Indianapolis, IN...Virginia Beach, VA...Omaha, NE...St. Louis, MO...Cincinnati, OH...
SPC AC 200722
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0222 AM CDT Thu Jul 20 2017
Valid 221200Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
MISSISSIPPI VALLEY AREA AND VICINITY SOUTHEAST TO THE MID ATLANTIC
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...AND INCLUDING PORTIONS OF THE CENTRAL PLAINS...
A broad area of severe weather risk is apparent from portions of the
northern and central Plains east across the Midwest to the mid
Some amplification within the faster west-northwesterly flow field
over the northern U.S. is expected Day 3/Saturday, as a short-wave
trough digs southeast out of the Canadian Prairies/northern Plains
into the upper Mississippi and mid Missouri Valleys and into the
upper Great Lakes area late in the period. Ahead of this stronger
short-wave trough, multiple smaller-scale disturbances will continue
moving quickly east southeastward across the Midwest and central
Appalachians and into the mid Atlantic region.
At the surface, a cold front will shift slowly south across the
central Plains, while a weak/quasi-stationary front lingers across
the Midwest and east into the central Appalachians. These fronts,
and a weak/reinforcing push of cool air across the upper Mississippi
valley vicinity, suggest a broad area of convective/local severe
risk from the central and north central U.S. east the mid Atlantic
...Upper Mississippi Valley and vicinity southeast to the
Relatively widespread showers and thunderstorms are expected to be
ongoing across portions of the Day 3 severe risk area at the start
of the period, which should linger into the afternoon hours.
Eventually, local heating/destabilization should fuel a gradual
increase in convective coverage and intensity, with ample
west-northwest mid-level flow aiding convective organization. As a
result, risk for hail and locally damaging winds will exist across a
broad zone from the Great Lakes/Midwest across the central
Appalachians, and into the mid-Atlantic region. Storms -- and at
least some severe risk -- will likely continue into the overnight
A somewhat separate area of strong/locally severe storms may occur
farther northwest into the upper Mississippi Valley/western Upper
Great Lakes area, nearer the digging upper system. Hail and locally
damaging wind gusts will be possible, mainly during the afternoon
and evening hours.
...Portions of the central Plains vicinity...
Destabilization along a cool front shifting southward across the
central Plains should support development of at least isolated
storms by late afternoon, most likely across the southern
Nebraska/northern Kansas area and vicinity. As the belt of stronger
mid-level flow sags southward into the region as the north-central
U.S. trough digs southeastward, a few stronger cells may organize
and pose risk for locally damaging winds and large hail through much
of the evening.
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z