392
FXUS65 KBOU 281155
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
555 AM MDT Mon Sep 28 2026

.KEY MESSAGES...

- Rain chances will prevail Monday afternoon through early
  Thursday. Highest potential for heavy rain will be on
  Wednesday. Best chance for higher rain amounts will be in our
  southeastern counties.

- Rain chances decrease late Thursday, leading to warmer and drier
  conditions for the weekend.

&&

.DISCUSSION /Through Sunday/...
Issued at 1105 PM MDT Sun Sep 27 2026

Looking at water vapor on satellite, the upper level trough we`ve
been talking about for the past few days is finally moving onto
the West Coast. Ahead of this deep trough, southwesterly upper
level winds are funneling in moisture from Post-Tropical Cyclone
Odalys into our area. At lower levels overnight, south/southeast
surface winds will continue to increase moisture at the surface.
This increase in moisture combined with upper level lift ahead of
the approaching trough will bring a round of showers and storms
Monday afternoon and evening. Showers are forecast to move into
our area from the southwest, progressing northeast through the
evening. This activity is expected to be primarily rain showers,
dropping anywhere from a few hundredths to around half an inch of
rain. However, we could see a few storms develop in the later
afternoon and evening, which could produce some locally heavy
rainfall exceeding an inch.

Rain chances will continue on and off through at least Thursday
morning as that upper trough approaches and then sits just to the
southeast of our area. A cold front will move through early
Tuesday, bringing slightly cooler temperatures and the potential
for surface convergence leading to a band of some heavier precip
sometime Tuesday morning. QG forcing from the upper low and
PWs are forecast to peak on Wednesday. This is the day we`re most
concerned about. There`s still significant discrepancies on where
the axis of heavier precip will form (which is expected), with
models in pretty good agreement that there will be a swath of
area that sees 3+ inches with this event. We will likely be right
at the northern edge of this swath, meaning it could stay just to
our south and east or portions of our area could see very heavy
rainfall and flash flooding. Right now, Denver is sitting at a
medium chance (~40%) of seeing at least an inch of rain on
Wednesday, with chances increasing as we go southeast. Lincoln
county is the most likely area in our CWA to see the higher
rainfall totals, with a 60% to 70% chance of at least an inch on
Wednesday.

The forecast precipitable water values for Tuesday, Wednesday,
and potentially Thursday are VERY high. Models are showing
widespread PWs of 200% to 250% of normal, with potential for it
to reach 300% of normal. With this much moisture, any shower or storm
that can get going will have the potential to produce very heavy
rainfall and flash flooding. So, even if we get missed with the
main swath of heavy rain and don`t receive the widespread heavy
rainfall across our area, there still will be a very real threat
for localized flash flooding for any area that ends up with a
storm.

As for mountain snow chances, temperatures still look very
marginal, which does not bode well for snowfall totals. Areas
above 12,000ft will likely see at least a round or two of snow
flurries in the Tuesday through Thursday time period (best chance
Wed and Thu mornings), leading to a dusting of snow for those
areas above 12,000ft. But chances for much more than that are low
at this time. Rain chances will start to decrease on Thursday as
the upper level system moves off to the east. Temperatures Friday
through the weekend will warm closer to normal.

&&

.AVIATION /12Z TAFS through 12Z Tuesday/...
Issued at 550 AM MDT Mon Sep 28 2026

An elevated drainage wind of 15-25 kts has been ongoing overnight
at KDEN and KAPA with KBJC keeping light and VRB winds. These
trends will continue with southerly winds at KAPA and KDEN
approaching gusts of 20-25 kts through this evening. KBJC should
remain light and VRB until the showers arrive this afternoon.

Several waves of showers are likely- starting at 19/20z and then
lasting through the end of the TAF period- at all three sites, but
KDEN and KAPA will be most favored. Prevailing -SHRA at KDEN and
KAPA are in place this afternoon (and into the evening at KAPA).
KBJC has a TEMPO for these showers and the possibility of some
gusty winds and lowered ceilings. We wanted to illustrate the
following trends in the latest CAMs: (1) KAPA is likely to
continue to see the most numerous showers through Tuesday morning
and possibly beyond (2) KDEN could have showers lingering at least
in the vicinity through early Tuesday morning and (3) KBJC is
least likely to see showers after this evening.

Ceilings start to lower by late afternoon, especially by 00z
Tuesday (Monday evening) and beyond. Ceilings are forecast to drop
to 6000 ft AGL around 4z at KDEN. A front will push through all
three sites between 9z and 12z bringing in low stratus and thus
lower ceilings. Cross sections and soundings show high levels of
moisture to work with through the lower atmosphere. Thus, we have
KDEN ceilings dropping to 1000 ft AGL and lowered visibility with
this northerly push. Low stratus is forecast to continue beyond
this TAF period and likely (70% confidence) into Wednesday.

&&

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

&&

$$

DISCUSSION...AP
AVIATION...MV

NWS BOU Office Area Forecast Discussion