689
FXUS65 KBOU 171151
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
551 AM MDT Thu Jul 17 2025

.KEY MESSAGES...

- Patchy dense fog across portions of the I-25 corridor and
  northeast plains this morning.

- Warmer today with scattered showers and storms, mainly across
  the higher elevations.

- Active pattern continues into the weekend, with scattered
  afternoon showers and storms each day. Higher chances for rain
  across the Front Range mountains and foothills.

- Trending warmer and drier next week.

&&

.UPDATE...
Issued at 243 AM MDT Thu Jul 17 2025

No significant updates to make tonight, with quieter weather in
the forecast today... but still a couple of things to note this
morning.

The morning forecast remains a little uncertain, with stratus
across most of the eastern plains. Some short term guidance hints
on a well-defined Denver Cyclone forming in the next few hours,
which should pull stratus and patchy fog into the northern I-25
corridor (mainly Boulder towards Fort Collins/Cheyenne). Did add
some patchy fog into the grids but don`t feel particularly
confident there. For the latter half of the day, there`s a pretty
good signal for isolated/scattered storms across the Front Range
with a few drifting into the urban corridor by the late afternoon.
The better rain chances look to set up across the southern
portions of our CWA (southern Foothills/South Park).

By Friday and Saturday, moisture is still expected to increase
across the region, leading to more widespread coverage of
afternoon convection, especially across the higher terrain.
Surface moisture will be the main wild card in this period with
quite a bit of spread across the overnight model runs. The best
chance of rain still looks to be Saturday afternoon/evening for
most of our forecast area.

Beyond that, a warming/drying trend is likely as we head into next
week. Model blends represent a good middle ground for this
period... and we`ll let the day shift look into it more.

&&

.DISCUSSION /Through Wednesday/...
Issued at 216 PM MDT Wed Jul 16 2025

Clouds have slowly eroded this past hour, allowing a brief moment
of surface heating across parts of the foothills and plains.
Current satellite imagery shows convection initiating over the
high country, with a few cells already having some impressive
vertical development as they approach the foothills. However, the
severe weather threat is still conditional at this time due to
the lack of sufficient surface heating. ACARS soundings still show
a well-defined cap in place over the plains, and anvil clouds
from the mountain convection will continue to block sunlight
sporadically.

Areas of further destabilization is expected, with SPC
mesoanalysis page showing 1000-1500 J/kg of MLCAPE and effective
bulk shear up to 40-45 kts over the next few hours. Due to the
expected conditions, some storms could overcome the capped
environment and increase in severity over the I-25 corridor and
into the adjacent plains. Hail up to 2" and winds damaging winds
up to 60 mph are possible with the strongest storms. In addition,
there could be brief moderate to heavy rainfall causing localized
flooding threats. Convection is expected through late tonight,
with showers and thunderstorms gradually weakening and ending from
west to east.

Thursday looks to be much quieter across our area as we will be
under weak westerly/northwesterly flow aloft due to an upper level
ridge building over the southern US. Orographic showers and weak
storms are possible in the afternoon, mainly over South Park and
the southern Front Range Mountains, as there will be drier air
aloft over northern Colorado. Did not make too many changes to the
forecast except for raising temperatures slightly, as hi-res
model guidance has been trending towards warmer temperatures.

Warm temperatures (90+ degrees) will return on Friday and into
next week as the broad upper level ridge amplifies. Ensemble
guidance is in good agreement of embedded shortwaves through the
weekend, creating daily chances for scattered showers and
thunderstorms. Model Skew-T soundings have high LCLs, so gusty
outflow winds will be the primary concern. By the beginning of
next week, a warmer and drier trend is likely.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 541 AM MDT Thu Jul 17 2025

Main TAF impacts will be through roughly 18z this morning, with
below normal confidence yet again. A weak Denver Cyclone has set
up over the city of Denver this morning. To the north and
northeast, a broad area of fog/stratus has developed, with
generally IFR/LIFR cigs/visby. Guidance lifts this cyclone off to
the ENE, essentially over DEN by 14-15z. That should bring lower
ceilings into BJC within the next hour or two, with a chance the
stratus could wrap up and into APA as well. For DEN, that leaves a
few different scenarios. Any sort of northeast component to the
wind would almost certainly bring brief IFR/LIFR conditions, but
the eventual passage of the cyclone (and daytime heating) should
limit any impacts to the field to just a few hours. If winds can
maintain an 090-120 direction, little or no direct impacts would
be anticipated during the period. Ultimately went with a short
TEMPO group as no obvious solution was out there for the morning
hours.

Beyond the cyclone, the rest of the day is a little more
straightforward, with east-southeast flow redeveloping during the
afternoon. Still a low chance of a brief shower/thunderstorm or
outflow boundary this afternoon. Should see a quick transition to
a drainage wind pattern this evening which should continue
overnight with VFR prevailing.

&&

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

&&

$$

UPDATE...Hiris
DISCUSSION...Ideker
AVIATION...Hiris