Mesoscale Discussion 1071

Issued

Jun 5, 2012, 12:54 PM MDT (18:54 UTC)

Expired

Jun 5, 2012, 3:00 PM MDT

In force

2 hr

Issued by

the Storm Prediction Center

Chance of a watch

95%

Counties Fremont County, ID, Teton County, ID, Broadwater County, MT, Carbon County, MT, Gallatin County, MT, Golden Valley County, MT, Madison County, MT, Meagher County, MT, Musselshell County, MT, Park County, MT, Stillwater County, MT, Sweet Grass County, MT, Wheatland County, MT, Yellowstone County, MT, Park County, WY, Teton County, WY

The Billings radar (KBLX), 155 km from the middle of the area, began a volume at 18:53 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.

• Severe Thunderstorm Watch 359Jun 5, 1:40 PM MDT

209 
ACUS11 KWNS 051855
SWOMCD
SPC MCD 051854
MTZ000-WYZ000-IDZ000-052100-

MESOSCALE DISCUSSION 1071
NWS STORM PREDICTION CENTER NORMAN OK
0154 PM CDT TUE JUN 05 2012

AREAS AFFECTED...SWRN/S-CNTRL MT...NWRN WY...PARTS OF SERN ID

CONCERNING...SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY

VALID 051854Z - 052100Z

PROBABILITY OF WATCH ISSUANCE...95 PERCENT

SUMMARY...THE THREAT FOR SVR THUNDERSTORMS WILL INCREASE THIS
AFTERNOON AS A POTENT PACIFIC STORM SYSTEM AFFECTS THE NRN
ROCKIES...WITH DAMAGING WINDS AND SEVERE HAIL OF CONCERN ACROSS
PARTS OF THE AREA. THE SVR THREAT WILL BE GREATEST ACROSS
S-CNTRL/SWRN MT...WHERE A SEVERE THUNDERSTORM WATCH WILL BE NEEDED
BY 20Z-21Z.

DISCUSSION...VISIBLE SATELLITE IMAGERY INDICATES THAT TOWERING
CUMULUS CONTINUES TO DEVELOP OVER THE MOUNTAINS OF SWRN MONTANA AND
ADJACENT PARTS OF WRN WY AND SERN ID...INCLUDING THE
GALLATIN...ABSAROKA...AND TETON RANGES. THIS IS PARTLY IN RESPONSE
TO DESTABILIZATION IN ASSOCIATION WITH /1/ INCREASING LARGE-SCALE
ASCENT IN ADVANCE OF A POTENT PACIFIC TROUGH...WITH 500-MB HEIGHT
FALLS IN EXCESS OF 90 GEOPOTENTIAL METERS PER 12 HRS...ALONG WITH
/2/ WIDESPREAD INSOLATION/DIABATIC HEATING. IN ADDITION TO
OROGRAPHICALLY-INDUCED ASCENT...MESOSCALE ASCENT IS ALSO BEING
SUPPORTED BY A COLD FRONT CROSSING THE REGION IN ASSOCIATION WITH
THE TROUGH...ROUGHLY EXTENDING FROM A SFC LOW NEAR BOZEMAN MT SWD
TOWARD SALT LAKE CITY UT. A WEAKENING STATIONARY FRONT EXTENDS ENE
OF THE SFC LOW INTO E-CNTRL MT...WITH A DEVELOPING WARM FRONT INTO
N-CNTRL MT.

ADDITIONAL DIURNAL HEATING...COMBINED WITH MODEST LOW-LEVEL MOISTURE
SOUTH OF THE STATIONARY FRONT/DEVELOPING WARM FRONT -- SFC DEWPOINTS
PRIMARILY IN THE MID 30S TO THE 40S -- WILL YIELD MLCAPE VALUES OF
400-1000 J/KG. THE HIGHEST OF THESE VALUES WILL BE IN
MONTANA...WHERE VERTICAL MIXING HAS NOT BEEN AS STRONG AS FARTHER
SOUTH ACROSS WY/ID AS WY/ID DEWPOINTS HAVE MIXED OUT INTO THE 30S.

CONVECTION IS FORECAST TO EVOLVE/INTENSIFY FROM THE AFOREMENTIONED
MOUNTAIN RANGES AS FORCING FOR ASCENT INCREASES...WITH AN INCREASING
SVR THREAT AS WELL. STRONG MERIDIONAL FLOW IN ASSOCIATION WITH THE
TROUGH -- E.G. SAMPLED BY THE SALT LAKE CITY UT AND POCATELLO ID
SITES INDICATING 30-50 KT OF SLY FLOW WITHIN THE 2-4-KM-AGL LAYER --
WILL LIKELY BE MIXED TO THE SFC VIA CONVECTIVE MASS TRANSPORT
PROCESSES AS LOW-LEVEL LAPSE RATES CONTINUE TO STEEPEN WITH
SUBSTANTIAL DEWPOINT DEPRESSIONS. EFFECTIVE BULK SHEAR MAGNITUDES OF
40-50 KT WILL SUPPORT ORGANIZED STORM STRUCTURES INCLUDING LINE
SEGMENTS AND PERHAPS SOME SUPERCELLS...WHICH WILL LIKELY BE
ACCOMPANIED BY SVR WIND GUSTS. AND...WITH 7-8.5 C/KM LAPSE RATES
WITHIN THE 700-500-MB LAYER COMBINED WITH THE STRONG DEEP
SHEAR...SVR HAIL WILL BE OF CONCERN...PARTICULARLY WITH SUPERCELL
STRUCTURES.

..COHEN/MEAD.. 06/05/2012

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

ATTN...WFO...BYZ...RIW...TFX...PIH...

LAT...LON   46510810 44950856 43430940 42761046 43021107 44371161
            45561205 46311203 46741049 46510810

Mesoscale Discussions in Montana, 2012Mesoscale Discussions in Idaho, 2012Mesoscale Discussions in Wyoming, 2012Every mesoscale discussion in 2012

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.