SPC MD 770


MD 0770 Image

Mesoscale Discussion 0770
NWS Storm Prediction Center Norman OK
0600 PM CDT Sat May 30 2020

Areas affected...western Montana

Concerning...Severe potential...Watch unlikely 

Valid 302300Z - 310030Z

Probability of Watch Issuance...5 percent

SUMMARY...A few strong to severe thunderstorms are possible across
western Montana into this evening. Marginally severe wind/hail are
the main threats, but a watch issuance is unlikely.

DISCUSSION...A vigorous upper low is moving northward over northern
California helping to displace an upper-level ridge over the
Intermountain West and lowering heights across the region. Broad
large-scale ascent is overspreading much of the Pacific Northwest
and into northern Rockies. However, with the strongest forcing for
ascent west of the northern Rockies, terrain-induced circulations
and temperatures rising to the upper 80s to low 90s F with dewpoints
in the 50s F have helped initiate convection over western Montana
and vicinity. Steep mid-level lapse rates (8+ C/km) per mesoanalysis
and forecast soundings and effective bulk shear of 30-40 knots
indicate the potential for stronger, organized updrafts capable of
large hail. Additionally, relatively high LCLs and steep low-level
lapse rates indicate the potential for downdrafts with DCAPE in
excess of 1200 J/kg per mesoanalysis and forecast soundings. 

Storms may persist beyond sunset. However, the storm environment
becomes less conducive over northern/central Montana, which is north
of the lifting surface front and within higher heights/warmer
mid-level temperatures. Overall, the severe threat is likely to
remain marginal and isolated.

..Nauslar/Thompson.. 05/30/2020

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


LAT...LON   47721154 47421108 46611046 46031053 45821085 45941148
            46051217 46271422 46791444 47391428 47851381 48081335
            48121275 47991210 47721154 

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