SPC AC 260730
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Wed Jul 26 2017
Valid 281200Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
MID ATLANTIC REGION AND THE CAROLINAS WEST ACROSS PARTS OF THE
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUND THE
EASTERN/SOUTHEASTERN U.S. SLIGHT RISK...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE CENTRAL AND NORTHERN HIGH PLAINS AREA...
Strong/locally severe storms are forecast across a large portion of
the eastern U.S. Friday, from the middle and southern Atlantic Coast
west-southwest across the Mid South and Southeast. A couple of
severe storms will also be possible over parts of the central and
northern High Plains vicinity.
While large-scale upper ridging largely predominates over the
western U.S. Friday, substantial amplification of troughing is
forecast over the eastern U.S. with time. While the models differ
fairly substantially with respect to timing and track, a strong
short-wave trough -- initially progged over the upper Great Lakes
area -- will dig southeast toward/into the central Appalachians
At the surface, a fairly strong cold front is forecast to shift
southeast into -- and across -- the Appalachians, with relatively
substantial cyclogenesis expected to occur along the front in the
vicinity of the Mid Atlantic region. Again, details with respect to
location and timing of surface system progression and
intensification differ, but expect a cold front to extend
southwestward across the Atlantic and Gulf Coast states through
latter stages of the period. Widespread -- and likely at least
locally severe -- convection is expected to precede frontal passage.
...Mid South and Southeast to the middle and southern Atlantic
While a large degree of uncertainty exists with respect to
timing/location, evolution of severe convection is expected across a
rather broad area of the southern and eastern U.S. Friday ahead of
the advancing cold front and associated/digging upper system. As
enhanced/diffluent flow aloft spreads across the area ahead of the
upper system, a favorable kinematic environment for
organized/fast-moving bands of storms will exist. The main
questions at this time revolve around timing of synoptic features,
and evolution of prior -- and ongoing -- convection, and related
effects on heating/destabilization potential. Given these
questions, a broad 15%/slight risk area is being included across
what appears to be the zone of greatest risk at this point, with
later adjustments to area and risk level likely to be required.
Along with risk across portions of the Mid Atlantic area ahead of
the anticipated track of the main vort max, the broad zone of
enhanced/diffluent northwest flow aloft across a large portion of
the southeast U.S. would also support potential for rather
widespread damaging wind risk with multiple, upscale-growing bands
of storms through the afternoon and evening hours.
...Portions of the central and northern High Plains...
As weak short-wave troughing crests the upper ridge and begins to
turn east -- and then southeast -- as it shifts across the High
Plains, isolated/afternoon storm development is expected in a
modestly destabilizing High Plains airmass. Aided by upslope flow,
storms may locally organize and move southeast off the high terrain
through the evening, perhaps as a small MCS. Locally damaging winds
would likely be the primary severe risk, along with some hail
potential before storms diminish into the overnight hours.
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