Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 202246
SWOMCD
SPC MCD 202245
NDZ000-SDZ000-MTZ000-210015-

Mesoscale Discussion 1370
NWS Storm Prediction Center Norman OK
0545 PM CDT Thu Jul 20 2017

Areas affected...Eastern MT...Western Dakotas

Concerning...Severe Thunderstorm Watch 425...

Valid 202245Z - 210015Z

The severe weather threat for Severe Thunderstorm Watch 425
continues.

SUMMARY...Severe threat appears to be focusing over the western
Dakotas. Severe thunderstorm watch may need to be expanded along the
eastern border toward BIS.

DISCUSSION...Intense boundary-layer heating across eastern MT has
aided thunderstorm development/intensification across western ND.
This activity is evolving just downstream of a pronounced surface
low primarily south of a well-defined wind shift where low-level
lapse rates are steep and dew points are holding in the 50s. Latest
MRMS data suggests large hail is common with this activity and
storms will likely linger well into the evening hours as LLJ is
expected to increase across the western Dakotas over the next
several hours, partly in response to upstream short-wave trough that
is expected to flatten the northern Plains ridge during the
overnight hours.

..Darrow.. 07/20/2017

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

ATTN...WFO...BIS...UNR...BYZ...GGW...

LAT...LON   45000546 48960489 48970135 45020219 45000546




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