964
FXUS65 KBOU 211819
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1219 PM MDT Tue Apr 21 2026

.KEY MESSAGES...

- Dry and unseasonably warm weather continues through Wednesday.
  Highs will be nearly 20 degrees above normal today and
  Wednesday.

- Critical fire weather conditions will occur on Wednesday due to
  gusty winds and very low humidity. Elevated to critical
  conditions are possible on Thursday.

- Pattern change to cooler and unsettled weather Friday through the
  upcoming weekend.

&&

.DISCUSSION /Through Monday/...
Issued at 1130 PM MDT Mon Apr 20 2026

The axis of an upper level ridge will be directly over Colorado on
Tuesday which will lead to very mild temperatures. The I-25
corridor and eastern plains will have no trouble getting into the
80s with plenty of locations reaching the mid 80s. There will be
mostly sunny skies with light winds and very dry humidity.

A shortwave trough will move from California to very far northwest
Colorado by late Wednesday afternoon. Ahead of this trough,
subsident, southwesterly flow will develop across our forecast
area. This will lead to the warmest temperatures this week as
highs across the I-25 corridor and eastern plains will be in the
mid to upper 80s. There will be significant fire weather concerns
due to very dry and breezy conditions and that are discussed
further in the fire weather section below. Otherwise, a few late
afternoon and evening snow showers are possible in the northern
mountains with minimal accumulation expected. Across the very far
northeast corner of the state, a dryline will either setup in
Phillips and Sedgwick Counties or just east in Nebraska. SPC has
those counties in a marginal risk of severe weather and if the
dryline does setup in Phillips and Sedgwick Counties, a brief
marginally severe storm could occur with strong winds and hail
possible.

A cold front will move across our forecast area Wednesday night
helping to cool temperatures and raise dew points slightly.
Thursday will see highs closer to normal with the mid to upper 60s
across the plains. The challenge with Thursday`s forecast will be
to predict the strength and coverage of the mountain wave winds. A
westerly push of wind behind the cold front with subsident flow
will help develop these mountain wave winds. The initial thinking
is that the strength of the inversion will be weak and the length
of time of the west winds will be brief. This would result in a
weak mountain wave where strong winds would not reach below 6,000
feet. However, there are a few ensemble members (10-20% of global
ensembles) that have 60-70 mph winds at KBDU. So while the chance
of strong winds reaching into lower elevations like Boulder and
Golden is low, it is certainty possible. If this mountain wave
pushes across lower elevations, a Red Flag Warning could be
needed.

Friday through early next week, a longwave trough will be
positioned over the western US. This will linger for a while due
to an omega block in southeast Canada. During a typical year, such
a long period of troughiness with multiple shortwave moving across
Colorado would lead to a wet period for our forecast area and
especially the northern mountains. So there is plenty of optimism
for this upcoming pattern and PoPs are relatively high for the
extended forecast. However, with such a significant drought
ongoing, we all know this isn`t a typical year. Humidity recovery
leading up to low pressure systems coming across our area has
been nothing short of terrible. So if we can overcome the lack of
moisture, this period will have plenty of opportunities for
healthy precipitation.

&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1140 AM MDT Tue Apr 21 2026

VFR conditions are expected through this TAF package. Winds are
light and variable across the terminals early this afternoon.
Winds will turn more easterly over the next hour or two,
increasing in speed from the SE around 23Z today. Wind gusts
around 19kts are expected at KAPA for a few hours this evening,
with a low chance for occasional gusts around 18kts at KDEN as
well. Winds will continue to turn clockwise, becoming more
southerly late this evening and increasing wind speeds closer to
16kts at KDEN for a a few hours. Winds overnight will turn more
SSW at all terminals, with speeds around 8 to 11kts. KAPA and
KDEN will start to see stronger SSW winds move into the area near
16Z, with gusts around 20 to 25kts. KBJC is a bit more uncertain
as to when the stronger winds will get there. It will likely be
around 18Z give or take an hour or two. So we`ve left mention of
gusts out of KBJC at this time, since it`s right at the end of
this TAF package.

&&

.FIRE WEATHER...
Issued at 1130 PM MDT Mon Apr 20 2026

Southwest winds will bring in exceptionally dry air on Wednesday.
Dew points could reach the low single digits and with
temperatures in the mid to upper 80s, relative humidity could fall
to 4% across the I-25 corridor and eastern plains. Therefore, the
fuels and the humidity will be at extremely critical levels.
Predicting the winds will be more difficult. During these
southwest flow events, winds can be slow to develop and sometimes
are weaker than expected for a while. Nonetheless, there is
confidence that winds will gust between 35-45 mph which is why the
Fire Weather Watch was upgraded to a Red Flag Warning. The
northern foothills were added to the warning because that area
will likely be the windiest spot.

There is a small chance (10-20%) a mountain wave will setup and
produce strong winds in Boulder and Golden and nearby areas on
Thursday. If this does setup, it would lead to critical fire
weather conditions due to the strong winds and low humidity around
15%. However, the chance of strong winds is low enough that no
highlights were issued at this time.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 10 AM Wednesday to midnight MDT Wednesday
night for COZ214>216-238>251.

&&

$$

DISCUSSION...Danielson
AVIATION...AP
FIRE WEATHER...Danielson

NWS BOU Office Area Forecast Discussion