SPC May 12, 2017 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 AM CDT Fri May 12 2017

Valid 121630Z - 131200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
CENTRAL AND SOUTHERN MS AND SOUTHEAST LA EAST ACROSS SOUTHWEST AL
AND WESTERN PARTS OF THE FL PANHANDLE...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS A LARGE
PORTION OF THE SOUTHEAST U.S....

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WESTERN AND CENTRAL MT...

...SUMMARY...
A few rounds of strong to severe storms are expected across portions
of the Deep South.  Damaging gusts and isolated severe hail are
possible, and a tornado or two cannot be ruled out.  Isolated severe
storms also may occur across parts of west-central Montana later
today and Georgia to parts of the Carolinas this evening, with
isolated gusty winds and hail.

...Synopsis...
As a large upper low/trough continues shifting slowly east into the
western U.S., a second/shorter-wavelength trough will continue
crossing the southeast U.S. through the period.

At the surface, a cold front associated with the western trough will
continue crossing the Intermountain West.  Meanwhile, a wavy cold
front will progress south/southeast across the Southeast/Gulf Coast
states through the period.

...Parts of MS and southeast LA east to southwest AR/western FL...
A loosely organized band of thunderstorms -- with embedded stronger
bowing clusters and occasional supercells -- continues moving east
across the lower Mississippi Valley/central Gulf Coast region.  The
storms are ongoing within a very moist airmass, where roughly 1000
J/kg mixed-layer CAPE is indicated.  With surface flow roughly
southerly beneath low- to mid-level west-southwesterlies that
increase with height through the mid levels, shear remains
sufficient for a continuation of organized severe risk as convection
tracks across the Gulf Coast region this afternoon.  For additional
short-term information, please refer to SWOMCD #704.

...Southeast AR/MS east to the SC vicinity...
Showers and isolated to scattered thunderstorms are forecast to
continue evolving ahead of the advancing upper system, near and
south of the slowly southeastward-moving cold front currently draped
roughly west-to-east across the Tennessee vicinity. 
Continued/modest destabilization this afternoon combined with
moderate flow aloft suggest mainly multicell organization, and thus
some attendant risk for locally gusty/damaging winds and marginal
hail across northern portions of the central Gulf Coast states and
into parts of the Georgia and South Carolina vicinity.  Greatest
risk will likely reside over the Mississippi area this afternoon,
nearest the colder air aloft associated with the
southeastward-moving mid-level center of circulation now moving
southeast into the Arklatex area.  For additional short-term
information, please refer to SWOMCD #705 and #706.

...Parts of western and central MT...
Continued/gradual eastward advance of the upper trough across the
Pacific Northwest will continue to provide an area of ascent,
supportive of an increase in thunderstorm development this afternoon
near and ahead of the associated surface cold front. 
Weak/high-based CAPE (mixed-layer values generally 500 J/kg or less)
may be sufficient to support a few stronger storms -- aided by
strong -- though southerly/meridional -- flow aloft.  CAM runs
remain consistent in depicting a few stronger storms/bands of storms
that will move quickly north-northeast in/near the marginal risk
area, where associated risk for locally gusty winds and possibly a
hail event or two remain evident into the evening before weakening
diurnally.

..Goss/Cohen.. 05/12/2017

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