SPC AC 082000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Thu Aug 08 2019

   Valid 082000Z - 091200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTHEAST...MID-ATLANITC...AND OHIO VALLEY...

   ...SUMMARY...
   Strong to severe storms should continue to produce isolated damaging
   wind gusts across parts of the Northeast into the Mid-Atlantic and
   mid/upper Ohio Valley through this evening.

   ...20Z Update...
   A bowing line segment producing wind damage and isolated measured
   severe wind gusts will continue moving eastward across parts of
   central/eastern NY this afternoon. This convection is occurring on
   the nose of a mid-level jet, and there is potential for strong to
   severe storms to persist into parts of western New England late this
   afternoon and early evening where weak instability exists.
   Therefore, have expanded wind probabilities eastward across this
   region. Behind the line of ongoing storms, severe probabilities have
   been reduced across western NY/PA and northern OH.

   A few storms have formed across parts of southwestern/central NE
   along a weak front. Even though large-scale forcing for ascent will
   remain weak across this region owing to upper ridging remaining
   centered over the Rockies, modestly enhanced mid-level winds and a
   veering wind profile are resulting in enough shear to support
   organized updrafts. Isolated strong to severe storms may occur
   through the early evening along/south of the boundary, with both
   large hail and severe wind gusts possible. Accordingly, have
   expanded the Marginal Risk to include this area.

   Across the southern Plains into the lower MS Valley, severe
   probabilities have been confined to a narrow corridor along and
   south of a convectively reinforced surface boundary. A weak
   mid-level perturbation associated with prior convection is present
   over north-central OK this afternoon per water vapor satellite
   imagery. Some short-term guidance suggests that a couple storms may
   strengthen across parts of central/eastern OK and then spread into
   western/central AR through the early evening. Strong diurnal heating
   has occurred to the south of the front, and isolated strong/gusty
   winds and perhaps some hail could occur with any robust storms that
   can form and then move southeastward along this boundary.

   Persistent cloud cover has hampered diurnal heating across parts of
   northern UT into far southern ID. The Marginal Risk has been
   adjusted slightly in NV/UT based on radar trends and where low-level
   lapse rates have been able to steepen this afternoon. With modest
   instability and shear noted, isolated strong/gusty winds will
   continue to be the main threat.

   ..Gleason.. 08/08/2019

   .PREV DISCUSSION... /ISSUED 1121 AM CDT Thu Aug 08 2019/

   ...Synopsis...
   A large trough will continue moving across eastern Canada and the
   eastern U.S. today, with another large trough surrounding a very
   slow-moving upper low over the eastern Pacific.  In between, ridging
   will continue to prevail over the Rockies and south-central U.S.
   through tonight.

   At the surface, a weak pressure field prevails.  A subtle cool front
   will continue crossing the lower Great Lakes/Ohio Valley today,
   while remnants of a prior/weak front linger from the southeastern
   U.S. west-northwestward into the Oklahoma vicinity.  These two
   boundaries, and weak disturbances aloft crossing the Great Basin
   area ahead of the Pacific low/trough, will support showers and
   thunderstorm activity, along with limited/local severe risk.

   ...NY/PA/OH/WV vicinity...
   Showers and thunderstorms are ongoing across western New York and
   adjacent northwest Pennsylvania, near a very weak cool front moving
   across the region.  As heating continues into the afternoon,
   resulting in additional/modest destabilization, an increase in
   convective coverage is expected, along with some uptick in intensity
   -- aided by moderate westerly/west-northwesterly flow through a deep
   layer.  With this flow promoting rather quick eastward storm motion,
   stronger convective elements will be capable of producing
   gusty/damaging winds, that may reach severe levels locally.  Risk
   should continue through the afternoon, diminishing with the onset of
   diurnal cooling early this evening.  For additional short-term
   information, please refer to SWOMCD #1674.

   ...Southern KS/OK east-southeast to northern MS...
   A large area of weak convection is ongoing from the southern Plains,
   east across the Ozarks to the northern Mississippi Vicinity.  An
   outflow boundary is observed from Oklahoma southeast to northern
   Mississippi, on the southern fringe of a stronger west-northwest to
   east-southeast band of storms.  Some intensification of storms
   within this band, and/or new convective development near the
   aforementioned outflow, may -- given the favorably moist/gradually
   destabilizing airmass away from active convection -- intensify to
   occasionally severe levels.  Gusty/locally damaging winds may occur
   with the strongest storms, along with some risk for large hail.  

   Storms -- and possibly some severe risk -- will continue into the
   overnight hours, as a south-southwesterly low-level jet develops
   across the southern Plains, aiding continued storm
   development/sustenance.

   ...Central and southern high Plains...
   Daytime heating of a seasonally moist boundary layer across the high
   Plains region will permit afternoon destabilization, supporting
   development of scattered to isolated thunderstorms.  Mid-level flow
   is not particularly strong across the region (generally 20 to 30 kt
   from the west), a weak easterly component to the low-level flow will
   help to provide both ample shear for a few organized storms, as well
   as some tendency for storms to progress southeastward off the higher
   terrain.  The strongest storms/storm clusters may be capable of
   producing gusty/damaging winds, along with some hail risk.  Severe
   risk should gradually decrease through the evening, as convection
   weakens.

   ...Parts of the Great Basin and vicinity...
   A relatively moist low-level airmass resides across the Great Basin
   vicinity, with dewpoints in the low 50s.  Showers and isolated
   thunderstorms are ongoing across parts of the region -- partly in
   response to several disturbances aloft moving across the area,
   embedded within cyclonic upper flow surrounding the eastern Pacific
   upper low.  Clearing is noted in morning visible imagery across
   parts of Nevada away from ongoing convection, which will aid in
   afternoon destabilization, and an associated increase in convective
   coverage.  Given moderate deep-layer southwesterly flow supporting
   semi-organized cells/clusters, potential for locally damaging winds
   will exist with a few of the strongest storms, before convection
   weakens this evening.

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