821
FXUS65 KBOU 281119
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
519 AM MDT Tue Jul 28 2026

.KEY MESSAGES...

- Threat of flash flooding over portions of northeast Colorado
  this afternoon and evening. Numerous showers and storms.

- A couple severe storms possible on the plains with damaging
  winds and marginal hail threat.

- Similar weather setup for Wednesday with more storms.

- Temperatures holding closer to normal today and Wednesday.

- Drying out again later in the week. Heat returns for next
  weekend.

&&

.DISCUSSION /Through Monday/...
Issued at 304 AM MDT Tue Jul 28 2026

The main concern both today and tomorrow will be for storms with
very heavy rainfall and a local flash flood threat. A couple
severe storms with damaging winds will also be possible. The
greatest threat of flash flooding and severe weather will be east
of the I-25 Corridor.

Here`s the setup. An easterly push of higher dewpoint air was
pushing back toward the I-25 Corridor in the wee morning hours,
a result of outflow from overnight storms in Nebraska and Kansas.
Dewpoints were in the lower to mid 60s over the northeast plains
behind that surge. That surge is expected to wash out along the
I-25 Corridor in the pre-dawn hours, but will be enhancing the low
level moisture and instability across a good chunk of the
northeast plains today. Unlike yesterday when the mesoscale
convective vortex (MCV) interrupted normal convective development
and evolution, today should be a little more straight-forward.
Barring the mid/high convective cloud remnants over the
south/eastern portions of our forecast area (at least early in the
day) we should see sufficient cloud thinning for boundary later
heating and destabilization. Forecast soundings also show a weaker
inversion, so we should be able to reach convective temps in all
areas. Storms will first fire over the mountains and foothills by
early afternoon, and then spread eastward across the plains in the
mean westerly flow aloft on the northern periphery of the ridge.

Regarding the heavy rain and flash flood threat, precipitable
water values are still forecast to range from 150-200% of normal
across the forecast area, reaching daily climatological maximums
(near 1.3" for Denver and 1.5+" for the eastern plains. Warm cloud
depths will also increase to ~5,000 feet driving rainfall
efficiency. Instability will also be greater, supporting stronger
and larger storms. The one limiting factor is expected storm
motion near 20 mph as the storms organize onto the eastern plains.
While the foothills and 2020/2024 burn scars will see locally
heavy rain, the storm size and motions should be sufficient to
keep most precipitation amounts below critical thresholds. That
could very well change as storms intensify as they head east of
I-25. That`s where they will encounter very rich dewpoints in the
lower to mid 60s and stronger instability with MLCAPE of 1500-2000
J/kg and even deeper warm cloud depths. Thus, I would expect
these storms to be very efficient rain producers with rain rates
of 2" or more in just 30-45 minutes. Local Probability Matched
Means (LPMM) suggest isolated 3-4" amounts in a relatively narrow
corridor from northern Weld/Logan Counties southward through
Morgan, Washington, and eastern Elbert and Lincoln Counties. Given
the ingredients, we`ve issued a Flood Watch for flash flooding
for those particular areas where the threat is greatest.

One other thing to note, there is a slight chance that once
stronger storms organize over the plains a resultant outflow
boundary backs into the foothills generating a second round of
storms for the evening. Thus, that`s something to watch for the
foothills and I-25 Corridor if we don`t have widespread convection
this afternoon that takes all the instability with it. Those
latter storms would be capable of producing heavier rainfall so
something to monitor through this evening.

Given the MLCAPE magnitude and profiles, the main severe weather
threat would be from organized linear structures and wet
microbursts. There would be some hail threat as well (would
normally be quite large given the MLCAPE, except today we`ll have
considerable melting of hailstones on descent in this warm/wet
environment).

For Wednesday, it looks like a rinse/repeat scenario for the most
part. This time, the deeper moisture and instability has a greater
chance to spread back to the I-25 Corridor so there would be
potential for stronger storms and heavy rainfall farther west.
That said, both days the more organized storms are expected east
of the I-25 Corridor so not all areas are guaranteed to receive
beneficial/soaking rainfall.

We don`t see much change in the ensemble forecasts for the latter
part of the week, showing gradual drying and lowering PW Thursday
through Saturday. We`ll transition into northwest flow aloft as
the upper level ridge retrogrades into the Desert Southwest. So
that should keep the hottest temperatures away until sometime this
weekend into early next week. It still looks like Sunday will be
heating up to near 100 degrees across the plains and I-25
Corridor, potentially lasting into Monday depending on the speed
of a shortwave moving across the U.S./Canadian border.

&&

.AVIATION /12Z TAFS through 12Z Wednesday/...
Issued at 514 AM MDT Tue Jul 28 2026

Light SW-W winds have resumed after the brief surge from the east
overnight. These winds will trend more NW 14Z-15Z, and eventually
NE-E 16Z-20Z.

The main concern will shift toward likely occurrence of thunderstorms,
most favored 21Z-24Z and perhaps as early as 20Z at KBJC. The
threat of stronger storms is greater than yesterday so we`ll have
TEMPO G35-40kts, TSRA, and some visibility restriction to
5-6SM...although if a direct hit occurs visibility could go down
as low as 1SM given potential for heavy rain with storms. There`s
a PROB30 that -SHRA/TSRA could linger as late as 05Z. Outside of
that, look for mid level ceilings above 8,000 feet AGL and fairly
normal diurnal wind patterns. There`s a low (10-20%) chance of
stratus after 08Z tonight, depending on any easterly low level
flow in the wake of this evening`s convection.

&&

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

&&

$$

DISCUSSION...20
AVIATION...20

NWS BOU Office Area Forecast Discussion