Johnstown, Colorado 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

495
FXUS65 KBOU 131106
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
506 AM MDT Fri Jun 13 2025

.KEY MESSAGES...

- A few severe storms possible over the plains late this afternoon
  and evening. Less coverage and less intense showers/storms (but
  still gusty winds) over most of the I-25 Corridor and mountains.

- Drying trend this weekend with the chance for thunderstorms
  mostly confined to the northeast plains.

- Summer heat this weekend through Monday. Brief respite Tuesday
  and Wednesday, but then hot again end of next week.

&&

.UPDATE...
Issued at 303 AM MDT Fri Jun 13 2025

A little update early this morning. One for adding patchy fog on
the northeast plains early this morning, where low level moisture
continues to advect west across the High Plains. This easterly
upslope low level wind push is a direct result of storm outflows
originating in Nebraska and Kansas. That low level moisture
progression will have to be watched closely today, since generous
low level moisture east of that boundary will support MLCAPE of
1800-2500 J/kg. At this time, given the recent trends and
observations, we think anywhere roughly along/east of a line from
Greeley to Deer Trail to Limon would have the highest MLCAPE,
while odds of severe would grow as storms develop into an even
higher bouyancy airmass over the northeast plains (Fort
Morgan/Akron/Sterling and points east). While shear is quite
marginal for sustained supercells, damaging hail and wind gusts
would certainly be possible given the large MLCAPE today.

&&

.DISCUSSION /Through Thursday/...
Issued at 219 PM MDT Thu Jun 12 2025

Another round of afternoon and evening showers and thunderstorms
will track across the area. The airmass over the higher terrain
and nearby plains is little more moist and unstable compared to
yesterday with mid 30s to mid 40s dew points and MLCAPE up of 300-
800 J/kg. This will result in mainly high-based showers and
thunderstorms with gusty outflow winds the main threat. Brief
heavy rain and small hail will also be possible. Southeast winds
over the eastern plains are advecting moisture into the area. Dew
points here are in the 50s with 60s nearby in Kansas and Nebraska.
MLCAPE in this area is 1000-2000 J/kg. Thus, some of the storms
over the northeast plains could become severe with large hail and
damaging winds. Models are in good agreement the northeast corner
of Colorado will see a round of storms this evening, 6 PM to 10
PM. To the west showers and thunderstorms will be ending during
the evening hours.

Water vapor satellite imagery showing drier air off to the west.
This drier will shift eastward for Friday. This will lead to fewer
and weaker showers and thunderstorms across the higher terrain
and nearby plains. Over eastern Colorado, southeast winds will
continue to bring moisture, with dew points in the 50s to lower
60s. It will be unstable again with MLCAPE of 1500-2500 J/kg.
Models vary how far west the best instability and moisture make
it. Most models keep it over far northeast Colorado, though the
NAM model has it as far west as Greeley and just east of DIA.
Outflow from thunderstorms tonight over Nebraska may help push the
southeast winds westward more than the models show.

For this weekend and Monday, ridging intensifies over the Central
and Southern Rockies, leading to warmer temperatures and drier
conditions. Most locations over northeast Colorado are expected to
top 90F degrees. With precipitable water falling below a half
inch along the Front Range and below a third inch over the higher
terrain, not expecting enough moisture for showers and
thunderstorms. Again, the best chance for storms will be over far
northeast Colorado where southeast winds may bring enough moisture
for thunderstorms, some of which could end up being severe.

For Tuesday, the latest model runs have been trending towards an
upper level trough pushing through the area and knocking down the
ridge. This will lead to cooler temperatures with highs in the 80s
across northeast Colorado. It may also bring enough moisture for
showers and thunderstorms, though not all models show this, but
enough do to mention showers and thunderstorms for Tuesday
afternoon and evening.

On Wednesday and Thursday, a flat upper level ridge will prevail
over Colorado. Wednesday`s temperatures may stay below 90F over
the plains, but by Thursday temperatures are expected to heat up
into the 90s again. Some of the longer term models are showing
temperatures well into the 90s and nearing 100F towards next
Friday- Sunday (June 20th to 22nd). Drier air will be over the
area as well with little to no chance for showers and
thunderstorms, unless we see more moisture than expected.

&&

.AVIATION /12Z TAFS through 12Z Saturday/...
Issued at 506 AM MDT Fri Jun 13 2025

Satellite shows a stratus deck 30 miles to the northeast of KDEN.
While it had earlier shown a rather steady westward progression,
it has since slowed since 10Z and thus KDEN should stay VFR this
morning with any low clouds or patchy fog holding to the northeast
of the airport.

Otherwise, the main concern will shift to another round of
potentially variable and gusty winds due to high based showers and
storms 20Z-24Z. DCAPE values range from 1200-1500 J/kg so this
could translate to wind gusts as high as 45 kts (10-20% chance),
although highest probabilities (30-50%) are for gusts closer to 35
kts. Coverage of thunder would be limited enough for Prob30 -TSRA
with the gusty outflow winds, although TEMPO gusty winds may be
needed given KDEN`s propensity for such. There is reasonable
agreement in short term guidance that the storms will shift east
of the TAF sites by/before 00Z.

With regard to winds, we`ll start with light westerly til around
15Z, then becoming variable before a diurnal east/southeast wind
around 7-10 kts develops by 17Z-18Z. Prevailing winds will likely
become quite messy due to high based convection 20Z-24Z. While winds
could still be a bit variable post-convection, we do expect them
to settle down from a southeast to eventually south/southwest
direction overnight.

&&

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

&&

$$

UPDATE...Barjenbruch
DISCUSSION...Meier
AVIATION...Barjenbruch