SPC AC 171254

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0754 AM CDT Fri May 17 2019

   Valid 171300Z - 181200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF NEBRASKA AND SOUTHEAST SOUTH DAKOTA...AS WELL AS PARTS OF WESTERN
   TEXAS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN OHIO
   EAST-SOUTHEASTWARD ACROSS MUCH OF MARYLAND AND VIRGINIA...

   ...SUMMARY...
   Severe storms with very large hail, damaging winds, and a few
   tornadoes (a couple of which could be strong) are expected, mainly
   from the central High Plains northeastward to the mid Missouri
   Valley.  Several severe storms -- capable of producing very large
   hail and damaging winds, and a couple of tornadoes -- will also be
   possible across portions of the western half of Texas.  Finally,
   scattered afternoon storms -- capable of producing locally
   gusty/damaging winds will be possible from Ohio through the Middle
   Atlantic region.

   ...Synopsis...
   Large-scale upper trough over the western U.S. will shift eastward
   through Friday night as a pronounced jet streak becomes established
   over the central/southern Plains.  A strengthening surface low over
   northeast CO/western NE, along with the eastward progression of the
   upper trough, will result in strengthening low/mid-tropospheric wind
   fields and favorable deep-layer shear for organized/severe storms. 
   A warm front will extend east from the surface low, transitioning
   into a cold front across the OH Valley/mid-Atlantic region, while a
   surface dryline extends southward across western portions of KS/TX
   by late afternoon. Lower/mid-60s surface dew points will be
   transported northward beneath an expansive EML, resulting in
   moderate/strong surface-based instability by afternoon.

   ...Central Plains/mid Missouri Valley Region...
   Strong/isolated severe storms will remain possible this morning
   vicinity of southern IA where a modest/veering low-level jet has
   resulted in warm advection/lift in the 700-800 mb layer. MUCAPE of
   500-1000 J/kg supports some risk for hail.

   Large-scale ascent with the upper trough and left exit region of the
   aforementioned jet streak should contribute to severe thunderstorm
   development near/north of the warm front and surface low over
   southeast WY/northeast CO this afternoon. A supercell mode will be
   favored with a risk for very large hail, damaging winds and some
   tornado risk.  With time, additional thunderstorm development is
   anticipated across western/central NE aided by strong low-level warm
   advection near the warm front as the surface low moves northeast.
   With strong deep-layer shear and effective SRH at or above 300 m2/s2
   near the warm front, supercell storm mode will initially be favored
   with a risk for a few tornadoes, a couple of which could be strong,
   very large hail, and damaging winds. Upscale growth into an MCS
   north of the front should occur this evening, with large hail as the
   primary risk.

   Farther south along the dryline, warm mid-level temperatures at the
   base of the EML should result in very sparse storm coverage, however
   given the favorable large-scale environment, a conditional risk for
   very large hail/damaging gusts and possibly a tornado will exist
   with any storm that develops. 

   ...Southern Plains...
   Diurnal heating of a moist air mass (upper 60s surface dew points)
   and steep mid-level lapse rates will result in strong surface-based
   instability and gradually diminishing CINH by late afternoon. A
   conditional severe risk with all severe hazards possible will exist
   with any storm that can develop along the dryline over the eastern
   TX Panhandle/far western OK this afternoon. Lift associated with a
   perturbation lifting northeast across eastern NM/West Texas should
   contribute to thunderstorm development by evening across southwest
   TX, with an initial supercell mode evolving into a linear/bowing
   storm mode overnight as storms move into north/northwest TX and
   southwest OK. The more discrete storm phase will see a risk for very
   large hail, damaging winds and a couple tornadoes, with damaging
   winds potentially a greater concern late associated with the
   linear/bowing structure. Large hail and some tornado risk will
   remain during the overnight as moderate/strong instability and
   around 40 kts of southwesterly deep shear persists. 

   ...Ohio Valley/Mid-Atlantic Region...
   A convective complex over WV/southwest VA this morning should
   continue to weaken as it moves south/southeast within a weakly
   buoyant environment. Daytime heating will result in pockets of
   moderate surface-based instability near the front, and 35-40 kts of
   west-northwest mid-level flow will result in sufficient shear to
   support organized storms. Frontal convergence should lead to
   additional scattered thunderstorm development during the day, with a
   risk for damaging gusts and perhaps large hail.

   ..Bunting/Jewell.. 05/17/2019

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