U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 190536 
Storm Prediction Center ac 190535 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1235 am CDT sun Aug 19 2018 

Valid 191200z - 201200z 

..there is a marginal risk of severe thunderstorms this afternoon 
and evening across parts of the south Central Plains into Ozark 

Strong thunderstorms may impact parts of the south Central Plains 
into Ozark Plateau this afternoon and evening, accompanied by at 
least some risk for severe weather. 

While the stronger mid-latitude westerlies remain north of the 
Canadian/U.S. Border, much of the U.S. Will remain under the 
influence of a weaker branch of westerlies extending from Pacific 
northwest through the mid Atlantic coast and adjacent western 
Atlantic. Within this regime, models indicate one low amplitude 
wave will gradually progress across and east of the northern mid 
Atlantic coast today through tonight. A more amplified upstream 
wave is forecast to dig southeast of the Wyoming/Colorado rockies, 
before turning eastward across the Central Plains, while another 
wave digs inland of the Oregon/northern California coast. 

Guidance is suggestive that the impulse over the interior U.S. May 
be accompanied by at least modest cyclogenesis. A broad/weak 
low-level baroclinic zone to the north of the Red River valley into 
the Texas/Oklahoma Panhandle vicinity may provide the focus for the 
developing surface wave, which is forecast to migrate northeastward 
across the Central Plains into the lower Missouri Valley by late 

..south Central Plains/Ozark Plateau vicinity... 
Although discrepancies exist among the various model output 
concerning the details of the developing cyclone, strengthening of 
lower/mid tropospheric wind fields to 30-40+ kt within its warm 
sector appears possible. Including considerable veering with 
height, associated vertical shear may become potentially supportive 
of organized severe weather potential later today through tonight. 
The extent of this potential, however, remains at least somewhat 

The lack of stronger instability may be one considerable limiting 
factor. The continuation of ongoing convective development, now 
spreading east/southeast of the central and southern High Plains, 
into the day may hinder insolation and associated warm sector 
boundary layer destabilization. And mid-level lapse rates probably 
will not be especially steep. 

However, in the wake, or on the southern periphery, of lingering 
early day convection, guidance is suggestive that moderate 
mixed-layer Cape May develop across central and eastern Oklahoma 
into Arkansas by late this afternoon or evening. Coupled with 
forcing for ascent associated with low-level warm advection and 
perhaps differential cyclonic vorticity advection, discrete storms 
(possibly including a couple of supercells), and a few small upscale 
growing convective clusters and/or bands, may evolve. Some of this 
will probably be accompanied by a risk for severe wind and hail. An 
isolated tornado or two might not be out of the question. 

.Kerr/leitman.. 08/19/2018 


Mesoscale Discussion

acus11 kwns 182334 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 182334 

Mesoscale discussion 1321 
National Weather Service Storm Prediction Center Norman OK 
0634 PM CDT Sat Aug 18 2018 

Areas affected...the southern High Plains 

Concerning...severe potential...watch possible 

Valid 182334z - 190130z 

Probability of watch issuance...60 percent 

Summary...storms are expected to continue developing southeastward 
toward the OK/Texas Panhandle region, with an overall increase in 
coverage through evening. A few storms may produce severe wind or 

Discussion...scattered storms currently exist from western Kansas into 
northeast nm, ahead of a weak cold front and shortwave trough aloft. 
The area is characterized by a moderately unstable air mass with 
modest lapse rates aloft, and weakly veering winds with height. 
Storm Mode has been mixed through early evening, but a more linear 
structure has formed over northeast nm, which will be entering into 
the western panhandles shortly. Other slow-moving cells persist over 
western KS, with isolated severe hail cores noted on radar. 

As the shortwave trough continues to shift southeast, lift will be 
maintained over the region. Visible satellite imagery shows a 
substantial cumulus field over the Texas/OK panhandles, indicative of little 
if any inhibition and likely supportive of continued storm 
formation/sustenance. As such, a watch will be considered. 

.Jewell/Thompson.. 08/18/2018 

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


Latitude...Lon 35850475 36790370 37670274 38360237 38660204 38490155 
38150100 37650046 37220028 36270003 35470029 34990085 
34640185 34410275 34740363 35080434 35300463 35850475