Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210350

Area Forecast Discussion
National Weather Service Denver/Boulder CO
850 PM MST Mon Feb 20 2017

Issued at 842 PM MST Mon Feb 20 2017

Flat upper ridge over Colorado with increasing westerly flow aloft
tonight through Tuesday. Cross sections show increasing gusty
winds expected over mountains and east slopes. Cross barrier flow
indicates speeds in the 30-60 mph possible later tonight,
strongest from 09-15z over wind prone areas. Still looks like a
dry, windy, and warm day on Tuesday with record setting
temperatures possible.


.SHORT TERM...(This evening through Tuesday)
Issued at 141 PM MST Mon Feb 20 2017

tonight...the ridge axis will shift to the east with the flow
aloft transitioning from northwest to westerly. NAM12 spatial
cross sections show a weak mountain wave developing after 06z so
stronger gusts to around 50 mph will occur in and near the
foothills. The wave will persist through 15z Tuesday morning
then break down. Some moisture passing to the north and west of
the cwa tonight, with a slight chance of some showers in zone 31.
Mild temperatures tonight in and near the foothills in the windier
areas. On Tuesday, the flow aloft increases during the day with
any moisture over the northwest part of the cwa, otherwise dry.
Pacific moisture will increase over northwestern CO late in the
day ahead of the next storm system with the assistance of a 120 kt
jet max that will be moving across the central Rockies and Great
Basin regions at that time, favoring zone 31 almost exclusively.
The combination of gusty winds, unseasonably warm temperatures,
low relative humidities will produce a high fire danger in the
aftn. Strongest winds in the afternoon will be in the foothills
and along the northern border.  Reference the fire weather
discussion below. Some temperatures records will likely be
broken including the high of 71 for Denver set in 1995.

.LONG TERM...(Tuesday night through Monday)
Issued at 141 PM MST Mon Feb 20 2017

Southwest flow aloft will prevail as the upper level ridge axis
shifts east of the region. A surface low is expected to form over
southeast Colorado Wednesday with a cold front dropping south
across eastern Colorado. It will be mild Wednesday, but about ten
degrees cooler than Tuesday. The southwest flow aloft will help
transport Pacific moisture into the area. This will bring a chance
for snow to the mountains beginning Tuesday night. The best
chance at this time appears to be over the north central

For Wednesday night through Thursday night, an upper level trough
moves across the Great Basin and over the Central Rockies. Snow
will be likely over the mountains beginning Wednesday night and
continue through Thursday night. Eastern Colorado will be under a
the left exit region of the jet, which will provide lift. In
addition to this, a northeast upslope flow is expected to bring
snow to the Front Range and eastern plains. The best chance and
highest amounts are expected to be over northern parts of the
area, closer to the upper level low. Precipitation across the
lower elevations may begin as rain. If it does, it will be short
lived as the airmass cools.

The upper level trough moves east of the Rockies by early Friday.
Moisture embedded in the northwest flow behind the exiting system is
expected to produce snow showers over the mountains. Snow will
decrease through the day Friday as drier air moves in. For the
lower elevations, it will be cool with a slight chance for
lingering snow.

Zonal flow aloft will prevail Saturday. Other than a few light
mountain snow showers, dry conditions are expected across the area.
Temperatures will continue to be on the cool side with highs in the
30s across northeast Colorado.

Zonal flow is forecasted to continue over the Central Rockies Sunday
and Monday. Models are struggling to figure out the short wave
details. The GFS shows a strong wave for Sunday with heavy mountain
and while the ECMWF is dry. For now, will go with temperatures near
to slightly below normal with a chance for mountain snow.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 842 PM MST Mon Feb 20 2017

Surface winds working their way back to southerly this evening and
should hold through the night. BJC may begin showing a shift and
increasing west wind later tonight as mountain wave activity
increases. Good mixing on Tuesday will result in increasing gusty
winds at rest of terminals by mid to late morning.


Issued at 141 PM MST Mon Feb 20 2017

Fire weather danger will increase further on Tuesday. Have
upgraded the Fire Weather Watch to a Red Flag Warning fm 1100-1800
MST Tuesday. Mountain wave developing overnight will limit the rh
recovery in the foothills overnight, especially below 7500 feet.
although the mountain wave will break down after 0900 MST Tuesday,
gusty winds to 40 mph will continue into the afternoon. The
combination of unseasonably warm temperatures, gusty winds will
result in very low relative humidities. The highest fire danger
threat will be near the foothills and along the northern tier
counties where the strongest winds will be.


Red Flag Warning from 11 AM to 6 PM MST Tuesday for COZ215-216-



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