Longmont, Colorado 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

449
FXUS65 KBOU 041920
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
120 PM MDT Sat Jul 4 2026

.KEY MESSAGES...

- Scattered strong to severe storms expected this afternoon and
  early evening, with large hail and gusty winds the main
  hazards.

- A few storms expected each day of the coming week, with the
  highest probabilities shaping up for Tuesday and Wednesday from
  the Front Range eastward.

- Isolated dry thunderstorms in mountains could spark new
  wildfires.

- Good agreement that significant heat wave arrives by next
  weekend.

&&

.DISCUSSION /Through Saturday/...
Issued at 120 PM MDT Sat Jul 4 2026

Convective initiation has occurred in the front Range Mountains
and Foothills as expected. As of 1 pm, the cap on the nearby
plains has nearly eroded per latest ACARS soundings. MLCAPE was
growing to 1000+ J/kg roughly along and east of a line from
Greeley to Strasburg and Kiowa, with values expected to grow to
1500+ J/kg over the northeast plains prior to convective
development there. Meanwhile, MLCAPE was lower (~500 J/kg) farther
west including much of the I-25 Corridor. Therefore, it appears
the main threat of severe weather would now be shifting eastward
to the richer CAPE environment along and east of the aforementioned
line. Effective bulk shear isn`t too strong, but slowly increasing
to 25-35 kts (strongest south). That should still be enough for
supercells, that could potentially organize into more linear
structures and high wind producers as they move east across the
plains. Large hail will also be a growing threat as storms
move/develop into the more unstable airmass across the plains.

Most of the storms should exit the far eastern plains toward 8-9
pm. Weak subsidence is still noted to build in for this evening,
and the airmass will stabilize further post this initial round of
convection and with loss of daytime heating. Thus, most mid to
late evening activities should be relatively quiet weather-wise.
However, post outflow winds from the southeast could spell breezy
conditions lingering into any evening fireworks shows.

For Sunday and Monday, an upper level ridge will amplify across
Colorado. While this will tend to stabilize things a bit, it will
still be hot and residual moisture means a chance of storms each
afternoon and evening. The majority of these should be focused
over Park County and the Front Range Mountains into the Palmer
Divide area, with probabilities dropping off rather quickly to the
north and east. High temperatures will likely reach the lower to
mid 90s over the plains.

For Tuesday and Wednesday, the upper level ridge is forecast to
flatten with weak zonal flow developing across the forecast
area. Modest low level moisture is expected to remain in place
east of the Rockies. In addition, a weak embedded shortwave or two
during this time should support an uptick in storm coverage.
Instability also builds slightly and shear improves so scattered
thunderstorms are expected both days, with potential for a couple
severe storms. Temperatures will remain a few degrees above
normal, although slight cooling is expected with higher
probabilities of a frontal push by Wednesday. The more unsettled
weather could linger into Thursday especially along/east of the
Front Range.

Drying is expected by Friday as there is still good confidence
that the ridge over the southwest U.S. starts to amplify again.
However, we could still see enough moisture for a few storms
east of the Front Range. Temperatures will likely start to warm
as the ridge builds, and ensembles show average highs pushing
into the mid to upper 90s across the plains and I-25 Corridor.

We will have to watch potential (>70% chance) for an extended
heatwave by next weekend into early the following week. There
remains excellent agreement in the various ensembles of a high
amplitude closed upper level high building over the Great Basin
and Central Rockies. This appears to be on the higher end of
climatology, with forecasts generally residing anywhere between
600 and 604 decameter (dm) 500 mb heights. Even ensemble averages
had a 600 dm contour by next Sunday! Ensemble members show
average high temperatures near or slightly above 100F in Denver
starting next Saturday, the 11th, which could potentially last a
good 4 days before monsoonal moisture gradually builds under this
monster of a ridge.

Finally, mountain areas may be prone to isolated dry lightning as
they reside on the edge of better low level moisture and
instability for the next several days. Thus, new fire starts will
be possible. The only favorable parameter with regard to fire
weather in the coming days will be generally light breezes under
a fairly dominant ridge.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1125 AM MDT Sat Jul 4 2026

VFR conditions expected to prevail for all terminals through the TAF
period. Some weakening of the current southerly flow is anticipated
in the coming hours, before isolated high-based convection starts
to initiate and drift east into the I-25 corridor early
afternoon.

Latest guidance indicates more questionable moisture availability
for thunderstorms this afternoon at the terminals, though even
elevated SHRA would be capable of producing robust outflow gusts of
35-40 kts. Thus, will maintain the PROB30 groups for now. As the
afternoon and early evening progresses, east and southeast flow
should take hold as convection becomes more widespread over the
plains. Some potential for gusts to persist into the early evening,
particularly if we see numerous developing east to west outflows.
Expect a return to drainage during the evening with clearing skies,
and lighter/more VRB winds prevailing Sun AM.

Smoke coverage is somewhat less this morning, and smoke production
from ongoing fires is expected to continue to trend downwards as
fire activity moderates. As such, anticipating a gradual reduction
in the potential for slant range visibility impacts tonight and
particularly for Sunday.

&&

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

&&

$$

DISCUSSION...20
AVIATION...BRQ