Day 1 Outlook Day 2 Outlook Day 3 Outlook Days 4-8 Outlook

Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1200Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion


000
ACUS01 KWNS 280602
SWODY1
SPC AC 280600

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0100 AM CDT Sun May 28 2017

Valid 281200Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHWEST
TEXAS TO THE TENNESSEE VALLEY...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
GREAT LAKES TO THE CAROLINAS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE RIO
GRANDE VALLEY TO THE ATLANTIC COAST...

...SUMMARY...
Isolated to scattered severe thunderstorms will be possible from
portions of southern/central Texas northeastward to the lower Great
Lakes and Carolinas today. With these storms, the primary threats
will be damaging winds and large hail, although a tornado or two
will be possible as well.

...Synopsis...
Along the southern periphery of a closed mid-level cyclone over
southern Manitoba and western Ontario, several shortwave troughs
will translate eastward across the central Plains and Great Lakes
region. Meanwhile, several impulses (some likely convectively
generated) embedded within the southern stream will move from the
lower Mississippi Valley to the Carolinas. Farther west, a highly
amplified ridge will remain positioned near the Pacific Coast.

...Southern/central Texas to the Tennessee Valley...
The corridor of highest severe potential across this region today
remains somewhat uncertain due to the southward evolution of a
series of convective systems (and related outflow) currently
stretching from the Red River Valley eastward to the Tennessee
Valley. The highest confidence in vigorous thunderstorm development
this afternoon/evening exists across Texas, with the cold front
(augmented by storm outflow) likely positioned from the Hill Country
northeastward to the Sabine Valley/ArkLaTex by afternoon. Diurnal
heating, surface dew points in the lower/mid 70s, and steep
mid-level lapse rates will yield strong surface-based buoyancy over
the region, with MLCAPE values upwards of 3000-4000 J/kg. In turn,
storms will rapidly develop during the afternoon, with an attendant
threat of large hail and damaging winds. Despite high buoyancy
values, modest/marginal effective shear may temper updraft
organization sufficiently to preclude multiple very large hail
reports. However, later forecasts may be able to identify a corridor
of higher potential, resulting in an upgrade to an enhanced risk.

...Lower Mississippi and Tennessee Valleys...
Slightly higher uncertainty regarding the severe potential exists
here, as convection is currently ongoing over the region. In turn,
the possibility of sufficient destabilization (both at low and mid
levels) by afternoon/evening is somewhat in question, and the slight
risk may need adjustment in future outlooks. Nonetheless, as
convection weakens through the overnight and early morning hours,
enough recovery of the air mass is possible such that
moderate/strong buoyancy develops near and ahead of the surface
trough/front. Effective shear will be higher here than points
farther west, offering a conditional potential for mid-level updraft
rotation and an increased threat of large hail, damaging winds, and
perhaps a tornado. However, due to the aforementioned uncertainty,
no upgrade appears warranted at this time.

...Portions of the lower Great Lakes to the Carolinas...
With one or more impulses embedded in westerly flow approaching the
lower Great Lakes and mid/upper Ohio Valley, convection is forecast
to gradually organize during the afternoon along a surface trough
extending from northern Indiana/Ohio southeastward to the Carolinas.
Surface dew points in the 60s and zones of diurnal heating will
yield MLCAPE values around 1500-2500 J/kg across the region, with
the greatest buoyancy likely focused over the Carolinas, where a few
storms will be capable of large hail, damaging winds, and perhaps a
tornado. Farther north, while buoyancy will be somewhat lower,
forcing for ascent will be notably stronger. Modest effective shear
and fairly straight hodographs suggest convection will organize into
a few splitting storms and linear segments, with strong/damaging
winds and a few large-hail reports possible.

...Portions of the upper Midwest...
Cold temperatures aloft and modest, but adequate, boundary-layer
moisture will yield weak/marginal surface-based buoyancy across the
region this afternoon. Widely scattered thunderstorms are forecast
to develop, and a few stronger cores may be capable of small hail
and gusty winds. However, tropospheric flow and related shear
profiles will not be particularly strong during peak heating, likely
precluding a higher severe potential. As such, marginal
probabilities are not introduced at this time.

..Picca/Marsh.. 05/28/2017

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