Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 191711
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1011 AM MST Mon Feb 19 2018

.UPDATE...
Issued at 1010 AM MST Mon Feb 19 2018

With such a deep and cold post frontal airmass stretching all the
way to the southern Colorado border, not expecting too much
warming this afternoon when the expected cyclone develops and
causes southerly flow over the Palmer. Overall, lowered
max temperatures across the plains by several degrees. Southerly
winds may still induce some warming with the downslope direction,
but likely keeping in the low 30s. Just enough light moisture in
the cold temperatures over the plains for light snow to continue
to be developed. Added this to the forecast grids. Next thing will
look at will be potential for thunder in the high country later
today. A very convective look on satellite and webcams, with
around 200 J/kg of forecasted CAPE pushing in from Western
Colorado. For now will leave out, but will monitor the system
pushing into the west for lightning. Will keep the advisories
going even though there are several pockets of sunshine as the
system slowed slightly, but with a good amount of lift headed our
way.

&&

.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 1010 AM MST Mon Feb 19 2018

MVFR cigs at DEN and APA with LIFR-IFR at BJC and other areas
against the foothills. Ceilings should slowly lift through the
morning with possible breaks in the overcast over southeastern
sections of the metro area by late morning. Should still see
light snowfall through the morning and into the afternoon, with
less of a chance at APA however as southerly winds may dry things
out. By early afternoon should see south- southeast wind of 8-16
kts mainly at APA, where winds should stay north-northeast at BJC
and DEN. Then back to IFR cigs with a return to a northeast winds
at all airports 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 until 5 AM MST Tuesday for COZ030-031-
033.

Winter Weather Advisory until 5 AM MST Tuesday for COZ032-034-
035.

&&

$$

UPDATE...Kriederman
SHORT TERM...Baker
LONG TERM...Entrekin
AVIATION...Kriederman



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