Valid 072000Z – 081200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MIDWEST…CAROLINAS TO NORTHEAST…AND CENTRAL PLAINS INTO
THE MID-SOUTH…
…SUMMARY…
Strong to locally severe thunderstorms, capable of producing both
wind damage and hail, will be possible across parts of the Upper
Mississippi Valley and central Plains through tonight. Additional
storms, and associated risk for isolated damaging wind gusts, will
continue from parts of the Carolinas northward into the Northeast
through this evening.
…20Z Update…
The Marginal Risk has been nudged southward to include more of
north-central OK. A outflow boundary from earlier convection across
MO/KS has stalled across this area, with the 18Z LMN sounding
showing around 30 kt of northwesterly flow at 500 mb and a
well-mixed boundary layer. Any storm that can form in this
environment would be capable of producing isolated severe wind gusts
and large hail given the strong instability present along with
sufficient shear.
Based on radar and observational trends, only minor changes have
been made to the Marginal and Slight Risk areas extending from the
Carolinas to the Northeast. Damaging wind gusts should continue to
be the main threat with ongoing storms through this evening,
although isolated marginally severe hail may also occur. See
Mesoscale Discussions 1667 and 1668 for more information on the
near-term severe threat across these regions.
The Marginal and Slight Risk area across southern/central MO have
been trimmed as a loosely organized clusters of storms continues
southward into AR and western TN this afternoon. Isolated damaging
winds will continue to be the main threat with these storms.
..Gleason.. 08/07/2019
.PREV DISCUSSION… /ISSUED 1133 AM CDT Wed Aug 07 2019/
…Synopsis…
Large-scale upper ridging is forecast to remain across much of the
western and south-central U.S. this period, upstream of a low/trough
residing over the eastern Pacific/off the West Coast. Meanwhile, a
second upper trough will shift gradually across the
Appalachians/eastern U.S. today and tonight.
At the surface, a trough to the lee of the Appalachians will focus
diurnal showers and storms today, while farther west, a cold front
will shift southeastward across the Upper Great Lakes, and south
across the central Plains/mid Missouri Valley region through
tonight.
…Western New England/eastern New York to the Carolinas…
Showers and thunderstorms are forecast to continue developing into
this afternoon, largely east of the Appalachian crest, and
particularly near/east of a surface trough analyzed from eastern New
York south to central North Carolina.
Moderate, deep-layer westerly/southwesterly flow aloft resides
across the area, which — given the very moist/destabilizing airmass
near and east of the aforementioned surface trough — will
contribute to weakly organized storms, and some potential for
upscale growth into bands of convection. Locally gusty/potentially
damaging winds will be the primary risk with the strongest storms
through the afternoon, though hail will also be possible. Risk
should diminish into the evening hours with the onset of diurnal
cooling.
…Upper Great Lakes/upper Mississippi Valley area…
Afternoon showers and thunderstorms are expected to develop
near/ahead of a southeastward-moving cold front currently residing
over western Lake Michigan and adjacent northwestern
Wisconsin/southeast Minnesota. Moderately strong/unidirectional
west-northwesterly flow above the boundary layer suggests that as
the airmass destabilizes this afternoon, rather fast-moving,
organized storms/storm clusters should evolve, particularly across
the SLGT risk area. Gusty/locally damaging winds will be possible
with the strongest storms, along with some risk for hail. Risk will
gradually diminish after dark.
…Central Plains/Ozarks southeast to western Tennessee/northern
Mississippi…
A somewhat disorganized cluster of thunderstorms continues moving
southeastward across eastern Kansas and southern Missouri at this
time, which has been slightly elevated above the nocturnally stable
boundary layer. However, some intensification of storms is
indicated over south-central Missouri, as filtered sunshine through
cirrus anvil blowoff permits gradual heating of the moist boundary
layer. Clearer skies, and even higher surface dewpoints downstream
into Arkansas and the mid Mississippi Valley area has already
resulted in strong destabilization, with 2500 to 3500 J/kg
mixed-layer CAPE indicated.
As the gradually strengthening storms continue shifting
southeastward into the very unstable/favorable thermodynamic
environment, continued organization of storms is expected — aided
by moderate northwesterly flow aloft. As such, risk for damaging
winds is apparent, along with some hail risk. Therefore, the SLGT
risk is being expanded southeastward across the Ozarks and into
portions of western Tennessee/northern Mississippi to capture the
evolving potential.
Later this afternoon, and into the evening, storms developing over
the central High Plains area should increase substantially in
coverage across parts of southern Nebraska and into Kansas, as a
low-level jet develops, and warm advection increases near a residual
surface/outflow boundary. Large hail, and locally damaging winds,
will be possible as the convection increases/expands through the
evening and continues into the overnight hours.
$$