Alert archive / Montana / Mesoscale Discussions in 2021

Mesoscale Discussion 1851

October 13, 20214 states

The Storm Prediction Center issued this mesoscale discussion at Oct 13, 2021, 3:58 AM MDT for 4 states. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Oct 13, 2021, 3:58 AM MDT (09:58 UTC)
Expired: Oct 13, 2021, 10:00 AM MDT
In force: 6 hr
Issued by: the Storm Prediction Center
Concerning: Heavy snow

Counties Carter County, MT, Custer County, MT, Dawson County, MT, Fallon County, MT, Powder River County, MT, Prairie County, MT, Wibaux County, MT, Bowman County, ND, Golden Valley County, ND, Butte County, SD, Harding County, SD, Lawrence County, SD, Campbell County, WY, Converse County, WY, Crook County, WY, Goshen County, WY, Niobrara County, WY, Platte County, WY, Weston County, WY

The radar

The Rapid City radar (KUDX), 142 km from the middle of the area, began a volume at 09:56 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

Rapid City, SD (KUNR), launched 00:00Z, 10.0 hours before the alert went out and 140 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: 1 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 496 m above ground
0-6 km bulk shear: 62 kt
0-1 km storm-relative helicity: 542 m²/s²
0-3 km storm-relative helicity: 1101 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

426 
ACUS11 KWNS 130959
SWOMCD
SPC MCD 130958 
SDZ000-NDZ000-NEZ000-MTZ000-WYZ000-131600-

Mesoscale Discussion 1851
NWS Storm Prediction Center Norman OK
0458 AM CDT Wed Oct 13 2021

Areas affected...Portions of eastern WY...the extreme western NE
Panhandle...the far western Dakotas...and southeastern into
east-central MT

Concerning...Heavy snow 

Valid 130958Z - 131600Z

SUMMARY...Moderate to heavy snowfall, with rates around 1-1.5 inches
per hour, should occur this morning. Near-blizzard conditions are
also possible with strong/gusty winds.

DISCUSSION...A mature mid/upper-level cyclone evident on water vapor
satellite imagery will continue to eject northeastward across the
central/northern High Plains this morning. A deformation band on the
back side of the cyclone is beginning to fill in as low/mid-level
frontogenetic forcing increases. Current expectations are that a
mostly north-south oriented band of moderate to heavy snow will
develop over parts of eastern WY/MT into the western Dakotas over
the next few hours this morning, and gradually shift northward with
time. Even though low-level temperatures are marginal (generally
28-33 degrees F), strong cooling aloft associated with the upper low
should support snow as the main precipitation type. Lift through the
saturated dendritic-growth layer and consensus of latest
high-resolution guidance both suggest snowfall rates of 1-1.5 inches
per hours will likely be common, with locally greater rates
possible. Finally, near-blizzard conditions with reduced
visibilities should also occur across this region, as a strong
pressure gradient and gusty winds will exist on the back side of a
surface low that will develop northward from NE into central SD this
morning. Indeed, blizzard conditions have recently been reported at
KDGW in eastern WY.

..Gleason.. 10/13/2021

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

ATTN...WFO...BIS...UNR...CYS...BYZ...GGW...RIW...

LAT...LON   42910372 41880397 41810465 42120527 42820597 44540615
            45750611 46820566 47510489 47660416 47460363 46330348
            45170341 44030337 43740364 42910372

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Oct 13, 2:10 PM MDT	Mesoscale Discussion	SPC	Dickey, LaMoure, McIntosh, Ransom, Sargent	65 min

Nearby

Mesoscale Discussions in Montana, 2021 Mesoscale Discussions in Wyoming, 2021 Mesoscale Discussions in South Dakota, 2021 Every 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.