Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 231045
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
345 AM MST Fri Feb 23 2018

.SHORT TERM...(Today and tonight)
Issued at 233 AM MST Fri Feb 23 2018

Current synoptic pattern has an upper trough digging into the
Great Basin with the upper jet pushing out of the SW. The
anticyclonic side of the jet is moving over the state helping to
bring some stability to the NE region of the state. This will
slightly diminish precipitation in the mountains and bring
clearing conditions to the plains. With the increased drying low
level moisture will help to create fog on the plains into the
early morning hours. Expect areas over the Urban Corridor and
eastward to the Kansas border to see areas of fog development.
With the southerly flow to the south of I-70 fog will be less with
the help of drying off the Palmer Divide. Visibility could get
down to a mile or less in some areas so caution is advised for
early morning travelers.

The next batch of energy provided by the cyclonic side of the
approaching jet will increase snow in the mountains starting this
afternoon and continue through Saturday morning. The upper jet
will once again provide the instability needed for banding snow
potential. QG ascent numbers are good with -40 in the mid levels
and upwards of -7 at the surface. Convective snow bands are always
a challenge to pin down but model guidance is in decent agreement
with some setting up from a line moving NE from Boulder into
Larimer county later this evening. Went ahead and increased pops
for these areas. Most areas will see some light snow potential but
under the bands a quick inch of snow accumulation will be
possible. Further east on the plains ahead of the main convective
band there will be enough low level moisture to allow freezing
drizzle for a couple of hours late this evening. As the jet
pushes ESE the column will cool changing the freezing drizzle
over to snow where periods of heavy snow will be possible into
the early morning hours on Saturday. A winter weather advisory
has been issued for various counties in the NE plains due to local
impacts from the freezing drizzle and possible heavy snow. As
mentioned before, with this type of convective set-up advisory
criteria can be reached quickly so it is possible that areas on
the plains under the bands will see quick accumulation. The
situation will be monitored closely through the day but caution
is advised for travelers if you are caught under one of these
bands due to greatly reduced visibility and slick roadways.

Temperatures today will stay on the cool side with highs in the
mid to upper 20s. Overnight lows will drop into the teens.

.LONG TERM...(Saturday through Thursday)
Issued at 233 AM MST Fri Feb 23 2018

Storm system will be exiting to the east Saturday morning, with
snow diminishing and ending from west to east across the northeast
plains. We`ll keep the Winter Weather Advisory in effect until 9
AM for now as most snow should be over by then. Along the I-25
Corridor, downslope flow will be kicking in with gusty
west/northwest winds expected as stronger subsidence develops
behind the trough axis. Despite the winds and added mixing,
temperatures will remain quite cold with strong cold advection
occurring. Highs will barely make it to freezing on the plains,
and with gusty northwest winds it will feel more like the teens.
In the mountains, orographic light snow showers will also be
decreasing and coming to an end during the day as dry, subsident
air moves in. Highs there will only be in the single
digits/teens, with wind chill readings holding below zero.

By Saturday night, the next short wave will begin to approach the
region so should see snow showers redevelop across the high
country as mid level moisture increases in an unstable
environment. Those should linger into Sunday morning with
generally light to moderate accumulations expected, as best
synoptic scale lift will be passing by to our south. The plains
should remain under dry, downslope flow during this period.
Temperatures will remain well below normal under the influence of
the sweeping cold trough across the northern Rockies/High Plains.

Some moderation in temperatures will finally occur by Monday
as a deeper trough digs down the west coast of the U.S.  That
should lead to short wave ridging and warm advection across
Colorado, while lee troughing will aid downslope warming. We
still might have to watch for weak backdoor cold fronts given
short waves riding across the northern U.S. into Tuesday. Then a
piece of that upper level trough may push across the forecast area
by Wednesday with slight cooling. This could also bring a return
of light snow showers. Temperatures should stay near or just
below normal for the middle of next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 233 AM MST Fri Feb 23 2018

Impacts to local area airports today with mist and fog early on
replaced with snow potential. BR will be possible at KDEN through
12z. Lowered MVFR ceilings will be possible after 16z with the
onset of increasing clouds ahead of the next system. IFR ceilings
and light snow will hit BJC first with KDEN and APA shortly after
around 18z. Snow will continue through 06z with periods of IFR
ceilings and reduced visibility due to heavier bands of snow.
Snow will diminish after 12z with ceilings improving after 15z.
Winds through the period will remain light with winds turning more
NE by the afternoon then NW by 03z Saturday. Winds will move
westerly between 10 and 12z Saturday with the deepening of a lee
side low behind the departing system.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 PM this afternoon to 9 AM MST
Saturday for COZ048>051.

&&

$$

SHORT TERM...Bowen
LONG TERM...Barjenbruch
AVIATION...Bowen



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