U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 210509 
Storm Prediction Center ac 210507 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1207 am CDT sun Sep 21 2014 

Valid 211200z - 221200z 

..no severe thunderstorm areas forecast... 

scattered showers and thunderstorms -- and possibly a few marginally 
severe storms -- will be possible from the lower Great Lakes 
vicinity southwestward across the central Appalachians to the 
Tennessee and middle-Mississippi Valley region. Scattered 
thunderstorms are also expected across parts of the southwest...with 
isolated/marginal severe potential possibly evolving across the Utah 
vicinity during the afternoon and evening. 

Synoptic-scale pattern amplification is expected over the eastern half 
of the country Sunday...as an upper trough initially over the upper 
Great Lakes/Midwest region expands eastward/southeastward with time. 
Meanwhile...the western U.S. Will remain under the influence of 
large-scale ridging. Within the broader ridge...a weakening upper 
low will continue drifting northeastward across the Great Basin vicinity. 

At the surface...a cold front -- trailing southwestward across the Midwest 
from a low initially over Quebec -- will advance quickly 
ewd/sewd...with the boundary likely to reach the Atlantic and Gulf 
coasts late in the period. Meanwhile...high pressure will prevail 
in the wake of the front over the central Continental U.S....with weak/diffuse 
low pressure expected over the intermountain west. 

..lower Great Lakes southwestward to the middle MS valley... 
Showers and scattered thunderstorms are expected to be ongoing 
Sunday morning across the Great Lakes/Ohio Valley region ahead of the 
advancing cold front...with relatively widespread cloud cover 
spreading across the Appalachians. While the resulting hindrance of 
stronger heating in many areas should limit warm-sector 
destabilization potential...some diurnal increase/expansion of 
convection is expected -- aided by relatively strong/cyclonic flow 
aloft. At this time...it still appears that modest cape will limit overall 
severe risk...and therefore -- while low-probability severe risk is 
being expanded west-southwestward across the Tennessee/middle MS valley region...slight 
risk upgrade will not be included this forecast. Severe risk should 
peak during the late afternoon...and diminish into the evening 

..UT and vicinity... 
Widespread/largely sub-severe convection will continue through 
Sunday across parts of the intermountain west...ahead of the 
weakening upper low shifting northeastward across the Great Basin vicinity 
through the broader-scale ridging. With clouds/precipitation likely 
to limit destabilization potential and flow aloft to remain 
similarly modest...any afternoon/early evening severe risk should 
remain low-end and isolated. 

.Goss/cohen.. 09/21/2014 

Mesoscale Discussion

acus11 kwns 210556 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 210555 

Mesoscale discussion 1752 
National Weather Service Storm Prediction Center Norman OK 
1255 am CDT sun Sep 21 2014 

Areas affected...western lower Michigan 

Concerning...severe potential...watch unlikely 

Valid 210555z - 210730z 

Probability of watch issuance...20 percent 

Summary...strong wind gusts may produce localized tree damage with 
qlcs approaching the Eastern Shore of Lake Michigan. 

Discussion...minor intensification and solidification of 
high-reflectivity cores have recently occurred with the long-lived 
qlcs crossing Southern Lake Michigan to the chicagoland area. 63-65 degree f surface 
dew points persist downstream across Southern Lower Michigan...with modified 
00z grb/apx radiosonde observations supportive of meager surface-based buoyancy 
/largely at or below 500 j/kg/ amidst modest inhibition. With very strong 
speed shear sampled in GRR vwp data /0-6 km values near 70 knots/ and 
current linear motion around 40 knots...it appears probable that 35-45 
knots wind gusts should accompany embedded bulging segments within the 
line as it reaches the western lower Michigan Lake shore. 

.Grams/Edwards.. 09/21/2014 

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


Latitude...Lon 43878675 44388664 44618644 44638620 44608594 44408545 
43808513 42938520 41808596 41608667 41778727 42568680 
43338660 43878675