Mesoscale Discussion 1876

Issued

Oct 19, 2021, 11:22 AM MDT (17:22 UTC)

Expired

Oct 19, 2021, 3:15 PM MDT

In force

4 hr

Issued by

the Storm Prediction Center

Concerning

Heavy snow

Counties Albany County, WY, Converse County, WY, Natrona County, WY, Platte County, WY

The Riverton/Lander radar (KRIW), 190 km from the middle of the area, began a volume at 17:24 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.

268 
ACUS11 KWNS 191723
SWOMCD
SPC MCD 191722 
WYZ000-192115-

Mesoscale Discussion 1876
NWS Storm Prediction Center Norman OK
1222 PM CDT Tue Oct 19 2021

Areas affected...portions of eastern/central Wyoming

Concerning...Heavy snow 

Valid 191722Z - 192115Z

SUMMARY...Ongoing moderate to heavy precipitation will gradually
transition to snow this afternoon across central and eastern WY
impacting travel conditions. Snow rates above 1 inch per hour with
occasional reductions in visibility due to heavy and blowing snow
are possible.

DISCUSSION...As of 1700 UTC, WV imagery showed the core of a
well-defined upper low was located near the western CO, UT and WY
borders. To the north and east of the upper low, large-scale forced
ascent was supporting the development of widespread stratiform
precipitation across much of western and central Wyoming. 

Over the last hour, regional radar imagery showed additional banded
precipitation developing ahead of the low from the vicinity of KRIW
to KLAR. Likely in response to increasing lift near a region of
strong 700 mb frontogenesis, as well as orographic ascent,
additional precipitation development/intensification within this
band appears likely over the next several hours. Surface
temperatures across much of Wyoming remain just above freezing
suggesting initial precip type will be rain below 7k feet. However,
as column saturation takes place, dynamic cooling and increasing
low-level cold advection from surface pressure falls ahead of the
upper low should result in a transition to snow by early afternoon. 

As the upper low continues eastward along the CO/WY border, strong
height falls (60-90 DM/12 hr) should support moderate to heavy snow
within the developing frontogenetic band as it wraps
north/northwestward around the low. Hi-res guidance and regional
model soundings show support for snow rates near or exceeding 1 inch
per hour through the afternoon driven in part by steep mid-level
lapse rates near the cold core of the upper low. Additionally, weak
convective buoyancy as well as negative EPV (indicative of
slant-wise instability) suggest some potential for convective
elements/banding favorable for locally higher snow rates through the
afternoon. While the transition from rain to snow is likely to be
gradual, moderate to heavy snow appears likely across much of
central and eastern Wyoming through the afternoon. The potential for
heavy snow and gusty north winds may result in occasional blowing
snow/low visibility disruptive to travel. Weakening ascent and
increasingly dry mid-level air should end the heavy snow threat as
the upper low shifts to the northeast this evening.

..Lyons/Bunting.. 10/19/2021

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

ATTN...WFO...UNR...CYS...RIW...

LAT...LON   43590504 43330483 42870478 42530471 42240473 41850484
            41670516 41580560 41700621 42100671 42460760 42580804
            42860833 43260838 43730775 43820720 43810640 43790598
            43590504

Mesoscale Discussions in Wyoming, 2021Every mesoscale discussion in 2021

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.