U.S. Severe Weather Forecast (Konvekční výhled)

Třetí den

acus01 kwns 241232 
Storm Prediction Center ac 241230 

Day 1 convective outlook 
National Weather Service 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 

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 Michigan to Tennessee through tonight... 
A well-defined midlevel trough over the mid MO valley this morning 
will amplify while progressing eastward to the Great Lakes and Ohio 
Valley tonight, as an associated surface cyclone deepens while 
moving northeastward from west central Illinois across lower Michigan to Lake 
Huron. Ongoing elevated thunderstorms will persist through the 
morning across lower Michigan 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 Michigan 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 Michigan. 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 


Mesoscale Discussion

acus11 kwns 240554 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 240554 

Mesoscale discussion 0202 
National Weather Service Storm Prediction Center Norman OK 
1154 PM CST Thu Feb 23 2017 

Areas affected...far eastern SD/NE...southern Minnesota...northern Iowa...and 
much of WI 

Concerning...winter mixed precipitation 

Valid 240554z - 241200z 

Summary...a heavy snow band, with rates around 1 inch/hour, will 
persist through 12z. A mix of winter precip, including snow, sleet, 
and freezing rain, will be possible across parts of northern Iowa into 
southern WI. 

Discussion...an ongoing deformation band of moderate to heavy snow 
across far eastern NE/South Dakota into southern Minnesota and northern Iowa is 
associated with strong low and mid-level frontogenesis and related 
ascent. As a shortwave trough over the northern/Central Plains moves 
northeastward overnight, the heavy snow band should likewise shift 
northeastward across southern Minnesota/northern IA, and into WI through 
12z. Snowfall rates around 1 inch/hour (locally higher) will be 
possible within the core of the heavy snow band. Strong 
northerly/northeasterly surface winds of 25-35 mph, with some higher 
gusts, may allow for near-blizzard conditions, particularly across 
parts of southern Minnesota/northern Iowa where precipitation remains all 
snow. A narrow corridor of mixed winter precipitation including 
snow, sleet, and freezing rain may occur across parts of northern Iowa 
into southern WI. Across this area, forecast soundings show a warm 
nose aloft (generally between 850-700 mb) which should act to 
partially/completely melt frozen hydrometeors. Sleet/freezing rain 
rates will be convectively enhanced due to elevated instability and 
thunderstorms moving across this area. 

.Gleason.. 02/24/2017 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 42129464 41839531 41449600 42149652 42649667 43729671 
44839277 45458931 45368778 45008710 44088739 43588764 
43348939 42939114 42439315 42129464