Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

552
FXUS65 KBOU 182054
AFDBOU

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

.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.

&&

.Fire Weather...
Issued at 146 PM MDT Mon Sep 18 2017

Critical fire weather condition anticipated for Tuesday due to
above normal temperatures, very low relative humidities and
increasing wind. A Red Flag Warning is in effect for the Front
Range Foothills, Middle Park, South Park, the north central
mountains around Summit County, the Palmer Divide, eastern Larimer
and northwest Weld County from 1100-2000 mdt Tuesday. In
addition, a Fire Weather Watch is in effect for the rest of the
northeast plains. The highest confidence will be in the warning
area where very warm temperatures, rh values around 10 percent and
gusty winds to 50 mph are expected. Not as confident in the wind
potential in the watch area but the other critical factors are
there which is why those zones are in a Fire Weather Watch at this
time.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 146 PM MDT Mon Sep 18 2017

Boundary over KDEN/KAPA is making for a difficult wind forecast
this afternoon. Although more variable at this time, still expect
an east/southeast wind component to set up this afternoon. normal
drainage patterns by 03Z this evening. There will be no ceiling
issues. On Tuesday, increasing southwesterly winds aloft with
stronger pressure gradient near the foothills, with stronger gusts
20-25 kts possible near KBJC by 18z.

&&

.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.

&&

$$

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.