U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 231946 
Storm Prediction Center ac 231945 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0245 PM CDT Fri Mar 23 2018 

Valid 232000z - 241200z 

..there is a slight risk of severe thunderstorms along the 
Kansas/Nebraska border area... 

..there is a marginal risk of severe thunderstorms surrounding the 
slight risk across portions of the central Great Plains... 

Isolated large hail and strong wind gusts are expected between 6 to 
11 PM CDT along parts of the Kansas-Nebraska border. 

..20z outlook update... 
Latest convection-allowing models and radar/satellite observations 
continue to depict isolated to scattered convection initially in 
northeastern Colorado that will spread eastward along/near the 
Nebraska/Kansas border region through tonight. Point forecast 
soundings/thermodynamic profiles suggest higher-based activity 
posing a hail/wind threat initially given steep low-level lapse 
rates and deeply mixed boundary layer profiles. This risk will 
evolve into primarily a hail threat through the evening given steep 
mid-level lapse rates, speed shear through the cloud-bearing layer, 
and stabilizing low-levels. Severe potential remains elevated 
enough to continue the ongoing marginal/slight risk (and attendant 
hail/wind probabilities) for this update. 

.Cook.. 03/23/2018 

Previous discussion... /issued 1123 am CDT Fri Mar 23 2018/ 

..KS/NE border area... 
Have upgraded to a narrow slight risk for large hail given the 
potential of a persistent supercell or two developing this evening 
in association with an eastward-moving surface cyclone. 

A surface cyclone over northeast Colorado should peak in intensity across 
northwest Kansas at 00z, in response to Lee cyclogenesis and forcing for 
ascent downstream of a low-amplitude shortwave trough approaching 
from the eastern Great Basin. This will draw a modifying Gulf air 
mass (boundary-layer dewpoints in the low-mid 50s) northward beneath 
an elevated mixed layer, resulting in a capped warm sector east of a 
sharpening dryline. However, deep mixing and forcing for ascent near 
the triple point (close to the Kansas/NE/co border region) should Foster 
high-based convection in the late afternoon. Strong deep-layer shear 
yielding elongated hodographs amid very steep mid-level lapse rates 
around 8-8.5 c/km from 700-500 mb could support a moderate-lived 
discrete supercell or two in the early to mid evening, capable of 
large hail and strong outflow winds. This activity may be maintained 
into the late evening via elevated parcels in a zone of robust 
low-level warm advection northeast of the eastward-moving surface 
cyclone. Elevated storms will weaken overnight given a cluster 
convective Mode on the periphery of weak buoyancy. 


Mesoscale Discussion

acus11 kwns 232045 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 232045 

Mesoscale discussion 0167 
National Weather Service Storm Prediction Center Norman OK 
0345 PM CDT Fri Mar 23 2018 

Areas affected...KS/NE border area 

Concerning...severe potential...watch possible 

Valid 232045z - 232245z 

Probability of watch issuance...60 percent 

Summary...isolated thunderstorm development is anticipated by 23z 
which should evolve into a eastward-moving supercell or two along 
portions of the Kansas/NE border. While the spatial extent of the risk 
will be latitudinally small, a persistent swath of large hail and 
strong outflow winds is possible this evening and may necessitate 
Severe Thunderstorm Watch issuance. 

Discussion...20z surface analysis placed a 999 mb cyclone near the 
Kansas/co/NE borders with a warm front arcing east across north-central 
Kansas to southwest MO. Forcing for ascent tied to a low-amplitude 
shortwave trough should result in the surface cyclone tracking 
east-southeast into central Kansas through this evening. A plume of 
middle 50s surface dew points is evident across central Kansas beneath 
an elevated mixed-layer and is contributing to weak buoyancy with 
MUCAPE of 500-1000 j/kg. High-based convection near the cyclone 
should deepen into isolated thunderstorms as it impinges on this 
modest moisture plume. Very steep mid-level lapse rates (likely 
around 8-9 c/km from 700-500 mb) and strong speed shear above the 
level of free convection should yield a discrete supercell or two with large hail as the 
primary hazard, along with strong outflow winds. This risk should be 
maximized in a spatially narrow west-east corridor near the 
north-central Kansas/south-central NE border, given large warm-sector 
mlcin. However, it appears probable that a moderate long-lived 
supercell threat will exist between about 23-04z, and a small Severe 
Thunderstorm Watch could be warranted. 

.Grams.. 03/23/2018 

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


Latitude...Lon 39750091 40250070 40359955 40439811 40299711 40059688 
39559721 39459803 39419939 39510067 39750091