SPC AC 191727
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1227 PM CDT Wed Sep 19 2018
Valid 201200Z - 211200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
MINNESOTA INTO CENTRAL WISCONSIN...
Severe storms are expected across parts of the Upper Mississippi
Valley and Great Lakes on Thursday, with the greatest threat from
southeast Minnesota into central Wisconsin where damaging winds are
most likely, along with an isolated tornado threat.
A shortwave trough will move rapidly eastward across the northern
Plains during the day with substantial cooling aloft while an upper
high holds over the Southeast. The tightening height gradient
between the two will result in strengthening winds through the
period, with 70-80 kt midlevel winds by evening from SD into MN. At
the surface, low pressure will begin the day over central NE, and
will deepen with time as it approaches Lake Superior by 06Z.
Preceding the low will be an east-west oriented baroclinic zone and
eventual warm front, reinforced by early day precipitation, which
will move across southern MN and WI during the afternoon. Despite
relatively warm midlevel temperatures initially, rapid warm
advection in the low-levels will result in a destabilizing situation
by late afternoon and evening ahead of the surface low with storms
focused near the surface low track and warm front. A cold front will
also surge eastward across the upper MS Valley during the evening,
providing an additional focus for storms.
To the south, convergence along the trailing cold front will also
support afternoon storms from NE into KS, with marginally severe
hail or wind possible.
...MN and IA into WI and the U.P. of MI...
An extensive area of rain and scattered thunderstorms is expected to
be ongoing from SD into MI in association with a broad region of
warm advection and north of the developing surface low and warm
front. A few of the storms could contain hail early in the day. The
warm front will then begin to move northward, with rapid
destabilization due to a southwesterly low-level jet of 55 kt by
00Z. Initially elevated storms are expected to focus just north of
the warm front by early afternoon from MN into WI, and these will
likely contain hail. With time, and as the surface low approaches,
some of these cells may become surface based with bows and isolated
supercells possible. The most likely area for significant wind
damage or a tornado will be near the low as it tracks along the
lifting warm front. Due to the expected narrow zone of greatest
threat, and early precipitation potential, will defer any
hatched/SIG area to later updates. Shear profiles will be quite
strong, supporting a continued severe threat in this corridor
perhaps into Upper Michigan. Farther south, a few severe storms may
occur into IA along the cold front with a hail and wind threat.
...NE and KS...
Strong heating will occur ahead of the cold front which will extend
from eastern NE into north-central KS by late afternoon. The
presence of 60s F dewpoints will lead to an axis of sufficient
instability supporting a few strong to severe storms, and hodographs
suggest multicellular mode with localized damaging winds or hail
possible for a few hours before storms weaken.
...MAXIMUM RISK BY HAZARD...
Tornado: 5% - Slight
Wind: 30% - Enhanced
Hail: 15% - Slight
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z