515
FXUS65 KBOU 210847
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
247 AM MDT Tue Jul 21 2026

.KEY MESSAGES...

- Storm coverage and intensity increases through Wednesday and
  Thursday as monsoonal moisture moves into the region. Storms
  from today onward will be capable of producing locally heavy
  rainfall, and some threat of flash flooding.

- Storm coverage expected to decrease again by Friday into this
  upcoming weekend, although mountain areas should see at least
  scattered storm coverage each afternoon and evening.

- Temperatures will rise back into the upper 90`s to lower 100`s
  over northeast Colorado for the weekend.

&&

.DISCUSSION /Through Monday/...
Issued at 243 AM MDT Tue Jul 21 2026

The upper level high will weaken a bit and shift somewhat to the
southeast today.  As a result, this will allow for monsoon moisture
to move into most of the area with weak flow aloft.  Meanwhile, a
cool front was moving across nern CO early this morning with
easterly low level flow behind it. As a result, it won`t be as hot
across the plains as readings this aftn will range from the upper
80`s to mid 90`s.

As fas as precip, will see sct slow moving showers and storms this
aftn over the higher terrain.  PW values will be 150% to 175% above
normal over the higher terrain so expect some heavier rainfall in
some areas.  As far as the plains, outflow boundaries from tstms
over the higher terrain will move across the I-25 Corridor by late
aftn or early evening.  Models disagree on where main focus will be
as HRRR and GFS favor Fort Collins northward while ECMWF is further
south over the Denver metro.  Overall, expect aditional tstm
activity to develop by late aftn or early evening from Denver north
to the WY border. With increasing ESE low level flow this evening
along with PW`s above 150%, may see heavier rainfall across nrn
portions of the I-25 Corridor. Meanwhile, depending on how far
outflow boundaries move across the plains, additional showers and
storms may linger overnight over portions of the nern plains.

For Wed, will continue to see monsoon moisture moving across the
area as the main upper level high is centered to the southeast of
the area.  PW`s across the high terrain will be from 150% to 200%
above normal so expect areas of heavier rainfall during the aftn
with the stronger storms.  Across the plains, the low level flow
will become southeast so expect a Denver cyclone to develop by aftn.
Should see tstms develop along the associated convergence zone with
storms move slowly to the east from late aftn thru the evening
hours.  Additional storms may also develop along outflow boundaries
moving across from the higher terrain as well.  Once again with PW`s
aoa 150% or normal expect areas of heavy rainfall. Highs on Wed,
will remain in the upper 80`s to mid 90`s over nern CO.

By Thu, monsoon moisture will continue over the area as a weak upper
level trough moves across the area. PW`s are still fcst to be
from 150% to 200% above normal. Thus should see another round of
showers and storms across much of the area with areas of heavy
rainfall. Highs on Thu will be in the upper 80`s to lower 90`s
across the plains.

Looking ahead to Fri and Sat, the upper level high will gradually
build back into the area as monsoon moisture decreases.  As a
result, will see tstm activity more sct over the higher terrain with
only a slight chc of storms over the plains both days. Highs will be
warmer as well as readings rise back into the mid 90`s to lower
100`s across the plains by Sat.

For Sun, an upper level high will extend from the Great Basin across
Colorado.  There are substantial differences between the ECMWF and
GFS with regards to whether there will be another surge of
monsoon moisture. The ECMWF shows another surge while the GFS
doesn`t so it`s not clear how much tstm activity there will be.
Meanwhile temperatures will remain in the mid 90`s to lower 100`s
for highs across nern CO.

&&

.AVIATION /06Z TAFS through 06Z Wednesday/...
Issued at 1123 PM MDT Mon Jul 20 2026

A weak cool front is making its way southward late this evening
and should arrive between 06z and 07z as winds shift to a more
E/ENE direction.  Sct -shra along with a few weak tstms have been
developing by this front so have kept in Prob30`s for -shra at
DEN and BJC from 07z-10z. Can`t rule out a weak tstm as well but
will leave out of current Tafs for now.  Meanwhile another surge
may move across by 10z with a wind shift to the north. This surge
could bring some smoke to the area by 10z.

On Tue, winds will be ENE by 15z and then shift to more easterly
by 18z. Smoke may linger thru 18z as well. By 21z winds will
become SE and continue thru Tue evening. At this time, it appears
best tstm chances Tue evening will stay north or the area.
However, if an outflow boundary from convection to the north were
to move into the area then tstm chances would increase. For now
have kept a Prob30 starting at 01z.

&&

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

&&

$$

DISCUSSION...RPK
AVIATION...RPK

NWS BOU Office Area Forecast Discussion