Alert archive / Montana / Mesoscale Discussions in 2012

Mesoscale Discussion 1374

July 3, 201213 counties in Montana

The Storm Prediction Center issued this mesoscale discussion at Jul 3, 2012, 12:58 PM MDT for 13 counties in Montana. It was in force for 92 min.

The area

The outline as issued.

The facts

Issued: Jul 3, 2012, 12:58 PM MDT (18:58 UTC)
Expired: Jul 3, 2012, 2:30 PM MDT
In force: 92 min
Issued by: the Storm Prediction Center
Chance of a watch: 80%

Counties Custer County, MT, Daniels County, MT, Dawson County, MT, Garfield County, MT, McCone County, MT, Petroleum County, MT, Phillips County, MT, Prairie County, MT, Richland County, MT, Roosevelt County, MT, Sheridan County, MT, Valley County, MT, Wibaux County, MT

The radar

The Glasgow radar (KGGW), 77 km from the middle of the area, began a volume at 18:56 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 457Jul 3, 1:35 PM MDT

The nearest sounding before it

Glasgow Intl Airport, MT (KGGW), launched 12:00Z, 7.0 hours before the alert went out and 77 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: 2166 m above ground
0-6 km bulk shear: 44 kt
0-1 km storm-relative helicity: 198 m²/s²
0-3 km storm-relative helicity: 299 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.

459 
ACUS11 KWNS 031859
SWOMCD
SPC MCD 031858
NDZ000-MTZ000-032030-

MESOSCALE DISCUSSION 1374
NWS STORM PREDICTION CENTER NORMAN OK
0158 PM CDT TUE JUL 03 2012

AREAS AFFECTED...ERN MT

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 031858Z - 032030Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...THUNDERSTORM INITIATION IS FORECAST TO OCCUR ACROSS
PORTIONS OF ERN MT DURING THE 19-21Z TIME PERIOD...AND THEN GROW
UPSCALE INTO A LINE AS ACTIVITY APPROACHES WRN ND LATER THIS
EVENING. THREAT FOR DAMAGING WIND GUSTS AND LARGE HAIL WILL
EXIST...WW IS LIKELY.

DISCUSSION...AFTERNOON MESOANALYSIS SHOWS AN AREA OF SURFACE LOW
PRESSURE OVER SWRN SK AHEAD OF A MIDLEVEL SHORTWAVE TROUGH EJECTING
OUT OF THE NRN INTERMOUNTAIN W. A COLD FRONT EXTENDED SWWD FROM THE
LOW INTO SWRN MT...WITH TEMPERATURES AHEAD OF THE FRONT WARMING INTO
THE 90S...AND DEWPOINTS RANGING FROM THE 40S OVER CNTRL MT TO THE
LOW 60S OVER FAR ERN MT/WRN ND. COMBINATION OF STRONG BOUNDARY LAYER
DESTABILIZATION/STEEPENING LOW-LEVEL LAPSE RATES AND FRONTAL FORCING
FOR ASCENT IS AIDING IN HIGH BASED CUMULUS DEVELOPMENT OVER CNTRL
MT. AS THE FRONT AND DEVELOPING CUMULUS ENCOUNTERS DEEPER MOISTURE
OVER ERN MT...THUNDERSTORM INITIATION WILL BE LIKELY. GIVEN LINEAR
FORCING ALONG THE FRONT AND LARGE SURFACE TEMPERATURE-DEWPOINT
SPREADS...LINEAR STORM ORGANIZATION SHOULD OCCUR FAIRLY QUICKLY.
GIVEN THE PRESENCE OF STEEP LOW AND MIDLEVEL LAPSE RATES...MLCAPE
VALUES FROM 1000-2000 J/KG...AND EFFECTIVE BULK SHEAR NEAR 40
KT...LINE SEGMENTS WITH EMBEDDED STRONGER CORES WILL BE CAPABLE OF
PRODUCING DAMAGING WIND GUSTS AND LARGE HAIL.

..GARNER/THOMPSON.. 07/03/2012

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

ATTN...WFO...BIS...BYZ...GGW...TFX...

LAT...LON   48630415 47250399 46350436 46160576 46250744 46610821
            47290853 48350837 48940748 49070523 48630415

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 3, 1:41 PM MDT	Severe Thunderstorm Watch	SPC	Daniels, Dawson, Garfield, McCone, Petroleum, Phillips and 6 more	8 hr
Jul 3, 5:15 PM MDT	Mesoscale Discussion	SPC	Daniels, Dawson, Prairie, Richland, Roosevelt, Sheridan and 1 more	2 hr

Nearby

Mesoscale Discussions in Montana, 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; radar from the NEXRAD Level II archive.