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Area forecast discussion
National Weather Service Cheyenne Wyoming
753 PM MST Mon Jan 23 2017

Update...
issued at 738 PM MST Mon Jan 23 2017

The main forecast challenge for the evening update concerns mainly
snowfall accumulations through Tuesday afternoon. The upper low is
rapidly intensifying this evening, and the latest infrared loop is
showing considerable enhancement W/ very cold cloud tops over much
of southeast Wyoming. We have even seen a few lightning strikes in
northern Carbon County. There is a threat for more convection into
the overnight hours with the models showing around 100-200 j/kg of
elevated cape with the low-level warm advection. Some of our high-
resolution guidance is showing some impressive snow totals for our
northern tier of zones, so need to monitor trends closely. We have
bumped up snowfall totals closer to 8 inches at Chadron, but could
need to update further. Will also need to consider adding Converse
County to the warning, and Bordeaux to the advisory. Mountain amts
may also exceed warning criteria, so will be looking into upgrades
for those within the next hour or two as well.

&&

Short term...(this evening through Tuesday night)
issued at 245 PM MST Mon Jan 23 2017

Tonight...as the upper low moves to north central Colorado, snow
will become widespread over our northern and western counties with a
deeply saturated airmass and plenty of upward vertical motion
progged. Snow will quickly spread from west to east overnight
especially over our northern counties. Our far southeast Wyoming
counties and southern Nebraska Panhandle will be in a low level
downsloping situation which will limit the areal coverage of snow.

In coordination with our neighboring offices, we will upgrade to
winter storm warnings for Niobrara County and for the northern half
of the Nebraska Panhandle, with winter weather advisories for
locations from Rawlins to Douglas to Torrington to Scottsbluff and
Bridgeport. Although snowfall amounts may be less than criteria,
impacts may be greater due to expected gusty winds producing areas
of blowing snow and reduced visibilities.

Tuesday...fortunately, the progressive upper low will move eastward
to eastern Nebraska by late afternoon with decent upward vertical
motion across our northern counties, and lesser so further to the
south. Behind the system, low level north winds will crank up and
produce areas of blowing snow and near zero visibility at times.
With the lift waning somewhat, the late morning expiration of our
lower elevation winter weather advisories looks good for the lower
elevations west of the Laramie valley.

Tuesday night...as the upper low moves even further to the east,
lift will wane with snow decreasing in coverage across Wyoming and
especially so in western Nebraska after midnight. We will thus end
the Wyoming hilites around 6 PM Tuesday with western Nebraska
hilites ending around midnight Tuesday night.

Long term...(wednesday through monday)
issued at 245 PM MST Mon Jan 23 2017

A generally cool and mainly dry weather pattern expected over the
cwa during the period with a north to northwesterly upper flow
across the area. Favorable orographics and some weak impulses
should keep snow showers going at times over the higher mtns
through Thursday night before moisture decreases with Friday
through the weekend looking dry. A cool surface high will hold
over the rocky mtns/northwest Continental U.S. Through Friday keeping
temperatures on the chilly side across the County Warning Area before moderating
some over the weekend...closer to average. Also looking rather
breezy for much of the period though high winds not expected.

&&

Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 443 PM MST Mon Jan 23 2017

Snow is expected to increase in coverage/intensity tonight through
Tuesday morning. As a result, IFR to LIFR conditions are likely to
develop across much of southeast Wyoming, and the western Nebraska
Panhandle. Poor flying conditions will persist through much of Tue
afternoon.



&&

Fire weather...
issued at 245 PM MST Mon Jan 23 2017

No concerns due to widespread snowfall event and
expected humidities.

&&

Cys watches/warnings/advisories...
Wyoming...Winter Weather Advisory from midnight tonight to 6 PM MST
Tuesday for wyz101-107-108-116.

Winter Weather Advisory until 11 am MST Tuesday for wyz103>105-
109>111-113.

Winter Storm Warning from midnight tonight to 6 PM MST Tuesday
for wyz102.

Winter Weather Advisory until 6 PM MST Tuesday for wyz112-114.

NE...Winter Storm Warning from midnight tonight to midnight MST
Tuesday night for nez002-003-095-096.

Winter Weather Advisory from midnight tonight to midnight MST
Tuesday night for nez019>021.

&&

$$

Update...clh

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