879
FXUS65 KBOU 151131
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
531 AM MDT Tue Jul 15 2025

.KEY MESSAGES...

- Hot again today with highs in the mid/upper 90s across the
  plains. An isolated strong to severe thunderstorm across the far
  northeast corner of the state this afternoon.

- Conditional severe storm threat across the I-25 corridor and
  plains on Wednesday, but low confidence at this time.

- Active pattern continues into the weekend, with scattered
  afternoon showers and storms each day. Best chance of rain
  across the Front Range/Foothills and South Park most afternoons.

&&

.UPDATE...
Issued at 301 AM MDT Tue Jul 15 2025

Intriguing forecast pattern for the next couple of days, with one
last day of hot temperatures before a potentially widespread (but
highly conditional) severe threat evolves on Wednesday.

Today should be relatively quiet across most of the forecast area,
as drier air has worked into the region underneath a broad ridge.
Across the higher elevations, there`s still enough moisture along
with steep low/mid-level lapse rates for some weak convection this
afternoon, with at least a few gusty showers or storms expected to
drift into the I-25 corridor by late afternoon. Meanwhile, a weak
shortwave is expected to track across southern Wyoming into
southwestern Nebraska this afternoon, and a few stronger storms
could develop across far northeastern Colorado where richer
boundary layer moisture persists. With a narrow corridor of
20-30kt 500mb winds, there should be just enough CAPE/shear
overlap to support a couple of multicell clusters or perhaps a
brief supercell, though for the most part forecast guidance keeps
stronger storms over Nebraska.

By tonight, a cold front should push across the forecast area,
bringing better surface moisture as far west as the urban corridor
by Wednesday morning. Surface dew points should remain in the 50s
Wednesday afternoon, with guidance suggesting as much as 1000-1500
J/kg of MLCAPE along with 40-50kt effective layer shear. However,
like many severe weather threats here, the setup is obscured
somewhat by morning stratus. Both deterministic and statistical
guidance favor a thick stratus deck Wednesday morning, which would
certainly hamper surface heating/destabilization later in the day.
As is often the case, I suspect that some high resolution guidance
(HRRR/RAP) are too aggressive with their boundary layer mixing...
and thus capping is going to be a significant hindrance on any
severe threat if stratus is slow to erode. The SPC marginal risk
seems appropriate at this time, but stay tuned for updates later
today and Wednesday AM.

&&

.DISCUSSION /Through Monday/...
Issued at 202 PM MDT Mon Jul 14 2025

Mountain convection had an early start this morning, with storms
initiating along the Continental Divide around 9AM. Temperatures are
quickly climbing towards convective temperature across the plains,
with multiple observation sites reporting 90+ degrees. As of 11:30
AM (Monday) ACARS soundings are showing just over 500 J/kg of
MLCAPE, large dewpoint depressions, and DCAPE of over 1000 J/kg.
This will be sufficient for thunderstorms to sustain themselves as
they move onto the lower elevations, or for storms to develop once
the convective temp is reached. These storms will be capable of bringing
gusty outflows and dry microbursts between 30-40 mph, with a few
as strong as 50-55 mph. With weak flow aloft, slow moving storms
may bring some localized heavy rainfall (generally over the higher
elevations), but with weak shear in place, storms are not
expected to become severe, however, small hail will be possible.
Cloud cover will help cool temperatures off this evening before
clearing from west to east overnight.

Flow aloft begins to increase on Tuesday as a shortwave moves across
the northern Rockies. At the surface, a lee trough will stretch from
across the plains of Colorado to South Dakota. Forecast soundings
show MLCAPE values near 1000 J/kg with modest amounts of shear (30
to 40 kts) over the northern corner of Colorado in the
afternoon/evening, where dewpoints will be in the 50s. This would
support an isolated severe threat, with large hail and gusty
winds being the main hazards. Elsewhere across the forecast area,
scattered showers and weaker storms will be possible.

A cold front/shortwave combo is expected to bring widespread
precipitation and brief cooldown on Wednesday and Thursday. Some
localized heavy rainfall will be possible as ensembles show PWAT
values between 120-160% of normal from the Continental Divide
eastward. A few stronger storms will be possible along and behind
the front, especially along the northern plains where shear will be
strongest, and the severe threat will be higher. Temperatures will
feel cool compared to the rest of the week, but still climb into the
mid to upper 80s across portions of the plains, with high 70s for
areas along the Wyoming/Nebraska borders.

By Friday, the ridge reamplifies and temperatures rebound to the
90s across the plains. Ensembles hold 90 degree temperatures
steady for the foreseeable future. A more active pattern will
continue through the forecast period with shortwaves passing
through the upper-level flow, and scattered afternoon showers and
storms will be possible each afternoon.

&&

.AVIATION /12Z TAFS through 12Z Wednesday/...
Issued at 527 AM MDT Tue Jul 15 2025

VFR through the evening. Drainage winds will transition to a
northwesterly direction later this morning and persist through
most of the afternoon. At least a few gusty showers are forecast
this afternoon, though overall coverage will be sparse. Main
concern with these will be variable/gusty outflow winds during the
mid/late afternoon hours.

Winds should gradually turn to the north or northeast this
evening, with a gradual moistening trend still expected. Guidance
is in fairly good agreement developing a stratus deck between
08-11z tonight, with better odds at DEN compared to APA/BJC. At
least a brief period of MVFR to IFR ceilings is expected at all of
the terminals. Stratus should slowly rise and scatter out through
Wednesday morning.

&&

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

&&

$$

UPDATE...Hiris
DISCUSSION...Bonner
AVIATION...Hiris