986 
FXUS65 KBOU 250558
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1158 PM MDT Thu Sep 24 2026

.KEY MESSAGES...

- Patchy to locally dense fog Friday 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 /06Z TAFS through 06Z Saturday/...
Issued at 1150 PM MDT Thu Sep 24 2026

There were very minimal changes made for these TAFs since the 
last forecast update. Winds have been light and variable to even 
calm over the last few hours. At KDEN and KAPA in particular, 
winds have been mainly southeasterly. There is a ~20% chance that 
a rain shower could make it off the foothills and into the 
vicinity of KBJC through about 8z.

The main focus continues to be on the fog/low stratus potential 
this morning. The wind direction overnight continues to be the 
most scrutinized aspect of the forecast as this will directly 
affect any fog development and in turn the afternoon rainfall 
chances. As discussed previously, a more northerly component to 
the winds would lead to a increased fog potential. 

There is decent agreement that a cyclone will develop early this 
morning. Although, the exact placement remains quite uncertain. We
are most confident that KDEN and KBJC have the highest potential 
for north/northeast winds and thus fog potential. Dewpoint 
depressions are forecast to be around or less than 1 degree
particularly at KBJC and KDEN. Hi-res model guidance shows that 
KAPA could remain with southerly winds this morning, which would 
limit the fog potential. The period of highest concern is from 
about 11z to 15z. A TEMPO covers the possibility for visibility to
drop to 1/2 SM or less for this period if the fog potential were 
to be realized. Confidence is high enough that this TEMPO is in 
place for all three sites. Confidence is higher that there will be
VCFG to the north and northeast of KDEN.

Guidance remains in good agreement that any fog and low stratus 
will clear between 15z and 17z, increasing the potential for 
afternoon storms. If fog and low stratus were to clear more 
slowly, then afternoon storm chances could decrease. If fog and 
low stratus clear more quickly, afternoon storm chances could 
begin a bit earlier than what is currently in the TAF. TEMPO 
groups from about 21/22z to 1z are in place for Friday afternoon 
at all three sites. Hi-res model guidance shows that 
thunderstorms could move off the higher terrain first affecting 
KBJC and then eventually KDEN and KAPA. Given more instability 
than Thursday is expected, the TEMPO groups include the chance for
some gusty and erratic winds up to about 35 kts as well as 
briefly lowering ceilings to ~5,000 ft AGL. There is a low chance 
that showers and storms could linger a bit after the TEMPO. Winds 
should quickly turn to drainage with cloud cover starting to 
decrease by late evening and into the overnight.

&&

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

&&

$$

DISCUSSION...AP/AGS
AVIATION...MV