive short wave impulse (within the larger-scale
   mid-level troughing digging to the lee of the southern Rockies), may
   contribute to scattered weak thunderstorm development, mainly
   Tuesday evening into Tuesday night.

   ...Colorado Rockies vicinity...
   Forecast soundings suggest that profiles may become marginally
   conducive to scattered convection capable of producing lightning by
   Tuesday afternoon, aided by orographic lift and forcing for ascent
   associated with at least one short wave impulse traversing the
   region.

   ...Lower Great Lakes vicinity...
   Forecast soundings suggest that cooling in the 700-500 mb layer may
   contribute to deepening convective development near and to the lee
   of the southeastern shores of Lake Ontario by late Tuesday
   afternoon.  Some of this activity may extend into and through
   favorably cold mid-levels to allow for occasional lightning.

   ..Kerr.. 11/01/2021

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