Storm Prediction Center Discussions

MD 1153 Image

Mesoscale Discussion 1153
NWS Storm Prediction Center Norman OK
0312 PM CDT Mon Jun 26 2017

Areas affected...Portions of central/eastern WA...OR...and
western/northern ID

Concerning...Severe potential...Watch unlikely 

Valid 262012Z - 262245Z

Probability of Watch Issuance...5 percent

SUMMARY...An isolated threat for strong to locally damaging winds
will develop this afternoon and evening. Some hail may also occur.
Watch issuance is not expected due to the overall isolated/marginal
severe risk.

DISCUSSION...Recent visible satellite and radar imagery have shown
an increase in convective coverage along the crest of the Cascades
into eastern OR. This activity is likely occurring in association
with large-scale lift attendant to a shortwave trough moving over
the northern CA/southwestern OR Coast as of 20Z. A seasonably moist
low-level airmass is in place across the northern Great Basin into
the northern Rockies per 12Z area soundings and 20Z surface
observations. Plentiful diurnal heating has allowed surface
temperatures to warm mostly into upper 80s to mid 90s across lower
terrain along and east of the Cascades, and combined with modestly
steep mid-level lapse rates, weak instability (MLCAPE) of 250-1000
J/kg has developed.

Modestly enhanced mid-level winds of 30-40 kt associated with the
mid-level shortwave trough are encouraging similar values of
effective bulk shear, which will likely be sufficient to support at
least some thunderstorm organization through the evening hours as
storms spread northeastward into eastern WA and western/northern ID.
Steep low-level lapse rates will allow convectively enhanced
downdraft winds to reach the surface, and isolated strong to locally
damaging winds will likely be the primary severe threat given DCAPE
in excess of 1000 J/kg across much of this region. Some marginally
severe hail may also occur with the strongest updraft cores. Even
with locally scattered convective coverage expected, the overall
severe threat will likely remain too isolated/marginal given the
thermodynamic/kinematic environment present, and watch issuance is
not expected at this time.

..Gleason/Guyer.. 06/26/2017

...Please see for graphic product...


LAT...LON   44511456 42821493 42521509 42281575 42131657 42091837
            42461881 42851946 43032027 42732116 42052257 42412302
            43082270 44312151 46302147 46742078 47672021 47741733
            47161594 44511456 

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Updated 26 June 2017 | 3:13 pm