212
FXUS65 KBOU 220533
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1133 PM MDT Wed Oct 21 2026

.KEY MESSAGES...

- Warm and dry conditions continue across the lower elevations for
  the next few days, with scattered light rain and snow showers
  across the higher elevations.

- An uncertain precipitation forecast, but cooler, wetter weather
  likely returns this weekend.

- At least a brief warm-up likely sometime next week.

&&

.DISCUSSION /Through Wednesday/...
Issued at 1120 PM MDT Wed Oct 21 2026

Widespread moisture remains over the state this evening,
underneath a broad plume of moisture embedded in south-
southwesterly flow extending into Baja California and the east
Pacific. While some light showers have occasionally made it into
our forecast area today (including a couple sprinkles across the
Denver metro!), the more significant precipitation remains over
the southwestern half of the state, where significant rainfall is
likely over the next 24-48 hours.

The main synoptic features will not change significantly on
Thursday, leading to a largely similar forecast here. A broad
ridge will remain centered over the southern Great Plains, while a
strong upper level low drifts from the southern California
coastline towards the central CA/NV area by Thursday evening. The
fetch of deep moisture will remain in place across the state, with
forecast specific humidity, integrated vapor transport, and
precipitable water all reaching standardized anomalies of 4-6
sigma... falling well outside the climatology for this time of
year. Indeed, GJT`s 00z sounding yielded a precipitable water of
0.96" which shattered the daily record there. Of course, most of
our forecast area is shielded by a few mountain ranges in this
type of flow, meaning that we`ll only see a few rounds of light to
moderate showers across the mountains on Thursday afternoon and
evening when more organized convection can make it this far
north/east. Across the plains... while soundings and ACARS data
confirm there`s plenty of moisture aloft (PW near 0.7-0.8" at
DEN), the deep dry/mixed layer below ~650mb and surface dew point
depressions close to 30F will keep things relatively quiet,
outside of a couple weak showers during the afternoon. Very warm
700mb temperatures - as warm as +8-10C - should lead to high
temperatures in the 70s for the plains, with snow levels as high
as 12-13kft over the mountains.

The main upper low should transition back to an open wave on
Friday, as it begins to interact with a piece of a northern stream
trough/jet. The primary shortwave with this trough is expected to
track from southwestern Utah into western Wyoming, turning the
flow a towards the southwest, leading to a gradual drying trend
across the region. Mid-level flow does increase across the region,
but the stronger QG subsidence is off to our northwest and lee
cyclogenesis will confine most of the stronger wind gusts to the
southeast metro and plains (roughly along/south of I-76). In
addition to the warm temperatures (highs in the upper 70s to near
80F), there could be some spotty elevated/near critical fire
weather conditions where lower RH overlaps with the gusty winds
Friday afternoon.

The aforementioned interaction between the former cutoff low and
the northern stream is where forecast uncertainty really begins to
grow, leading to a few different scenarios for the weekend/early
next week. A second, weaker, cutoff low is expected to develop
over the desert southwest by early Saturday. Meanwhile, a surface
cold front should work through the lower elevations Saturday
morning. We`re confident that temperatures will be much cooler -
with forecast highs somewhere in the 50s across the plains. As the
upper low drifts towards the Four Corners region, low/mid level
moisture is expected to increase. At the very least, this should
allow for widespread cloud cover to redevelop, with chances for
precipitation increasing towards Saturday evening into Saturday
night. Weak QG ascent combined with very weak/shallow upslope
should be enough for scattered showers across most of the area,
with guidance favoring the mountains south of I-70 and portions of
the far eastern plains (where isentropic lift is more prominent),
leaving most of the I-25 corridor in a relative minimum of QPF.

The upper low is expected to weaken as it lifts into northern
Colorado by Sunday and Monday, though there is a rather large
spread in both temperature and QPF forecasts across most of our
forecast area in this period. Subtle differences in the
strength/track of the 700/500mb lows will ultimately determine if
we get another round of rain and snow late Sunday through Monday,
or if we start to quickly dry out to start the week. A bi-modal
distribution in QPF has been noted in some ensemble guidance
today. Given that we`re still 4-5 days out, I would expect it`ll
take at least a couple days before we can feel confident about the
timing or precipitation amounts anywhere in our CWA. Either way,
near/below normal temperatures are likely to continue Sunday and
Monday.

While the overall forecast pattern remains murky, there is a
fairly consistent signal for a modest warming/drying trend by mid-
week next week, with forecast high temperatures returning to near
or slightly above normal values.

&&

.AVIATION /06Z TAFS through 06Z Friday/...
Issued at 1120 PM MDT Wed Oct 21 2026

A few high based showers have occurred late this evening which was
allowing for some mixing of stronger SSW winds in the lower levels.
Most of this has been affecting APA but not BJC or DIA.  Will keep
in a prob30 at APA until 07z for gusty SSW winds.  Otherwise winds
will remain SSW thru 10z with speeds mainly in the 10-15 mph range.
By 11z winds will become more WSW with decreasing speeds.

For the aftn, there will be a chc of high based showers (30-40%) and
possibly a tstm (10%).  Have kept a prob30 in the Tafs between 21z
and 01z Thu evening for this activity.  May also see brief gusts up
to 30 mph as well with any of the showers. Winds by 21z will mainly
be from the SW.

By early Thu evening there will still be a threat of higher based
showers (30-40%) thru 06z. Latest data still shows rather stg SSW
low level flow so may see gusty SSW winds at APA and DIA as these
stronger winds mix down to the sfc. Finally, ceilings with any of
the shower activity should stay at or above 7000 ft.

&&

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

&&

$$

DISCUSSION...Hiris
AVIATION...RPK

NWS BOU Office Area Forecast Discussion