U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 020102 
Storm Prediction Center ac 020100 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0800 PM CDT Monday Sep 01 2014 

Valid 020100z - 021200z 

..there is a slight risk of severe thunderstorms from part of southern Kansas and northern OK 
through central/southern MO...northwestern Arkansas and southern Illinois... 

Isolated severe storms are expected from along the Oklahoma/Kansas 
border area into the middle-Mississippi Valley through tonight. A 
tornado threat and very large hail will remain possible during the 
early evening...with a threat for damaging winds and hail extending 
eastward into the middle-Mississippi Valley and lower Ohio Valley into 

A broad longwave trough will be maintained through tonight across 
the northern tier of states and southward into the Central Plains and lower MO 
valley. An embedded shortwave trough within this flow regime will 
track from western/central Nebraska reaching the middle MS valley by 12z 
Tuesday. A band of 50-65 knots westerly 500-mb winds accompanying the Nebraska 
trough will spread downstream across MO to the southern Great Lakes with 
midlevel winds also increasing into the Ohio Valley. 

..srn plains to middle MS/lower Ohio valleys... 
While a weak cold front will move into lower Michigan...central MO and northern 
OK through tonight...the primary foci for a continued severe weather 
threat will be remnant convective outflow boundaries left over from 
convection/thunderstorm complexes early this morning in central/southern MO into 
southeastern Kansas/northestern OK. Strengthening southerly low level jet from OK into far southern Kansas and 
southwestern MO combined with increasing westerly midlevel winds will further 
enhance effective bulk shear and low-level shear for additional 
supercells. Any storms that can remain discrete with deviant motion 
will have a threat to produce a tornado...and this outlook has 
increased the tornado probability to 5 percent from northestern OK/southeastern Kansas 
into southwestern MO. However...this threat should be relatively 
short-lived /until around 03z/. At that time...storm mergers and 
backbuilding of storms with eventual upscale growth into an mesoscale convective system 
across southeastern Kansas/northestern OK and eastward through MO to southern Illinois should diminish 
the tornado threat...but maintain a threat for strong wind gust 
and/or hail. 

Additional strong to severe storms will remain possible through the 
evening across central MO to southwestern Illinois as strong effective bulk shear 
supports a continued potential for storm organization with the 
approach of the Nebraska trough. 

..parts of central/eastern Nebraska and extreme southeastern South Dakota... 
00z lbf sounding indicated steep midlevel lapse rates /around 7.5 c 
per km/ and westerly midlevel winds of 35-50 knots. This combined with 
residual steep low-level lapse rates suggest a few additional 
sustained thunderstorms will be possible this evening along the leading edge 
of ascent with the Nebraska shortwave trough. Locally strong winds 
and/or marginally-severe hail will be the primary threats into the 
middle evening prior to boundary-layer stabilization. 

.Peters.. 09/02/2014 

Mesoscale Discussion

acus11 kwns 020146 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 020145 

Mesoscale discussion 1661 
National Weather Service Storm Prediction Center Norman OK 
0845 PM CDT Monday Sep 01 2014 

Areas affected...north central/northestern OK...and southeastern Kansas into southwestern MO 

Concerning...Severe Thunderstorm Watch 486...487... 

Valid 020145z - 020315z 

The severe weather threat for Severe Thunderstorm Watch 

Summary...potentially damaging wind gusts...frequent cloud to ground 
lightning and heavy rainfall are expected to become the primary 
convective hazards within the next hour or so. A new severe weather 
watch...or extension in time of ww 486...probably will be needed by 

Discussion...a considerable increase in the number of 
storms/convective coverage has been underway during the past hour or 
so. This appears generally in response to large-scale ascent 
associated with a band of enhanced convergence and warm 
advection...based roughly around 850 mb. Forcing for ascent could 
still increase some with modest strengthening of the southerly 
low-level jet /30-35 knots at 850 mb/ through the 03-05z time 
frame...likely providing the focus for strongest storm development 
near the Kansas/Oklahoma border area...between Bartlesville and 
Joplin. Aided by inflow of seasonably high moisture content 
air...with sizable cape beneath lingering modestly steep middle-level 
lapse rates...the evolution of a small but increasingly organized 
convective system appears possible in the presence of strong 
vertical shear. Heavy precipitation loading and downward Transfer 
of momentum associated with 30 knots deep layer westerly mean flow will 
contribute to increasing potential for downbursts and surface gusts 
at least approaching...if not exceeding...severe limits. 

.Kerr.. 09/02/2014 

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


Latitude...Lon 37849524 37849324 36869295 36659496 36379654 36169748 
36399803 37069754 37849524