Mesoscale Discussion 1553

Issued

Jul 23, 2012, 1:27 PM MDT (19:27 UTC)

Expired

Jul 23, 2012, 4:00 PM MDT

In force

3 hr

Issued by

the Storm Prediction Center

Chance of a watch

20%

The Billings radar (KBLX), 115 km from the middle of the area, began a volume at 19:26 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.

401 
ACUS11 KWNS 231928
SWOMCD
SPC MCD 231927
MTZ000-WYZ000-IDZ000-232200-

MESOSCALE DISCUSSION 1553
NWS STORM PREDICTION CENTER NORMAN OK
0227 PM CDT MON JUL 23 2012

AREAS AFFECTED...SWRN/CNTRL/ERN MT...FAR NWRN WY

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 231927Z - 232200Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...AN ISOLATED THREAT FOR SVR WIND GUSTS WILL EXIST WITH
THUNDERSTORMS INTO THE EVENING HOURS. GIVEN THE ANTICIPATED SPORADIC
NATURE OF ANY SVR THREAT...THE ISSUANCE OF A WW IS CURRENTLY
UNLIKELY.

DISCUSSION...A COMPACT MID-LEVEL CYCLONIC CIRCULATION SPINNING JUST
NORTH OF THE ID/WA BORDER PER WATER VAPOR IMAGERY IS FORECAST TO
TRACK SLOWLY EWD THROUGH THE EVENING. THE STRONGEST MID-LEVEL HEIGHT
FALLS ACCOMPANYING THIS FEATURE ARE EXPECTED TO REMAIN NORTH OF THE
INTERNATIONAL BORDER...THOUGH MODEST HEIGHT FALLS/ASCENT SHOULD AID
DESTABILIZATION AS FAR SOUTH AS SWRN/S-CNTRL MT. AND...WITH
LOW-LEVEL ASCENT ACCOMPANYING A COLD FRONT LYING FROM N-CNTRL TO
SWRN MT AUGMENTED BY OROGRAPHIC EFFECTS...RECENT VISIBLE SATELLITE
IMAGES INDICATE PATCHES OF BOUNDARY-LAYER CUMULUS BECOMING BETTER
DEFINED FROM THE SWRN MT MOUNTAINS TO THE ABSAROKA RANGE. WITH
ADDITIONAL DIURNAL HEATING...ISOLATED TO WIDELY SCATTERED STORMS
WILL LIKELY EVOLVE FROM THE CUMULUS FIELD DURING THE NEXT COUPLE OF
HOURS...WITH ADDITIONAL STORM DEVELOPMENT POSSIBLE ALONG A
PRE-FRONTAL TROUGH/WIND-SHIFT AXIS EXTENDING FROM EAST OF HAVRE TO
WEST OF BILLINGS.

INSTABILITY IS RATHER LIMITED AHEAD OF THE FRONT...WITH DEEP
VERTICAL MIXING ALLOWING SFC DEWPOINTS TO HAVE DROPPED INTO THE
UPPER 40S TO THE MIDDLE 50S AS TEMPERATURES HAVE CLIMBED INTO THE
MIDDLE 80S TO THE MIDDLE 90S. MODIFIED 12Z GREAT FALLS AND GLASGOW
RAOBS INDICATE THAT 500-1000 J/KG OF MLCAPE EXIST...HIGHEST EAST OF
THE PRE-FRONTAL TROUGH AXIS WHERE SFC DEWPOINTS ARE RELATIVELY
HIGHER. THIS DEGREE OF INSTABILITY MAY BE SUFFICIENT FOR A FEW
INTENSE STORMS WITH SVR WIND GUSTS...AS STEEP LOW-LEVEL LAPSE RATES
SUPPORT DCAPE OF 1000-1500 J/KG IN MANY LOCATIONS.

IN ADDITION TO LIMITED INSTABILITY...THE PRIMARY MID-LEVEL SPEED MAX
AND STRONGEST DEEP SHEAR ARE ONLY FORECAST TO GRAZE NWRN PARTS OF
THE MARGINALLY UNSTABLE SECTOR. AS SUCH...ONLY LIMITED SPATIAL
OVERLAP OF THE AFOREMENTIONED BUOYANCY WITH EFFECTIVE BULK SHEAR
MAGNITUDES AOA 30 KT IS EXPECTED. THIS SHOULD LIMIT THE THREAT FOR
ORGANIZED/PERSISTENT STORMS. HOWEVER...STORM STRENGTH EAST OF THE
PRE-FRONTAL TROUGH AXIS MAY BE MARGINALLY BOLSTERED BY WEAK
LOW-TO-MID-LEVEL DIRECTIONAL SHEAR OWING TO RELATIVELY BACKED
LOW-LEVEL FLOW.

WHILE CONVECTIVE TRENDS WILL CONTINUE TO BE MONITORED...SVR TSTM
WATCH ISSUANCE IS CURRENTLY UNLIKELY OWING TO THE ANTICIPATED
ISOLATED NATURE OF ANY SVR THREAT.

..COHEN/HART.. 07/23/2012

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

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

LAT...LON   45860651 44781002 44561181 44561254 44991319 45631207
            46501083 47551051 48901013 48970927 48960790 48880667
            48480571 47270516 45860651

Mesoscale Discussions in Montana, 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.