Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
894
ACUS01 KWNS 272002
SWODY1
SPC AC 272000

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Thu Jul 27 2017

Valid 272000Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN WY
INTO THE WESTERN NE PANHANDLE...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTHERN AND CENTRAL HIGH PLAINS...

...SUMMARY...
Scattered large hail and isolated severe wind gusts are expected
late afternoon into this evening in the vicinity of eastern Wyoming
to western portions of the Nebraska Panhandle.

...Northern/central High Plains...
Storms will continue to develop this afternoon into the early
evening in vicinity of a lee trough and westward moving convective
outflow boundaries from southeast MT into eastern WY.  Short-term
details are available in SPC mesoscale discussion 1424, with some
potential existing for storms to develop/spread into western NE.  A
corridor of moderate instability extending from eastern WY into the
western portion of the NE Panhandle and an increase in effective
bulk shear supports an eastward expansion of the southern portion of
the Slight risk area.

...Southern Appalachians to Mid-Atlantic States...
An isolated strong wind gust may occur across this region through
the afternoon, though the overall severe-weather threat appears to
be too low to maintain a Marginal severe risk.  Objective analyses
and area VADs indicated the strongest effective bulk shear extended
from eastern KY and WV into VA, likely aiding in the development of
line segments so far .  However, extensive cloud cover spreading
east across these states has limited diabatic heating and overall
destabilization.  Meanwhile, farther south, instability is greater
from eastern TN through western GA and eastern AL, though deep-layer
shear is much weaker.  These factors support the reduction in severe
probabilities with this outlook issuance.

..Peters.. 07/27/2017

.PREV DISCUSSION... /ISSUED 1125 AM CDT Thu Jul 27 2017/

...Northern/central High Plains...
Isolated to scattered storms will develop off the Front Range and
Big Horns late this afternoon with a few supercells likely evolving
in a north/south corridor across the eastern WY vicinity. In this
corridor, surface dew points in the upper 50s to lower 60s are
prevalent with robust insolation underway. This should result in
MLCAPE reaching 1000-1500 J/kg. With approach of a decaying
mid-level impulse from ID maintaining a belt of enhanced high-level
westerlies, effective shear of 30-40 kt will support updraft
rotation. While mid/upper-level lapse rates will not be particularly
steep, they should still be sufficient for a risk of large hail and
locally severe winds.

...Southern Appalachians to Mid-Atlantic States...
Non-severe multicell clusters are ongoing across parts of the
Cumberland to Allegheny Plateau of KY/WV. As pockets of moderate
diabatic heating occur from NC to Delmarva, this activity along with
additional widely scattered storm development may become weakly
organized amid 20-25 kt effective shear. The marginal mid-level
lapse rate environment suggests buoyancy should remain modest.
Primary hazard will be isolated strong wind gusts producing tree
damage.

...OK to OH Valley...
Extensive cloud cover and areas of stratiform rain are ongoing
along/ahead of a frontal boundary extending from northern OK to the
Midwest. This will limit destabilization near the front with
diabatic heating more pronounced farther south within a weak
mid-level lapse rate and shear environment. Sporadic downbursts are
possible where widely scattered pulse storms form late afternoon
into evening, but the risk for organized severe storms appears
minimal.

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.