SPC AC 292011

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0311 PM CDT Wed Jul 29 2020

   Valid 292000Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN
   COLORADO INTO WESTERN/CENTRAL KANSAS AND PORTIONS OF THE
   OKLAHOMA/TEXAS PANHANDLES...

   ...SUMMARY...
   Scattered storms -- capable of producing locally severe wind gusts
   and hail -- will be possible during the late afternoon and evening
   across much of western Kansas.

   ...20Z Outlook Update...
   Biggest change to the ongoing outlook was to extend severe
   probabilities and categorical Marginal/Slight risk areas westward
   into eastern Colorado and southward across portions of southwest
   Kansas and the OK/TX panhandles.  Although recent CAMs are not
   particularly aggressive with convective initiation across the
   region, observations suggest that a weakly capped, strongly unstable
   airmass is in place with a few towering cumulus (with lightning)
   beginning to form across eastern Colorado and additional towering
   cumulus located over northwestern Kansas.  Expectations are that any
   convection that can organize across eastern Colorado will grow
   upscale into one or two linear segments and forward-propagate
   southeastward across the Marginal and Slight risk areas through the
   evening, with hail and damaging winds being the main threats.  An
   isolated tornado cannot be ruled out given vertically veering
   profiles with height, although low-level flow is generally weak. 
   Refer to MCD 1352 for more details on the shorter-term severe
   weather scenario.

   Elsewhere, a Marginal risk for damaging wind gusts remains unchanged
   across portions of New York State and adjacent areas of
   Ohio/Pennsylvania/southeastern Michigan.  A few thunderstorms have
   also been noted in northern Lower Michigan, and the general thunder
   line has been adjusted to include this area.

   ..Cook.. 07/29/2020

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Wed Jul 29 2020/

   ...Synopsis...
   An weakening upper low near James Bay is progged to gradually open
   into a positively tilted trough over eastern Canada, while the
   associated/surrounding belt of cyclonic flow aloft moves slowly
   eastward across the northeastern quarter of the country.  Meanwhile,
   weak short-wave troughing shifting southeastward out of the Rockies
   and across the Plains will phase weakly with the northeastern U.S.
   troughing, with the evolving cyclonic flow field  expanding to
   include most of the eastern 2/3 of the country by the end of the
   period.  In the West, upper ridging will prevail, though a
   fast-moving cyclonic disturbance over the eastern Pacific will
   approach the northern California coast late in the period.

   At the surface, an east-northeast to west-southwest cool front will
   make slow southward progress across New England and the Lower Great
   Lakes region, while the western extension of this boundary lingers
   across the Iowa/Nebraska area through the period.  High pressure
   will prevail over the southeastern U.S., and over the Rockies.

   ...Northern High Plains southeastward across Kansas and vicinity...
   Weak/complex short-wave troughing aloft will continue to contribute
   broad large-scale ascent across the central Plains vicinity today,
   with the aforementioned cold front, along with convective outflow
   across the northeastern Kansas vicinity acting as foci for continued
   convective development.  However, more substantial storms are
   expected to develop near lee troughing/low pressure extending from
   southwestern South Dakota southward to eastern Colorado/western
   Kansas.  Here, strong afternoon heating will support
   continued/moderate destabilization, and a subsequent, north-south
   zone of storm development from near the Black Hills to far eastern
   Colorado/western Kansas by mid afternoon.

   A belt of enhanced west-northwesterly mid-level flow over the
   Colorado vicinity will continue to spread eastward across the
   central High Plains into Kansas, providing favorable deep-layer bulk
   shear to support organized/rotating storms.  Initial risk for both
   large hail and locally damaging winds may transition more toward
   wind risk with time into this evening, with hints that storms may
   congeal into one or more semi-linear/southeastward-moving clusters. 
   Storms will likely continue overnight, though severe risk should
   begin to wane by late evening.

   ...Lower Great Lakes region...
   A belt of moderate westerly/cyclonic flow aloft will persist across
   the region today, as eastern Canada upper troughing moves very
   slowly eastward.  A weak surface cool front extending from the
   Adirondacks west-southwestward to southern Lower Michigan will
   provide a focus for convective development, as the airmass continues
   to modestly destabilize through the afternoon.  Given the
   aforementioned/enhanced flow aloft, a couple of
   organized/fast-moving storms/storm clusters will be possible, with
   attendant risk for a locally damaging wind gust or two.  Risk will
   diminish quickly through early evening, with the onset of diurnal
   cooling.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z