Severe Storm Outlook Narrative (AC)
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243
ACUS11 KWNS 242050
SWOMCD
SPC MCD 242050
NDZ000-SDZ000-242315-

Mesoscale Discussion 1417
NWS Storm Prediction Center Norman OK
0350 PM CDT Mon Jul 24 2017

Areas affected...Portions of western ND and northwest SD

Concerning...Severe potential...Watch unlikely

Valid 242050Z - 242315Z

Probability of Watch Issuance...20 percent

SUMMARY...There will exist some risk for isolated severe
thunderstorms to develop by late afternoon and continue into the
evening hours. While present indications are that Watch issuance is
unlikely, convective and environmental trends will continue to be
monitored.

DISCUSSION...The latest visible satellite imagery indicates
high-based cumulus development along the eastern extent of a plume
of 0-3-km lapse rates approaching dry adiabatic -- extending
northeastward into southwest ND. This lapse-rate plume intersects
the western periphery of modest return moisture along a surface
trough in the western Dakotas. With the approach of a band of
mid-level ascent trailing south of a cyclone crossing the southern
Canadian Prairies, convection may deepen from this cumulus field and
then spread into the moderately unstable air east of the surface
trough -- initially within the next couple of hours. Additional
storm development will be possible in proximity to the surface
trough into the evening, as mid-level height falls accompanying the
migratory cyclone graze the region.

With middle 50s surface dewpoints east of the surface trough
supporting around 750-1750 J/kg of MLCAPE -- aided by steep
mid-level lapse rates overspreading the region -- conditional severe
hail/wind potential will exist. However, with a relative minimum in
mid-level flow between an MCV in northeastern SD and the
aforementioned mid-level cyclone, the presence of only 20-30 kt of
effective shear may initially limit convective organization.
Furthermore, antecedent capping and the lack of stronger deep ascent
may limit severe coverage. Regardless, some isolated severe risk may
persist into the evening. If it were to appear that erosion of
antecedent capping becomes more substantial than presently
anticipated this evening -- while deep shear strengthens -- Watch
issuance probabilities could increase.

..Cohen/Grams.. 07/24/2017

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

ATTN...WFO...BIS...UNR...

LAT...LON   45800389 47430310 48910209 48870074 47700084 45310259
            45000352 45260391 45800389




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