Mesoscale Discussion 666

Issued

May 21, 2016, 2:10 PM MDT (20:10 UTC)

Expired

May 21, 2016, 3:15 PM MDT

In force

65 min

Issued by

the Storm Prediction Center

Chance of a watch

80%

Counties Blaine County, MT, Carbon County, MT, Fergus County, MT, Golden Valley County, MT, Musselshell County, MT, Petroleum County, MT, Phillips County, MT, Yellowstone County, MT

The Billings radar (KBLX), 106 km from the middle of the area, began a volume at 20:11 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 188May 21, 2:25 PM MDT

786 
ACUS11 KWNS 212011
SWOMCD
SPC MCD 212010 
MTZ000-WYZ000-212115-

MESOSCALE DISCUSSION 0666
NWS STORM PREDICTION CENTER NORMAN OK
0310 PM CDT SAT MAY 21 2016

AREAS AFFECTED...CENTRAL MT...FAR NRN WY

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

VALID 212010Z - 212115Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...INTENSE THUNDERSTORM DEVELOPMENT IS POSSIBLE LATER THIS
AFTERNOON WITH A THREAT FOR LARGE HAIL...DAMAGING WIND...AND A
TORNADO OR TWO. WATCH ISSUANCE WILL LIKELY BE REQUIRED SOON.

DISCUSSION...AT 20Z...CONVECTION IS ONGOING ON THE COLD SIDE OF A
NEARLY STATIONARY SFC BOUNDARY DRAPED FROM NWRN WY INTO CENTRAL MT.
A 998 MB SFC LOW IS LOCATED ON THE BOUNDARY ACROSS NWRN WY NEAR
CODY...WITH A WELL-DEFINED RISE-FALL COUPLET NOTED IN CONJUNCTION
WITH THE LOW. STRONG LOW-LEVEL SLY FLOW IS NOTED IN SFC OBS AND IN
THE RIW/BLX VWPS...WITH WIND GUSTS IN EXCESS OF 50 KTS NOTED AT TBX
AWAY FROM ANY CONVECTION. 

RELATIVELY STRONG HEATING IS UNDERWAY TO THE EAST OF THE SFC
BOUNDARY...WITH MID/UPPER 50S DEWPOINTS NOTED ACROSS MUCH OF
CNTRL/ERN MT. WHILE SOME MIXING/DRYING IS EXPECTED IN THE WARM
SECTOR THIS AFTERNOON...STEEP MIDLEVEL LAPSE RATES WILL SUPPORT
MODERATE INSTABILITY...WITH SBCAPE OF 1000-1500 J/KG ALREADY NOTED
IN RECENT MESOANALYSIS ON THE WARM SIDE OF THE BOUNDARY. AS THE LOW
PRESSURE MOVES NNEWD ALONG THE BOUNDARY...SFC-BASED STORM INITIATION
WILL BE POSSIBLE. EFFECTIVE SHEAR OF 50-70 KTS UNDERNEATH VERY
STRONG MIDLEVEL FLOW WILL BE MORE THAN SUFFICIENT FOR ORGANIZED
STORM STRUCTURES. 

RECENT CAM GUIDANCE INDICATES THE POTENTIAL FOR AT LEAST A COUPLE OF
SUPERCELLS MOVING NNEWD ALONG THE BOUNDARY...WHICH WOULD HAVE THE
POTENTIAL FOR LARGE HAIL AND DAMAGING WIND. SOME TORNADO THREAT WILL
ALSO EXIST GIVEN RELATIVELY STRONG LOW-LEVEL SHEAR AND THE POTENTIAL
FOR BOUNDARY INTERACTION...THOUGH THE COLD NATURE OF THE AIRMASS
WEST OF THE FRONT MAY TEMPER THIS THREAT TO SOME EXTENT. SOME
POTENTIAL ALSO EXISTS FOR EVENTUAL UPSCALE GROWTH INTO BOWING LINE
SEGMENTS WITH A GREATER THREAT FOR DAMAGING WIND.

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

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

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

LAT...LON   44820908 45830928 46720928 47620930 48780912 48960883
            48960763 48730740 47910729 46750736 45750762 44910802
            44620886 44820908

Mesoscale Discussions in Montana, 2016Every mesoscale discussion in 2016

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.