604
FXUS65 KBOU 251752
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1152 AM MDT Fri Sep 25 2026

.KEY MESSAGES...

- Patchy to locally dense fog this morning, primarily for areas
  north of I-70 and along and east of I-25.

- Another round of showers and isolated storms Friday afternoon
  and evening.

- 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 chances (40% to 60%) for mountain snow above 11,000ft
  late Monday into Tuesday.

&&

.DISCUSSION /Through Thursday/...
Issued at 1134 PM MDT Thu Sep 24 2026

Most of today`s precipitation has cleared out of the area, with some
small showers still hanging around over the foothills and up in
northern Larimer County. Winds are starting to settle in a more east-
southeast pattern, and are expected to stay that way overnight,
allowing for fog/low stratus to form over the plains and north
Denver metro area. We expect the densest fog to be over the Ft.
Morgan area and into southern Weld County, with patchy fog extending
into the northern Denver metro. Fog/low stratus should dissipate in
the morning but mid-level cloud cover should remain into the
afternoon.

Models are in pretty good agreement on tonight and tomorrow
morning`s south-southeast flow kicking off a Denver Cyclone by mid-
day. Upslope winds from the low-level cyclone coupled with the upper-
level shortwave forecast to move through the area in the afternoon
should initiate some isolated to scattered showers off the higher
terrain, which should then propagate east along the trough axis. How
strong these showers become will be dependent on how much cloud
cover we retain into the late afternoon, and subsequently how much
surface heating we get. If we do end up with an isolated
thunderstorm or two, we could see some localized heavy rainfall.

Most of the model guidance is in agreement on there being convection
over the southern foothills/Palmer Divide and moving over the
southern portions of our CWA, which could warrant some minor
flooding concerns for the areas that have seen more precipitation
over the last couple of days. Should the current HRRR and RAP
solutions pan out, we could see more widespread coverage, with
showers moving across most of the urban corridor in the late
afternoon and into the plains in the evening.

Temperatures will warm above normal for the weekend as upper level
ridging builds in behind the shortwave from Friday. A dryline is
forecast to push east through the area late Friday into Saturday,
bringing much lower dewpoints into the area. The drier air and
ridging aloft will decrease rain chances and bring warmer
temperatures through the weekend (highs in the 80s for much of
the plains).

The system next week still looks very uncertain. Models continue to
jump back and forth between runs with the speed, strength, and
positioning of the upper level trough next week. There are a few
concerning model runs and ensemble members that bring more
substantial rain totals to our area, but there are also a number
of ensemble members (~30%) that bring very little rainfall for
much of our forecast area. Right now, this system is a potentially
high impact, low confidence event, with serious bust potential
depending on the track of the upper low. The main thing to watch
is how Hurricane Polo gets absorbed into the flow aloft. The runs
which have Polo moving a bit more north, with moisture from this
tropical system flowing into the area from southwest flow aloft as
it moves into the continental U.S., and then have the upper low
sitting just southeast of the area with wrap around moisture
through the column are the more concerning solutions. Other
solutions, keep the moisture associated with this tropical system
and the better lift associated with the upper low to our
southwest, leaving us with significantly less precip.

We know that people are also very invested in the potential for
mountain snow next week. Since the rain amounts are highly
uncertain, the snow amounts are also highly uncertain. And with
the snow we have the added uncertainty of temperatures next week.
Model spread is still pretty significant with the 25th to 75th
percentiles differing by 8 to 15 degrees for a good portion of
the Front Range and plains for Tuesday through Thursday. If we`re
on the cooler side, SLRs will be higher and snow level could drop
a bit lower, giving us some higher snow totals. Right now, the
best chances for snow look to be Tuesday morning above 11,000ft,
with medium chances (40%-60%) for at least some light snow
accumulations. The moral of the story: the forecast for Monday
through Thursday will remain highly uncertain until we get closer,
and this system is definitely something to keep an eye on. Check
back as we get closer for more details about potential snow and
rain amounts.

&&

.AVIATION /18Z TAFS through 18Z Saturday/...
Issued at 1150 AM MDT Fri Sep 25 2026

Fog and stratus had lifted to a SCT deck (except at KBJC where it
was still BKN as of 1730Z). That, too should gradually lift and
break with further warming. ACARS soundings showed very little
convective inhibition, and a compact shortwave was lifting
east/northeast across the Wyoming/Nebraska border. With those
ingredients, we expect a round of thunderstorms to develop along
the Front Range and move east across the TAF sites 20Z-24Z. High
enough coverage and intensity/moisture to warrant TEMPO with some
visibility restriction and VRB G35kts. There is just a slight
chance that a shower/storm would linger past 00Z.

Then skies will clear overnight, with any storm influenced winds
turning more S-SSW 01Z-04Z. We expect a pretty solid drainage
winds at 8-12 kts and no cyclone, so that would limit any fog
threat to the the South Platte River valley well north and east of
the Denver area TAF sites.

&&

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

&&

$$

DISCUSSION...AP/AGS
AVIATION...20

NWS BOU Office Area Forecast Discussion