Severe Storm Outlook Narrative (AC)
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ACUS03 KWNS 250718
SWODY3
SPC AC 250717

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0217 AM CDT Wed Apr 25 2018

Valid 271200Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION
OF EASTERN OREGON...NORTHWEST NEVADA INTO SOUTHWEST IDAHO...

...SUMMARY...
Isolated strong thunderstorms capable of downburst winds and some
hail may occur from parts of eastern Oregon into southwestern Idaho
later Friday afternoon and evening.

...Synopsis...

Upper pattern is forecast to be characterized by a synoptic upper
trough over the eastern U.S., a ridge over the Intermountain West
and a closed upper low moving into the Pacific Northwest region. A
significant shortwave trough located within the base of the eastern
U.S. synoptic trough will advance through the Gulf Coast states. At
the surface a cold front will move off the Atlantic Seaboard early
in the period with trailing portion continuing through northern and
central FL. Farther west a cold front will advance through the
Pacific Northwest and Great Basin regions.

...Eastern Oregon through southwest Idaho and northern Nevada...

Model consensus is that another in series of vorticity maxima will
rotate through the closed upper low circulation and into northwest
NV and eastern OR near peak heating. Steep lapse rates and deeply
mixed boundary layers will support marginal instability with MLCAPE
from 300-500 J/kg. Development of more numerous high-based
convection should occur in response to the ascent being favorably
timed with maximum afternoon and evening destabilization. Some of
this activity could produce downburst winds and hail through mid
evening.

...FL...

A gradual moistening will occur across south FL as the Gulf boundary
layer modifies and surface winds return to southwesterly,
contributing to at least modest instability with MLCAPE from
500-1000 J/kg. Numerous showers and some thunderstorms are expected
across south into central FL during the afternoon and evening. An
increase in mid-upper level winds will occur over central and
southern FL as an upper jet accompanying a progressive shortwave
trough overtakes the frontal zone during the evening into the
overnight. However, low-level response is expected to remain weak
with modest westerly flow through 700 mb. Nevertheless, a few storms
could aquire some organization or weak mid-level updraft rotation,
and southern FL will continue to be monitored for low severe
probabilities in later updates.

..Dial.. 04/25/2018

$$



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