Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
365
ACUS01 KWNS 241232
SWODY1
SPC AC 241230

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0630 AM CST Fri Feb 24 2017

Valid 241300Z - 251200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN
LOWER MICHIGAN ACROSS EASTERN INDIANA AND WESTERN OHIO TO NORTH
CENTRAL KENTUCKY...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK AREA...FROM LOWER MICHIGAN TO EASTERN TENNESSEE...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...FROM THE GREAT LAKES TO PARTS OF THE SOUTHERN
APPALACHIANS...

...SUMMARY...
Severe thunderstorms are forecast to affect areas from Lower
Michigan southward to Tennessee, mainly this afternoon through
tonight.  The primary threat appears to be damaging wind, but some
hail and a couple of tornadoes will also be possible.

...Lower MI to TN through tonight...
A well-defined midlevel trough over the mid MO Valley this morning
will amplify while progressing eastward to the Great Lakes and OH
Valley tonight, as an associated surface cyclone deepens while
moving northeastward from west central IL across Lower MI to Lake
Huron.  Ongoing elevated thunderstorms will persist through the
morning across Lower MI in the zone of strong low-level warm
advection/frontogenesis immediately north of the eventual cyclone
track, with marginally severe hail possible in the strongest storms.

Modest low-level moisture (boundary layer dewpoints in the mid-upper
50s) will spread northward into southern Lower MI beneath an
elevated mixed layer, though the cap will likely delay surface-based
thunderstorm development until 21-00z.  Initial storm development is
likely close to the surface cyclone in southern Lower MI, along the
northwest edge of the modestly unstable warm sector (MLCAPE near
1000 J/kg).  Deep-layer vertical shear (effective bulk shear of
40-50 kt) will favor semi-discrete supercells with an associated
large hail/damaging wind risk into this evening across southern
Lower MI.  A couple of tornadoes will also be possible as any
sustained supercells can interact with the zone of stronger
low-level shear (effective SRH 200-300 m2/s2) and sufficient
moisture along the surface warm front.

Convection will develop southward through the evening as large-scale
forcing for ascent/height falls overspread the surface cold
front/west part of the warm sector and erode the cap associated with
the steep (8-9 C/km) midlevel lapse rates.  A mixed convective mode
of semi-discrete cells and line segments is expected initially along
and just ahead of the cold front, given somewhat boundary-parallel,
deep-layer shear vectors and ascent focused along the front.  Modest
low-level moisture/buoyancy, lingering steep midlevel lapse rates,
and 40-50 kt effective bulk shear will support organized line
segments and supercells capable of producing damaging winds/isolated
large hail.  The tornado risk well south into the warm sector is a
bit more uncertain given relatively straight hodographs and a
tendency toward more linear convection with time.  However, there
will still be some risk for embedded circulations in the solidifying
line of storms which will also be capable of producing damaging
gusts well into the overnight hours.

..Thompson/Kerr.. 02/24/2017

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.