Alert archive / Nebraska / Mesoscale Discussions in 2017

Mesoscale Discussion 721

May 15, 20176 counties in Kansas; 29 counties in Nebraska

The Storm Prediction Center issued this mesoscale discussion at May 15, 2017, 5:58 PM CDT for 6 counties in Kansas; 29 counties in Nebraska. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: May 15, 2017, 5:58 PM CDT (22:58 UTC)
Expired: May 15, 2017, 8:00 PM CDT
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 35 counties

Jewell County, KS, Norton County, KS, Osborne County, KS, Phillips County, KS, Rooks County, KS, Smith County, KS, Adams County, NE, Boone County, NE, Buffalo County, NE, Clay County, NE, Custer County, NE, Dawson County, NE, Franklin County, NE, Frontier County, NE, Furnas County, NE, Garfield County, NE, Gosper County, NE, Greeley County, NE, Hall County, NE, Hamilton County, NE, Harlan County, NE, Howard County, NE, Kearney County, NE, Merrick County, NE, Nance County, NE, Nuckolls County, NE, Phelps County, NE, Platte County, NE, Polk County, NE, Red Willow County, NE, Sherman County, NE, Valley County, NE, Webster County, NE, Wheeler County, NE, York County, NE

The radar

The Grand Island radar (KUEX), 90 km from the middle of the area, began a volume at 22:59 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 216May 15, 6:50 PM CDT

The nearest sounding before it

N. Platte/Lee Bi, NE (KLBF), launched 12:00Z, 11.0 hours before the alert went out and 117 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 225 J/kg
Mixed-layer CIN: -569 J/kg
Mixed-layer LCL: 1462 m above ground
0-6 km bulk shear: 33 kt
0-1 km storm-relative helicity: 295 m²/s²
0-3 km storm-relative helicity: 286 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

799 
ACUS11 KWNS 152259
SWOMCD
SPC MCD 152258 
NEZ000-KSZ000-160100-

Mesoscale Discussion 0721
NWS Storm Prediction Center Norman OK
0558 PM CDT Mon May 15 2017

Areas affected...south-central into central NE and north-central KS

Concerning...Severe potential...Watch possible 

Valid 152258Z - 160100Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms will likely move northeastward into the
discussion area from northwestern KS.  Isolated large hail/localized
severe gusts will be the initial threats.  The severe risk may
transition to primarily scattered strong/severe gusts later this
evening.

DISCUSSION...Subjective surface analysis places a stationary frontal
zone near the Platte River in south-central NE.  Radar mosaic early
this evening shows intensifying severe thunderstorms near the I-70
corridor in western KS/eastern CO.  This activity is forecast to
move downstream into the northern periphery of severe thunderstorm
watch 213 and eventually into south-central NE this evening as a
southerly LLJ strengthens to 50-kt across the central Great Plains. 
RAP model soundings depict very steep 700-500 mb lapse rates (8
degrees C/km).  The KUEX 88-D VAD shows strengthening and veering
flow with height in the lowest 2-km which is surmounted by 40-kt
500-mb flow---yielding 40-kt 0-6 km shear.  As low-level moisture
gradually increases this evening on the nose of the LLJ, diurnal
cooling will be slowed and large buoyancy will be maintained. 
Short-term models indicate scattered strong/severe gusts may evolve
with mature convection later this evening from rather efficient
downdrafts owing to the very steep lapse rate environment.  As a
result, a transition from a large hail/wind threat to primarily a
wind risk is anticipated during the late evening hours.

..Smith/Guyer.. 05/15/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...OAX...GID...LBF...GLD...

LAT...LON   41310066 42049918 41999779 41379705 39379851 39149952
            40240069 41310066

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 15, 3:06 PM CDT	Mesoscale Discussion	SPC	Finney, Gove, Grant, Gray, Greeley, Hamilton and 13 more	114 min
May 15, 3:44 PM CDT	Severe Thunderstorm Watch	SPC	Cheyenne, Decatur, Finney, Gove, Graham, Grant and 20 more	7 hr
May 15, 6:53 PM CDT	Severe Thunderstorm Watch	SPC	Jewell, Osborne, Phillips, Rooks, Smith	6 hr
May 15, 4:07 PM CDT	Mesoscale Discussion	SPC	Box Butte, Dawes, Scotts Bluff, Sioux	113 min
May 15, 5:40 PM CDT	Severe Thunderstorm Watch	SPC	Box Butte, Dawes, Sheridan, Sioux	7 hr

Nearby

Mesoscale Discussions in Nebraska, 2017 Mesoscale Discussions in Kansas, 2017 Every mesoscale discussion in 2017

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.