Alert archive / Nebraska / Mesoscale Discussions in 2017

Mesoscale Discussion 1502

August 15, 20177 counties in Colorado; 17 counties in Nebraska; 4 counties in South Dakota

The Storm Prediction Center issued this mesoscale discussion at Aug 15, 2017, 2:52 PM MDT for 7 counties in Colorado; 17 counties in Nebraska; 4 counties in South Dakota. It was in force for 113 min.

The area

The outline as issued.

The facts

Issued: Aug 15, 2017, 2:52 PM MDT (20:52 UTC)
Expired: Aug 15, 2017, 4:45 PM MDT
In force: 113 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 28 counties

Logan County, CO, Morgan County, CO, Phillips County, CO, Sedgwick County, CO, Washington County, CO, Weld County, CO, Yuma County, CO, Arthur County, NE, Banner County, NE, Box Butte County, NE, Chase County, NE, Cherry County, NE, Cheyenne County, NE, Deuel County, NE, Garden County, NE, Grant County, NE, Hooker County, NE, Keith County, NE, Kimball County, NE, McPherson County, NE, Morrill County, NE, Perkins County, NE, Sheridan County, NE, Thomas County, NE, Bennett County, SD, Jackson County, SD, Mellette County, SD, Todd County, SD

The radar

The North Platte radar (KLNX), 181 km from the middle of the area, began a volume at 20:54 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 452Aug 15, 4:05 PM MDT

The nearest sounding before it

N. Platte/Lee Bi, NE (KLBF), launched 12:00Z, 8.9 hours before the alert went out and 163 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: 418 J/kg
Mixed-layer CIN: -256 J/kg
Mixed-layer LCL: 763 m above ground
0-6 km bulk shear: 29 kt
0-1 km storm-relative helicity: 62 m²/s²
0-3 km storm-relative helicity: 71 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.5

Open this sounding in Storm Lab

The text

As transmitted.

748 
ACUS11 KWNS 152053
SWOMCD
SPC MCD 152052 
NEZ000-SDZ000-COZ000-WYZ000-152245-

Mesoscale Discussion 1502
NWS Storm Prediction Center Norman OK
0352 PM CDT Tue Aug 15 2017

Areas affected...Northeast CO...western NE...south central SD

Concerning...Severe potential...Watch possible 

Valid 152052Z - 152245Z

Probability of Watch Issuance...60 percent

SUMMARY...Storms will increase in coverage through evening, with a
wind and hail threat.

DISCUSSION...Visible imagery and surface obs show an old outflow
boundary lifting northward across central NE, with surface trough
curling back southwestward into northeast CO. South of these
boundaries, strong heating and ample moisture has led to strong
instability with MUCAPE of 2000-3000 J/kg. Trends have been for CU
to increase in these areas, with further post-outflow air mass
modification likely as heating persists.

The primary cold front extends from western SD into southeast WY,
with scattered storms ongoing over the higher terrain. Other
isolated activity was also noted near the Palmer Divide.

With time, storms over WY should reinforce the cold front, with an
eastward surge through evening into NE and damaging wind potential.
Other isolated cells with hail threat are expected from northeast CO
into southwest NE near the surface trough and outflow boundaries.

..Jewell/Weiss.. 08/15/2017

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

ATTN...WFO...ABR...LBF...UNR...GLD...BOU...CYS...

LAT...LON   39960220 39530286 39360333 39400367 39860422 40420446
            40890440 41620389 42570307 43270247 43790178 43760063
            43240011 41660042 40840095 39960220

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 15, 4:03 PM MDT	Severe Thunderstorm Watch	SPC	Logan, Morgan, Phillips, Sedgwick, Washington, Weld and 1 more	7 hr
Aug 15, 11:33 AM MDT	Mesoscale Discussion	SPC	Antelope, Blaine, Boyd, Burt, Cedar, Cuming and 15 more	87 min
Aug 14, 8:45 PM MDT	Mesoscale Discussion	SPC	Bennett, Jackson, Oglala Lakota	2 hr

Nearby

Mesoscale Discussions in Nebraska, 2017 Mesoscale Discussions in Colorado, 2017 Mesoscale Discussions in South Dakota, 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.