Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 170903

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

Issued at 158 AM MST Sat Feb 17 2018

Updated the forecast for the remainder of the night. Beefed up
wind speeds and raised min temperatures specifically within the
foothill and urban corridor zones 35..36..38..39 and 40. An
increase in mtn top subsidence and strengthening jet level flow
should cause an increase in mtn top and east slope winds next few
hours. This increase now showing up on radar. Also reduced cloud
cover along the Front Range with strong subsident flow coming off
the Front Range.

UPDATE Issued at 932 PM MST Fri Feb 16 2018

Pretty decent winds are beginning to push onto the plains at this
time. Directions are mostly westerly with some gusts to around 50
mph. New model data does point to a substantial mountains wave
set-up on the cross sections. Current wind highlights look good.
Will make a few changes to sky cover.


.SHORT TERM...(This evening through Saturday)
Issued at 310 PM MST Fri Feb 16 2018

Main concern surrounds winds later tonight and Saturday. The flow
aloft will be increasing rather quickly by midnight tonight as
strong 120+ knot Pacific jet plows across the northern Rockies.
The right front exit region of the upper jet will arrive 09Z-12Z
so we should see a sharp uptick in winds at that time. Cross
section shows cross mountain flow will increase to 45-50 knots,
and a mountain top stable layer quickly develops with the onset of
subsidence. As a result, we expect a high amplitude mountain wave
to develop and result in peak wind gusts of 75-85 mph on the
eastern slope of the Front Range mountains late tonight. Can`t
rule out stronger winds given the favorable parameters, and latest
HRRR is suggesting peak gusts reach 90+ mph in wind prone areas
of the foothills. There is some concern that the stronger gusts
may attempt to push out onto the nearby adjacent plains, so will
continue to monitor the Boulder-Golden corridor for possible high
winds in this setup.

There should be some light snow in the northern mountains as mid
level moisture increases. This wave of moisture is currently
pushing through western Wyoming and northern Utah and should reach
the northern Colorado mountains by mid evening. Moisture depth and
instability are limited so only light snow with a dusting to 2
inches expected from Rabbit Ears Pass and the Indian Peaks

On Saturday, winds are expected to gradually subside as mountain
top stable layer lifts, resulting in weakening mountain wave.
Westerly flow also gradually relaxes before next big push of winds
tomorrow night.

Temperatures will warm about 10 degrees more for Saturday with
warm advection in place. Should see highs on the plains reach the
50s, with 40s in the foothills, and 20s/30s in the mountains.

.LONG TERM...(Saturday night through Friday)
Issued at 310 PM MST Fri Feb 16 2018

Westerly winds at mountain top will increase Saturday night again
as a jet sinks south towards the area and as the surface pressure
gradients increase. Direction will begin to change to just south
of west...favoring the Mummy Range for seeing the strongest gusts.
Will allow the High Wind Warning to extend into Saturday night
with gusts up to 80 mph possible. Would not be surprised if we
could drop the zones including the mountains and foothills along
and south of I-70 from the warning that night where they`re less
likely to see the higher gusts.

A system will begin to drop into the Pacific Northwest Sunday
bringing warmer temperatures to the area in southwest flow,
readings will be in the low 60s over the plains. Flow will
increase as well, keeping windy conditions over the mountains. At
the surface, a low will deepen over the eastern plains before
sinking south that evening. Tight pressure gradients will increase
winds, bringing a fire weather concern to the plains with
humidity in the low teens. Slightly more humid airmass will push
into the northeastern corner of the state as the surface low sinks
south. Snow will push into western Colorado during the day, then
push into the mountains Sunday evening with up to a few inches
possible overnight.

Cold front will push down the plains Monday morning to bring snow
to the front range urban corridor. The front and will slow its
speed keeping the better chance of snow along and west of I-25,
before the better moisture and colder air pushes down Monday
evening. The upper trough will lift north Tuesday bringing the
moisture with it, but high surface pressure will slide south into
the Great Plains to keep some light upslope flow and cold air
damned into the area. Temperatures will struggle to get higher
than the low 20s. Initially at this time, snow fall amounts may be
in the 6 to 12 inch range for the mountains, and in the 1 to 5
inch range for the plains. But plenty of time between now and

Flow aloft will remain southwest Wednesday through Friday as a
series of shortwave upper troughs continue to pushes down from
the Pacific Northwest. A surface trough develops along the lee of
the mountains Wednesday and Thursday to allow for temperatures to
warm up. Enough moisture in the southwest flow may push in
Thursday and Friday for a chance of snow into the mountains.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 932 PM MST Fri Feb 16 2018

Pretty strong west-northwesterlies are blowing at DIA right now.
Models did not show this very well.  Will make appropriate
adjustments. Will keep a more westerly direction going all night and
not the normal drainage directions. There should be no ceiling
problems overnight.


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



SHORT TERM...Barjenbruch
LONG TERM...Kriederman
AVIATION...RJK is the U.S. government's official web portal to all federal, state and local government web resources and services.