866
FXUS65 KBOU 052037 RRA
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1251 PM MDT Sat Sep 5 2026

.KEY MESSAGES...

- A few strong thunderstorms and locally heavy rain possible late
  this evening over the northeast plains.

- Slight increase in afternoon shower and thunderstorm coverage is
  favored Sunday and Monday for most areas.

- Temperatures will remain very warm, with only slightly cooler
  conditions starting Tuesday.

&&

.DISCUSSION /Through Saturday/...
Issued at 1153 AM MDT Sat Sep 5 2026

Midday cumulus development is more expansive today, suggestive of
the modest increase in mid-level moisture regionwide. Near surface
moisture however is much more variable, with dewpoint fields
exhibiting a considerable zonal gradient between the I-25
corridor (~40-45F) and our eastern plains (~58-63F). Given
limited forcing, meager instability and drier low-levels, areas
from the urban corridor westward will be limited to largely
isolated high-based shower activity late this afternoon and
evening, producing brief localized gusts of 25-35 mph. Over the
eastern plains, the warm and moist advection regime will hold
steady through tonight, leading to an increasingly buoyant
environment with MLCAPE values of 1,500-2,500 J/Kg present across
our northeasternmost counties by late afternoon. Thunderstorms
look to develop come this evening, with the bulk of the activity
favoring the late evening period coinciding with a moderate LLJ
setup over the plains. A few will be strong to perhaps marginally
severe, with an initial wind and hail threat that will
nonetheless be tapered by the lack of shear, limiting overall
storm organization. Given the clustering potential and abundant
moisture (precipitable water values approach 1.5" this evening),
locally heavy rain can be expected with any storms.

We`ll gain a touch more moisture still on Sunday as moist
southerly flow continues and the trough to our west inches
slightly closer. The urban corridor also looks a little better
positioned to tap into higher surface dewpoints, supporting
modestly unstable conditions for the afternoon. Thus, anticipate
an increase in afternoon shower activity as well as potential for
actual convection. There will be minimal change as far as
temperatures are concerned though, with most of the lower
elevations breaking into the lower 90`s once more.

A slight waning in the high pressure on Monday will allow for the
intrusion of stronger northwest flow at upper levels and thus some
actual forcing, which should support a slight uptick in coverage
of showers and thunderstorms, and likely the best precipitation
chances of the next few days. Unsurprisingly, temperatures will
continue to hold mostly steady.

At risk of sounding like a broken record, ensemble guidance still
indicates a flattening of the ridge starting Tuesday (though more
pronounced Wednesday), followed by a westward shift of the ridge
axis over Colorado. Slightly cooler temperatures - albeit still
above - should result from the initial flattening and transition
to zonal flow, but this trend appears increasingly transient in
nature, with ensemble guidance favoring a return to hotter weather
for the second half of the week. As previous discussions have
alluded to, confidence in precipitation potential remains lower,
although we still look to retain at least some moisture beneath
the ridge and thus a few opportunities for afternoon showers and
thunderstorms.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1152 AM MDT Sat Sep 5 2026

Northeast winds will continue this afternoon and slowly turn
clockwise, becoming southeast this evening, after 00Z. The PROB30
for variable winds and showers was pushed back to begin at 02Z.
This lines up with recent model guidance which shows the best lift
occurring later. A wind shift or two will be possible from passing
by showers. For tomorrow, better instability and moisture will
lead to about a 30 percent chance for thunderstorms late Sunday
afternoon, after 22Z.

&&

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

&&

$$

DISCUSSION...BRQ
AVIATION...BM