U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 180539 
Storm Prediction Center ac 180537 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1237 am CDT Wed Jul 18 2018 

Valid 181200z - 191200z 

..there is an enhanced risk of severe thunderstorms across much of 
central and eastern Nebraska... 

Severe storms capable of large hail and damaging winds are expected 
across parts of the northern and Central Plains today. A few strong 
storms are possible over northern Arizona, southern Nevada, and the 

A low-amplitude shortwave trough will move from the northern rockies 
into the plains with mid to upper level northwesterly flow 
increasing to 40-60 kt. Low pressure will develop from southern South Dakota 
into the Central High plains during the day, with high pressure 
shifting eastward across the Great Lakes. This will maintain 
southeasterly surface winds across the plains, along with a plume of 
upper 60s f dewpoints along and west of a boundary extending from 
central South Dakota southeastward into the lower MO valley. As the upper wave 
moves into the plains, this boundary will lift north as a warm front 
across the mid MO valley. 

To the west, an upper ridge will remain situated across much of the 
southwestern states, with areas of moisture supporting a few strong 
daytime storms over northern Arizona. 

Warm advection courtesy of a southerly low-level jet may result in 
early day storms scattered about the state of SD, with some marginal 
hail threat as they generally dissipate and/or shift northeast. 
Otherwise, strong destabilization will occur across KS, NE, and 
parts of southern South Dakota as northwest flow increases aloft. The result 
will be afternoon storms redeveloping over South Dakota near the surface low, 
and southward into NE near the surface trough where heating will be 
strongest. A zone of veering winds with height will support 
supercells from the low southeastward along the warm front, and low 
LCLs may support a low-end tornado threat. Lengthening hodographs 
will support large hail with the initial cellular activity despite 
modest lapse rates aloft. Several cam solutions indicate an eventual 
mesoscale convective system moving into NE, and damaging winds will become a concern by late 
afternoon into the evening as activity moves toward the MO river. 

..northern Arizona... 
Daytime heating will combine with existing precipitable water of 1.00-1.50" to 
support a few strong storms during the afternoon and evening, 
focused over the higher terrain of northern AZ, and possibly 
shifting west into Nevada as winds aloft will be out of the east. 
Locally severe wind gusts will be the primary threat, although a few 
storms may produce small hail. 

..southwest MO into Arkansas... 
Scattered storms may be ongoing along and north of the surface 
boundary from central MO into northern Arkansas. Some of this activity 
could contain marginal hail, with redevelopment possible later in 
the day. Overall lift will be weak in this region, but the presence 
of strong instability and likelihood of at least isolated strong 
storms warrants low severe probabilities for wind or hail. 

.Jewell/squitieri.. 07/18/2018 


Mesoscale Discussion

acus11 kwns 180658 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 180657 

Mesoscale discussion 1073 
National Weather Service Storm Prediction Center Norman OK 
0157 am CDT Wed Jul 18 2018 

Areas affected...NE Panhandle...northwestern/western NE 

Concerning...severe potential...watch unlikely 

Valid 180657z - 180900z 

Probability of watch issuance...20 percent 

Summary...a few isolated severe gusts are possible across portions 
of western NE during the next several hours. Anticipated isolated 
nature of the threat is expected to preclude the need for a watch. 

Discussion...observation site at Alliance, NE (kaia) recently 
reported a 62 kt gust as the small convective line extending 
throughout the northern half of the NE Panhandle moved through. 
Airmass downstream is hostile to surface-based convection but steep 
mid-level lapse rates should allow for storm persistence, although 
increasingly elevated in character. Development will likely be 
favored along the western/southwestern extent of the line, largely a 
result of greater instability across western NE than 
central/north-central NE. Despite the increasingly elevated nature 
of the convective line, a few isolated severe gusts at surface are 
still possible, owing primarily to the maturity/organization of the 
line and strength of the cold pool. 

.Mosier/Edwards.. 07/18/2018 

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


Latitude...Lon 42480298 42770204 42490118 42170075 41930060 41650062 
41210073 41040121 41080194 41320262 41710304 42480298