Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171725
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1025 AM MST Sat Feb 17 2018

.UPDATE...
Issued at 1025 AM MST Sat Feb 17 2018

Indications from the morning model runs are that winds will be
increasing again this afternoon and evening over the mountains and
foothills. Will let the High Wind Warning continue. Temperature
forecasts seem to be on track and skies are mostly sunny, so no
need to make any changes to the forecast at this time.

&&

.SHORT TERM...(Today and tonight)
Issued at 400 AM MST Sat Feb 17 2018

Strong and very erratic winds in the mtns and foothills materialized
overnight as expected. Gusts in the 50 to 80 mph range were common
up along the Continental Divide and east slopes of the Front Range.
Saw one gust to 95 mph in the foothills west of Boulder around 2 AM
this morning. Gusty west-northwest winds also spread out onto the
plains overnight with gusts in the 30 to 50 mph range past few hours
across nern Larimer and northwest Weld Counties, and just south of
Larkspur along I-25 in southern Douglas County. The gusty winds kept
the boundary layer well mixed, resulting in warmer than expected
nocturnal temps. The right front quad of a 100 kt nwly jet now
moving over northern sections of the CWA has combined with
increasing mtn top static stability and a well formed lee side mtn
wave have to produce the very windy conditions overnight.

Next several hours, should see a gradual reduction in wind speeds in
the mtns and on the plains with the jet core shifting east of the
area. Cross sections also indication a relaxation in the mtn wave
and a weakening on the cross mtn barrier flow. However northwest
winds may remain quite gusty across the northeast corner of the
state through the morning and early afternoon before winds shift to
a southerly component mid to late afternoon with a strong sfc high
setting up in western Kansas. This shift in winds will help to warm
temperatures into the low to mid 50s on the plains, with warmest
readings in downslope areas along the foothills and Palmer Divide.
In the high country, gusty west-northwest winds will continue
through the day with gusts in the 35-55 mph range on ridgetops and
east slopes of the Front Range.

Meanwhile, the scattered light snow showers in the nrn mtns at the
present time should come to an end in the next few hours with
increasing stability and mid-level drying.

Tonight...flow aloft strengthening again as it becomes zonal. Lee
troughing and the formation of another high amplitude mtn wave
should result in another round of fierce mtn top and lee slope
winds. Cross mtn barrier winds are forecast to peak after midnight
in the 70-80kt range, the core of which may move farther down the
east face of the Front Range than it did tonight. Therefore, could
see stronger Chinook winds near the base of the foothills overnight,
which will produce warmer overnight temps in this area. Gusts in the
50-85 mph range will once again be likely overnight in mtn and
foothill zones 33.34..35 an d 36. Therefore, the high wind warning
now in effect for this area will remain in effect until 8 AM
Sunday.

.LONG TERM...(Sunday through Friday)
Issued at 400 AM MST Sat Feb 17 2018

Main concerns on Sunday will be continued high wind threat in the
mountains and foothills and elevated fire weather danger for
Sunday afternoon (see fire weather discussion below). Cross
sections show continue high wind threat Sunday morning with
50-70kt cross barrier flow and continue mountain top stable layer
until 16-17z and then stability/wave begins to break down.
Current high wind warning might be cutoff a bit too early but
won`t make any adjustments at this time. Highest winds Sunday
afternoon will be confined to the highest elevations. Continue
warm temperatures on Sunday with readings in the 60s across lower
elevations.

Next broad upper trof will develop over the Great Basin late
Sunday and Monday with an associated cold front which will move
through the northeast plains Sunday night. Colder on Monday behind
the front and there will be increasing low level moisture with at
least a stratus deck developing by early Monday morning. Initially
moisture depth to shallow for any precip early Monday and then
better chance of snow on Monday night as moisture depth increases
with secondary cold front and strong jet aloft moves over the
plains Monday night and early Tuesday morning. Does not look like
a great snow maker, and generally a light snowfall event of 1-3
inches looks reasonable. Could be some banded snowfall with the
jet so there could be some localized higher amounts.

The mountains will also see their share of snowfall, especially
zone 31 and possibly 34 where those locations look to be under the
jet for a longer period of time. Most locales would expect close
to advisory amounts but too early in the plan for that yet.

Expect drier and moderating temperatures for Wednesday and
Thursday time period as flow backs around more westerly again.
With this flow, expect still gusty winds a times over the
mountains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1025 AM MST Sat Feb 17 2018

Winds will be the only aviation impact through the rest of today
and tonight. Winds at KDEN should remain out of the south to
southeast through the afternoon as a lee trough of low pressure
intensifies along the foothills. Later tonight, there is a chance
the winds will go more westerly as there will be a fair amount of
westerly wind occurring along the foothills. KBJC will deal with
periods of westerly wind all afternoon and overnight as a strong
winds develop in the mountains and foothills.

&&

.FIRE WEATHER...
Issued at 400 AM MST Sat Feb 17 2018

Elevated fire danger expected by Sunday afternoon as humidity
levels drop to 10-15 percent during the afternoon and gusty
southwest winds surface across the Palmer Divide. Will issue a
fire weather watch in those areas for Sunday afternoon.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Sunday morning through Sunday afternoon
for COZ241-246-247.

High Wind Warning until 8 AM MST Sunday for COZ033>036.

&&

$$

UPDATE...Dankers
SHORT TERM...Baker
LONG TERM...Entrekin
AVIATION...Dankers
FIRE WEATHER...Entrekin


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