SPC AC 220559
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Sat Jul 22 2017
Valid 221200Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
VALLEY EASTWARD TO THE MID ATLANTIC...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
PLAINS EASTWARD TO THE ATLANTIC COAST...AND OVER THE UPPER
Scattered severe storms capable of hail or damaging wind are
possible from the Ohio Valley eastward into the Mid Atlantic, and
across parts of the upper Mississippi Valley today. More isolated
activity is expected across the central Plains.
A progressive shortwave trough will dive southeastward across the
upper MS Valley with increasing westerly surface winds behind a cold
front aiding in lift. To the east, modest west/northwesterly flow
aloft will extend from the OH Valley into the Northeast, with early
day storms associated with a weak disturbance roughly over IN/OH
early in the day. A moist and unstable air mass will remain across
the entire region, with an extensive low pressure trough from KS to
the Mid Atlantic, as well as across the upper MS Valley.
...IN/OH eastward to the Atlantic coast...
Substantial uncertainty exists regarding the timing of severe storms
today given likely ongoing storms early in the day. Most CAM
solutions suggest storms will extend from IL into OH at the start of
the period, moving across OH and PA during the day with perhaps some
low-end severe risk. Any outflow from this activity may provide a
focus for diurnally driven storms during the afternoon, most likely
across the slight risk area. Increasing westerly flow aloft and PWAT
suggest a few fast moving storms capable of damaging outflow winds.
Hail is also possible with any discrete storms away from the more
A weak pre-frontal trough will deepen over MN during the day as a
substantial shortwave trough provides cooling aloft. Early activity
now over the Dakotas should traverse the Arrowhead and move into
northern WI and the U.P. of MI during the day, perhaps with a
continued wind or hail threat. New afternoon activity is then
expected along any outflows from that activity, across
central/eastern WI, with other isolated cells possible farther west
over MN where wind profiles appear to favor splitting cells capable
of large hail. Isolated significant hail is possible given long
hodographs, ample instability and cool temperatures aloft.
...Northern KS...east central CO...central MO...
Very hot temperatures will lead to deep mixed layers and weak
instability near the east-west oriented surface trough. Little upper
support for ascent exists, but at least isolated late afternoon
storms are likely capable of locally damaging winds or marginally
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z