Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Cheyenne Wyoming
1126 PM MST Wednesday Nov 25 2015
issued at 920 PM MST Wednesday Nov 25 2015
Freezing drizzle has deposited perhaps up to 0.01 of ice to
outdoor surfaces across the southeast Wyoming plains this evening.
More snowflakes have been mixing in with the freezing drizzle at
the weather forecast office over the past few minutes. So suspect this will be the
beginning of the eventual change-over to snow which should occur
by around midnight here. Expect the freezing drizzle to occur a
little while longer across western Nebraska Panhandle locations.
Elsewhere...webcams show definite pockets of snow falling across
the southern Laramie range...where i80 is snow-covered and slick over
No changes to the current highlight package this evening as it has
things handled pretty well. Initial look at 00z model does show
slightly less snowfall across the area than previously
anticipated...so did decrease the lower bound of some of the
ranges in the warning as a result. Regardless of perhaps slightly
lower accumulations...Road impacts will still be significant
across the region especially in areas that observed freezing
Short term...(this evening through Thursday night)
issued at 407 PM MST Wednesday Nov 25 2015
Areas of freezing fog and drizzle have become quite prevalent in the
southern Laramie range foothills including I-80 between Cheyenne and
Laramie...as well as I-80 between Laramie and Elk Mountain. Road
temperatures have dropped below zero over the past few hours while
air temperatures are in the teens. Thus...think these areas will
begin to ice accumulation on various surfaces soon so started the
highlights now for these three zones. Once snow begins to fall later
this evening...roads could become extremely slick with the
combination of ice accumulation and snow...hence the upgrade of the
southern Laramie range foothills inclusion into the Winter Storm
Warning. Start time for remaining highlights was bumped up to 5 PM
to account for the earlier start time of fog/drizzle impacts over
Otherwise...forecast looks to be in good shape since the previous
update. Upper level lift will continue to increase over the forecast
area this evening which will strengthen easterly upslope winds and
general broadscale lift for precipitation production. Frontogenesis will
strengthen overnight as well...while midlevel moisture deepens from
north to south tonight. Thus...expect change over of any mixed
precipitation to light snow overnight with snow rates increase especially
along and west of a line from Lusk to Cheyenne. Light snow will
continue on Thanksgiving over much of the forecast area...along with
very cold temperatures. Gusty east-northeast winds will develop over
the I-80 Summit and eastern foothills...along with western Carbon
County to produce concerns with blowing snow. Drier air filtering in
from the north should shut off snow production Thanksgiving night.
Bitterly cold temperatures with wind chills well below zero will
settle in for early Friday morning.
Long term...(friday through tuesday)
issued at 330 am MST Wednesday Nov 25 2015
Friday...cold upper trough continues to remain nearly stationary
over southern Nevada with cold surface high pressure entrenched over
our counties. Slight chance of light snow over the southern half of
our counties with adequate low and middle level moisture and weak
upward vertical motion primarily due to upslope. Continued quite
cold with fresh snowpack...700 mb temperatures near -11 celsius and
Saturday...one lobe of the upper low rotates across eastern Wyoming
producing a few snow showers. Continued cold per prognosticated 700 mb
temperatures...cloud cover and snowpack.
Sunday...upper trough lifts into the northern rockies and northern
plains states with our flow aloft turning southwest helping for a
slight warming trend. Still though enough residual cloud cover and
orographics for scattered snow showers over our snowy and Sierra
Madre ranges...dry elsewhere.
Monday...pesky upper trough rotates across either the Dakotas...as
per the GFS...or over Nebraska...per the European model (ecmwf). In either
case...cold temperatures aloft will promote at least isolated snow
showers over our counties with temperatures remaining quite
cold...and perhaps even colder than our current forecast indicates.
Tuesday...finally...a return to slightly warmer weather as the flow
aloft backs to west or northwest allowing surface Lee troughing to
strengthen and helping a moderation in the cold airmass.
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1123 PM MST Wednesday Nov 25 2015
Wyoming tafs...IFR prevails. Becoming MVFR at Rawlins after 18z...
otherwise IFR at Laramie and Cheyenne.
Nebraska tafs...IFR prevails...except at Chadron where MVFR
develops after 21z.
issued at 407 PM MST Wednesday Nov 25 2015
No fire weather concerns anticipated in the near term due to snow
through the end of the week...and very cold temperatures through the
Wyoming...Winter Weather Advisory until 5 PM MST Thursday for wyz102.
Winter Storm Warning until midnight MST Thursday night for
Winter Weather Advisory until midnight MST Thursday night for
Winter Storm Warning until 5 PM MST Thursday for wyz101.
NE...Winter Weather Advisory until 5 PM MST Thursday for nez019>021-