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Day 1 Outlook Convective Tornado
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 Forecast Discussion

  
808 
ACUS01 KWNS 221644
SWODY1
SPC AC 221643

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1143 AM CDT Thu Jun 22 2017

Valid 221630Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE GULF
COAST/LOWER MS VALLEY TO TN VALLEY...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
HIGH PLAINS AND CO/WY FRONT RANGE...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MIDWEST/GREAT LAKES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE GULF
COAST/LOWER MS VALLEY TO TN VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE HIGH
PLAINS TO THE GREAT LAKES/NORTHEAST STATES...

...SUMMARY...
A few tornadoes and isolated damaging gusts are possible over a
broad area across the Gulf Coast states, lower Mississippi Valley
northward into the Tennessee Valley. Elsewhere, severe thunderstorms
with damaging winds and large hail are possible from the central
High Plains to portions of the Great Lakes.

...Gulf Coast States/lower MS Valley into TN Valley...
Tropical Depression Cindy, centered over far west-central LA as of
mid/late morning, is expected to continue to drift slowly
north-northeastward through the afternoon into tonight. Even while
the system may begin to fill with a tendency for a weakening surface
low, strong low/mid-level southerly winds on the eastern periphery
of the system will continue to yield the possibility of low-topped
supercells and at least some tornado risk over a relatively broad
area of the region. A few weakly rotating cells have been noted this
morning across the western FL Panhandle as well as southeast LA into
southern MS, and this same scenario/supportive environment should
somewhat expand north-northwestward through the afternoon and
evening. The overall tornado risk, which appears relatively modest
overall across a broad region, should diurnally peak this afternoon
into early/mid-evening, although some tornado risk could continue
into the overnight and early morning hours of Friday.

...CO/WY Front Range and Central/southern High Plains... 
Isolated high-based storms are expected to develop by late afternoon
along the south/southeastward-moving front spanning portions of KS
into southeast NE. Where storms develop, moderate amounts of
CAPE/vertical shear will allow for semi-organized clusters of storms
capable of isolated large hail aside from a locally damaging wind
risk with outflow dominant convection.

Other storms are likely to develop this afternoon within an evolving
post-frontal upslope flow regime, with initial development along and
just east of the CO/southeast WY Front Range. As an increasingly
moist environment develops into the region and the boundary layer
destabilizes, relatively long/straight hodographs will support the
possibility of splitting supercells capable of large hail.
Severe-caliber wind gusts will also possible given relatively
deep/well-mixed sub-cloud layers.

...Upper Midwest/Great Lakes...
Ahead of a southeastward-moving cold front, a fast-moving cluster of
storms will continue eastward from southeast MN into southern WI
today to the north of an outflow boundary and weakening convection
across eastern IA/far southern WI and far northern IL. Widespread
cloudiness across WI to the north of the outflow boundary should
largely curb surface-based severe potential, with storms otherwise
likely to develop by mid/late afternoon along the
southeastward-moving front across IA and possibly into far southeast
MN/southwest WI. While the strongest winds aloft will tend to lag
(to the west/northwest) the cold front, sufficient vertical shear
(30-40 kt) in the presence of moderate buoyancy (generally 1500-2500
J/kg MLCAPE) will yield multicells and some supercells capable of
large hail and damaging winds especially late this afternoon into
evening.

..Guyer/Gleason.. 06/22/2017

$$