Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 140135
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
735 PM MDT Fri Oct 13 2017

.UPDATE...
Issued at 734 PM MDT Fri Oct 13 2017

Increased coverage of patchy fog further west and south over the
plains, with hires models showing some move in after 06z on
consecutive runs. Have also removed rain showers over the far
northeast plains as conditions are too dry.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 300 PM MDT Fri Oct 13 2017

Upper trough is presently over the northwest CONUS with a
ribbon of strong (100-140kt) southwest flow aloft stretching
from srn CA to the northern Great Lakes. RAP indicates 125-130kts
winds crossing over nrn and wrn CO. some of this high altitude
momentum has managed to mix down into the high valleys of nrn CO
where swly winds at a number of reporting sites across North and
Middle Parks have been gusting in the 20-30kt range. On the
plains, a weak cyclonic upslope flow persists, while the extensive
low cloud deck that this flow generated has all but dissipated
this afternoon with heating.

Tonight,the upper trough out west is forecast to swing down over
Idaho/wrn Wyoming/Utah, and an associated sfc cold front down
across nwrn CO/sern WY. On the plains, HiRes models show the
boundary layer saturating across the nern corner of the CWA
overnight, the product of a moist low-level sely winds. Have added
patchy to areas of fog acrs the far northeast counties after
midnight in line with neighboring CWAs. In the high country,
strengthening swly 700-500mb flow and a steady increase in static
stability will likely result in an increase in ridgetop winds
overnight. Stronger ridgetop and Front range east slope winds
likely to set up after midnight and more so near sunrise with
amplification of the mtn wave. Could see gusts on the ridges and
higher east slopes in the 40-55kt range. With the nearing trough,
could see a few light snow showers developing over the highest
ridges in the northern mtns towards morning with cold air
advection behind the passing cold front.

On Saturday, this stand-up cold front sweeps out across the plains
during the morning flattening the rise in temps. Should see gusty
west-northwest Bora-type winds of 35-65kts continuing on the mtn
ridges and east slopes for most of the day. May even see an uptick
in snowfall in the northern mtns during the morning. Snow totals
on the higher slopes probably no more than a few inches by midday.
On the plains, frontal passage in the morning will set off gusty
nwly winds areawide. But its not until late late morning when
winds are likely to be at their strongest the the back side of the
passing upper trough. Expect to see some the 45-55kt nwly 700 mb
flow mixing down onto the plains producing peak gusts in the
30-40kt range. These strongest winds are expected to materialize
east of the I-25 corridor after 17z. Fortunately, an increase in
base line RH values with cooler temperatures will reduce the
rangeland fire danger, even with the gusty winds. As a rule,
highs tomorrow will be some 8-10deg f, even with plenty of
sunshine around.

.LONG TERM...(Saturday night through Friday)
Issued at 200 PM MDT Fri Oct 13 2017

Gusty winds will be diminishing during the early evening hours
Saturday as gradients relax and subsidence/mixing decrease.
We should see light winds in all but the higher mountains by mid
to late evening. Temperatures will drop below freezing over the
entire forecast area Saturday night, with 20s over most of the
plains and teens mountains.  Freeze Warnings will no longer be
issued this season as we observed a hard killing freeze last
Monday night/Tuesday morning.

By Sunday, we`ll start a warming trend as a prolonged period of
dry, warm, westerly flow develops across the Central Rockies.
We`ll see highs push back close to normal by Sunday, and then
warm to several degrees above normal Monday through Friday. Dry
conditions will persist through Thursday. Then the next embedded
weather disturbance may reach the mountains and bring a few
showers into the picture by late Friday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday afternoon)
Issued at 734 PM MDT Fri Oct 13 2017

VFR conditions expected next 24 hours. Northerly winds will trend
to the northwest over the next couple hours before going to
drainage by midnight under 10 kts overnight. An exception to this
will be near the foothills such as at KBJC where west- southwest
winds of 15-25kts could develop after 06z tonight. On Saturday, a
dry cold front is expected to sweep eastward across the Denver
metro area between 14z-16z, causing gusty west-northwest winds of
15-30kts through the afternoon. By evening, look for speeds to
decrease as winds become more northerly in direction.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Fri Oct 13 2017

On Saturday, a dry cold front will sweep eastward across northeast
Colorado during the late morning and early afternoon hours,
causing a shift to gusty west-northwest winds of 25 to 40 mph.
Strongest winds are likely to be found east of the I-25 corridor
and particularly across the northeast corner of the state during
the afternoon hours. Fortunately, relative humidities levels will
be higher tomorrow in response to anticipated cooler post-frontal
temperatures. So, no fireweather highlights are planned at this
time.

&&

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

$$

UPDATE...Kriederman
SHORT TERM...Baker
LONG TERM...Barjenbruch
AVIATION...Kriederman
FIRE WEATHER...Baker



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