Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 190235
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
835 PM MDT Mon Sep 18 2017

.UPDATE...
Issued at 817 PM MDT Mon Sep 18 2017

Main concern for the rest of tonight is increasing gusty west
winds expected in the mountains and foothills after midnight.
Strong upper trof continues to develop over the Pacific Northwest
with an increasing sw flow aloft over Colorado. Cross sections
indicate cross barrier flow increasing to 30-40kt later tonight
along with developing mountain top inversion. This should help
amplify the winds a bit in the higher foothills. Main changes to
tonight forecast was increase overnight lows in the foothills/adj
plains and bump up wind speeds slightly.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 146 PM MDT Mon Sep 18 2017

A storm system will drop out of British Columbia and into the
Northern Rockies by Tuesday afternoon. The flow aloft will
increase tonight through Tuesday, as a 120KT upper jet on the
south side of the trough stretches from the Oregon coast eastward
across Wyoming. The airmass will be dry with increase downslope
winds over the western part of the cwa and a surface trough over
northeast CO in the morning. Gusty southwest winds likely in and
near the foothills and Palmer Divide on Tuesday where the surface
pressure gradient will be strongest. Gusts there could reach the
40-50 mph range in the afternoon. In addition, temperatures will
climb 7-10 degrees above seasonal normals with relative humidities
dropping in the 8-14 percent range. Extreme fire danger expected,
see the fire weather discussion and associated highlights below.
Temperatures at 700 mb around 14c for Denver in the afternoon. Mid
level cold air advection develops over northwest CO after 21z but
this will not make it into the cwa until Tuesday evening.

.LONG TERM...(Tuesday night through Monday)
Issued at 146 PM MDT Mon Sep 18 2017

A cold front will drop south across Colorado Tuesday evening.
Northerly winds behind the front will usher in cooler temperatures
and higher relative humidities, bringing an end to the Red Flag
conditions. May be enough moisture and orographic lift behind the
front to produce a few showers over the mountains of North Central
Colorado.

For Wednesday and Thursday, an upper level trough digging south
along the west coast will produce a southwest flow aloft over
Colorado. This will keep the warm and dry conditions in place.
Wednesday will be the cooler of the two days because of cooler air
behind Tuesday`s cold front. On Thursday, temperatures climb back
into the mid 80s. Expect fire danger to be elevated Thursday due
to the warm temperatures, low relative humidities, and breezy
conditions in places.

The upper level trough is expected to move into the Great Basin
Friday. This will bring a transition to Colorado. A surface low
forming over northeast Colorado will bring northerly winds and
cooler temperatures to northern parts of the area. Southern
sections should stay mild through Friday afternoon. Eventually the
front will push through the area Friday evening.

North to northeast surface winds will prevail over the area this
weekend. This will transport cooler air into the area. The upper
level low is expected to stay west of Colorado. Disturbances will
rotate around the low and bring periods of showers and
thunderstorms to the area. Best chance looks to be Saturday night
when models agree that a wave will pass over the state. Overall
for the Saturday through Monday time frame, will have below normal
temperatures with isolated to scattered pops. Snow will be
possible for the higher elevations, above 11000 to 12000 feet MSL.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 817 PM MDT Mon Sep 18 2017

surface winds will continue to shift southeast to south at KDEN
through 04z, while winds already southerly at APA. Winds at BJC
will shift westerly overnight and could see some gusts towards
daybreak. All terminals will see increasing gusty west winds
Tuesday afternoon as good mixing brings down stronger winds from
aloft. Airmass dry so VFR conditions continue.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Tuesday morning through Tuesday evening
for COZ239-240-242>245-248>251.

Red Flag Warning from 11 AM to 8 PM MDT Tuesday for COZ212>216-
238-241-246-247.

&&

$$

UPDATE...Entrekin
SHORT TERM...Cooper
LONG TERM...Meier/Sullivan
AVIATION...Entrekin


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