Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211636
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
936 AM MST Sun Jan 21 2018

.UPDATE...
Issued at 936 AM MST Sun Jan 21 2018

Area of deformation visible on satellite imagery with cloud tops
cooling is moving north up over the Palmer Divide, helping to
enhance snowfall rates. This is expected to bring heavier snowfall
rates for the next 2 to 3 hours over the urban corridor, Front
Range mountains and foothills as well as the eastern plains.

Snowstorm totals and impacts still on track. Overall snowfall
totals as of now are in the 1-3 inch range over the plains east
of I25 and north of Longmont near Fort Collins, 3-5 inch range
from Boulder south through the western Denver suburbs, 6-8 inch
range over the foothills and 6-12 inch range in the higher
mountains. As the system progresses east slowly through the day,
heavier snow amounts will fall over the eastern plains, with
increasing northerly winds to create hazardous conditions in
blowing snow. Blizzard Warning still looks like a good upgrade.

&&

.SHORT TERM...(Today and tonight)
Issued at 407 AM MST Sun Jan 21 2018

Mountain areas have picked up about 6 inches of snow overnight as
the main deformation band has been moving over the central part of
the state. The moderate and heavy snow over the mountains should
last a few more hours as the diffluent southerly flow aloft
continues. The zone of diffluence and deformation will be
translating out onto the eastern Colorado plains by mid-morning.
The leading band of snow associated with the dynamic forcing has
produced a couple inches of snow along the Front Range foothills
over the last couple hours. The center of the upper circulation
is currently over northwestern New Mexico and continuing an
eastward motion. As the upper low continues moving eastward it
should produce surface pressure falls over the Oklahoma panhandle
which will increase pressure gradients across eastern Colorado.
Should see a steady increase in northerly winds through the
afternoon as the storm system matures. Still expecting several
inches of snow today across northeast Colorado as the storm system
progresses. As the winds increase in the afternoon, blizzard
conditions will develop east of a Limon to Sterling line. These
hazardous conditions are expected to continue well into the
evening, so will upgrade the Winter Storm Warning to a Blizzard
Warning for zones 46 through 51. Will carry the Blizzard Warning
through midnight. The latest model runs have been a little slower
with moving the storm system out onto the plains, so that
improving conditions along the I-25 corridor may not arrive until
the early evening. Moderate snowfall on the eastern plains will
also continue well into the evening. Mountain areas will see snow
shower activity continue, even after the main storm system begins
moving east of the state.

Have not made too many changes to the snow amount forecasts, just
adjusted the timing, and raising the Blizzard Warning over the far
eastern counties. Most plains locations should see between 5 and 8
inches of snow, but locally up to 10 will be possible. Travel
should be difficult across eastern Colorado through much of the
day.

.LONG TERM...(Monday through Saturday)
Issued at 407 AM MST Sun Jan 21 2018

The strong storm system will be over northeast Kansas 12Z Monday.
Snowfall associated with it is expected to be east of Colorado by
Monday morning. Breezy conditions will linger for most of Monday
over the northeast plains and may produce a little blowing snow in
areas. Temperatures will be cool with highs mainly in the 30s.
For the mountains, a weak system may bring light snow to the
northern mountains Monday night and Tuesday. Not much moisture
will accompany this system. Where it does snow, accumulations are
expected to be less than 3 inches.

An upper level ridge will move across Colorado Wednesday and
Wednesday night. Flow aloft turns southwesterly ahead of a upper
level trough moving through the western states Thursday. This
pattern will produce dry and mild conditions for Wednesday and
Thursday.

The upper level trough is expected to move across the Central
Rockies Friday. Downslope may limit or prevent snow from forming
across the lower elevations. Best chance will be over the
mountains where orographic lift should produce some snowfall
Friday and Friday night. Temperatures will cool to near normal to
slightly below normal under the trough.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 936 AM MST Sun Jan 21 2018

Low IFR conditions should prevail through this afternoon before
they begin improving in the evening. Snowfall intensities of 1/2
to 3/4 inch per hour will be increasing over the next few hours
as good lift aloft squeezes out the moisture. North winds will
increase this afternoon as snow intensities begin a gradual
decrease. Wind gusts of 25 to 40 mph this afternoon could cause
periods of blowing and drifting snow. The storm will be moving out
of the state tonight with drier air moving in from the west by
midnight. Total snow accumulations at the area airports are
expected to be 6 to 9 inches by this evening.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Blizzard Warning until midnight MST tonight for COZ046>051.

Winter Storm Warning until noon MST today for COZ031-033>036.

Winter Weather Advisory until noon MST today for COZ030-032.

Winter Storm Warning until 5 PM MST this afternoon for
COZ039>042-044-045.

Winter Storm Warning until 2 PM MST this afternoon for COZ038-
043.

&&

$$

UPDATE...Kriederman
SHORT TERM...Dankers
LONG TERM...Meier
AVIATION...Kriederman


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