U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 300535 
Storm Prediction Center ac 300534 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1234 am CDT Sat Aug 30 2014 

Valid 301200z - 311200z 

..there is a slight risk of severe thunderstorms late this afternoon and evening 
across parts of the northern High Plains... 

A few severe storms are possible late this afternoon and evening 
across parts of the northern High Plains. Other strong storms are 
possible today in a corridor arcing from the central Gulf Coast into 
the Tennessee Valley...and across lower Michigan and adjacent 
portions of the Great Lakes region. 

Larger scale middle/upper troughing within the westerlies is forecast 
to continue progressing inland during this forecast period...east of 
the Canadian rockies...and across northern and central portions of 
the U.S. Intermountain region and rockies. As this occurs...the 
remnants of a closed low within the southern branch of the split 
downstream westerlies are expected to turn eastward across the Great 
Lakes region...around the northwestern periphery of prominent 
subtropical ridging centered near the South Atlantic coast. At the 
same time...models suggest that the remnants of an impulse emerging 
from the western Gulf of Mexico will gradually continue 
northeastward around the western periphery of the ridge...across the 
central Gulf Coast/lower Mississippi Valley...toward the central 
Appalachians. Forcing associated with these features is expected to 
contribute to the development of considerable thunderstorm activity 
today...across the northern and central rockies into the northern 
plains...and across the lower Mississippi Valley...northward through 
the lower Great Lakes region. Some of these storms probably will be 
accompanied by at least some severe weather potential. 

..central Gulf Coast into lower Ohio/Tennessee valleys... 
Models continue to indicate the northeastward advection of a plume 
of seasonably high precipitable water content /2 to 2.25 inches/ in 
association with the impulse emerging from the Gulf of Mexico. This 
appears likely to coincide with a Lower/Middle tropospheric belt of 
southerly flow strengthening to 25-35+ across Louisiana and 
Mississippi during the day. Although insolation may be 
limited...and lapse rates generally weak with this 
regime...sufficient cape and forcing for ascent should exist to 
support vigorous updrafts. Given modestly large and clockwise 
curved low-level hodographs...in the presence of high boundary layer 
moisture content and relative humidity...the risk of isolated brief 
tornadoes does not appear out of the question. Otherwise...heavy 
precipitation loading and downward momentum transport in the more 
persistent convection could eventually pose a more substantive risk 
for strong wind gusts at least approaching...if not briefly 
exceeding...severe limits. This threat may spread northeastward 
into parts of western/middle Tennessee and Kentucky this evening. 

..Michigan and adjacent portions of the Great Lakes region... 
Strengthening Lower/Middle tropospheric flow...on the order of 30-50 
knots...appears likely across lower Michigan during the day with the 
approach of the middle/upper impulse. Early period convective cloud 
cover and precipitation may hamper boundary layer destabilization 
..but with surface dew points near 70f...Subsequent insolation 
beneath an eastward advecting middle-level dry slot could contribute to 
moderately large mixed layer cape by late afternoon. It does not 
appear out of the question that there will be a window of 
opportunity for scattered vigorous convective development...with 
isolated supercells possible...accompanied by the risk for locally 
damaging wind gusts...perhaps a tornado or two. 

..northern High Plains... 
Models suggest that the cyclonic belt of flow spreading into western 
North America may become increasingly split during this 
period...with one prominent impulse within one stream progressing 
east of the Canadian rockies...while another digs within another 
stream across the northern Great Basin. However...guidance does 
generally indicate that an area of substantive large-scale forcing 
for ascent will spread east northeastward across the mountains of 
southwest Montana through the northern plains by late tonight. As 
this encounters a moistening boundary layer beneath steep middle-level 
lapse...near a developing surface low across the northern High 
Plains...potential appears to exist for strong/severe storm 
development late this afternoon and evening. Aided by increasing 
shear associated with a strengthening southerly low-level 
jet...supercells are possible...at least initially. It does not 
appear out of the question that large-scale forcing could support an 
upscale growing convective system which could generate a few severe 
wind gusts before weakening across the central Dakotas this evening. 

.Kerr/leitman.. 08/30/2014 

Mesoscale Discussion

acus11 kwns 292326 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 292326 

Mesoscale discussion 1636 
National Weather Service Storm Prediction Center Norman OK 
0626 PM CDT Friday Aug 29 2014 

Areas affected...portions of central and north-central WI 

Concerning...severe potential...watch unlikely 

Valid 292326z - 300130z 

Probability of watch issuance...20 percent 

Summary...isolated strong to marginally-severe wind gusts will 
remain possible through early to middle evening across central into 
north-central WI. Generally sub-severe hail will also be possible. 
Limited coverage of the stronger storms precludes the need for a 
watch. The threat for stronger storms should begin to diminish by 
middle-evening as the boundary layer stabilizes with the loss of 
daytime heating. 

Discussion...at 23z...mosaic radar imagery showed a SW-NE corridor 
of storms from north-central WI to northestern Iowa. This activity developed 
within a differential-heating boundary this afternoon...while 
additional more isolated storms are forming in vicinity of a west-east oriented 
warm front moving northward through central to northern WI. Given the movement 
of this latter boundary...destabilization continues into northern 
portions of WI to the west/northwest of grb. A rather moist warm sector with 
precipitable water exceeding 1.5 inches and above-normal surface temperatures are 
resulting in moderate instability /MLCAPE 1000-2000 j per kg/... 
despite the lack of stronger lapse rates. This latter factor is 
likely limiting the potential for more stronger storms into this 

40-60 meter 500-mb height falls are expected as the eastern Nebraska/western Iowa 
shortwave trough and eastward-moving northern plains trough approach the upper 
MS valley and western Great Lakes region. Forcing for ascent attendant 
to this system will support additional thunderstorm development through this 
evening. Effective bulk shear of 35-40 knots oriented nearly parallel 
to the SW-NE band of storms will continue to result in primarily 
quasi-linear storm structures with locally strong wind gusts being 
the primary threat. 

.Peters/Edwards.. 08/29/2014 

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


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43898989 43939053 44039095 44379117