520
FXUS65 KBOU 122028
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
228 PM MDT Wed Aug 12 2026

.KEY MESSAGES...

- One last day of warm temperatures today. Cooler temperatures
  arrive by Thursday and Friday, with a slow warming trend by next
  week.

- A few strong to severe thunderstorms will be possible over the
  northeast CO plains this afternoon, with damaging winds and
  large hail as the primary hazards.

- Monsoon moisture arrives and lasts through the weekend, bringing
  scattered showers and thunderstorms most days. Locally heavy
  rainfall possible. The best chance of rain across the I-25
  corridor is still Thursday/Friday.

&&

.DISCUSSION /Through Wednesday/...
Issued at 137 PM MDT Wed Aug 12 2026

Scattered convection has developed across the mountains this
afternoon, with the plume of deeper monsoon moisture working its
way into the forecast area. Most of this convection so far has
been fairly weak, which isn`t much of a surprise with only modest
instability noted on SPC Mesoanalysis. Scattered storms should
continue through the next several hours before diminishing after
sunset.

Meanwhile, it`s a different story across most of the metro. A few
weak showers have cooled temperatures in the Boulder area, but
temperatures across the metro have warmed into the low to mid 90s
(currently 94F at DEN), with dew points still sitting in the low
to mid 40s in many locations. Unsurprisingly, this has left a
majority of the urban corridor with ~250 J/kg of MLCAPE, but also
150 J/kg of MLCIN. It`s going to be difficult to get much of any
meaningful precipitation given that sort of setup, which has been
consistently advertised by CAMs over the last 24 hours or so.

Finally, there`s a well defined moisture gradient across the
eastern plains, with surface dew points in the low to mid 60s
along and east of a line from roughly Sterling to Burlington.
Guidance eventually tries to strengthen the existing cluster of
weak convection over the Palmer Divide once it hits the more
favorable environment in far east/northeastern Colorado later this
afternoon. Forecast soundings would imply both a marginal
hail/wind risk through tonight despite a relatively uncertain
convective evolution.

As we get into tomorrow, moisture is expected to increase across
most of the forecast area, with PW standardized anomalies close
to 2-3 sigma (roughly about 125-200% of normal). Despite the
relatively favorable environment featuring moderate buoyancy and
continued upslope flow, there are still many questions
surrounding convective evolution - particularly across the metro -
that lead to low confidence in our PoP/QPF forecasts. While there
is still some subtle synoptic support, the overnight cold front
and/or outflow boundary is not well-defined. For most folks along
the I-25 corridor, rainfall chances will likely be very dependent
on favorable mesoscale influences that are generally not well
represented by CAMs. Any storms that do develop will be relatively
slow moving and capable of producing heavy rain, but it`s
difficult to come up with the "where" part of the forecast here.
Understandably there is a lot of spread in the HREF/REFS at this
time which will hopefully be better resolved once we get through
today`s convection.

Our cooler and unsettled pattern is likely to continue through the
weekend here with above normal moisture sticking around. Again
there are mixed signal across guidance during most of this
period. A few models try to push a weak front through at some
point, while others are less bullish. With meager synoptic forcing
to work with, heavier rainfall potential would generally favor the
Front Range mountains and foothills, with lower chances again
across the metro. NBM PoPs and QPF are far more optimistic than I
am during this period, and while I did bring down both PoP/QPF for
the weekend, I wouldn`t be surprised if we make further
adjustments over the next couple days.

Ridging is expected to slowly build back towards our area by early
next week, which should gradually push the deeper moisture plume
out of the forecast area. It doesn`t look nearly as warm or dry as
it did to start the month... and extended range ensemble guidance
still favors a return of moisture during the latter half of the
week.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1150 AM MDT Wed Aug 12 2026

Winds are currently light and VRB due to a cyclone. A little
uncertain with the wind direction for the next few hours as the
cyclone evolves, but expect a general east/northeast wind early
this afternoon. However, there is a chance winds could turn more
southeast instead.

We are still on track for convection to begin across the high
terrain, with outflow winds making a direction change most likely
to the west/northwest. Some guidance has hinted at the I-25
Corridor missing out on the bulk of precipitation this afternoon
(convection becomes more organized east of the airports), so have
changed to a PROB30 instead of a TEMPO to reflect that
uncertainty. Regardless, any nearby convection should bring strong
wind gusts. With the amount of moisture in the atmosphere, some of
the strongest storms will produce heavy rainfall, so have reduced
visibility in the PROB30 group.

Some uncertainty with wind direction behind the convection this
evening, however generally think it will have an easterly
component to it due to outflow winds from storms east of the
terminals. Light winds expected overnight, with the potential for
low clouds coming in by 10Z-12Z. Have kept the TEMPO in there as
is, but some models indicate ceilings lower than 2000 feet.

For tomorrow, another round of showers and thunderstorms are
possible in the afternoon. With better moisture entering the
region, it is more likely that any shower that occurs will produce
heavy rainfall. For this reason, have introduced a PROB30 with 3SM
as the visibility.

&&

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

&&

$$

DISCUSSION...Hiris
AVIATION...MAI