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Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 2000Z Outlook
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

ACUS01 KWNS 211954
SPC AC 211952

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0252 PM CDT Sat Jul 21 2018

Valid 212000Z - 221200Z


Strong to severe thunderstorms are expected across parts of the
southeastern U.S. and the northern High Plains.

...20Z Update...

Overall scenario outlined in the previous outlook discussion
(appended below) remains valid. Scattered thunderstorm development
is still anticipated across the higher terrain of the southern
Appalachians with storm motion into the moist and unstable airmass
extending across the Piedmont and into central GA. Vertical shear is
supportive of storm organization and resulting threat for damaging
wind gusts and hail. More short-term forecast details about this
area can be found in MCD 1122. 

Scattered thunderstorms are also still anticipated across the
northern and central High Plains. Southeasterly low-level flow
beneath moderate westerly flow aloft is resulting 40 to 50 kt of 0-6
km shear. This vertical shear, in tandem with moderate to strong
instability, supports the potential for isolated severe
thunderstorms. Primary severe threats are large hail and damaging
wind gusts. Recent guidance and visible satellite trends suggest
slightly higher severe storms coverage is likely farther south into
more of the NE Panhandle. Consequently, the Slight Risk was extended
southward into more of this region. Eastern extent of the threat is
mitigated by relatively cooler temperatures across the central
Dakotas. Additional information about this area is available in MCDs
1120 and 1121.

..Mosier.. 07/21/2018

.PREV DISCUSSION... /ISSUED 1123 AM CDT Sat Jul 21 2018/

...South GA into North FL...
A long-lived band of thunderstorms is tracking southward across
southern GA.  The air mass ahead of the storms is very
moist/unstable with dewpoints in the upper 70s and temperatures
warming into the 90s.  Increasing northwesterly mid level winds and
remnant mesoscale organization of convective band suggest the risk
of damaging winds across the region through the afternoon.

...North GA/western Carolinas...
In the wake of morning convection, skies are mostly clear across
northern GA into western NC and upstate SC.  Rapid heating and
dewpoints remaining in the lower 70s will yield strong afternoon
CAPE values.  A shortwave trough evident in water vapor imagery over
western KY/TN will approach the region and lead to the development
of scattered thunderstorms.  Strong effective shear values and
relatively steep mid-level lapse rates suggest the potential for
rotating storms capable of large hail and damaging wind gusts.  This
activity may persist through the evening and track across eastern GA
and much of SC.

...Northern High Plains...
Scattered thunderstorms will develop this afternoon from the plains
of eastern MT southward into eastern WY/CO.  Forcing mechanisms are
hard to identify this morning, and the region is under the upper
ridge axis.  Nevertheless, a consensus of 12z model solutions
indicate a few of these storms will become intense with large hail
and damaging winds possible.  Storms should remain strong as they
spread into the western Dakotas and western NE this evening.