SPC AC 110054
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0754 PM CDT Tue Aug 10 2021
Valid 110100Z - 111200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
FAR SOUTHEAST WISCONSIN AND NORTHEAST ILLINOIS...
...SUMMARY...
Severe thunderstorms capable of wind damage and isolated large hail
will be possible this evening across parts of the Upper Midwest and
Great Lakes. Marginally severe winds will also be possible from
parts of the central Plains into the Ohio Valley, with a few strong
gusts also possible across the Mid-Atlantic.
...Upper Midwest/Great Lakes...
A shortwave trough is evident on water-vapor imagery from near the
Arrowhead of Minnesota extending southward into far eastern Iowa. An
MCS is ongoing ahead of the shortwave trough from far eastern
Wisconsin into northeast Illinois. The MCS is located along an axis
of strong instability, analyzed by the RAP just to the west of Lake
Michigan, where MLCAPE is estimated in the 3500 to 5000 J/kg range.
Concerning the wind shear, the WSR-88D VWP at Milwaukee and Chicago
both have 0-6 km shear near 20 kt with most of the speed shear with
the lowest one kilometer above ground level. This combined with very
steep low-level lapse rates will be favorable for damaging wind
gusts along the leading edge of the stronger multicells. Isolated
large hail could also occur. The wind-damage threat should be
greatest over the next hour before the line of storms moves over
Lake Michigan. A severe threat is expected to continue this evening
as the MCS moves into southern Lower Michigan and northwestern
Indiana but should be more isolated due to weaker instability in
those areas...see MCD 1468 and WW 421.
...Central Plains...
A pattern with broad cyclonic mid-level flow is currently located
across the north-central U.S. At the surface, a trough of low
pressure is analyzed from the Oklahoma Panhandle northeastward into
Iowa along which moderate to strong instability is present. Isolated
thunderstorms have developed early this evening along the
instability axis where low-level convergence is enhanced, from far
eastern Colorado into central Kansas. The RAP has MLCAPE maximized
across north-central Kansas where MLCAPE is estimated to be near
4000 J/kg. This combined with 20 to 30 kt of deep-layer shear and
very steep low-level lapse rates should be favorable for a marginal
wind-damage threat. Hail could also occur with the stronger
updrafts. The severe threat may persist for a couple more hours
before instability weakens substantially across the region.
...Mid-Atlantic...
The latest surface analysis shows an ill-defined trough from central
Pennsylvania southward into the Carolinas. A very moist airmass is
located to the east of the trough with surface dewpoints in the
lower to mid 70s F. An axis of moderate instability is analyzed to
the east of the surface trough where isolated strong thunderstorms
are ongoing. MLCAPE in the 1000 to 2000 J/kg range along with steep
low-level lapse rates may be enough for a few marginally severe
gusts early this evening.
..Broyles.. 08/11/2021
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0600Z
| 
)
