U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 200050 
Storm Prediction Center ac 200049 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0749 PM CDT Friday Sep 19 2014 

Valid 200100z - 201200z 

..no severe thunderstorm areas forecast... 

isolated severe thunderstorms are possible across portions of 
extreme northern Minnesota and from northeast 
Colorado...northeastward into southern Minnesota. Large hail and 
gusty winds are the primary threats into the late evening hours. 

..upper MS valley... 

Robust convection developed along secondary frontal surge over southeastern 
mb late this afternoon along northestern plume of steeper low level lapse 
rates. This activity has slowly developed southward into northwestern Minnesota where 
southern-most storm has exhibited supercell characteristics and even 
produced large hail along with a tornado. While this lone supercell 
likely remains severe...further movement downstream will prove 
detrimental as airmass across the boundary waters region is 
substantially more stable...especially in the boundary layer. 
Boundary layer remains capped at inl this evening and mu parcels are 
near 900mb. For this reason ongoing convection should gradually 
weaken as inflow layer becomes increasingly elevated in nature. 

..cntrl plains to southern Minnesota... 

Surface-based cumulus field along the front over northern Nebraska appears to be 
weakening with loss of daytime heating. However...agitated altocumulus castellanus 
appears to be increasing in areal coverage across southern Minnesota/southeastern South Dakota. 
This activity should gradually deepen and thunderstorms should evolve 
beneath veered low level jet. Isolated hail may accompany the strongest 
updrafts across this region. 

Weak upslope flow across northestern Colorado appears to be aiding scattered strong 
convection within steep lapse rate environment. 00z sounding at dnr 
exhibits very steep lapse rates through 3km and sufficient middle-level 
flow for this activity to spread southeastward with some intensity for the 
next few hours. Gusty winds and marginally severe hail are the 
primary threats. 

.Darrow.. 09/20/2014 

Mesoscale Discussion

acus11 kwns 200335 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 200334 

Mesoscale discussion 1734 
National Weather Service Storm Prediction Center Norman OK 
1034 PM CDT Friday Sep 19 2014 

Areas affected...extreme northestern Nebraska / northwestern Iowa / extreme southeastern South Dakota 

Concerning...severe potential...watch unlikely 

Valid 200334z - 200530z 

Probability of watch issuance...20 percent 

Summary...increasingly isolated/localized occurrences of large hail 
are forecast over the next several hours. The greatest severe 
threat will likely favor the more discrete updrafts. 

Discussion...radar mosaic imagery over the past few hours has shown 
the development of initially discrete storms --some of which were 
supercells-- growing upscale into a linear cluster of storms from 
extreme northestern Nebraska northeastward into far S-central Minnesota. Surface analysis and 
kfsd VAD data show the effective cold front nearing the nwwd-moving 
convective outflow from the SW-NE oriented band of storms. More 
specifically...kfsd VAD data shows the wind shift /I.E. Northwesterly winds/ 
2 km deep. As weak middle-level height falls and the effective front 
continue to exert influence on the region...continued upscale growth 
and a less favorable convective Mode will likely result in an 
overall lessening in the large hail threat. 

.Smith/Goss.. 09/20/2014 

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


Latitude...Lon 42709710 43379586 43519456 43339419 43039417 42409586 
42309707 42709710