U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 220041 
Storm Prediction Center ac 220040 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0640 PM CST sun Jan 21 2018 

Valid 220100z - 221200z 

..there is a slight risk of severe thunderstorms this evening 
across parts of southeastern Oklahoma and northeastern Texas into 
western/central Arkansas and northwestern Louisiana... 

..there is a marginal risk of severe thunderstorms across 
surrounding areas of the southeastern plains and Mississippi 

A risk for severe storms capable of producing damaging wind gusts, 
and perhaps a couple of tornadoes, continues this evening, mainly 
across parts of southeastern Oklahoma and northeastern Texas into 
western and central Arkansas and northwestern Louisiana. 

..01z outlook update... 
Latest model output suggests that a period of more rapid deepening 
of the surface cyclone may not be until later this evening into the 
overnight hours, across parts of northeastern Kansas into 
northwestern Missouri, before it begins to occlude. To this point, 
thunderstorm development has been largely confined to the narrow 
plume of modest low-level moisture return emanating from the western 
Gulf of Mexico, where a combination of relatively warm mid-levels 
(allowing for only weak cape) and weak low-level lapse rates have 
tended to minimize the overall severe weather potential. 
There may be little overall change to convective trends for another 
couple of hours, before the leading edge of stronger lower/mid 
tropospheric cooling begins to overspread the better low-level 
moisture return toward the 03-04z time frame. This may contribute 
to at least some further intensification of storms, and perhaps 
organization of storms into an evolving squall line. 

Although this will coincide with a gradual cooling and 
stabilization of the axis of weak boundary layer instability 
(supported by daytime heating) across central/eastern Texas into 
eastern Oklahoma/western Arkansas, a period of increasing severe 
weather potential still appears possible this evening. This may be 
primarily in the form of damaging wind gusts, aided by downward 
momentum Transfer near a southerly 850 mb jet which is forecast to 
strengthen to 50-70 kts across The Ark-la-tex and Ozark Plateau, 
through the Lower/Middle Mississippi Valley. However, sizable 
clockwise curved low-level hodographs will also contribute to at 
least some risk for tornadoes, particularly with any continuing 
discrete storm development. As storms tend to develop eastward into 
the Lower/Middle Mississippi Valley, weaker instability, 
particularly in the near surface layer, is expected to result in 
diminishing severe weather potential by late tonight. 

.Kerr.. 01/22/2018 


Mesoscale Discussion

acus11 kwns 220336 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 220335 

Mesoscale discussion 0036 
National Weather Service Storm Prediction Center Norman OK 
0935 PM CST sun Jan 21 2018 

Areas affected...northeast Texas across Arkansas and into far 
southern Missouri 

Concerning...Tornado Watch 1... 

Valid 220335z - 220530z 

The severe weather threat for Tornado Watch 1 continues. 

Summary...the threat of a couple tornadoes as well as damaging winds 
will likely spread east of the existing watch, and a new watch may 
be needed by 5z. 

Discussion...a southwest-northeast oriented zone of thunderstorms 
has become more productive over the past few hours, as wind fields 
continue to increase. Only modest levels of instability exists, but 
low-level flow is strong. A few storms have shown signs of 
possible/brief tornadoes with little or no lightning, suggesting 
minimal instability is needed. 

Sporadic severe storms currently exist from northeast Texas across 
western Arkansas. Additional storms may develop southward into 
east-central Texas and northwest la, with shear favoring supercells and 
perhaps a tornado or two. 

As the cold front reaches the existing batch of storms, they will 
likely merge into a line and accelerate eastward. Models suggest 
that some threat will likely persist across central AR, and perhaps 
far southern MO as warm advection creates minimal instability there. 
Overall, the threat is expected to weaken as it approaches the MS 
river late tonight. 

.Jewell/Thompson.. 01/22/2018 

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


Latitude...Lon 31889345 31709423 31829504 32159540 32499564 32979568 
34529495 36019416 37089296 37269174 36979108 36119105 
34339184 32999249 32509268 31889345