U.S. Severe Weather Forecast (Konvektivereignisse)

Day Three

acus01 kwns 241957 
Storm Prediction Center ac 241956 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0156 PM CST Fri Feb 24 2017 

Valid 242000z - 251200z 

..there is an enhanced risk of severe thunderstorms over a portion 
of the Ohio Valley into southeast lower Michigan... 

..there is a slight risk of severe thunderstorms from the Tennessee 
and Ohio valleys into lower Michigan... 

..there is a marginal risk of severe thunderstorms over a large 
part of the Tennessee and Ohio valleys into the Great Lakes... 

Severe thunderstorms are forecast to affect areas from lower 
Michigan southward to Tennessee later this afternoon through 
tonight. The primary threat appears to be damaging wind, but some 
hail and a few tornadoes will be possible. 

..Southern Lower Michigan through the Ohio and Tennessee valleys... 

Only minor adjustments have been made to previous outlook. Storms 
are expected to undergo a gradual increase through the evening 
hours. Pre-frontal band of storms along warm conveyor belt from 
southern in to southeast lower Michigan has been slow to intensify. This 
appears to be due to a residual inversion and modest cape which are 
limiting overall updraft strength. As deeper forcing for ascent 
continues to act on the inversion layer, further increase in 
convection within this band will probably occur. Additional storms 
will likely develop along the cold front this evening. Initial storm 
modes will be primarily discrete, but evolution to lines segments 
may occur, especially within zone of stronger linear forcing along 
the front. Warm sector wind profiles are unidirectional, but with 
strong effective bulk shear supporting potential for organized 
storms including a few supercells and bowing segments. Though a few 
tornadoes remain possible, overall tornado threat may be mitigated 
to some extent by modest cape and 0-1 km hodograph size. Otherwise 
primary threat is expected to trend toward damaging wind, especially 
as storms develop and organize along the cold front. 

.Dial.. 02/24/2017 

Previous discussion... /issued 1026 am CST Fri Feb 24 2017/ 

..Southern Lower Michigan/northern in... 
Only minor changes have been made to the ongoing forecast. Water 
vapor loops show a large upper trough over the Central Plains, while 
a deep surface low tracks northeastward across northern Illinois. The 
initial severe concern will be ahead of the surface low and into the 
vicinity of the warm front lifting northward into Michigan. Relatively 
strong heating and low level moisture advection will result in 
MLCAPE values around 1000 j/kg along and south of the boundary. 12z 
model solutions are consistent in developing scattered thunderstorms 
along this corridor this afternoon and early evening. Forecast 
soundings suggest a favorable vertical shear profile for discrete 
supercells capable of large hail and damaging winds. This portion 
of the outlook area holds the greatest concern for supercell 
tornadoes later today. 

The forecast scenario for this area remains on track. Thunderstorms 
are expected to develop along the cold front over in and central Kentucky 
this afternoon and spread eastward across the risk area this 
evening. Strong wind fields and steep low level lapse rates will 
promote a fast-moving squall line capable of damaging winds and 
hail. If sufficient mesoscale organization can occur along the 
line, isolated qlcs tornadoes could also be a threat. 


Mesoscale Discussion

acus11 kwns 242007 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 242007 

Mesoscale discussion 0204 
National Weather Service Storm Prediction Center Norman OK 
0207 PM CST Fri Feb 24 2017 

Areas affected...far eastern Illinois...much of Indiana...Southern 
Lower Michigan...Northwest Ohio 

Concerning...severe potential...watch possible 

Valid 242007z - 242230z 

Probability of watch issuance...60 percent 

Summary...scattered thunderstorms are likely to develop ahead of a 
developing low and cold front from near the Illinois/Indiana border 
into Southern Lower Michigan where a warm front may also focus 
development. Storms may eventually affect western Ohio. Hail, wind, 
and an isolated tornado are all possible. 

Discussion...a pre-frontal line of midlevel convection continues to 
move across Indiana and into southeastern lower Michigan creating 
widespread clouds which is hampering destabilization. The northern 
end of this line is now interacting with the warm front over 
southeastern lower Michigan, where damaging winds, hail, and perhaps 
a brief tornado could occur around the Detroit area. For more 
information on this area see mesoscale discussion 203. 

To the west, a cold front continues eastward across eastern 
Illinois, with a surface low near Southern Lake Michigan as of 20z. 
Ahead of this front, only a narrow zone of mid 50s dewpoints exists, 
resulting in around 500 j/kg MUCAPE. Also noted in recent surface 
analyses are veering winds, which is reducing low-level shear. 

With time, scattered storms are likely to form along the front, and 
also near the surface low which will track from Northwest Indiana 
across Southern Lower Michigan. The warm frontal portion of the 
threat area will have the greatest conditional tornado threat with 
enhanced low-level shear and effective srh around 200 m2/s2. 
However, only elevated hail is likely north of the warm front. To 
the South, Strong mixing over the warm sector as a whole combined 
with the veering winds and a capping inversion suggest a somewhat 
mixed storm Mode, with mainly hail and wind. 

.Jewell/Hart.. 02/24/2017 

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


Latitude...Lon 39258686 38868772 38918809 39258829 39878794 40448769 
41158755 41608713 42208612 42608460 42638404 42408385 
41918382 41458396 40678503 39258686