Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 140350
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
850 PM MST Tue Feb 13 2018

.UPDATE...
Issued at 850 PM MST Tue Feb 13 2018

Only minor adjustments to the gridded forecast package this
evening. An upper jet moving over the state from the south tonight
and tomorrow will increase the flow over the state. An amplified
mountain wave is forecast to develop which will produce gusty
winds in and near the foothills. The mountain wave structure is
expected to remain in place through the day tomorrow, producing
the gusty winds into tomorrow evening. Peak gusts could be in the
40 to 50 mph range, strongest from about 6 AM through 2 PM. Areas
west of I-25 along with the foothill areas of Larimer County will
see the strongest winds. Temperatures tomorrow will be warmer
again due to warm advection from the westerly flow.

The other thing we will be keeping an eye on is the expected snow
in the mountains tomorrow night through Thursday. At that time,
moisture will be increasing from the northwest as the entrance
region of the upper jet linger over the state. Will not issue any
highlights at this time, but a decent shot of snow sure looks to
be in store. No other changes to the forecast at this time.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 1219 PM MST Tue Feb 13 2018

The upper low that was over the SW has continued to retrograde
into the Pacific with increasing SW flow over the state. Light
snow over the northern mountains will be light with lingering
moisture and orographics providing for light snow through the
day. At lower elevations temperatures will be warmer than the
last few days with highs reaching into the mid 50s. A 120+ kt jet
streak will make its way NE and into central Colorado overnight
greatly increasing SW flow over the mountains and plains. Speeds
will gradually increase in the mountains through the early morning
hours. Model cross sections are not showing much amplification or
stable layer so do not expect winds to make it too far east on
the plains but lower foothills out to BJC could gust into the 30s
and low 40s at times during the morning hours. Winds will increase
however over the far eastern plains with the possibly of light
gusting and sustained winds of 12 to 15 mph. RH levels are in the
low 20s with decent fuel moisture provided by snow but winds and
temperatures reaching into the low 60s for Wednesday will increase
fire weather concerns for drier areas.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 1219 PM MST Tue Feb 13 2018

For Wednesday night through late Thursday, the next upper level
disturbance will move across Colorado with more widespread
snowfall developing again for the mountains during late Wednesday
night and Thursday. With still a fair amount of wind could see
advisory amounts, especially over zone 31 and 33. An associated
cold front will mover the plains Thursday morning with colder
temperatures expected. Moisture looks rather limited so will only
have a slight chance of snow expected mainly in the afternoon
with increased instability.

Following the upper trof on Thursday, Colorado will transition to
a drier northwest flow pattern for Friday and Saturday. Still
chilly on Friday but warmer on Saturday. Flow aloft shifts back
west and southwest by late Saturday and Sunday as next stronger
system drops in the Great Basin. This system could effect Colorado
in the late Sunday through almost the middle of next week. There
are considerable model differences in the handling of the
amplification and timing with the incoming wave. The European
solution is quicker with the main trof position closer to Colorado
with higher chances of precip as early as Sunday evening for the
mountains and on the plains by Monday. The GFS is slower and
doesn`t even bring snow in the mountains until early Tuesday
morning. This GFS solution is much slower than the runs from
yesterday and ensemble data is quite varied. The Canadian run is
even displaced further West. Bottom line, confidence is low on
any one solution, and will keep pops chances on the low side and
broad brush through early next week. The big contrast is in
temperatures where the European solution has a high at Denver of
14, while the GFS has a high of 55 for Monday. Yikes.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 850 PM MST Tue Feb 13 2018

VFR conditions will prevail through the period as ceilings and
visibilities will not be an issue. The main impact affecting
operations will be the gusty winds forecast late tonight through
tomorrow evening. BJC will see the gustiest winds and for the
longest period as sustained winds of 20 to 34 knots are forecast
with wind gusts up to 46 knots between 12 and 20Z. Have increased
the winds at DEN and APA due to growing confidence that winds will
gust to 30 knots during the late morning and early afternoon as a
lee trough will be strengthening. Winds will begin to decrease late
tomorrow afternoon as the boundary layer begins to decouple.

&&

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

$$

UPDATE...Dankers
SHORT TERM...Bowen
LONG TERM...Entrekin
AVIATION...Danielson



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