356
FXUS65 KBOU 250026
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
626 PM MDT Thu Sep 24 2026

.KEY MESSAGES...

- Some showers this evening and overnight, followed by some patchy
  fog.

- One last round of showers/storms likely Friday afternoon.

- Drier and warmer this weekend before an upper level trough
  brings cooler temperatures and potentially our next chances for
  showers/storms early next week.

- Medium chance (30% to 50%) for mountain snow above 10,000ft
  late Monday into Tuesday.

&&

.DISCUSSION /Through Thursday/...
Issued at 124 PM MDT Thu Sep 24 2026

It`s been a relatively cool and cloudy day across most of our
forecast area, though there`s been little rain to speak of so far.
There have been a few areas of slightly deeper cumulus across the
northern mountains and along a weak surface boundary in Weld
county which have produce some light showers. A few additional
showers could develop along any convergent boundary this afternoon
and evening, but otherwise the rest of the afternoon should remain
fairly quiet.

As we get into the evening hours, a very weak mid-level low is
forecast to slide into northwestern Colorado, leading to a brief
period of east-southeast upslope developing across the forecast
area. Combined with some modest surface convergence and increasing
MUCAPE, this should allow for a cluster of showers and
thunderstorms to develop over the northern foothills this evening
into the early overnight hours. If the HREF/REFS members are to
be believed, some locally heavy rainfall would be possible before
upslope quickly diminishes after midnight. Moist easterly surface
flow overnight should allow for widespread fog and stratus to
develop across the plains, with that wrapping into the
northern/northwestern half of the Denver metro by early Friday.

The overall forecast changes very little tomorrow. The
broad/disorganized upper trough will kick out one last weak
shortwave on Friday. We should see isolated to scattered
showers/thunderstorms develop by midday over the higher
elevations, with this activity pushing eastward through the
afternoon and evening. Deterministic guidance remains fairly
bullish with metro precip chances, though I`d want to see how the
overnight fog/stratus plays out before committing to higher PoPs.

The exiting upper trough will quickly be replaced by weak ridging
across the region by Saturday, leading to a warm and dry weekend.
Most statistical guidance warms temperatures into the mid 80s on
both Saturday and Sunday, with only enough moisture for some
scattered cloud cover across the higher elevations on Sunday.

Attention then turns to the potential for a stronger storm system
to impact the region by sometime early/mid-week. Guidance
generally agrees that a sharp upper trough axis will reach the
northern California coastline by Sunday evening, which then drifts
into the desert southwest towards the Four Corners region by
Tuesday. Forecast confidence quickly decreases during this period,
with solutions ranging from a strong cutoff low over Baja
California to a positively tilted trough that quickly swings into
western Texas, with a few more favorable solutions scattered in
between.

There are a few interesting tidbits across the past couple model
cycles that are worth noting. First, while ensemble mean solutions
look favorable for precipitation here, there is a distinct bi-
modal distribution in forecast QPF within each respective ensemble
system. This would imply that this storm is "boom or bust", with a
fairly even split between boom/bust at this point in time. There
are also additional complications from the interaction with what
would be the future remnants of Hurricane Polo. While the
deterministic forecast (NBM) is a fairly reasonable middle ground
(i.e., cooler and increasing chances of rain/mountain snow),
predictability and forecast confidence will be low for the next
several days.

&&

.AVIATION /00Z TAFS through 00Z Saturday/...
Issued at 538 PM MDT Thu Sep 24 2026

Moist upslope flow brought a few showers around and over the
Denver TAF sites this afternoon, while they haven`t been heavy
rainers, there were a few microbursts in fairly close proximity
to KDEN/KAPA. Current radar shows many lingering boundaries reside
across the plains at this time, with some nearly stationary
showers across Weld County. The PROB30 was kept in place through
3Z this evening to account for shower potential as well as
potential wind shifts due to the aforementioned boundaries.
Expecting winds to turn to the southeast by around 3Z, turning the
greater shower potential towards the north, decreasing shower
potential across the TAF sites. With showers expected to develop
to the NW of the TAF sites, can`t rule out potential for an
outflow to slide south across the TAF sites, but will have to
monitor as showers develop with the onset of the southeasterly
winds.

A cyclone is expected to develop Friday morning that brings low
confidence in wind direction and fog development in the early
morning hours, and as such, will have some impacts on afternoon
storm development too. If the airports manage to hold onto a more
southerly wind component, fog may manage to stay just outside of
the TAF sites, but any northerly winds will advect fog across the
airfields. KBJC will have the highest likelihood of fog as there
is some consistency amongst guidance that the cyclone will bring
northerly winds between 7Z-9Z, with fog moving across the field
between 12Z-15Z, but while the low certainty remains, there is
enough confidence with the right ingredients in place for VCFG and
a TEMPO for a few hours of fog reducing VIS to around 1/2 SM
between 11/12Z-15Z across all the TAF sites.

Depending on how quickly fog and stratus clear out in the morning
may impact afternoon storm development. Guidance does show
consistency in stratus breaking up around 15Z-16Z, which does lead
to slightly higher confidence in afternoon storms moving across
the TAF sites for the later afternoon hours, especially with a
shortwave expected to trek across the area in the afternoon. A
TEMPO is now in place at all TAF sites, with storms expected to
impact KBJC around 21Z before shifting east across KAPA and KDEN
shortly thereafter. Expecting some stronger winds than today,
with gusts between 35-40 kts possible with passing storms, and CIG
dropping as low as ~5,000 feet AGL.


&&

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

&&

$$

DISCUSSION...Hiris
AVIATION...9