249
FXUS65 KBOU 122110
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
310 PM MDT Sat Jul 12 2025

.KEY MESSAGES...

- A few strong thunderstorms with locally heavy rain can be
  expected this afternoon roughly along and south of I-70.

- Afternoon showers/thunderstorms to continue most days, albeit
  with slightly lesser coverage Sunday and Monday.

- High temperatures to linger in the 90s across the plains from
  Sunday through mid-week.

&&

.DISCUSSION /Through Saturday/...
Issued at 224 PM MDT Sat Jul 12 2025

This morning`s (Saturday) low clouds have finally scattered out
across the forecast area and a Denver Cyclone has developed. Current
satellite imagery shows some cumulus starting to build along the
higher terrain, with a few weak reflectivity returns starting to
show in northern Park/western Jefferson Counties where surface
heating has been greatest so far today. With enough instability in
place as shown by the 500 to 1000 J/kg of MLCAPE shown in the SPC
Meso Analysis, these cumulus are expected to transition into
scattered showers and storms by early this afternoon. With a
prominent cap in place across the lower elevations as portrayed
in the latest ACARS sounding, these showers and storms won`t have
much luck of persisting onto the lower elevations where CAPE is
far more robust. However, with WNW to NNW steering flow in place,
storms that form will have potential to move along the higher
terrain where the cap is already broken, and we could see an
isolated threat for severe hail and some gusty outflows through
the early evening. With the cyclone in place, there is a chance
that the convergence zone could aid in breaking the cap along the
Palmer Divide and slightly north onto the adjacent plains where
the more robust CAPE will be in play, but have kept the greatest
PoPs south and west of the urban corridor where guidance continues
to portray things staying along and south of I-70 in the
mountains and foothills.

Light NNW flow aloft will persist into Sunday as the ridge over
the southwest remains in place. Instability will increase over the
mountains as forecast soundings show SBCAPE reaching 700-800 J/kg
and mid-level lapse rates steepening to 9+C/km by the afternoon.
This will promote scattered afternoon and evening convection, with
showers and storms expected to remain anchored to the higher
terrain. Temperatures will return to the 90s across the lower
elevations on Sunday and persist there through the first half of
the week.

Models are fairly consistent for the first half of the week,
keeping pulses of afternoon mountain convection each day, becoming
more widespread by Tuesday. Some discrepancies with timing of a
shortwave trough entering the Pacific Northwest on Tuesday are
evident between the ensembles, with the GFS supporting a cooldown
on Tuesday/Wednesday, whereas the ECM ens keeps an extra day of
90F+ for the plains, seeing a cooldown for Wednesday/Thursday
instead. The NBM seemed like a reasonable solution based on the
differences, so little changes were made past Monday for this
package. While the timing may be off, the signal is in place that
a brief cooldown will occur by mid-week. Past that, ensembles show
that the 90s will return and look to stick around across the
plains through at least the last week of July.


&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1129 AM MDT Sat Jul 12 2025

Winds are currently light and vrb across the Denver TAF sites as a
Denver Cyclone becomes more developed late this morning. Once the
cyclone settles in, winds are expected to have a NNE component
before making their way towards the east by ~22Z to 23Z this
afternoon for KDEN/KBJC. There are uncertainties with how today
will unfold with regards to KAPA as the cyclone may produce a
convergence zone over or near the airfield as portrayed in a few
hi-res CAMs. This would also allow for a better environment to
break the cap that is currently in place as shown in the latest
ACARS sounding, and why the PROB30 is in place for TS over KAPA
later this afternoon. Or, the convergence zone stays south of
KAPA, and winds keep a more NNE component through the afternoon. While
there is a small chance (15-20%) that convection develops a
little more northward that could impact KDEN, the more likely
scenario is that the cyclone helps keep convection to the south,
keeping the cap in place.

Winds are expected to follow the normal diurnal pattern for the
overnight hours tonight through the morning on Sunday.

&&

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

&&

$$

DISCUSSION...Bonner
AVIATION...Bonner