358
FXUS65 KBOU 181149
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
549 AM MDT Tue Aug 18 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms expected today and
  Wednesday. Isolated severe thunderstorm threat both afternoons
  and evenings.

- Above normal temperatures through the weekend. Drier Thursday
  and Friday, but some monsoonal moisture likely returns by the
  weekend.

&&

.DISCUSSION /Through Monday/...
Issued at 148 AM MDT Tue Aug 18 2026

A weak cold front is forecast to move through the plains late
this morning into the early afternoon. Our severe weather threat
today will depend on available boundary layer moisture and
therefore potential instability. Some models have the I-25
corridor mixing and drying out prior to the cold fronts arrival,
with a lag between the cold front and the higher dewpoints. While
others have dewpoints staying a bit higher for late this morning,
with higher dewpoints moving in right behind the front. Another
potential hiccup in the moisture/severe weather forecast for
today is an outflow boundary which could stall over the area. As
of 1:30AM, the boundary was moving through Weld county, with
dewpoints increasing behind it. If this boundary does end up
stalling over the area, it could keep moisture higher and act as
another source of lift. The dewpoints/surface moisture will play
an important role in instability today. Areas that see the higher
boundary layer moisture will have much better instability and
higher chances of severe weather, as 0-6km shear increase behind
the front. The highest chance for strong to severe storms today
will be in our far northeastern plains counties, with decreasing
confidence as we go further west. The primary hazards will be
large hail and strong winds.

Tomorrows convective activity looks like its trending further south.
Models now have the shortwave over southern Colorado, putting the
best rain chances in our southern counties and south. However,
models are showing what looks like a stalled boundary over our
area Wednesday afternoon. This could allow for surface convergence
and some isolated to scattered activity in our northern counties
as well. While coverage of storms is forecast to decrease for
Wednesday compared to today, the severe weather threat will
continue as shear remains high and instability increases.

The upper level ridge with build over the area Thursday into the
weekend. Temperatures will remain well above normal for this time
period, with lower rain chances for the plains on Thursday and
Friday. The higher terrain could still see some isolated activity
in the afternoons. Precipitable water values will start to
increase for the weekend, with models showing values approaching
150% of normal again by Sunday. The higher moisture and a
shortwave aloft will bring increased rain chances across our
forecast area for the end of the weekend and start of next week.

&&

.AVIATION /12Z TAFS through 12Z Wednesday/...
Issued at 537 AM MDT Tue Aug 18 2026

Winds will be out of the west for the next few hours before
becoming light and variable starting around 15Z to 17Z. Winds
will pick up out of the northeast around 19Z to 20Z as a weak cold
front moves through the area. Models are trending higher in rain
coverage for this evening, so we`ve added a tempo for
thunderstorms for KBJC and KDEN for a few hours starting at 02Z.
There will be scattered activity around the area in the late
afternoon and early evening as well, but confidence is lower in
impacts to the airports, so we`ve left it as a prob30 for now.
After the rain moves out of the area, winds will be light and
variable at KBJC and KAPA. At KDEN, winds will likely be from the
north for a couple hours before turning south.

&&

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

&&

$$

DISCUSSION...AP
AVIATION...AP

NWS BOU Office Area Forecast Discussion