Keystone, Colorado Weather Forecast Discussion

418
FXUS65 KBOU 051740
AFDBOU
Area Forecast Discussion
National Weather Service Denver/Boulder CO
1140 AM MDT Sun Oct 5 2025
.KEY MESSAGES...
- Cooler today across the region, with highs in the 60s across the
  I-25 corridor and plains.
- Rain showers developing across the Front Range later this
  afternoon into tonight, with accumulating snow of a few inches
  likely (70-80%) in the northern Front Range Mountains and
  higher northern foothills.
- Cool and cloudy on Monday with a few afternoon showers, and only
  a little warmer Tuesday... but above normal temperatures likely
  to return by mid/late week.
&&
.UPDATE...
Issued at 329 AM MDT Sun Oct 5 2025
Overall forecast remains on track today, with cooler weather on
the horizon. Surface observations suggest that the secondary cold
front is near KCPR/KDGW in Wyoming, and this should steadily crawl
towards our forecast area through the day. This doesn`t look like
it will be a particularly sharp front, with
anticyclonic/northeasterly surface flow gradually developing
through the day. With cooler temperatures filtering in, high
temperatures will likely stall in the mid/upper 60s across the
plains.
More importantly, the deepening upslope along with the gradual
increase in moisture will lead to rain and snow showers developing
across the Front Range by the late afternoon hours, continuing
through at least the early overnight hours. Overnight QPF guidance
continues to converge, with a swath of 0.25-0.5" of liquid falling
across the northern half of the Front Range mountains/foothills,
with a well defined gradient across the I-25 corridor. Areas above
9,000ft look like they`ll see at least light accumulations (1-2")
with some spots potentially picking up several inches of snow by
Monday morning.
While precipitation will come to an end Sunday night, the stratus
deck across northeast Colorado will be slow to erode (if at all)
on Monday given a continued moist/upslope regime. Highs should
only reach the mid 50s across most of the plains. There are hints
for another round of light rain/snow showers Monday evening but
QPF looks very light overall.
Beyond that, the longer term pattern remains consistent and no
changes were made from the overnight model blend.
&&
.DISCUSSION /Through Saturday/...
Issued at 243 PM MDT Sat Oct 4 2025
Satellite shows a significant upper level trough lifting northeast
into Wyoming, with the trailing end of QG forcing moving across
the forecast area. The main batch of showers/storms is expected to
continue pushing eastward across the plains late this afternoon
and evening, bringing with them a threat of strong, damaging
winds. Strong mid level flow and a well mixed boundary layer with
pre-existing gusts to ~35 kts, means it won`t take much
acceleration to produce local storm scale severe winds of 50 kts
or greater. And, the existing DCAPE of 800-1200 J/kg on the plains
would be enough to support that so a couple severe storms still
expected mainly on the leading front of showers/storms. Most
showers/storms will exit rather quickly to the east and into
Nebraska and Kansas by 8-9 pm, with only a few showers lingering
in the high country this evening due to orographic forcing.
Of other note for tonight, there`s a window of strong mountain
wave induced winds for the foothills after the trough passage.
Earlier, there was a hint of a mean state critical layer and
higher threat of strong winds 01Z-04Z, but that chance has now
diminished. However, there is still a rather strong mid level
gradient combined with a more favorable stability profile 03Z-09Z.
Therefore, with 40 kts cross mountain flow we still expect some
60+ mph gusts over the higher foothills and eastern slope of the
Front Range mountains tonight, but shy of any High Wind Criteria.
For Sunday, we`ll see another frontal surge push across northeast
Colorado during the mid to late morning. This will usher in even
cooler air, with temperatures steadying out or even slowly falling
during the afternoon. Easterly anticyclonic upslope will deep
through Sunday afternoon and evening, leading to deepening
moisture profile and eventually saturation below 600 mb. As a
result, we expect precipitation to develop and expand in coverage
during this period, with the highest coverage in/near the Front
Range along/north of I-70. Snow levels also lower during this
period, and QPF amounts have increased a couple more tenths from
previous runs. We think the snow level will come down closer to
8,000 feet in the northern foothills, with at least some light
snow accumulations of a couple inches above that. Given the recent
trends, there`s a 60-70% chance that a few spots get several
inches of snow. This could cause some travel impacts for Trail
Ridge Road in Rocky Mountain National Park and Highway 14
approaching Cameron Pass.
The lower clouds, showers, and cool high pressure building in
through Sunday night means Monday will be quite chilly. At this
time, we expect a high probability (>80%) that high temperatures
only make it into the 50s across all of the plains and I-25
Corridor, and that could very well only be the lower to mid 50s!  We
probably won`t clear out that much or have too much low level
moisture for much of a frost threat for Monday night, but
nonetheless it will be quite chilly through this period.  There
should be just slight moderation by Tuesday.
The bigger warmup is still on track for the middle to end of next
week. There are some slight differences with weak embedded
shortwaves riding around the ridge, but overall there is good
agreement that general ridging occurs over the Central Rockies,
supporting a return of above normal temperatures and mostly dry
conditions.
&&
.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1140 AM MDT Sun Oct 5 2025
Main concern is for the lowering ceilings in this TAF period. Cold
front has pushed through, with increasing NE-E winds in it`s wake.
Sustained winds 10-14 kts with a few gusts to around 20 kts
expected through 02Z. Stratocumulus is already developing,
especially along the northern Front Range but appears KDEN will
become BKN050 with IMC by ~23Z and earlier to the north. Rain
showers will also develop in the area 23Z-06Z with the most
persistent rain likely to stay near KBJC and points W/NW into the
Front Range. Upstream observations show relatively close T/Td
spreads so with further advection through the night we`ll lean
toward the NAM solutions with lower MVFR/IFR ceilings. However,
any visibility restriction should be confined to where the cloud
deck intersects with terrain in the foothills (>6500 MSL). Areas
of light drizzle will also be likely behind this evening`s rain,
persisting into Monday morning. It appears to be a slow ceiling
recovery Monday with moist and cool easterly flow holding in
place.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Hiris
DISCUSSION...Barjenbruch
AVIATION...Barjenbruch

NWS BOU Office Area Forecast Discussion