Mesoscale Discussion 172

Issued

Mar 13, 2021, 7:39 PM MST (02:39 UTC)

Expired

Mar 14, 2021, 1:45 AM MST

In force

6 hr

Issued by

the Storm Prediction Center

Concerning

Heavy snow

The Cheyenne radar (KCYS), 72 km from the middle of the area, began a volume at 02:40 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.

527 
ACUS11 KWNS 140239
SWOMCD
SPC MCD 140239 
NEZ000-COZ000-WYZ000-140845-

Mesoscale Discussion 0172
NWS Storm Prediction Center Norman OK
0839 PM CST Sat Mar 13 2021

Areas affected...Eastern Colorado into Wyoming and western Nebraska

Concerning...Heavy snow 

Valid 140239Z - 140845Z

SUMMARY...Heavy snow with rates around 1 in/hr will continue
periodically through the next several hours. Widespread heavy snow
with rates of 1 to 2 in/hour in the Plains, and 3+ in/hr in the
foothills/mountains will likely expand in coverage late this evening
and overnight.

DISCUSSION...*Corrected for Wording* Evening water vapor imagery
showed a deep upper-level low atop the Four Corners with a 100 kt
500 mb speed max rotating around the low across the High Plains.
Surface low pressure across the Texas Panhandle will gradually
intensify and shift northwestward across Kansas through this evening
and overnight. A TROWAL signature was also noted to the northeast of
the center of the low in response to strong mid-level warm advection
occurring to the east. 

00Z operational RAOBS and university/research soundings show a deep
layer of saturated east northeasterly upslope flow stretching from
southeastern Wyoming into northeastern Colorado. This deep
orographic lift is supporting moderate to heavy stratiform
precipitation along the I-25 corridor. Snowfall rates of 1 in/hour
are likely within the heavier bands of precipitation through the
next several hours. The most likely location for the heaviest
snowfall rates will be along the eastern slopes of the northern
Front Range, southern Laramie Range, and the Cheyenne Ridge where
orographic enhancement will be maximized. Expansion of the snowfall
deeper into the Nebraska panhandle is also expected this evening as
nocturnal/dynamic cooling of the column promotes a changeover to all
snow this evening.

More widespread heavy snow will likely develop after 04z this
evening and overnight as the main forcing for ascent from the upper
low spreads eastward across Colorado. The TROWAL will move
east/southeast centered across northern Colorado and southern
Wyoming supporting intense lift and precipitation through the
overnight hours. Localized blizzard conditions may develop across
portions of northern Colorado and southern Wyoming in response to
increasing surface pressure falls from the strengthening lee low
across western Kansas. Snowfall rates of 1 to 2 in/hr will be
possible across the Plains with very heavy rates of 3+ in/hr
possible in the foothills and mountains northwest of Denver.

..Lyons.. 03/14/2021

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

ATTN...WFO...PUB...BOU...CYS...RIW...

LAT...LON   42960627 42590650 42260610 41580580 41250575 40840579
            40220586 39840601 39570606 39290605 38930600 38720591
            38510567 38390542 38360508 38340446 38410401 38410388
            38510383 38760373 39020362 40120334 40730326 41270314
            41730314 42430326 42790363 42990420 43060514 43060590
            42960627

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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.