662
FXUS65 KBOU 182252
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
452 PM MDT Sat Jul 18 2026

- Hot weather continues through Monday, with highs pushing near
  100F over the I-25 Corridor and adjacent plains. A Heat
  Advisory remains in effect for the Denver Metro/I-25 corridor
  from 10 AM Sunday through 9 PM Monday.

- Scattered afternoon/early evening storms in the mountains
  expected through Sunday, with the plains remaining dry.

- Arrival of monsoonal moisture still getting delayed slightly,
  but once it arrives it should last into late next week. Storms
  from Tuesday or Wednesday onward will be capable of producing
  locally heavy rainfall.

- Trend to cooler weather next week is weakening.

&&

.DISCUSSION /Through Saturday/...
Issued at 101 PM MDT Sat Jul 18 2026

Main concern is the heat in the short term, shifting to potential
for locally heavy rainfall starting late Monday in the mountains
and closer to late Tuesday and moreso Wednesday and Thursday for
the lower elevations.

For the rest of today, it will be hot across the plains with just
some fair weather cumulus. Meanwhile, mountain areas will see
isolated to scattered showers and a few storms with sufficient
moisture, strong daytime heating, and weak instability. Those will
be ending early this evening as they continue to shift off to the
west. Despite mostly clear skies overnight, look for rather mild
temps across the plains with lows mostly in the mid 60s, and some
upper 60s in the Denver/Boulder area and lowest foothills.

For Sunday, the mid level thermal ridge will intensify as we
remain in a subsident environment under the heart of the upper
level ridge. Thus, with another 1-2C warming we`ll see high
temperatures push into the upper 90s across the I-25 Corridor. For
the mountains, it will also be a bit warmer but still expect
enough moisture present for isolated to scattered afternoon
showers and a few storms once again. There may just a slight
uptick over the northern mountains as the monsoonal moisture plume
inches closer to us. Sunday night will be quite mild, with parts
of Denver likely only dropping to near 70F for overnight lows.

Monday will be another hot one, and in fact will likely end up the
hottest day of the week as we continue to see mid level subsidence
and warming under the ridge axis. THE GFS continues to be the
hottest guidance, while the ECMWF and NAM are slightly "cooler"
(700 mb temps +18-20C vs +22C on the GFS). The average of those
would still be supportive of high temperatures near 100F for the
I-25 Corridor, and 100+F for some of the lower elevations as we
lose any "cool" advection from the east that we`ve had over the
last week. We`ll continue with the Heat Advisory for the Front
Range considering the overnight warmth Sunday night and the heat
that builds through Monday. Heat Advisory criteria is hotter for
the eastern plains (generally 105F) so we`ll likely stay just shy
of that. For the mountains, convective coverage is expected to
increase further Monday as the monsoonal moisture plume shifts
ever so slowly eastward under the ridge. Again, the highest
coverage would be favored over the northern tier of mountains,
with a couple storms potentially sneaking out of the northern
foothills with gusty outflow winds and lighter showers offering
up some late day cooling.

More substantial monsoonal moisture is expected to arrive Tuesday
and especially by Wednesday as the ridge shifts slightly eastward
and we get in light south/southwest flow aloft. However, there
were signals over the last 24 hours (yet again) that the best
moisture arrival could be delayed a bit more into Wednesday and
Thursday. Forecast precipitable water (PW) and 700/500mb specific
humidity approach or exceed the ECMWF ensemble climatology for
those two days, with only a gradual decline in moisture late in
the week. 500-700 mb specific humidity values are still forecast
to increase to 6-8 g/kg, with PW values likely increasing per
ensemble averages to 1.2-1.35 inches across the I-25 Corridor and
nearby plains, although the EC ENS was even a little higher. At
the same time, the airmass as a whole remains very warm with 500
mb temperatures holding near -3C. So, despite the proximity to
climatological maxes, the airmass may still not be saturated. That
said, the overall synoptic setup and ingredients remain favorable
for slow moving, heavy rain producing thunderstorms. Of course,
the daily chances of locally heavy rain and/or even a localized
flash flood threat will come down to mesoscale features (e.g.
frontal surges, upslope, stratus, stability, moisture profiles,
etc.).

There is still a fair amount of uncertainty as to which day or
days offer up the highest precipitation chances. There were signs
of a weak shortwave moving over top of the ridge late Wednesday,
so that could lead to increased coverage of showers/storms.
However, given model timing performance as of late we can`t get
too caught up in the details and if anything that would be a later
arrival. Another interesting note is the lack of any significant
cooling in some of the latest model runs, keeping high
temperatures near/above 90F through the entire week ahead. At
least there should be some cooling with the initial front Tuesday
and extra cooling from at least scattered if not numerous
afternoon and evening showers and storms.

&&

.AVIATION /00Z TAFS through 00Z Monday/...
Issued at 441 PM MDT Sat Jul 18 2026

VFR conditions expected throughout the TAF period. East winds
will persist well into the evening and will slowly shift to the
southeast at all terminals through roughly 06-08Z. Overnight,
winds will become drainage with light speeds.

Winds will be very light Sunday morning with sunny skies. East-
northeast winds will develop in the afternoon but gusts should stay
below 18 knots.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 10 AM Sunday to 9 PM MDT Monday for
COZ038>040-043.

&&

$$

DISCUSSION...20
AVIATION...Danielson

NWS BOU Office Area Forecast Discussion