521
FXUS65 KBOU 291147
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
547 AM MDT Wed Apr 29 2026

.KEY MESSAGES...

- Areas of patchy fog, resulting in low visibilities for the
  Phillips and Sedgwick Counties through mid morning.

- Scattered showers and isolated weak afternoon thunderstorm.

- More active pattern continues through Friday with highest chance
  of precipitation in/near the Front Range Thursday - Thursday
  night.

- Warmer and drier conditions expected for the weekend.

- Chance of showers returns early next week.

&&

.UPDATE...
Issued at 341 AM MDT Wed Apr 29 2026

Increased PoPs for this morning. A band of showers stretches
across the southern part of the Denver area and onto the plains.
The showers should hold together through mid morning. Additional
showers are expected later this morning ahead of a shortwave
trough currently over southern Utah, southern Nevada, and
northernArizona. Lift from this wave shifts east of the area this
afternoon. However, scattered showers are expected to continue
this afternoon due to a slightly unstable airmass and a weak
northeast upslope flow. Precipitation amounts are expected to be
light, less than a quarter inch and in most cases less than a
tenth inch.

The next system (2 pieces) starts to affect the region tonight as
a trough drops south-southeast out of the Northern Rockies. QG
ascent will be weak. Upslope flow will be deep, reaching 650-700
(mb), but weak with speeds of 5 to 15 knots. The second piece of
this system travels east-northeast out of eastern Pacific Ocean
and then along the Mexico border. A good amount of moisture will
accompany this, but stays well south of the forecast area. Most
model QPF seems overdone, because lift (QG ascent & upslope) will
be weak and the best moisture stays well south of the area. The
00Z ECMWF, along with AIGFS and ECMWF-AIFS all keep precipitation
amounts less than a half inch across the forecast area late
Wednesday night through Friday. For areas north and northeast of
Denver, precipitation will be light and may not occur at all over
the northeast plains. Cut QPF and snowfall amounts because of this.
If this trend continues, precipitation amounts will need further
reduction.

&&

.DISCUSSION /Through Tuesday/...
Issued at 1118 PM MDT Tue Apr 28 2026

Current radar imagery shows decreasing showers over the forecast
area, with upslope flow allowing a few additional rain showers along
the Urban Corridor. As subsidence filters in behind the exiting
upper level shortwave, expect showers to gradually end in the next
few hours, with partly cloudy skies behind it. Due to this,
radiation fog is likely across our northeastern plains through
Wednesday morning.

The break in precipitation will be shortlived as another weak
shortwave trough treks across Colorado Wednesday afternoon. Increase
in QG lift and mid-level frontogenesis will permit another round of
scattered showers (and light mountain snow), particularly for the
southern foothills, Palmer Divide, and Lincoln county areas due to
best forcing. Afternoon instability should grow, with MLCAPE between
100-500 J/kg to support isolated weak thunderstorms. Temperatures
will likely reach up to the low 60s for most of the plains, however
that will still keep us about 4-6 dg F below seasonal averages. A
weak cold front in the late afternoon/evening will bring cooler
temperatures for Thursday.

Some uncertainty still remains in the forecast for Thursday into
Friday, despite being about 48-hrs out. A 500-mb closed low
associated with a longwave trough over central U.S. will begin
trekking east from southern California into New Mexico on Thursday.
For our forecast area, this will result in weak QG ascent and
potentially light upslope flow, from the surface up to about
700-mb according to cross-sections. These two forcings will
promote precipitation, mainly for our Front Range
mountains/southern foothills, Urban Corridor, and Palmer Divide.
Places farther north and east unfortunately likely won`t see most
of this precipitation.

QPF amounts vary between guidance, however models do agree that the
southern Front Range mountains/foothills and portions of the Palmer
Divide will receive the most QPF, with some guidance indicating
about 1.00" of QPF by Friday morning. For the Urban Corridor,
anywhere from 0.20"-0.60" QPF likely depending on the strength and
duration of upslope flow. For portions of Weld county and east to
the northeastern plains, T-0.20" QPF due to overall less forcing. It
is interesting to note that both the AIGFS and ECMWF-AIFS seem less
enthusiastic with QPF compared to the deterministic runs. In
addition, there are discrepancies between hi-res guidance, with
the NAM also less enthusiastic compared to the HRRR. This large
spread in QPF values will lead to some uncertainty with total
snowfall amounts for our mountains and foothills. Temperatures on
Thursday will support snowfall above 6500-7000 ft. If guidance
starts honing in on wetter solutions, winter weather highlights
will be warranted, as travel will likely be impacted on Thursday
and possibly Friday morning, particularly for the I-70 mountain
corridor. Will hold off on any highlights for now due to the
uncertainty.

For the weekend, warmer and drier weather is expected as an upper
level ridge builds over the Rockies. Ensemble guidance is now in
better agreement of temperatures rising above normal, reaching the
low 70s by Sunday. This will be shortlived, however, as models try
to resolve multiple disturbances early next week, which will bring
almost daily chances for precipitation.

&&

.AVIATION /12Z TAFS through 12Z Thursday/...
Issued at 547 AM MDT Wed Apr 29 2026

The next system will continue to bring scattered showers and low
to mid clouds today. Ceilings are expected to be in the 4000 to
8000 foot range. Winds will shift to the north to northeast late
this morning (16-18Z). Showers increase after 18Z, with ceilings
under the showers falling to around 3000 feet. A brief weak
thunderstorm is possible 18-02Z (a 10-15% chance). The chance for
showers continues through 06Z, and then decreases 06-12Z.
Ceilings will lower slowly after 00Z Thursday falling to 1500 to
3000 feet after 06Z.

&&

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

&&

$$

UPDATE...12
DISCUSSION...MAI
AVIATION...12

NWS BOU Office Area Forecast Discussion