Alert archive / Montana / Mesoscale Discussions in 2016

Mesoscale Discussion 667

May 21, 20168 counties in Montana; 8 counties in Wyoming

The Storm Prediction Center issued this mesoscale discussion at May 21, 2016, 2:54 PM MDT for 8 counties in Montana; 8 counties in Wyoming. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: May 21, 2016, 2:54 PM MDT (20:54 UTC)
Expired: May 21, 2016, 5:00 PM MDT
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 40%

Counties Carter County, MT, Custer County, MT, Dawson County, MT, Fallon County, MT, Powder River County, MT, Prairie County, MT, Richland County, MT, Wibaux County, MT, Campbell County, WY, Converse County, WY, Crook County, WY, Goshen County, WY, Laramie County, WY, Niobrara County, WY, Platte County, WY, Weston County, WY

The radar

The Rapid City radar (KUDX), 178 km from the middle of the area, began a volume at 20:57 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 189May 21, 5:00 PM MDT

The nearest sounding before it

Rapid City, SD (KRAP), launched 12:00Z, 8.9 hours before the alert went out and 173 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: 13 J/kg
Mixed-layer CIN: -492 J/kg
Mixed-layer LCL: 762 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 9 m²/s²
0-3 km storm-relative helicity: 148 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

817 
ACUS11 KWNS 212055
SWOMCD
SPC MCD 212054 
SDZ000-NDZ000-NEZ000-MTZ000-WYZ000-212300-

MESOSCALE DISCUSSION 0667
NWS STORM PREDICTION CENTER NORMAN OK
0354 PM CDT SAT MAY 21 2016

AREAS AFFECTED...ERN MT...ERN WY

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 212054Z - 212300Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE LATER THIS
AFTERNOON/EVENING...WITH A PRIMARY THREAT OF LARGE HAIL AND DAMAGING
WINDS.

DISCUSSION...CONVECTION HAS THUS FAR BEEN SLOW TO DEVELOP ACROSS
PORTIONS OF ERN WY/MT...WITH CLOUDINESS LIMITING THE AMOUNT OF
HEATING THUS FAR. HOWEVER...SOME BREAKS HAVE RECENTLY BEEN NOTED
ACROSS SERN MT INTO ERN WY...WITH TEMPERATURES RISING INTO THE
MID/UPPER 70S. STEEP MIDLEVEL LAPSE RATES ARE SUPPORTING SBCAPE OF
1500-2000 J/KG ACROSS THE AREA...WHILE MODERATE MIDLEVEL FLOW IS
RESULTING IN EFFECTIVE SHEAR OF 40-50 KTS. THESE PARAMETERS WOULD
SUPPORT A RISK OF SUPERCELLS IF DEEP CONVECTION CAN INITIATE. THERE
IS SOME VARIANCE IN RECENT GUIDANCE REGARDING TIMING AND COVERAGE OF
INITIATION...BUT MOST GUIDANCE SUGGESTS AT LEAST ISOLATED
DEVELOPMENT BY 22-00Z. LARGE HAIL WILL BE POSSIBLE GIVEN MODERATE
INSTABILITY AND STEEP MIDLEVEL LAPSE RATES...WHILE ISOLATED DAMAGING
WINDS WILL ALSO BE POSSIBLE...ESPECIALLY IN AREAS THAT EXPERIENCE
GREATER HEATING/MIXING OF THE BOUNDARY LAYER. WW ISSUANCE IS
POSSIBLE SOMETIME IN THE NEXT 1-2 HRS IF IT APPEARS THAT INITIATION
IS IMMINENT AND COVERAGE WARRANTS.

..DEAN/HART.. 05/21/2016

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...BIS...UNR...CYS...BYZ...GGW...

LAT...LON   41240565 43020584 45150581 47020587 47930557 47970445
            46030403 44130408 41450402 41150435 41160519 41240565

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 21, 2:10 PM MDT	Mesoscale Discussion	SPC	Blaine, Carbon, Fergus, Golden Valley, Musselshell, Petroleum and 2 more	65 min
May 21, 2:26 PM MDT	Severe Thunderstorm Watch	SPC	Big Horn, Daniels, Dawson, Fergus, Garfield, Golden Valley and 13 more	7 hr
May 21, 4:37 PM MDT	Mesoscale Discussion	SPC	Big Horn, Garfield, Musselshell, Petroleum, Phillips, Rosebud and 3 more	53 min
May 21, 5:03 PM MDT	Severe Thunderstorm Watch	SPC	Carter, Custer, Fallon, Powder River	5 hr

Nearby

Mesoscale Discussions in Montana, 2016 Mesoscale Discussions in Wyoming, 2016 Every mesoscale discussion in 2016

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.