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000
FXUS65 KBOU 020325
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
925 PM MDT Sat Apr 1 2023

.UPDATE...
Issued at 925 PM MDT Sat Apr 1 2023

The dry airmass remains in place over the CWA, as the active
wildfires in the mountains and foothills attest too.  The low level
winds are pretty weak tonight in most areas with drainage patterns
beginning to set up. There is some high cloudiness pushing
southeastward across the forecast area currently. Will only need
some minor wind and sky GFE grid updates this time around.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 245 PM MDT Sat Apr 1 2023

Water vapor imagery shows dry westerly flow over Colorado with
mountain waves to the lee of the Front Range mountains. There is a
shortwave trough over the Pacific Northwest that will move well
north of our forecast area tonight and tomorrow. Flow aloft will
stay westerly tonight and tomorrow and will increase in strength
as another trough moves its way into the Pacific Northwest. There
will be minimal moisture associated with this westerly flow so the
vast majority of our forecast area will be dry through tomorrow
evening. The only area that could see some light snow showers is
the Park Range mountains and far northern Front Range mountains
although minimal, if any, accumulation is expected. Another mild
day with mostly sunny skies is expected Sunday. Highs will be in
the 60s across the plains and in the 40s in the mountain valleys.

There are two main weather concerns tonight and Sunday which are
strong winds and fire weather conditions. Strong flow aloft with
subsidence in the mid levels will allow for a mountain wave to
form tonight. Wind gusts could reach up to 75 mph in the higher
northern foothills. There was some consideration for a High Wind
Warning but the gusts up to 75 mph should be limit in coverage so
a warning was not issued. The mountain wave will diminish somewhat
during the day as stability decreases and winds will decrease
slightly in the mountains and foothills as a result. Elsewhere,
the winds will increase in speed over the plains and South Park.
Gusts could reach 50 mph in South Park and up to 40 mph across the
plains. With winds this strong, critical fire danger will develop
across any areas that have low enough humidity. The fire weather
is discussed further below.

.LONG TERM...(Sunday night through Saturday)
Issued at 223 PM MDT Sat Apr 1 2023

A stg storm system will move into the Great Basin late Mon and then
move eastward across the area on Tue.  Ahead of the system, stg sfc
low pres will develop over ern CO on Mon and then move into into wrn
CO by Tue.

Overall, as the upper level low moves into the Great Basin, a stg
upper level jet will combine with increasing QG ascent and decent
lapse rates to produce an increasing chc of snow showers mainly
over the Park Range on Mon. Otherwise, expect mainly dry and windy
conditions elsewhere. Temperatures across the plains will be
mainly in the 60s, however, near the WY-NE border where a fntl
boundary may stall out readings may hold in the upper 40s to mid
50s.

For Mon night thru Tue, the main upper level low will move across
with the current track expected along the CO-WY border.  Analysis of
500 mb height falls and 250 mb WAA suggest it could track a bit
further south but for now will go with the ECMWF track.  As the
system moves across, there will be stg QG ascent along with steep
lapse rates.  As a result, may see a convective band of heavier snow
in the mtns Mon night which will then transition to more of an
orographic event on Tue as the winds become more WNW.

Across the plains, there should be a band of convective driven
precip Mon night into early Tue with a quick changeover to snow.
Based on current expected track of the main upper level low can`t
completely rule out some potential for heavy snow near the WY-NE
border.  In addition, expect gusty north winds to develop over the
plains as well.  Temperatures will drop into the 30`s over nern CO
on Tue.

Looking ahead to Tue night and Wed, an intense upper level low
will be over South Dakota withe WNW flow aloft across the area.
Lingering moisture in the mtns will allow for periods of light
snow. Over nern CO it will be mainly dry. However, a secondary
surge of cold air may combine with a disturbance embedded in the
flow to produce a chc of light snow in and near the foothills
mainly Wed night.

On Thu, drier air in WNW flow aloft will spread across the area with
a decreasing chc of snow in the mtns.  Across the plains, it will be
dry with highs remaining below normal.  Little change is expected
for Fri, however, downslope low level flow will allow for
temperatures to rise back to seasonal levels over nern CO.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 925 PM MDT Sat Apr 1 2023

South-southwesterly winds are in place at DIA already this evening.
This should continue into Sunday morning. Models are showing the
stronger westerly winds to get going again at DIA at around 19Z
Sunday afternoon.  There will be no ceiling issues.

&&

.FIRE WEATHER...
Issued at 223 PM MDT Sat Apr 1 2023

Winds will be strong during the day on Sunday with gusts up to 50
mph in South Park and up to 40 mph across the plains especially
along the Palmer Divide. The limiting factor for fire weather
conditions will be relative humidity. The best chance for
relative humidity to drop below 15 percent is across the Palmer
Divide and east-central plains of Colorado. Therefore, a Red Flag
Warning was issued for there. In addition, South Park will be
close to having humidity in the teens and with stronger winds
there and a fire already ongoing, a Red Flag Warning was issued
there. There remains uncertainty over the Denver metro and
northern I-25 corridor as to whether Red Flag conditions will
develop. There will be some extra moisture north of I-70 that
will keep relative humidity a bit higher there. In addition, winds
will likely be weaker, only gusting to 25 mph. It is possible
that areas to the west of I-25, like Boulder, Longmont, and Fort
Collins, may end up needing a Red Flag Warning if dew points end
up being lower than forecast and winds are on the higher side of
guidance.

Critical fire danger will be in place on Monday over the Palmer
Divide extending into Lincoln county.  Gusty south to southwest
winds up to 40 mph along with very low humidity will be in place.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday evening through Tuesday evening
for COZ031.

Red Flag Warning from 11 AM to 8 PM MDT Sunday for COZ214-241-
246-247.

&&

$$

UPDATE.........RJK
SHORT TERM.....Danielson
LONG TERM......RPK
AVIATION.......RJK
FIRE WEATHER...Danielson/RPK