SPC AC 220728
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0228 AM CDT Sat Jul 22 2017
Valid 241200Z - 251200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTH CENTRAL U.S....
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
Isolated strong/severe storms may occur over portions of the
northern Plains vicinity, as well as across parts of the central
Appalachians and mid Atlantic region.
As an upper trough over the northeast U.S. lifts gradually
northeastward and a weak trough/low lingers off the West Coast,
large-scale ridging will prevail across a large portion of the
country. Once other exception will be over the far north-central
portion of the country, as a mobile upper low traverses the Canadian
Prairies and brushes the adjacent portions of the U.S.
At the surface, a weak low pressure system will move across parts of
the Northeast in conjunction with the upper system crossing the
area, while a stronger cold front trailing south from the Canadian
Prairie storm system is forecast to shift southeastward across the
north-central states through the period.
...Northern Plains region...
While stronger ascent and more favorable flow aloft associated with
the central Canada upper system will remain largely north of the
international border, moderate mid-level westerlies will spread
across the Dakotas and vicinity. As such, isolated storms
developing within an amply unstable warm sector near the trailing
cold front may become locally organized/severe during the afternoon
and evening hours. Combination of potentially limited storm
coverage, and differences in timing of this system amongst various
models, suggest that MRGL/5% risk is most appropriate to introduce
to the forecast at this time.
...Parts of the Northeast...
Relatively widespread convection and associated cloud cover will
likely linger across the northeast U.S. for much of the period, as
the upper trough moves gradually across the area. However, pockets
of heating/destabilization will likely occur over portions of the
area, which will likely support locally stronger afternoon storms --
aided by moderate cyclonic mid-level flow field atop the region.
While a lack of clarity prevails regarding details at this point,
will introduce a MRGL/5% risk over portions of the central
Appalachians and east to the mid Atlantic and southern New England
Coasts, for locally gusty/damaging wind and marginal hail risk.
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