701
FXUS65 KBOU 061109
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
509 AM MDT Sat Sep 6 2025

.KEY MESSAGES...

- Still hazy/smoky through this evening.

- Isolated to scattered showers and storms most days this week,
  but mainly over the higher terrain.

- Warmer for much of the week ahead, but chance of storms may
  increase along with cooler temperatures by the end of the week.

&&

.DISCUSSION /Through Friday/...
Issued at 137 PM MDT Fri Sep 5 2025

An upper level ridge centered over the Great Basin will produce a
northwest flow aloft. This will continue to help transport
wildfire smoke from the Pacific Northwest and western Canada into
Colorado today and Saturday. There will be enough moisture and
instability for scattered showers and thunderstorms. The
showers/storms will be most numerous across the higher terrain
south of I-70. For the lower foothills and eastward, cloud cover
and smoke will help keep the airmass cool and capped. Chances for
showers or storms to move off the higher terrain are low. If a
couple happen too, they are expected to be weak and short lived.
Much of the same is expected for Saturday, though high
temperatures warm up into the mid to upper 70s.

The ridge flattens some by Sunday as it begins to drift eastward.
Temperatures warm more with highs expected to reach to the lower
to mid 80s across northeast Colorado. Another round of afternoon
and evening showers and thunderstorms are expected over the higher
terrain. Chances for showers and thunderstorms will be higher
across the urban corridor and eastern plains Sunday, due better
instability, weaker cap, and westerly flow pushing the storms more
eastward.

For next week, the upper level ridge will slide east across
Colorado Monday. This will bring warmer temperatures with highs
climbing into the 80s across northeast Colorado. There may be
enough moisture for weak showers and storms over the higher
terrain, but most areas should remain dry.

The upper level ridge will be east of Colorado Tuesday and stays
east of the state through Thursday. This will produce a southwest
flow aloft through at least Thursday. High temperatures will be
above normal under this pattern with mid to upper 80s expected
over northeast Colorado each day. The GFS and ECMWF ensemble
members don`t favor any organized waves or precipitation events
Tuesday through Thursday. However, there`s just enough moisture
for isolated/scattered showers and thunderstorms, mostly over the
higher terrain each day.

For Friday and into next weekend, models trending towards an
upper level trough digging south into the Desert Southwest or
southern California. This should produce some sort of southwest to
southerly flow aloft across Colorado. Too soon to tell how much,
but this pattern should be able to tap into some subtropical
moisture. Will trend temperatures down and PoPs up for this
pattern, but if this pattern is slow to evolve, we could see
another warm and dry day.

&&

.AVIATION /12Z TAFS through 12Z Sunday/...
Issued at 509 AM MDT Sat Sep 6 2025

VFR conditions will persist, but the main issue will be smoke and
reduced arrival rates due to IMC during daylight hours. It appear
the smoke plume will stay largely unchanged from yesterday, so
we`ll mention FU in the TAFs (surface vis should stay above 6SM
but slant range visibility will be affected). We do expect some
convective cloud buildups 18Z-03Z, but the main threat of any
passing showers or storms would stay confined to the high country
and Palmer Divide, and chances less than 20% for the TAF sites.
Normal diurnal wind patterns will persist, with speeds around 10
kts or less.

&&

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

&&

$$

DISCUSSION...Meier
AVIATION...Barjenbruch