893
FXUS65 KBOU 220010
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
610 PM MDT Fri Aug 21 2026

.KEY MESSAGES...

- Heat eases, along with an increase in shower and storm coverage
  this weekend.

- Gusty outflow winds from a few high based showers/storms into
  this evening. Isolated severe storm threat over the plains.

- Highest coverage of showers and storms expected Saturday, along
  with a few severe storms on the plains Saturday and then again
  Sunday.

- Gradual drying next week, but continued storm chances through
  at least Wednesday or Thursday. Slight cooling but temperatures
  still above normal.

&&

.DISCUSSION /Through Friday/...
Issued at 1258 PM MDT Fri Aug 21 2026

It`s a hot one today with temperatures early this afternoon already
in mid to upper 90s along the I-25 Corridor, and approaching
records in some spots (Denver`s record is 99F set in 2023). There
was some slight relief over the northeast plains due to outflow
from earlier Nebraska convection, so temperatures have been
running a few degrees below expectations there. Given the strong
surface heating and steep low/mid level lapse rates along the
Front Range, we are seeing high based convection develop. These
will be capable of producing strong microburst winds as DCAPE has
grown into the 1400-1600 J/kg range. Meanwhile, farther east the
low level moisture is holding steady with dewpoints in the lower
to mid 60s in the easterly flow. While this easterly surge is
expected to weaken during peak heating, it will provide for higher
instability and a richer storm environment should storms be able
to fire. Thus, a couple severe storms will be possible through
this evening over the northeast plains given MLCAPE of 1200-2000
J/kg and bulk shear near 30 kts.

For Saturday, monsoonal moisture will increase as the upper level
ridge axis tilts ever so slowly eastward. Precipitable water
values are forecast to reach near 150% of normal. However, the
airmass is quite warm so we think most storms that originate over
the mountains and then push onto the I-25 Corridor in the
afternoon will still be relatively high based, and thus mostly
outflow dominated. We think the majority of the storms with more
widespread and beneficial rains will develop just east of the I-25
Corridor where outflows intersect with a richer low level
environment. That`s where HREF ensembles show higher concentration
of stronger storms. Locally heavy rain totals upwards of 1.5-2
inches will be possible there, and potentially the Palmer Divide,
based on the environment and HREF Local Probability Matched Means
(LPMM). Meanwhile, there will also be a threat of a few severe
storms as MLCAPE once again grows to 1200-2000 J/kg and bulk shear
of 25-35 kts is forecast.

For Sunday, there is good agreement that the mid and upper levels
will dry slightly as a more westerly component develops under a
flattening ridge. Thus, storm coverage should decrease a little,
in the absence of any forcing mechanisms. A few severe storms
will once again be possible across the plains as we expect
sufficient low level moisture and instability, with the greatest
risk once again hovering just east of the I-25 Corridor.

For much of next week, deterministic forecasts and ensembles are
averaging toward flat ridging and weak westerly flow aloft. That
likely keeps us too zonal for deep monsoonal moisture, but just
enough for scattered storms most afternoons and evening. While
individual model runs vary, there is still potential for a weak
backdoor cool front or two. They will offer up very little in the
way of cooling, but should keep us a few degrees "cooler" (mostly
lower 90s for highs on the plains and I-25 Corridor) versus the
full on summer heat experienced today. Ensembles are supportive of
a decrease in precipitable water (PW) by the end of next week,
which would support less, or only isolated, storm possibilities
and a return of much above normal temperatures. &&


.AVIATION /00Z TAFS through 00Z Sunday/...
Issued at 609 PM MDT Fri Aug 21 2026

Storms are starting to move out of the vicinity of the TAF sites,
but we can`t rule out the possibility of more updrafts and gusty
winds in the next few hours, especially with the current showers to
the south and west sending out outflows. Because there`s been so
many scattered storms across the metro area, confidence is low as to
where the winds will be in a few hours. Models show varying wind
directions, though observations would suggest an easterly component.
Of course, any further convection or outflows could shift the wind
in variable directions. After storms move out of the area to the
east, winds should start turning towards drainage, getting there by
around 02Z and staying generally S/SW  overnight.

Winds turn northward again in the morning, around 15/16Z, and
staying north/northeast until storms start to move through in the
afternoon. Current model guidance has more moisture in the
environment tomorrow afternoon than we had today, and the CAMs
remain in fairly good agreement on convection initiating around 22Z
and lasting through 06Z on Sunday. DCAPE values in the most recent
model runs also look to have increased from previous runs, so gusty
outflows will most likely be a concern for tomorrow`s storms, as
well.


&&

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

&&

$$

DISCUSSION...20
AVIATION...AGS