136 
FXUS65 KBOU 200015
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
615 PM MDT Sat Sep 19 2026

.KEY MESSAGES...

- Another round of scattered showers/t-storms this afternoon for 
  the mountains and urban corridor.

- Numerous showers/t-storms over the plains, where some will be 
  strong to severe through this evening, producing locally heavy 
  rain, strong outflow winds, and hail.

- Trending drier Sunday into Monday, although scattered 
  afternoon/evening storms may continue Sunday, particularly along
  and south of  I-70.

- Cooler temperatures expected Sunday into Monday, before
  warmer temperatures return. Next week will bring a few
  additional opportunities for precipitation.

&&

.DISCUSSION /Through Saturday/...
Issued at 1213 PM MDT Sat Sep 19 2026

In the foothills and areas west of I-25 (except Larimer County 
where clouds slowed warming), temperatures have warmed into the 
mid to upper 70s already, reaching their convective temperatures. 
Thunderstorms have formed and are moving across parts of the 
Denver metro area. MLCAPE for the urban corridor is 300-700 J/kg, 
so the storms are expected to stay sub-severe. There is also some 
drier air over eastern Boulder and Larimer Counties where dew 
points have fallen into the 40s. We lowered PoPs slightly for the 
west side of the urban corridor because of this. Hi-Res models 
still favor numerous thunderstorms for the eastern plains this 
afternoon and evening, but they have been inconsistent regarding 
storm evolution and timing. There's still a threat for severe 
thunderstorms over the eastern plains, south of I-76 with large 
hail and winds up to 60 mph. If northern parts of the urban 
corridor miss this first batch of storms, a second batch could 
form later this afternoon. By mid evening (8-9PM), storms are 
expected to be finished, expect a few possible stragglers over the
far eastern plains. 

Showers will be possible tomorrow morning across northern 
Colorado due to lift ahead of an upper level low moving across 
Wyoming. These showers could continue into the afternoon over the 
northeast corner of the state. The airmass will continue to cool 
with the low nearby. Highs are expected to be in the mid 60s to 
lower 70s. The cooler temperatures are expected to be found over 
the northeast plains where cloud cover is anticipated most or all 
of the day. Models have backed off on cloud cover some for 
tomorrow afternoon along the I-25 corridor. Where temperatures 
reach the lower 70s, MLCAPE is expected to reach 300-800 J/kg, and
be slightly higher along and east of the Palmer Divide. Storm 
chances tomorrow will be lower due to less moisture, subsidence, 
and possible capping. Though if storms can form, a couple severe 
ones are possible over and east of the Palmer Divide where better 
instability will reside. 

The upper level low weakens and shifts east of the region on 
Monday. Replacing it, will be shortwave ridging. Temperatures will
be slightly warmer than Sunday, but a little below normal with 
highs in the lower to mid 70s across northeast Colorado. Looking 
upstream, a closed low will move across southern California on 
Monday. This low begins to weaken Tuesday as it runs into the 
ridge. The low lifts northeastward Tuesday and Tuesday night. On 
Wednesday, this now open trough will be over Wyoming. As it passes
north of Colorado, it could bring scattered showers and 
thunderstorms sometime Tuesday afternoon through Tuesday night. If
it slows slightly, we could see them on Wednesday.  

For Wednesday through Saturday, the large scale weather pattern 
will feature a large upper level ridge over the central part of 
the country and a longwave trough off the west coast. For 
Colorado, we'll see southwest flow for most of this period with a 
couple of minor fluctuations possible. Temperatures under this 
pattern will be at or slightly above normal with highs in the mid 
70s to lower 80s. Chances for precipitation will mainly come from 
shortwave troughs and moisture lifting northward out of the 
eastern Pacific and Mexico. There's very little model agreement 
identifying these shortwave troughs, precipitation chances will be
low at this time.

&&

.AVIATION /00Z TAFS through 00Z Monday/...
Issued at 614 PM MDT Sat Sep 19 2026

A cluster of storms is currently located just southeast of KAPA, 
with radar velocity still showing up to 45KT winds with the 
leading edge and core of the storm. Although this is the strongest
thunderstorm currently over the the Denver metro region, 
additional showers and weaker storms are still developing over the
foothills as well as over the eastern CO plains. Shower activity 
will diminish by around 03Z this evening. Most model guidance 
suggests winds turning light and variable, or a light northeast 
wind (<07KT) later tonight and through tomorrow morning. 

Light surface winds and residual moisture from today's showers will 
give way to patchy fog starting at 09Z, with the best chance for fog 
and reduced visibilities between 11Z and 13Z. Even if fog is unable 
to develop, soundings show enough low-level moisture for SCT low 
clouds (<1000ft AGL) and a good chance (65%) for IFR conditions 
at KDEN. Ceilings will improve after 15Z and winds will become 
northeasterly in the early afternoon, generally remaining light 
(<10KT). At this time, we expect Sunday afternoon's storm activity
to stay well to the southeast of KDEN, with little to no TSRA 
impacts. 

&&

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

&&

$$

DISCUSSION...BM
AVIATION...AA