Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210307
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
907 PM MDT Wed Sep 20 2017

.UPDATE...
Issued at 905 PM MDT Wed Sep 20 2017

Typical diurnal wind pattern has taken hold at this hour, and
according to HiRes models it should remain in place overnight.
What will be different with the winds overnight will be their
speeds as a strengthening southwest flow aloft could mix downward
from time to time, esply over higher elevations including the
Palmer Divide, which would keep speeds a bit higher than normal.
This would slow the fall of temperatures and result in poor RH
recovery in spots. Otherwise, no precip and perhaps some mid and
high cloudiness spreading over the northwest corner of the CWA by
morning. On Thursday...the day may start out pretty breezy esply
at higher elevations and along the Palmer Divide. And with poor RH
recoveries overnight, it won`t take too look for min RH values to
reach Red Flag Warning criteria acrs the southeast corner of the
CWA. Will temperature, wind speed and min RH meet Red Flag Warning
thresholds elsewhere, such as in the high alpine valleys and even
on the higher mtn slopes? Will wait to see what the new model
guidance has in store before making any changes to the ongoing Red
Flag Warning domain.


&&

.SHORT TERM...(This evening through Thursday)
Issued at 305 PM MDT Wed Sep 20 2017

Southwest flow aloft around an upper level trough over the
western part of the country will continue over Colorado tonight
and Thursday. Airmass will continue to be dry with only a few
clouds over the higher terrain. The dry airmass will allow
temperatures to fall tonight where winds become light. Expect lows
in the 40s to lower 50s over northeast Colorado.

On Thursday, it will be a very warm day with gusty southwest
winds over parts of the area. The windy conditions combined with
low relative humidity will increase the fire danger. Upgraded the
Fire Weather Watch to a Red Flag Warning because of the windy and
dry conditions over the Palmer Divide and near by plains. Record
high for Denver tomorrow is 89 degrees and could be reached.

.LONG TERM...(Thursday night through Wednesday)
Issued at 305 PM MDT Wed Sep 20 2017

A deep upper level trough of low pressure covers the western half
of the United States Thursday night with an area of low pressure
centered over southwestern Idaho. Colorado is on the leading edge
of the trough...under the influence of a moderate southwesterly
flow aloft. The atmosphere looks to be somewhat dry...therefore
precipitation is not expected across the CWA. Gusty south to
southwest winds and low relative humidities will result in
increased fire danger across the Palmer Divide and portions of the
northeastern plains through the evening hours.

On Friday...models show a 90KT+ jet oriented from southwest to
northeast across the western two thirds of Colorado. QG forcing
associated with the jet combined with increased mid level
moisture will result in a better chance for showers and
thunderstorms...mainly across the high country. Temperatures on
Friday should also be a few degrees cooler than Thursdays readings
due to increased cloud cover and some cold air advection.

Much cooler temperatures are expected across all of north central
and northeastern Colorado over the weekend into early next week
as the upper trough moves across the Rocky Mountain Region and a
series of cold fronts move across the northeastern plains of
Colorado. The combination of upslope flow...increased low and mid
level moisture and QG lift from a 90kt+ upper level jet should
result in better precipitation chances as well. Snow levels should
remain above 10,000 feet.

There is quite a bit of difference when comparing the NAM with
the GFS and ECMWF in Saturday`s weather. The NAM sounding and
cross section suggest drizzle and light rain in Denver much of the
day with high temperatures only in the 40s...while the GFS and
ECMWF runs have temperatures in the upper 50s to lower 60s along
with scattered showers possible. Think the NAM is too cool and
wet...while the NAM and ECMWF may be a little too warm and dry.
Therefore...have decided to do a compromise of the models and have
lowered Saturday`s max temperatures a few degrees while raising
pops slightly.

Sunday should be a cool and cloudy day across northeastern
Colorado with scattered to numerous rain showers possible. Max
temperatures will only be in the 50s across most plains locations.
Precipitation chances should taper off on Monday as the main
upper trough weakens and lifts northeast out of the area.
However...temperatures should remain on the cool side. A gradual
warming and drying trend is expected by the middle of next week.
However...temperatures should still remain below normal values.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 905 PM MDT Wed Sep 20 2017

VFR conditions in store for the next 24 hours. Winds will
generally remain southerly at 6-14kts across the Denver metro
area, though KAPA and KDEN could see occasional gusts to around 20
kts throughout the night. On Thursday...expect little change in
wind direction but speeds will be on the increase through the day,
particularly for KAPA and KDEN where afternoon gusts could
periodically reach 30 kts.


&&

.FIRE WEATHER...
Issued at 305 PM MDT Wed Sep 20 2017

Still on track for windy and dry conditions over the Palmer
Divide and across parts of the eastern plains Thursday afternoon.
Upgraded the Fire Weather Watch to a Red Flag Warning. Windy
conditions are expected for the mountains and foothills, however
relative humidities are expected to remain above 15 percent.

Dry and windy conditions are expected Friday over most of the area
ahead of a cold front.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 7 PM MDT Thursday for COZ241-
245>247-249.

&&

$$

UPDATE...Baker
SHORT TERM...Meier
LONG TERM...Kalina
AVIATION...Baker
FIRE WEATHER...Meier



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