Alert archive / Montana / Mesoscale Discussions in 2012

Mesoscale Discussion 31

January 18, 20127 counties in Montana; Park County, Teton County, Wyoming

The Storm Prediction Center issued this mesoscale discussion at Jan 18, 2012, 1:44 PM MST for 7 counties in Montana; Park County, Teton County, Wyoming. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Jan 18, 2012, 1:44 PM MST (20:44 UTC)
Expired: Jan 18, 2012, 5:45 PM MST
In force: 4 hr
Issued by: the Storm Prediction Center

Counties Carbon County, MT, Golden Valley 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 radar

The Billings radar (KBLX), 112 km from the middle of the area, began a volume at 20:42 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

Riverton, WY (KRIW), launched 12:00Z, 8.7 hours before the alert went out and 217 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: 1932 m above ground
0-6 km bulk shear: 138 kt
0-1 km storm-relative helicity: 275 m²/s²
0-3 km storm-relative helicity: 507 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.

560 
ACUS11 KWNS 182044
SWOMCD
SPC MCD 182044 
MTZ000-WYZ000-190045-

MESOSCALE DISCUSSION 0031
NWS STORM PREDICTION CENTER NORMAN OK
0244 PM CST WED JAN 18 2012

AREAS AFFECTED...NWRN WY...S-CNTRL MT

CONCERNING...HEAVY SNOW 

VALID 182044Z - 190045Z

SNOWFALL RATES AOA 1 INCH PER HR /APPROACHING 2 INCHES PER HR AT
HIGHER ELEVATIONS OF NWRN WY/ ARE LIKELY AFTER 21Z. 

20Z SFC OBS SHOW AN ALGID ARCTIC AIR MASS WEDGED ACROSS THE NRN
PLAINS IN THE LEE OF THE BIG HORNS/NRN ROCKY MTNS...WHERE
TEMPERATURES OF -5 TO -10 DEG F HAVE BEEN OBSERVED. LIGHT SNOWFALL
HAS BEEN FALLING OVER THE PAST SEVERAL HRS ACROSS THIS AREA AS WELL.
A GENERAL INCREASE IN SNOWFALL RATES IS EXPECTED TO OCCUR THROUGH
21Z AS A LONG FETCH OF MIDLEVEL MOISTURE ASSOCIATED WITH A STRONG
POLAR JET OVERSPREADS THE AREA. THE HIGHEST RATES EXPECTED TO OCCUR
OVER THE ABSAROKA RANGE AND PORTIONS OF YELLOWSTONE NP...WHERE
STRONG WLY UPSLOPE FLOW /30-40 KTS IN 0-2 KM AGL LAYER PER SFC VWP
DATA/ AND A DEEP DENDRITIC GROWTH LAYER WILL CONTRIBUTE TO SNOWFALL
RATES APPROACHING 2 INCHES PER HR. FARTHER N...OVER PORTIONS OF
S-CNTRL MT...WEAK UPSLOPE NELY FLOW OVER THE HIGH PLAINS...COMBINED
WITH FAVORABLE POSITIONING OF LOW/MIDLEVEL FRONTOGENETIC
MAXIMUM...WILL SUPPORT SNOWFALL RATES NEAR 1 INCH PER HR.
ADDITIONALLY...THE EXCEPTIONALLY COLD AIR MASS WILL RESULT IN
SNOWFALL-LIQUID EQUIVALENT RATIOS EXCEEDING 35-1. MULTI-MODEL
CONSENSUS SUGGESTS PRECIPITATION WILL PERSIST OVERNIGHT...BUT THE
GENERAL TREND IS FOR RATES TO WEAKEN AFTER 03Z.

..ROGERS.. 01/18/2012

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

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

LAT...LON   43930943 43060959 42840995 43271093 44871103 46451031
            46810957 46480847 46210782 45780728 45500737 45250795
            45140885 44840947 44570956 43930943

Nearby

Mesoscale Discussions in Montana, 2012 Mesoscale Discussions in Wyoming, 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.