Alert archive / Montana / Mesoscale Discussions in 2012

Mesoscale Discussion 1684

August 2, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Aug 2, 2012, 1:44 PM MDT for 4 states. It was in force for 31 min.

The area

The outline as issued.

The facts

Issued: Aug 2, 2012, 1:44 PM MDT (19:44 UTC)
Expired: Aug 2, 2012, 2:15 PM MDT
In force: 31 min
Issued by: the Storm Prediction Center
Chance of a watch: 80%

All 27 counties

Carter County, MT, Custer County, MT, Dawson County, MT, Fallon County, MT, McCone County, MT, Powder River County, MT, Prairie County, MT, Richland County, MT, Roosevelt County, MT, Wibaux County, MT, Adams County, ND, Billings County, ND, Bowman County, ND, Dunn County, ND, Golden Valley County, ND, Hettinger County, ND, McKenzie County, ND, Slope County, ND, Stark County, ND, Williams County, ND, Butte County, SD, Harding County, SD, Lawrence County, SD, Meade County, SD, Perkins County, SD, Campbell County, WY, Crook County, WY

The watches that followed

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

Severe Thunderstorm Watch 551Aug 2, 2:05 PM MDT

The nearest sounding before it

Rapid City, SD (KRAP), launched 12:00Z, 7.7 hours before the alert went out and 269 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 2040 m above ground
0-6 km bulk shear: 30 kt
0-1 km storm-relative helicity: -120 m²/s²
0-3 km storm-relative helicity: -117 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

841 
ACUS11 KWNS 021945
SWOMCD
SPC MCD 021944
SDZ000-NDZ000-MTZ000-WYZ000-022015-

MESOSCALE DISCUSSION 1684
NWS STORM PREDICTION CENTER NORMAN OK
0244 PM CDT THU AUG 02 2012

AREAS AFFECTED...ERN MT/WRN ND/NERN WY/WRN SD

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 021944Z - 022015Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...A SEVERE TSTM WATCH WILL LIKELY BE NEEDED PRIOR TO 20Z
ACROSS MUCH OF FAR ERN MT...NERN WY INTO WRN ND AND NWRN SD.
PRIMARY THREATS WILL BE DAMAGING WINDS AND LARGE HAIL.

DISCUSSION...AFTERNOON SURFACE ANALYSIS SHOWED AN AREA OF LOW
PRESSURE CENTERED OVER EAST CENTRAL MT WITH A DRY LINE/LEE TROUGH
EXTENDING SWD THROUGH SERN MT INTO ERN WY.  REGIONAL RADAR IMAGERY
INDICATED A FEW TSTMS HAVE ALREADY DEVELOPED ALONG THE DRY LINE IN
CUSTER AND POWDER RIVER COUNTIES MT AND NERN JOHNSON AND CAMPBELL
COUNTIES WY.  DESPITE MARGINAL MOISTURE /SURFACE DEWPOINTS IN THE
UPPER 40S TO LOWER 50S/...OBJECTIVE ANALYSES INDICATED THE AIR MASS
HAS BECOME MODERATELY UNSTABLE WITH MLCAPE UP TO 1500 J/KG ALONG AND
E OF THE DRY LINE.

THE PRIMARY THREAT AREA IS EXPECTED TO BE OVER ERN MT TO NERN WY
WITH ACTIVITY SPREADING EWD INTO WRN ND AND NWRN SD.  OTHER ONGOING
STORMS OVER EAST CENTRAL MT INTO WRN/SWRN ND ARE ATTENDANT TO LOW
LEVEL WAA AND ARE NOT EXPECTED TO BECOME SEVERE DUE TO LIMITED
INSTABILITY WITH EWD EXTENT.  THUS...ADDITIONAL SURFACE HEATING E OF
THE DRY LINE WILL FURTHER DESTABILIZE THE AIR MASS.  THIS COMBINED
WITH MORE THAN SUFFICIENT BULK SHEAR AROUND 35 KT...MULTICELLS AND A
FEW SUPERCELLS WILL BE POSSIBLE. DAMAGING WINDS WILL BE A THREAT
GIVEN THE DEEPLY MIXED BOUNDARY LAYER...STEEP LOW LEVEL LAPSE RATES
AND LARGE DCAPE OF 1000-2000 J/KG.  STEEP MIDLEVEL LAPSE RATES WILL
INCREASE THE HAIL THREAT.

..PETERS/WEISS.. 08/02/2012

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

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

LAT...LON   44210605 45540581 47280671 48320666 48600472 48530296
            48110233 46400184 45680156 44250306 43950443 44210605

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 2, 2:03 PM MDT	Severe Thunderstorm Watch	SPC	Carter, Custer, Daniels, Dawson, Fallon, Garfield and 8 more	7 hr
Aug 1, 6:35 PM MDT	Mesoscale Discussion	SPC	Brookings, Codington, Deuel, Grant, Hamlin, Kingsbury and 3 more	55 min
Aug 1, 7:19 PM MDT	Mesoscale Discussion	SPC	Bon Homme, Clay, Union, Yankton	56 min

Nearby

Mesoscale Discussions in Montana, 2012 Mesoscale Discussions in North Dakota, 2012 Mesoscale Discussions in South Dakota, 2012 Every mesoscale discussion in 2012

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.