Alert archive / Montana / Mesoscale Discussions in 2021

Mesoscale Discussion 1955

December 4, 20216 counties in Montana

The Storm Prediction Center issued this mesoscale discussion at Dec 4, 2021, 1:46 PM MST for 6 counties in Montana. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Dec 4, 2021, 1:46 PM MST (20:46 UTC)
Expired
Dec 4, 2021, 4:15 PM MST
In force
2 hr
Issued by
the Storm Prediction Center
Concerning
Heavy snow

Counties Dawson County, MT, McCone County, MT, Phillips County, MT, Richland County, MT, Roosevelt County, MT, Valley County, MT

The radar

The Glasgow radar (KGGW), 24 km from the middle of the area, began a volume at 20:47 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

Glasgow Intl Airport, MT (KGGW), launched 12:00Z, 8.8 hours before the alert went out and 26 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-pSkew-T log-p diagram, Glasgow Intl Airport, MT at 12:00Z on 2021-12-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Glasgow Intl Airport, MT at 12:00Z on 2021-12-04The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 84 square meters per square second.1939587897117136156Sfc1 km3 km6 km9 kmRMLM
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
1407 m above ground
0-6 km bulk shear
102 kt
0-1 km storm-relative helicity
84 m²/s²
0-3 km storm-relative helicity
16 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

621 
ACUS11 KWNS 042047
SWOMCD
SPC MCD 042046 
MTZ000-042315-

Mesoscale Discussion 1955
NWS Storm Prediction Center Norman OK
0246 PM CST Sat Dec 04 2021

Areas affected...Northeast Montana

Concerning...Heavy snow 

Valid 042046Z - 042315Z

SUMMARY...A snow band will lift across northeast Montana over the
next 2 hours bringing snowfall rates in excess of 1.5 inches per
hour within the heaviest band.

DISCUSSION...A band of heavy snow has developed in a region of
moderate isentropic ascent across northeast Montana, on the western
extent of strengthening low to mid-level frontogenesis. This band
will continue to lift northeast through the afternoon. The transient
nature of the band may limit higher accumulations in any one
location, but snowfall rates of 1.5+ inches per hour will be
possible for an hour or two as the band passes.

..Bentley.. 12/04/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GGW...TFX...

LAT...LON   48670815 48740667 48490516 48020408 47340408 47150518
            47480652 47780789 47950881 48170900 48340873 48670815

Nearby

Mesoscale Discussions in Montana, 2021Every mesoscale discussion in 2021

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.