902
FXUS65 KBOU 181823
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1223 PM 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 /18Z TAFS through 18Z Wednesday/...
Issued at 1141 AM MDT Tue Aug 18 2026

To begin, all TAF sites should start with a more north to
northeasterly direction before a more easterly direction
develops, especially for KDEN. This afternoon/evening scattered
showers will develop with a ~40% chance of lightning in some
storms. Storms that develop will be capable of bringing variable
winds and microburst gusts up to ~30-35 kt. Due to the current
observations in temperature spreads, dewpoints, and pressure, a
cold front/outflow will move through KDEN around ~2-4z, KBJC
~1-3z, KAPA around ~2-5z with northerly winds gusting to 35 kts.
Isolated gusts could potentially near 40 kts at times.

After ~5z, model guidance indicates there could be some lingering
showers in the area to monitor, but for now have decided to leave
out the mention of a prob 30 for the overnight hours. Depending on
how convection goes this afternoon, changes could be added in the
TAF to account for this activity. Bearing any convection, drainage
will kick in around ~8z before turning clockwise back to the
northeast by 18z tomorrow afternoon. There is also a ~10% chance
of fog/low clouds at KDEN and KBJC in the morning, ~10-14z
timeframe.

A prob 30 was almost introduced for Wednesday afternoon/evening,
but a little hesitant on the chances for convection so decided to
hold off for now.





&&

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

&&

$$

DISCUSSION...AP
AVIATION...Schnell

NWS BOU Office Area Forecast Discussion