U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 161958 
Storm Prediction Center ac 161957 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0257 PM CDT Thu may 16 2019 

Valid 162000z - 171200z 

..there is a slight risk of severe thunderstorms from the Great 
Lakes and Ohio Valley through the Central Plains and northern 

Severe storms remain possible from the Great Lakes, Ohio Valley and 
westward through the Central Plains and a portion of the northern 


Only minor adjustments have been made to previous outlook. Mesoscale convective system will 
continue southeast along instability gradient into southern in and 
possibly northern Kentucky where it should weaken. Will maintain slight risk 
area over the Great Lakes upstream from Ohio Valley mesoscale convective system. 
Stabilization has occurred in the wake of this feature. However, 
moist advection associated with southwesterly winds and diabatic 
warming will allow for the atmosphere to recover in pre-frontal warm 
sector from southern WI into Michigan where additional storms may develop 
by early evening with damaging wind and large hail possible. Farther 
west high-based storms are developing south of the stationary front 
over western NE and these may intensify as they continue northeast 
into zone of greater destabilization and higher surface dewpoints 
near the front. Other storms will develop tonight along and north of 
this boundary as the low-level jet strengthens and enhances 
isentropic ascent in frontal zone. 

.Dial.. 05/16/2019 

Previous discussion... /issued 1130 am CDT Thu may 16 2019/ 

Considered increasing tornado probabilities and adding significant 
hail but low confidence exists in whether supercells can be 
sustained in the warm sector across IL/in. 

A slowly decaying mesoscale convective system is ongoing near the Illinois/WI border within a warm 
advection regime. Morning cam guidance has poorly handled with most 
struggling to maintain any semblance of convection beyond 
initialization. The stratiform region across Lake Michigan should have an 
impact on downstream destabilization in lower Michigan given that Richer 
boundary-layer moisture characterized by low to mid 60s surface dew 
points is currently confined from Illinois west. It is possible that the 
mesoscale convective system may not entirely dissipate as warm advection persists through 
the period. Renewed development on the upshear side would seemingly 
be most likely along trailing convective outflow. Along the eastern 
extent of the Great Plains elevated mixed layer at peak heating, 
robust upstream diabatic heating should result in large buoyancy 
with MLCAPE of 2000-3000 j/kg. Veering of the wind profile with 
height on the periphery of moderate mid-level northwesterlies will 
favor supercell structures. An evolution to another mesoscale convective system with 
wind/hail risks appears probable tonight towards the Ohio Valley. 

Minimal change this outlook beyond adding low tornado probabilities 
across the northern/eastern Wyoming vicinity. 

Easterly upslope flow will be maintained through the period on the 
cool side of the stalled front (just north of the Lee cyclone), with 
the somewhat Richer low-level moisture/buoyancy confined mainly to 
central NE east. Gradual height falls in advance of the expansive 
western trough will combine with the upslope flow and daytime 
heating in cloud breaks to support scattered thunderstorm 
development along the Lee of the central rockies during late 
afternoon, which will persist into this evening. The storm 
environment will support a few high-based supercells capable of 
mainly producing large hail and isolated severe wind gusts. 
Strengthening warm advection this evening yielding isentropic ascent 
along the largely west/east-oriented front across Iowa towards 
northern Illinois should result in scattered to widespread storms with a 
mix of isolated severe hail/wind amid a cluster convective Mode. 

..northern rockies... 
Have added a small slight risk for the expectation of a few 
supercells around peak heating. 

Increasing mid-level height falls and DCVA downstream of the 
expansive Pacific coast trough will Foster substantial ascent across 
the region at peak heating. With mid 40s to low 50s surface dew 
points prevalent, a corridor of modest buoyancy should develop where 
diabatic heating is greatest across northern Idaho into far western Montana. 
Veering of the low-level wind profile with height beneath moderate 
mid-level southerlies should support a few supercell structures 
capable of mainly isolated severe hail. 

..eastern Great Basin... 
The zone of strongest forcing for ascent in advance of the mid-level 
trough and along the cold front will reach western Utah and eastern Idaho 
later this afternoon through this evening. Though low-level moisture 
will be limited, weak buoyancy is expected ahead of the front. 
Thunderstorms will be capable of producing isolated 
strong/damaging gusts in an environment characterized by weak 
buoyancy, steep low-level lapse rates, and strong deep-layer 
southerly shear. 

..southeast nm and far West Texas... 
The surface Lee trough will sharpen today in response to increasing 
southwest flow aloft over the southern rockies. This area will lie 
along the northwest edge of the Richer returning low-level moisture, 
which will likely be offset today by deep mixing. Still, some 
increase in deep-layer shear and sufficient buoyancy suggest that a 
couple of high-based supercells will be possible immediately east of 
the high terrain in the late afternoon and evening. Marginally 
severe hail and strong outflow gusts will be the main threats. 


Mesoscale Discussion

acus11 kwns 161947 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 161947 

Mesoscale discussion 0640 
National Weather Service Storm Prediction Center Norman OK 
0247 PM CDT Thu may 16 2019 

Areas affected...parts of central Illinois into central Indiana 

Concerning...Severe Thunderstorm Watch 168... 

Valid 161947z - 162145z 

The severe weather threat for Severe Thunderstorm Watch 168 

Summary...the risk for severe thunderstorms continues, with rapid 
new thunderstorm development possible near the Champaign vicinity by 
4-5 PM CDT. Trends will continue to be monitored for the 
possibility of an additional watch, or southward watch extension. 

Discussion...the leading edge of the convective outflow and stronger 
associated thunderstorm development continue to progress 
southeastward at 30+ kt (across and southeast of the central 
Illinois/Indiana state border area). At least some recent general 
weakening of ongoing convection is evident in latest mrms cappi 
data, and this may continue with activity spreading into the less 
unstable environment across Indiana. However, mixed-layer cape has 
increased in excess of 3000 j/kg along and to the southwest of the 
southwestern flank of the convective outflow, northeast of 
Springfield through the Decatur, Champaign and Mattoon vicinities, 
where it appears that mid-level inhibition has yet to increase 
substantially. As weak mid-level convection, now evident in 
satellite imagery south through east of Peoria, progresses 
southeastward along the outflow boundary, there appears potential 
for rapid new intense thunderstorm development by 21-22z. This may 
include a supercell or two initially, with a risk for severe hail 
and perhaps a tornado. 

.Kerr.. 05/16/2019 

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


Latitude...Lon 40398677 40698628 40128581 39678633 39348788 39888934 
40488904 40228792 40398677