Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 231005
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
305 AM MST Tue Jan 23 2018

.SHORT TERM...(Today and tonight)
Issued at 305 AM MST Tue Jan 23 2018

Satellite showing a weak wave over Montana and Wyoming at this
time. This is enough moisture and orographic lift in the northwest
flow aloft to produce light snow over parts of the mountains. Web
cameras are showing light snow is mainly at higher elevations.
Drier air is starting to move into northern Colorado. This will
bring decreasing snowfall with snow ending this morning for most
locations. Additional snowfall is expected to be less than two
inches.

Elsewhere, this drier air moving into the area will bring mostly
clear skies around sunrise. High clouds may linger a little longer
over the eastern plains. High temperatures look to be close to
yesterday to a few degrees cooler. Breezy conditions are expected
over far northern Colorado, near the border with Wyoming and
Nebraska.

.LONG TERM...(Wednesday through Monday)
Issued at 305 AM MST Tue Jan 23 2018

A tall upper ridge, accompanied by an abnormally warm and dry
airmass, is still projected to make steady eastward progress over
the central Rocky Mtn region Wednesday through Thursday. Core of
warmest air aloft passes over the forecast area Thursday as the
mean layer flow turns southwesterly. High temps Wednesday are
expected to run 6-10 deg f above average for the date, and on
Thursday another 4-6 deg f above those readings with highs in
the mid 50s to lower 60s along the Front Range and out across the
Palmer Divide. As the ridge passes, cross sections also show a
pronounced increase in mid-level stability which promotes the
formation of a high amplitude mtn wave over the Front Range
Wednesday night into Thursday. These same cross sections show
cross barrier winds peaking around 50 kts late Wednesday night and
again early Thursday night in the 55-65kt range near mtn top
level. Could see some of this momentum mixing down to the base of
the foothills both nights possibly producing gusts in the 25-40
mph range in wind prone areas such as around Boulder, along Hwy
93 between Golden and Boulder, and around Lyons and in the
foothills west of Loveland. Could see winds over the higher
foothills approaching high wind criteria, esply Thursday night.

The warm temperatures, low Rhs and south-southwesterly winds of
20-25 mph on the Palmer Divide Thursday afternoon would normally
elevate the rangeland fire danger to at least high. However, the
recent snowfall and wet fuels should ease the threat of wildfire
in this area.

Late Thursday night into Friday, attention turns to a upper air
disturbance which models show swinging in from the northern Great
Basin. System does not appear to contain all that much moisture,
yet still enough instability, cold air and Q-G forcing for ascent
to generate QPF/snowfall starting over the Park and Gore ranges
Thursday evening, and remaining mtn areas after 07z/Friday. By
Friday morning, higher west-northwest facing slopes and ridgetops
could end up with 2-5 inches of snow by late Friday morning. High
mtn valleys could also see an inch or two of snow. East of the
mtns, dry and mild conditions give way to cooler and slightly
more moist air with passage of a cold front around 12z/Friday.
This may be sufficient to generate a few morning snow showers,
maybe in the Denver area but more likely on the higher Palmer
Divide south-southeast of Denver. Do not expect to see any
accumulation with these brief showers. Models differ on how quick
this system and its precip departs the area. GFS shows it exiting
the CWA Friday afternoon, while the ECMWF and Canadian models
show it lingering until evening. At any rate, Friday should be a
noticeably cooler day with gusty Bora downsloping winds in and
near the foothills once the showers move out.

Looking ahead to the weekend and early next week, models hint at a
weak weather system brushing over the nrn mtns on Sunday, possibly
producing scattered snow shower over the higher slopes and
ridgetops during the day. Then, a trend towards warmer and drier
conditions with a large upper level ridge building in from the
lower Great Basin and Desert Southwest for Monday and Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 305 AM MST Tue Jan 23 2018

VFR conditions will prevail today and tonight. Clouds will
continue to decrease through the early morning hours with mostly
sunny skies prevailing today and tonight. Wind direction will be
difficult to forecast, but winds speeds are expected to stay
under 15 knots.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Meier
LONG TERM...Baker
AVIATION...Meier



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