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000
FXUS65 KBOU 211003
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
403 AM MDT Sun Apr 21 2024

.KEY MESSAGES...

- Areas of dense fog across the lower foothills, I-25 corridor,
  and adjacent plains early this morning.

- Warmer and mainly dry weather through Wednesday Warming and
  drying trend begins on Sunday, with highs back in the 50s or 60s

- Potential for stormier weather pattern starting late Thursday
  into this coming weekend.

&&

.SHORT TERM /Through tonight/...
Issued at 218 AM MDT Sun Apr 21 2024

Current radar shows a few lingering showers in the mountains and an
occasional brief weak echo around the Denver Metro area. Low level
moisture is still intact across the region. Nighttime microphysics
satellite imagery shows low stratus over a good portion of northeast
Colorado early this morning. The potential for fog early this
morning is still up in the air (no pun intended). Patchy fog is
being reported in parts of northern Weld County. The Denver Metro
has been under a consistent layer of low stratus. Some locations
such as DIA reporting reduced visibility (2-5 miles) this AM with
"mist" and lower ceilings. There is high confidence that this low
stratus stays put this morning with reductions in visibility in
spots. Areas of fog in northern Weld and Logan Counties will result
in lower visibilities (< 1 mile) at times. As for the urban
corridor, fog is still pretty low confidence even this close, but
given the shallow moisture and mist already reported, can`t be ruled
out. Generally looking at the fog/low stratus breaking up and
eroding out in the 15-18z timeframe. By the afternoon, we will be
able to see something we haven`t seen much of the past few
days...the sun! Temperatures will likely warm back into the 50s for
the plains. If the low stratus ends up burning off on the earlier
end, could see highs nearing 60.

Tonight, a weak mountain wave sets up, enhancing winds in the higher
mountains and will likely stay confined to those areas. Winds will
peak early Monday morning with gusts up to 55 mph.


&&

.LONG TERM /Monday through Saturday/...
Issued at 330 AM MDT Sun Apr 21 2024

Monday will continue the warming trend with stronger downslope
westerly flow. This will bring breezy conditions to most of the
forecast area, with windier weather and gusts to 30-45 mph in/near
the foothills, and gusts to 60 mph above timberline. The northeast
plains will see an exception, however, as a backdoor cold front is
expected to slip in during the morning hours, and then essentially
stall during the period of max heating in the late morning and
afternoon. Thus, winds will be lighter and high temperatures will
be a little cooler there with upper 60s more likely over the
northern border area. Mid 70s should be reserved for most of the
I-25 Corridor and Denver metro area. Mountain areas will see a
continuation of mild weather with 50s and a few lower 60s showing
up in valley locations. An isolated high based shower/storm would
be possible mainly over the mountains or perhaps the Palmer Divide
late in the day, but only a brief period of light rain/sprinkles
would be possible given the deep and dry subcloud layer. Most
areas will remain dry.

For Tuesday, there has been a slow trend toward cooler
temperatures with a stronger surface high pressure building over
the Central Plains. We still think we`ll be able to sneak into the
lower to mid 60s over the plains and I-25 Corridor, but a low
probability (20-30% chance) of some upper 50s over the eastern
plains.

Wednesday will then turn warmer as expected, with highs likely
pushing into the upper 70s, and still a chance (40-50%) that we
get near 80F per 500-1000 mb thickness reaching 570 dm. That said,
the slower trend of retreating high pressure to the east could
also keep us a few degrees cooler. Nonetheless, a warm day is in
store with breezy southerly winds over the eastern plains -
lending itself to elevated fire weather conditions.

For Thursday and beyond...there`s more certainty of a lead
shortwave reaching Colorado by late Thursday, as the EPS is now in
more agreement with earlier and faster runs of the GEFS. Thus,
we`ll likely (60-70% chance) start our return to unsettled weather
by Thursday afternoon and evening as we destabilize ahead of the
first ejecting shortwave. Behind that, we`ll probably see some
sort of drying/ridging before another deeper trough arrives
sometime next weekend. The National Blend of Models (NBM) was
quite aggressive with PoPs this entire time, so we did scale back
some especially on Friday which has the greatest potential to be
in between shortwaves. It still looks to be an unsettled period
with daily chances of showers and storms. Greater coverage will
occur with each passing shortwave, and especially with the deeper
trough/closed low that is likely (~70% per ensembles) to reach
our forecast area toward next Sunday. That last storm system
will have the greatest potential to bring more widespread and
heavier precipitation, and also lowering snow levels through the
foothills if the stronger and colder solutions verify.

&&

.AVIATION /06Z TAFS through 06Z Monday/...
Issued at 1205 AM MDT Sat Apr 20 2024

A few snow showers are around the terminals early this morning
with a few of them reducing visibilities to a 1/2SM at times.
The overnight period will be the trickiest part of the forecast.
There is high confidence that there will be low stratus intact
overnight at terminal with at least periods of BR. The lower
confidence element remains the fog potential. The
consistency/coverage of the fog and exact timing are hard to
pinpoint, even out a few hours from now. Either VCFG or FG have
been messaged in the TAF. Gradual improvement in ceilings is
likely from 16-18z with a low chance for lingering BR or IFR cigs
at or after 18z. Light and variable winds become SE/ESE this
afternoon at 08-11 kts. Winds transition to S/SW drainage early
this evening. Later this evening, once drainage is established,
winds increase closer to the 09-14 kt range.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM MDT this morning for COZ036-
038>043-045-046.

&&

$$

SHORT TERM...Mensch
LONG TERM...Barjenbruch
AVIATION...Mensch