Alert archive / Montana / Mesoscale Discussions in 2012

Mesoscale Discussion 859

May 21, 201219 counties in Montana

The Storm Prediction Center issued this mesoscale discussion at May 21, 2012, 2:35 PM MDT for 19 counties in Montana. It was in force for 85 min.

The area

The outline as issued.

The facts

Issued: May 21, 2012, 2:35 PM MDT (20:35 UTC)
Expired: May 21, 2012, 4:00 PM MDT
In force: 85 min
Issued by: the Storm Prediction Center
Chance of a watch: 20%

Counties Broadwater County, MT, Cascade County, MT, Chouteau County, MT, Deer Lodge County, MT, Fergus County, MT, Gallatin County, MT, Golden Valley County, MT, Jefferson County, MT, Judith Basin County, MT, Lewis and Clark County, MT, Madison County, MT, Meagher County, MT, Musselshell County, MT, Park County, MT, Petroleum County, MT, Powell County, MT, Silver Bow County, MT, Sweet Grass County, MT, Wheatland County, MT

The radar

The Great Falls radar (KTFX), 129 km from the middle of the area, began a volume at 20:36 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 nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 8.6 hours before the alert went out and 98 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: 2214 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 95 m²/s²
0-3 km storm-relative helicity: 91 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.

252 
ACUS11 KWNS 212035
SWOMCD
SPC MCD 212035 
MTZ000-212200-

MESOSCALE DISCUSSION 0859
NWS STORM PREDICTION CENTER NORMAN OK
0335 PM CDT MON MAY 21 2012

AREAS AFFECTED...W-CNTRL/CNTRL MT

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 212035Z - 212200Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...MARGINALLY ORGANIZED FAST MOVING LINE SEGMENTS POSING A
THREAT FOR ISOLATED DAMAGING WIND GUSTS WILL BE POSSIBLE THIS
AFTERNOON AND EVENING OVER PORTIONS OF W-CNTRL/CNTRL MT. A WW IS NOT
LIKELY.

DISCUSSION...SURFACE OBSERVATIONS AT 20Z SHOW TEMPERATURES WARMING
INTO THE 80S FROM SWRN INTO ERN MT...WITH 60S AND 70S MORE COMMON
OVER WRN INTO CNTRL MT. THIS SURFACE HEATING COMBINED WITH MARGINAL
LOW-LEVEL MOISTURE /DEWPOINTS GENERALLY IN THE 40S/ IS AIDING IN THE
DEVELOPMENT OF MUCAPE VALUES FROM 250-500 J/KG. THIS DESTABILIZATION
IS RESULTING IN GRADUAL STRENGTHENING OF CONVECTION OVER THE AREA.
GIVEN THE PRESENCE OF 15-20 KT LOW-LEVEL W-SWLY FLOW INCREASING TO
50 KT AT 5 KM AGL /PER TFX VWP/...FAST MOVING LINE SEGMENTS WILL BE
POSSIBLE THROUGH THE AFTERNOON INTO THE EVENING. THOUGH ISOLATED
DAMAGING WIND GUSTS MAY OCCUR...MARGINAL MOISTURE AND INSTABILITY
SHOULD PRECLUDE THE NEED FOR A WW.

..GARNER/WEISS.. 05/21/2012

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

ATTN...WFO...BYZ...GGW...TFX...MSO...

LAT...LON   45990821 45321072 45281246 45971349 47141330 47881169
            48170880 47640767 46800756 45990821

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.