Severe Thunderstorm Warning 290, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
543 PM 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 Tuesday/...
Issued at 1228 PM MDT Tue Jul 28 2026

GOES-18 satellite data early this afternoon show that robust
convective initiation is ongoing across the Front Range Foothills.
Radar estimates and precipitation gauges suggest that some of
these initial storms have still been efficient rainfall producers
across the foothills... meaning that burn area flash flooding is
still a concern this afternoon.

However, much like the past several days... initial convection
has struggled once making it into the urban corridor. Why is this?
There are several possible explanations. Despite a relatively
favorable environment (T/Td of 90/57 at DEN), ACARS soundings
still maintain a subtle stable layer between roughly 750-675 mb.
While there's still 1500-2000 J/kg MLCAPE in that sounding there's
also a relatively deep, weakly buoyant region above the LFC that
would be prone to some entrainment. With little/no synoptic
ascent through this layer, it would likely take larger, mature
updrafts to overcome this. It's possible additional CI attempts
across the Foothills will lead to more sustained convection across
the Denver metro, but it appears more likely that our favored
terrain (northern Front Range and Palmer Divide) will see the
bulk of the rainfall this afternoon, with gradual upscale growth
towards east of the I-25 corridor later this afternoon and
evening.

As that cluster of convection shifts eastward, the increased
precipitable water and deeper warm cloud layer depths would favor
the potential for some brief but rather heavy rainfall rates this
evening. Recent REFS 3hr PMM QPF hints at as much as 3-5" of
rainfall this evening in Washington county... with broad support
from today's HREF members as well. I saw no reason to adjust the
existing Flood Watch across the plains, which will remain in
effect from 3-10 PM. As the midnight shift noted, there is still a
slim possibility that this cluster of storms eventually sends some
outflow back towards the metro, which would provide another
opportunity for some showers/storms that would be capable of
producing some heavy rain.

Wednesday looks to be the last day of well above normal moisture,
though similar concerns remain about the coverage of storms across
the region. Overall we expect a fairly similar convective setup
compared to today, with perhaps a bit more coverage along/west of
I-25. Storm chances will be dictated by the amount of moisture
return tonight/tomorrow morning. Assuming we do see low/mid 60s
dew points across the urban corridor tomorrow morning, there would
be some heavy rain potential once again.

The latter half of the week will feature a quick drying trend,
with warmer temperatures likely returning by the weekend. Chances
for showers/storms will continue for Thursday but should quickly
diminish by Saturday or Sunday as a 600 dam ridge at 500mb
develops near the Four Corners region. Guidance hints that we
could see a return of upper 90s/low 100s by the end of the
weekend, which then persist through early next week.

&&

.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 542 PM MDT Tue Jul 28 2026

The latest radar imagery as of 2330z shows convection ongoing
well to the east of KDEN. Gusty winds between 15 and 25 kts have
been occurring at times at all three TAF sites for the last
several hours. The convection has sent off an outflow boundary in
southeast Weld County that is currently moving to the west. There
is a low chance (~30%) that showers/thunderstorms occur this
evening, but if they were to form they would likely be behind this
outflow boundary. So, we have gone ahead and kept the PROB30
through 5z tonight.

Winds should turn to drainage and remain under 12 kts by about
6z. There is still a low (10%) chance of a brief period of low
stratus clouds below 3000 feet tonight roughly between 9z and 15z
depending on how outflow boundaries from storms well to the east
behave overnight. Otherwise, we only expect a few clouds below
12,000 feet AGL tonight. Winds will slowly turn clockwise as the
morning progresses and should be NE to E by late tomorrow morning.

Tomorrow will be a similar setup to today with showers and
thunderstorms moving from west to east through all three TAF sites
between about 20z and 5z. TEMPO and PROB30 groups are in place to
cover this potential. Gusty winds of at least 30 knots,
TSRA/SHRA, and lowered visibility to about 4 SM are possible with
any showers or thunderstorms that pass near/over any of the TAF
sites.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 10 PM MDT this evening for COZ042-044>049.

&&

DISCUSSION...Hiris
AVIATION...MV