Johnstown, Colorado 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

056
FXUS65 KBOU 260526
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1126 PM MDT Mon May 25 2026

.KEY MESSAGES...

- Warm conditions expected through the week, with daily showers
  and a few thunderstorms expected most days in the
  afternoon/evening.

- Tuesday will bring windy conditions to the plains and potential
  for elevated fire weather conditions in areas that see little/no
  rain.

- Wednesday appears to be the most active day with more widespread
  shower and thunderstorm coverage.

- After somewhat of a lull Thursday, thunderstorm potential will
  increase again Friday into the weekend.

&&

.DISCUSSION /Through Monday/...
Issued at 229 PM MDT Mon May 25 2026

Current satellite imagery shows cumulus clouds developing over the
mountains this morning, with convection initiating slightly
earlier than yesterday. Expect scattered showers and isolated
thunderstorms to continue through late this evening. Current ACARS
show inverted-V soundings, with DCAPE values up to 1000 J/kg. SPC
mesoanalysis does have DCAPE increasing to 1500 J/kg by the late
afternoon, so gusty outflow winds are expected. However, given
steep mid-level lapse rates and modest shear, small hail is also
possible with the strongest storms.

On Tuesday, an upper level closed low will trek from the Pacific
Northwest into western United States. Over Colorado, winds aloft
will turn more south/southeasterly and increase in magnitude. With
modeled Skew-T soundings showing mixing heights up to 600mb, winds
will likely mix down to the surface. Hi-res guidance continues to
show widespread wind gusts up to 35-40 mph at times for much of the
plains on Tuesday. This could bring about elevated fire weather
concerns for areas that haven`t received precipitation from these
past few events. However, that combined with marginal relative
humidity values, these conditions will be localized. By the
afternoon, a weak shortwave embedded in the upper level flow will
bring another round of precipitation. However, coverage should be
mainly confined to the mountains/foothills and areas west of the
I-25 Corridor due to better synoptic forcing (the plains look too
stable for widespread precipitation). Guidance does favor decent
instability over the high country with gusty winds and small hail
as the main threat. In addition, with PWAT values climbing up to
0.50" to 0.75" some of the stronger storms could produce brief
heavy rain. However, flooding concerns will be marginal given how
fast the storm motion is expected to be.

The upper-level closed low will likely stay positioned over the
western U.S. Wednesday and Thursday as a blocking pattern sets up
with an upper level high over the Great Plains. This will leave
Colorado in between these two features, with relatively weak flow
aloft and mid-level moisture being continuously advected into the
forecast area. Guidance is in good agreement with the best
instability building over the plains on Wednesday, with
thunderstorm coverage increasing in the afternoon. We could have
heavy rain associated with these thunderstorms, given PWAT values
up to 0.90" and modeled hodographs showing slow storm motion.

By Friday, the blocking high pressure will shift eastward with the
western upper level low getting absorbed by another upper level
trough. At the surface, guidance is in good agreement with lee-side
troughing occurring over the plains. Daily precipitation chances
(with potential for thunderstorms given decent instability in place)
are possibly into the weekend, particularly for the northern
foothills and plains. Temperatures should stay slightly above
normal, with highs in the low 80s across the plains.

&&

.AVIATION /06Z TAFS through 06Z Wednesday/...
Issued at 1118 PM MDT Mon May 25 2026

Band of high based showers moved across which led to brief gusts
from 40 to 50 mph earlier. Overnight, will have south winds with
a few gusts from 20 to 25 mph thru 09z. By 14z Tue, south winds
will increase at APA and DIA with gusts frm 25 to 30 mph thru 18z.
After 18z, south winds will continue with gusts from 35 to 40
mph. At BJC expect lighter south winds by 07z with winds going
light and variable by 09z. On Tue, winds at BJC will increase from
the south by 18z with gusts up to 25 mph thru the aftn.

Meanwhile, it appears there is only a slight chc of shower/tstm
activity on Tue late in the aftn thru Wed evening. Thus have kept
prob30`s in for APA and DIA from 00Z thru 04z. BJC may have a
slight chc of showers/tstms as early as 20Z so have started the
prob30 earlier.

&&

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

&&

$$

DISCUSSION...MAI
AVIATION...RPK