Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 191147
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
447 AM MST Mon Feb 19 2018

.SHORT TERM...(Today through Tuesday night)
Issued at 330 AM MST Mon Feb 19 2018

Forecast concerns deal with timing of heavier snow onset and snow
amounts today/tonight followed by windchill temperatures.

Currently...Arctic front being analyzed on surface analysis from
near Colorado Springs, northwest to near Baggs and then to Jackson
this morning. Enhanced cloud tops confined to a line along and
west of a line from just north of Rapid City to Douglas to
Rawlins this morning. METARS at Rawlins and Douglas have been
showing very poor visibility, down under a mile for several hours
now. WYDOT webcams confirming ground getting quite snow covered
along this line with road closures near Muddy Gap due to winter
weather conditions. As predicted by the day shift, GOES16 water
vapor imagery did show a dry slot from Laramie, northeast to just
north of Alliance this morning. This dry slot is beginning to
shift east into western Nebraska.

Going to keep headlines as they are this morning as short term
guidance shows this enhanced area of convergence/frontogenesis
shifting eastward through the day. Dry slot may have had some
impacts on snow totals, but given the stronger winds forecast west
of the Laramie Range, do believe we are still going to see impacts
from snow and blowing snow. LAMP guidance at Laramie late morning
and afternoon showing wind gusts increasing to close to 35kts at
18Z, so blowing snow is going to be a concern out there, despite
the reduced snow totals. Near blizzard conditions are still a
possibility from Rawlins to the I-80 Summit through the day.

Heavier snow likely east of the Laramie Range here at Cheyenne,
Pine Bluffs and the southern Panhandle after 00Z that continues
into Tuesday morning. Still have some time on upgrades for areas
east of the Laramie Range today.

Very cold overnight as well with 700mb temperatures falling to
-22C across Converse County and -18C here at Cheyenne. Pretty sure
 the day shift is going to need to issue windchill headlines
 tonight as am getting -30F across Niobrara and northern Panhandle
 counties overnight. Windchill headlines also likely need for
 Tuesday night into Wednesday morning as skies clear and overnight
 lows fall well below freezing.

.LONG TERM...(Wednesday through Sunday)
Issued at 239 AM MST Mon Feb 19 2018

Wednesday...Slow warming trend continues as the flow aloft backs
from west southwest, to southwest. Atmosphere looks too dry to
support precipitation.

Thursday...Moist southwest flow aloft will generate scattered snow
showers over and near our Snowy and Sierra Madre Ranges, dry
elsewhere. The warming trend continues based on thickness trends.

Friday...Slow warming trend continues. Scattered orographic snow
showers continue over the Snowy and Sierra Madre Ranges, dry
elsewhere.

Saturday...Flow aloft becomes west northwest with a slow warming
trend continuing. Breezy to windy day per progged low and mid level
gradients.

Sunday...Temperatures about the same as the next shortwave trough
aloft and cold front move across our counties. Looks like more
orographic snow showers for the Snowy and Sierra Madre Ranges. Hard
to say elsewhere, though will keep it dry for now with a fast moving
pattern and confidence low in shortwave trough aloft timing.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 443 AM MST Mon Feb 19 2018

Wyoming TAFS...IFR at Rawlins until 00Z, then MVFR. IFR at
Laramie. IFR prevails at Cheyenne until 16Z and after 02Z,
otherwise MVFR.

Nebraska TAFS...IFR at Chadron and Alliance. IFR at Scottsbluff
and Sidney until 16Z and after 01Z, otherwise MVFR.

&&

.FIRE WEATHER...
Issued at 330 AM MST Mon Feb 19 2018

Arctic front laying across south central Wyoming this morning with
heavy snow from Rawlins to Douglas and points west. Light snow
occurring east of this line with the exception of Niobrara County
in east central Wyoming and the northern Panhandle. We expect this
band to begin shifting east as the day progresses with more
heavier snow beginning across areas further east. Very cold the
next 48 hours and with widespread snow, fire weather concerns will
be minimal.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Warning until midnight MST tonight for WYZ101>105-
     109>114.

     Winter Storm Warning until midnight MST tonight for WYZ106>108-
     115>117.

     Winter Weather Advisory from 2 PM this afternoon to 6 AM MST
     Tuesday for WYZ118-119.

NE...Winter Storm Warning until midnight MST tonight for NEZ002-095.

     Winter Storm Warning until midnight MST tonight for NEZ003-096.

     Winter Weather Advisory from 2 PM this afternoon to 6 AM MST
     Tuesday for NEZ019>021.

&&

$$

SHORT TERM...GCC
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...GCC



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