072
FXUS65 KBOU 181851
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1251 PM MDT Wed Sep 18 2024

.KEY MESSAGES...

- Dry and warm through Friday with elevated fire weather
  conditions.

- Cooler temperatures this weekend with good chances (30-60%) for
  rain, and accumulating snow in the Front Range mountains.

&&

.UPDATE...
Issued at 1002 AM MDT Wed Sep 18 2024

The fog by DIA has dissipated this morning and mostly clear skies
are expected the rest of the day. It will be breezy especially in
the higher terrain with gusts up to 40 mph. Otherwise, the
forecast remains on track.

&&

.SHORT TERM /Through Tonight/...
Issued at 326 AM MDT Wed Sep 18 2024

A subsident southwest flow aloft will prevail today behind
yesterday`s storm system. Weak ridging in the southwest flow aloft
will move over the state tonight and into Thursday. The airmass
dries out with mostly clear skies expected today and tonight.
Relative humidities fall into the lower teens today to elevate the
fire danger, but wind speeds here are expected to be less than 25
mph. Breezy conditions are expected over the higher terrain with
southwest winds gusting to 25 to 35 mph. In these areas relative
humidities will be in the upper teens and more so in the 20s. It
will be another warm day for this time of year with highs in the
lower to mid 80s over northeast Colorado.

For tonight, winds decrease with the ridging moving overhead. Low
temperatures will be chilly due to the dry airmass, light winds, and
clear skies. Most of northeast Colorado is expected to fall into the
40s with the mountains valley expected to dip below freezing (upper
20s to lower 30s).

&&

.LONG TERM /Thursday through Tuesday/...
Issued at 326 AM MDT Wed Sep 18 2024

Zonal flow will continue over northeastern Colorado as an upper
level ridge begins to transition eastward. Cross sections indicate a
relatively dry airmass Thursday which will lead to limited
precipitation over the region. With above normal temperatures and
the transition of upper level systems increasing pressure gradients,
low level southerly winds increase along the Palmer Divide, Lincoln
county and parts of the urban corridor. Although winds remain below
red flag warning criteria, near critical fire weather conditions are
possible Thursday afternoon for the areas listed above.
Additionally, similar conditions are possible Friday afternoon. The
combination of daytime heating, weak mid-level moisture, and QG
ascent could lead to isolated chances of a high based storm or two
along the higher elevations Friday afternoon. Thus decided to keep
low (10-20%) chances through Friday evening.

The next upper level trough arrives early Saturday morning. Both GFS
and ECMWF continues to display an abundance of QPF over our area. No
major changes from ensembles as Denver QPF ranges from 0.30-2.50
inches. Given that models have better agreement on the trough axis
placement providing a brief window of upslope flow, it isn`t out
of the question parts of the urban corridor could receive up to a
half an inch or higher with this system. The flash flood threat
increases over recent burn areas this weekend. There is still
lingering uncertainty in the speed of this system which could
affect our precipitation amounts. It is likely by Saturday
evening, the entire region should receive scattered to numerous
showers and storms. Also there is high confidence this weekend`s
afternoon temperatures will become cooler. In fact, 700-850mb
temperatures drop near 2-4C across the CWA which should result in
mid 60s to low 70s for the lower elevations. Higher elevations
cool significantly between 40-56 but areas above 11k should remain
cold enough for a few inches of light snow through Sunday. By
early next week, ensembles have been persistent keeping near
normal temperatures therefore decided to decrease NBM highs both
Monday and Tuesday afternoon.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1248 PM MDT Wed Sep 18 2024

VFR through the TAF period. Light southwest winds will eventually
become light northeasterly. Tonight, light drainage winds are
expected. Southeasterly winds will increase tomorrow afternoon
with gusts up to 20 knots possible.

&&

.FIRE WEATHER...
Issued at 326 AM MDT Wed Sep 18 2024

Southwest flow will bring dry weather to the area today. Relative
humidities fall into the lower teens this afternoon across the
plains. It will be somewhat breezy across the plains, mainly south
of I-70 where gusts of 15 to 25 mph are expected. Over the higher
terrain, southwest winds will be a little stronger with gusts of
25 to 35 mph. Relative humidities over the higher terrain will
range from the upper teens to mid 20s.

Relative humidities drop near 11-17 percent for the Palmer
Divide, Lincoln county and parts of the urban corridor both Thursday
and Friday afternoon. Winds remain below warning criteria thus
leading to near critical fire weather conditions. There is a greater
threat of near critical fire weather conditions Friday afternoon as
southerly winds may increase. Will continue to monitor.

&&

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

&&

$$

UPDATE...Danielson
SHORT TERM...Meier
LONG TERM...AD
AVIATION...Danielson
FIRE WEATHER...Meier/AD