Johnstown, Colorado 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

174
FXUS65 KBOU 302330
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
530 PM MDT Sun Mar 30 2025

.KEY MESSAGES...

- Scattered rain and mountain snow showers through this evening.
  Most numerous south of Denver where there is also a slight
  chance for thunderstorms.

- Occasional showers, mostly rain at lower elevations and snow at
  higher elevations, this week. The most significant system will
  bring snow, potentially heavy at times, to the mountains Monday
  night and Tuesday with travel impacts expected.

- Small potential for a larger snowfall across our forecast area
  next weekend but there is high uncertainty in the track of this
  system.

&&

.SHORT TERM /Through Monday/...
Issued at 215 PM MDT Sun Mar 30 2025

Water vapor satellite imagery showing a well defined shortwave
trough over the Great Basin with the best lift over eastern Utah
and western Colorado. Ahead of this wave, the airmass over the
higher terrain and south of Denver will become slightly unstable.
The combination of the wave, instability, and residing moisture is
expected to result in scattered showers later this afternoon and
evening. We could even see a few thunderstorms again to the south
of Denver where the best clearing has been. This will also be
location of the heaviest and most numerous showers. To the north
of Denver, overcast skies have prevailed through the day, keeping
the airmass stable. Can`t rule out a few showers surviving as they
move off the higher terrain, so will continue with scattered PoPs
for this area as well. Most of the showers will dissipate by
midnight, with a few weak snow showers over the mountain and weak
rain/snow showers over the plains lingering past midnight.
Precipitation type will mainly be rain again across the lower
elevation with a rain/snow possible later this evening over
eastern plains.

For Monday, weak ridging in the southwest flow aloft will pass
over the state with the ridge axis sliding east of the area during
the afternoon. This will bring a warmer and drier day to the
area. A surface trough forms east of I-25 during the day. To the
east/northeast of it just enough moisture and instability may
prevail for a few weak showers during the afternoon. Only other
chance for precipitation will be over the northern mountains and
valleys where orographic lift will help to produce scattered
showers through the day. As west-southwest flow aloft increases
during the afternoon, winds will pick up over the higher terrain
with west- southwest winds gusting up to 40 mph.

&&

.LONG TERM /Monday night through Sunday/...
Issued at 215 PM MDT Sun Mar 30 2025

A broad and strong trough will enter western Colorado on Monday
night and will move directly over our forecast area on Tuesday.
The main energy with this trough will move north of Colorado but a
cold front will pack a punch for our forecast area. The timing of
this front has moved up compared to recent model runs and it
moves through the mountains late Monday night or early Tuesday
morning. High resolution models show intense snowfall rates in
the range of 2-3" per hour around the time of the cold front
arrival. If the cold front moves through during the nighttime and
snowfall rates do reach those levels, it could lead to hazardous
travel conditions especially near the Eisenhower Tunnel and
Berthoud Pass. There was consideration for issuing a Winter
Weather Advisory for the central and northern mountains but the
timing of the cold front and associated impacts is still uncertain
so no highlights were issued at this time.

Across the plains, the cold front will likely generate some
showers during the afternoon. They will initially be rain but
towards the late afternoon and evening, some showers may switch
over to snow especially across the Palmer Divide. There are two
more concerns on Tuesday which is shaping up to be a busy day. The
trough will help to generate strong southwesterly winds
especially in Park County and from the Palmer Divide southward.
Winds will gust up to 60 mph in Park County and up to around 50
mph in southern Lincoln County. There may need to be high wind
highlights issued but the timing of the cold front will be
important as after the frontal passage the winds will decrease
slightly. The other concern is fire weather which is specific to
southern Lincoln County since other areas will have high relative
humidity and received healthy rainfall recently. Minimum relative
humidity in southern Lincoln could drop to 14 percent given a
slower cold front passage. So a Red Flag Warning is a possibility
in southern Lincoln Tuesday afternoon.

Models now show a more defined shortwave trough moving from Arizona
on Wednesday towards eastern Colorado on Thursday. In the low
levels, there are upslope, easterly winds that develop along with
some warm air advection. Ensembles now highlight Wednesday night
into Thursday as a period where there could be accumulating snow
on the eastern plains. PoPs were increased and the high
temperature was decreased for Wednesday and Thursday.

The system for Friday night through the weekend still shows up
well on the ensembles, mainly the ECMWF ensembles. However, over
the past 24 hours, the trend has been towards a moderate QPF event
and the amount of ensemble members with QPF amounts over 1.5" has
fallen significantly. Therefore, the odds of a widespread snowfall
is increasing across our forecast area but the odds of a
significant, heavy snowfall are decreasing.

&&

.AVIATION /00Z TAFS through 00Z Tuesday/...
Issued at 524 PM MDT Sun Mar 30 2025

Best chc of showers/storms early this evening will stay south
of DIA with some possible impact at APA.  This activity should
diminish by 03z. Ceilings will remain MVFR with winds trending
to more SE by 03z. Overnight there will be some potential of
dense fog developing especially at BJC and DIA by 08z or 09z.
Visibility may drop below 1/2 mile at times with ceilings blo
500 ft. The dense fog may linger thru 14z on Mon before lifting.
Ceilings should scatter out by 14z as well.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Monday evening through late Tuesday
night for COZ031.

&&

$$

SHORT TERM...Meier
LONG TERM...Danielson
AVIATION...RPK