493
FXUS65 KBOU 131135
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
535 AM MDT Thu Aug 13 2026

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms likely across
  the area today.

- Heavy rainfall rates may lead to localized flash flooding,
  especially over the eastern CO plains, where a Flood Watch is in
  effect from 3 pm to 10 pm.

- Monsoon moisture lasts through the weekend, bringing scattered
  showers and thunderstorms most days. A warming trend begins on
  Monday.

&&

.DISCUSSION /Through Wednesday/...
Issued at 416 AM MDT Thu Aug 13 2026

Weakening showers were slow to exit the northeast Colorado plains
in the last couple of hours, with estimated totals in that area
generally ranging from 0.5"-2.0", and perhaps a few spots
receiving as much as 3.0" of rain. Given the antecedent rainfall
and anomalous moisture expected once again this afternoon and
evening, we have decided to issue a Flood Watch for flash flooding
extending from eastern Weld and Logan County, down to parts of
Elbert and Lincoln counties.

As previous AFDs have highlighted, precipitable water (PW) values
for today continue to be 150%-200% of the climatological average for
this time of year, in the 1.3"-1.6" range for the low elevations and
as high as 1.0" over the mountains. Moisture this anomalous combined
with weak storm motion vectors (~15KT) and a relatively deep warm
cloud layer (5,000 ft) indicate a flash flood threat with the
strongest storms, particularly with training or redevelopment over
the same areas. Additionally, the lower levels of the atmosphere are
much moister than they were yesterday afternoon meaning that
rainfall production will be more efficient from the start. The
main weakness or failure mode for today`s shower setup would be
limited instability over the I-25 corridor and Denver metro given
the cooler temperatures and increased cloud cover. However, high-
res models do at least show some pockets of MLCAPE >1500 J/kg.
Even if showers are initially isolated in nature, any outflow
boundaries produced by those first few showers and storms will be
able to kickstart additional shower activity. For the high
terrain, there will not be many obstacles in the way of shower and
thunderstorm development as showers are already moving into the
Gore Range and central Colorado mountains.

For Friday and Saturday, PWs decrease slightly but values stay at or
above the 90th percentile of climatology. Scattered showers and
storms will be possible each afternoon and localized flash
flooding will still be a threat, particularly with storms tracking
over areas that received rainfall the previous day. Looking at
the synoptic pattern for the weekend, global models have begun to
suggest a weakening/widening of the upper level ridge over the
central U.S. as well as a weakening of the trough off the Pacific
coast. While this change would dilute monsoonal moisture
transport, flow aloft over the region will remain southwesterly
and moisture will not be cutoff completely. Showers and storms
will be possible each afternoon, although the spatial coverage may
not be as widespread.

Monday and Tuesday appear to be drier as flow aloft becomes more
zonal due to the upper level ridge axis temporarily retreating
westwards over the Four Corners. Long-range ensemble guidance
continues to suggest moisture returning to the region by the
middle of next week, as well as the passage of a few shortwaves. A
warming trend is still on track to begin on Monday, with
temperatures in the 90s likely returning by Tuesday afternoon for
the low elevations.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 524 AM MDT Thu Aug 13 2026

There is a patch of low clouds off to our east as of early this
morning. However, these lower ceilings should remain off to the
east today. Another round of showers and storms are expected this
afternoon and evening. The highest chances for storms today will
be from 20Z to around 01Z, with some lingering rain chances into
the late evening. Thunderstorms will have the potential to produce
heavy rainfall and gusty winds. After the storms move off to the
east, we could see lower ceilings and potentially fog build into
the area during the overnight period. Confidence is still too low
to include fog in this TAF package, but this is something we`ll
be monitoring.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 3 PM MDT this afternoon through this evening
for COZ042-044>046-048-049.

&&

$$

DISCUSSION...AA
AVIATION...AP

NWS BOU Office Area Forecast Discussion