Mesoscale Discussion 0621
   NWS Storm Prediction Center Norman OK
   0401 PM CDT Sun May 17 2020

   Areas affected...Far northeast Oregon...far southeast
   Washington...northern Idaho

   Concerning...Severe potential...Watch unlikely 

   Valid 172101Z - 172300Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Strong storm coverage is expected to increase through the
   rest of the afternoon into early evening. A few of the strongest
   storms may produce large hail and damaging gusts. Given the expected
   isolated nature of the severe threat, a WW issuance is not currently
   expected.

   DISCUSSION...Strong southwesterly mid-level flow will overspread
   much of the Pacific Northwest east of the Cascades as a mid-level
   trough gradually advances eastward. Surface lee troughing and modest
   diurnal heating from the Columbia Basin southward to the Harney
   Basin have promoted adequate low-level lift to support recent
   convective development, with a stronger cell noted in the
   Garfield/Whitman County WA vicinity. Further diurnal heating and
   eastward advancement of the upper trough is expected to foster
   additional storm development for the next several hours. 

   Modest low-level moisture (up to upper 40s surface dewpoints) and
   7.5-8.5 C km low-level lapse rates suggest adequate buoyancy is in
   place, with 150-400 J/kg MLCAPE supporting occasional robust updraft
   development (per latest Mesonanalysis). Meanwhile, strong mid-level
   flow will contribute to 45-55 knot effective bulk shear, also
   supporting storm organization and longevity. The most intense,
   organized storms may obtain transient supercell or small-scale
   bowing structures capable of producing large hail given modest (7
   C/km) mid-level lapse rates, and damaging gusts given steep
   low-level lapse rates and a well-mixed boundary layer.

   Nonetheless, the severe threat is expected to be relatively sparse,
   precluding a WW issuance at this time.

   ..Squitieri.. 05/17/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...MSO...BOI...OTX...PDT...

   LAT...LON   43881772 44881818 46321809 47951767 48401695 48381631
               48111610 47011537 46531506 46011493 44991527 44351567
               43881652 43881772