Alert archive / North Dakota / Mesoscale Discussions in 2018

Mesoscale Discussion 993

July 2, 20184 counties in Montana; 7 counties in North Dakota; Harding County, Perkins County, South Dakota

The Storm Prediction Center issued this mesoscale discussion at Jul 2, 2018, 11:01 PM MDT for 4 counties in Montana; 7 counties in North Dakota; Harding County, Perkins County, South Dakota. It was in force for 89 min.

The area

The outline as issued.

The facts

Issued: Jul 2, 2018, 11:01 PM MDT (05:01 UTC)
Expired: Jul 3, 2018, 12:30 AM MDT
In force: 89 min
Issued by: the Storm Prediction Center

Counties Carter County, MT, Custer County, MT, Fallon County, MT, Powder River County, MT, Adams County, ND, Bowman County, ND, Golden Valley County, ND, Grant County, ND, Hettinger County, ND, Slope County, ND, Stark County, ND, Harding County, SD, Perkins County, SD

The radar

The Rapid City radar (KUDX), 240 km from the middle of the area, began a volume at 05:03 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 258Jul 3, 12:55 AM MDT

The nearest sounding before it

Rapid City, SD (KRAP), launched 00:00Z, 5.0 hours before the alert went out and 245 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: 1927 J/kg
Mixed-layer CIN: -82 J/kg
Mixed-layer LCL: 1454 m above ground
0-6 km bulk shear: 56 kt
0-1 km storm-relative helicity: 203 m²/s²
0-3 km storm-relative helicity: 353 m²/s²
Significant tornado parameter: 1.5
Supercell composite: 18.0

Open this sounding in Storm Lab

The text

As transmitted.

977 
ACUS11 KWNS 030501
SWOMCD
SPC MCD 030501 
SDZ000-NDZ000-MTZ000-030630-

Mesoscale Discussion 0993
NWS Storm Prediction Center Norman OK
1201 AM CDT Tue Jul 03 2018

Areas affected...Portions of southeastern MT...southwestern ND...and
northwestern SD

Concerning...Severe Thunderstorm Watch 256...257...

Valid 030501Z - 030630Z

The severe weather threat for Severe Thunderstorm Watch 256, 257
continues.

SUMMARY...A few long-lived thunderstorm clusters should continue to
pose a large hail and damaging wind threat as they move eastward. A
small northward extension in area of WW 256 may be needed in western
ND if current radar trends continue.

DISCUSSION...The environment downstream of ongoing convection in
southeastern MT will probably remain conducive of at least some
severe hail/wind risk for the next couple of hours. Multiple
measured severe wind gusts have been observed since 03Z with this
activity, along with a few 1.00-1.75 inch hail reports. Strong
effective bulk shear around 50-65 kt and and MLCAPE of 500-1000 J/kg
will likely support continued supercell/short bowing segments.
Current trajectory of these thunderstorms suggest a small northward
extension of WW 256 in western ND may be needed (mainly for Golden
Valley and Billings counties). A longer-lived severe threat with
these thunderstorms into more of southern ND and northern SD remains
unclear, but there is at least some potential for an extension of WW
256 in time or a new Severe Thunderstorm Watch based on convective
trends.

..Gleason.. 07/03/2018

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

ATTN...WFO...ABR...BIS...UNR...BYZ...GGW...

LAT...LON   45310629 46310633 46840515 46980383 47020218 46720143
            45610144 45270202 45310629

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 2, 6:59 PM MDT	Severe Thunderstorm Watch	SPC	Big Horn, Carter, Custer, Fallon, Powder River, Rosebud and 2 more	6 hr
Jul 2, 8:50 PM MDT	Mesoscale Discussion	SPC	Big Horn, Carter, Custer, Fallon, Powder River, Rosebud and 2 more	115 min
Jul 3, 2:25 PM MDT	Mesoscale Discussion	SPC	Big Horn, Carter, Powder River	2 hr
Jul 3, 4:42 PM MDT	Severe Thunderstorm Watch	SPC	Carter	7 hr
Jul 2, 6:36 PM MDT	Severe Thunderstorm Watch	SPC	Adams, Bowman, Burleigh, Dickey, Emmons, Grant and 13 more	9 hr
Jul 2, 10:32 PM MDT	Mesoscale Discussion	SPC	Cass, Richland	88 min
Jul 3, 12:59 AM MDT	Severe Thunderstorm Watch	SPC	Adams, Barnes, Billings, Bowman, Burleigh, Cass and 26 more	7 hr
Jul 3, 3:15 AM MDT	Mesoscale Discussion	SPC	Adams, Barnes, Billings, Bowman, Burleigh, Cass and 26 more	90 min
Jul 3, 6:01 AM MDT	Mesoscale Discussion	SPC	Barnes, Cass, Dickey, Kidder, LaMoure, Logan and 6 more	119 min
Jul 3, 5:16 PM MDT	Mesoscale Discussion	SPC	Dickey, LaMoure, McIntosh, Ransom, Richland, Sargent	2 hr
Jul 3, 5:42 PM MDT	Severe Thunderstorm Watch	SPC	Brown, Clark, Day, Edmunds, Faulk, Hand and 8 more	4 hr

Nearby

Mesoscale Discussions in North Dakota, 2018 Mesoscale Discussions in Montana, 2018 Mesoscale Discussions in South Dakota, 2018 Every mesoscale discussion in 2018

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.