Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 191152
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
452 AM MST Mon Feb 19 2018

.SHORT TERM...(Today and tonight)
Issued at 445 AM MST Mon Feb 19 2018

Storm system to our west continues to undergo strengthening as it
slowly propagates eastward out of the Great Basin. In the warm
sector of this upper trough is a 100-140kt jet presently extending
from srn Utah to ern Wyoming. The bulk of the large scale lift
and moisture associated with this system is concentrated along the
jet axis and is well evident on radar and GOES satellite imagery.
Meanwhile, a shallow moist airmass now covers ern Colorado. Model
soundings show this layer of cold, nearly saturated air no more
than 7000-10000 feet deep. Areas up against the Front Range and
across the far northeast corner of the state only areas
experiencing any precip in the form of light snow and/or light
freezing drizzle. Coverage of the freezing drizzle does not appear
extensive, and in the past hour -fzdz falling out at KDEN had
ended. They is probably just temporary. That said, do not feel the
need to issue an advisory for it, but will stress in the HWO that
slippery roads, bridges and sidewalks a possibility within the
I-25 corridor through 9 AM this morning. During the day, models
show a partial break out of the low cloud cover to the south and
east of the Denver with a dry downslope flow off the Palmer Divide
produced by a Denver cyclone. This is where temperatures will be
warmest today, possibly in the lower 40s. To the north and west of
this stationary cyclone, north- northeast bndry layer winds
should keep the low clouds socked in all all day, preventing much
warming.

In the high country, snowfall will expand in coverage over the
northern mtn ranges and high valleys this morning as the
aforementioned jet stream nears the CWA. Through the day, should
see snowfall spreading south and east over the high country. Most
of this precip will fall from convective bands. By late afternoon/
early evening, should see this banded snowfall extending northeast
across the adjacent high plains. At this time, it appears the
best moisture, lift and conditional symethrical instability will
extend from the Summit and Grand County area to the Larimer and
nrn Weld area through late this evening. Winter Weather Advisories
for snow have already been issued for these area. Snow amounts
mentioned in these advisories look good. Farther south and east,
could see a period of light total snow amounts should quickly
taper off as the bulk of the precip produced by the jet is progged
to remain over nrn portions of the CWA. Snow totals in the Denver
area may end up being a tad lower than earlier predicted,
particularly on the south side and for points to the south and
east. May even see a bit more light freezing drizzle early this
evening.

Snowfall should taper off after midnight as the tail end of this
jet lifts out across Kansas and Nebraska. Most noticeable feature
late tonight will be the bitter cold temperatures. Any clearing
could result in min temperatures lower than those being
forecasted.

.LONG TERM...(Tuesday through Sunday)
Issued at 445 AM MST Mon Feb 19 2018

Much of the upcoming week will be more unsettled with weak
disturbances and a persistent cool airmass over Colorado. Temperatures
will be much below normal Tuesday and Wednesday, then some slow
moderation by the weekend. Best chances for snow in the mountains
will be Wednesday night through Friday morning and again Friday
night. Could also be a brief shot of light snow on the plains on
Thursday and Friday.

For the details, weak subsidence moving in over Northern Colorado
Tuesday morning as upper trof and jet streak lifts out into the
northern high plains. There will still remain some lingering
troughiness over the Great Basin which will keep some lingering
moisture in the mountains for continued scattered snow showers
through Wednesday. Additional energy continues to drop into the
mean trof position over the Great Basin through Friday. Another
piece of energy and 100kt jet streak with this trof will nose into
Colorado Wednesday night and Thursday with another batch of snow
for the mountains under moderate QG upward ascent. The final piece
of energy develops into a closed low over the desert southwest on
friday and moves across Arizona and New Mexico on Saturday. This
track and available moisture will favor much of southern and
southeast Colorado.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 445 AM MST Mon Feb 19 2018

Low overcast -ILS cigs- should gradually lift through the morning
with possible breaks in the overcast by mid-morning. Should still
see light snowfall and perhaps some freezing drizzle through 15z.
The light precip and fog may reduce visibilities to less than 2
miles at times during this early morning period. By early
afternoon should see MVFR conditions for a few hours at KAPA and
KDEN with a south-southeast wind of 8-16 kts. Then back to IFR
cigs with a return to a northeast winds of 10-15 kts after 23z.
In addition, expect to see bands of light to briefly moderate
snowfall over the metro area during the evening hours, the the
heavier snow bands staying north-northwest of the metro area.
After 07z tonight should see gradual improvement with precip
ending in most areas and cigs lifting towards morning.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 PM this afternoon to 5 AM MST
Tuesday for COZ038.

Winter Weather Advisory from 5 AM early this morning to 5 AM MST
Tuesday for COZ030-031-033.

Winter Weather Advisory from noon today to 5 AM MST Tuesday for
COZ032-034-035.

&&

$$

SHORT TERM...Baker
LONG TERM...Entrekin
AVIATION...Baker



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