Arvada, Colorado 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

388
FXUS65 KBOU 172318
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
518 PM MDT Thu Apr 17 2025

.KEY MESSAGES...

- Critical fire weather conditions for lower elevations south of
  I-70 through this evening.

- Moderate snow tonight through Sat AM will create hazardous mountain
  and foothill travel; A few inches of slushy accumulations for
  the urban corridor, with minor travel impacts, mainly Fri
  evening.

- Colder Friday into Saturday, with steady warming Sunday into
  next week.

&&

.SHORT TERM /Through Friday/...
Issued at 236 PM MDT Thu Apr 17 2025

It`s a battle of airmasses today as the southern half of our
forecast area remains under dry downslope flow, sustaining critical
fire weather conditions roughly along and south of I-70 through late
afternoon or early evening. Meanwhile, the northern plains remain
cooler after the passage of a first, weaker frontal boundary and
prevailing northeasterly flow. Moisture along the leading edge of
the approaching upper-level trough will steadily increase through
the day, and has been producing a few showers in our northern
mountains.

However, the bulk of our initial round of moisture won`t arrive
until later this evening and overnight, following the more robust
front that will push north to south late afternoon into early
evening. Gusts to around 45 mph can be expected with the frontal
boundary, tapering off to a lingering breeze after one or two hours.
There`s marginal instability with the front, as evidenced by the
shallow convection and isolated lightning currently observed
upstream, so we`re maintaining a chance of thunder in the forecast
for later today.

East of the mountains, it will take some time for moisture to deepen
sufficiently for more persistent precipitation to develop, with this
holding off until late evening as banded precipitation expands
eastward. A brief wintry mix will precede the transition to snow
(expected generally after midnight), and even some patchy and brief
freezing drizzle can`t be ruled out, mainly east of I-25 on the
front end of the precipitation. Snow will then increase in coverage
steadily through sunrise Friday, with the heavier accumulations
favoring areas north of I-70 (mountains) and I-76 (plains). Snowfall
intensity will remain on the lighter side during the first half of
this system. By the afternoon, low-level flow will turn more
easterly over the foothills and urban corridor, and southerly for
Park County, boosting the upslope component. With a modest increase
in lapse rates to boot, moderate snowfall will fill in across the
foothills, mountains and South Park, as well as adjacent lower
elevations. Daytime snow accumulations for the plains and urban
corridor will largely stay confined to colder surfaces like grass,
with primarily wet or occasionally slushy roads, although
temperatures should be cold enough by Friday evening to support more
widespread (albeit largely minor) accumulations on roads. As is
typical for April storms, the snow will be on the wetter/heavier
side, and could lead to damage to vegetation, with travel impacts
generally confined to the foothills and higher mountain/valley
elevations.

&&

.LONG TERM /Friday night through Thursday/...
Issued at 236 PM MDT Thu Apr 17 2025

Friday night, a positively tilted upper level trough will stretch
from Ontario Canada into the Southwestern States. This trough will
be split with the strongest piece of energy over Northern
Arizona/Southern Utah. Moist upslope flow east of the mountains
combined with QG lift, associated with an upper level shortwave,
should result in continued snow across much of the forecast area
through Saturday morning. The snow should be light across the plains
with little impact anticipated. The mountains and foothills could
see periods of moderate snow with additional accumulation expected
which could impact travel. Therefore, the Winter Weather Advisory
which is in effect for these areas still looks on track and added
the northern slopes of the Palmer Divide for late Fri PM through
Sat AM. The snow should wind down Saturday afternoon with a
couple inches of additional accumulation possible across the high
country.

Warmer and drier weather is expected on Sunday as upper level high
pressure builds over the Rocky Mountain Region. However, there may
be enough lingering mid level moisture combined with orographic lift
to produce scattered snow showers over the mountains.

Early next week, a zonal flow aloft will set up over the state which
should lead to mild and dry conditions across the region. The
exception may be a few light rain and snow showers possible across
the high country.

By mid week, the upper flow turns southwesterly in response to upper
level troughing over the Western States. Mild temperatures are
expected to continue with highs temperatures on the plains climbing
into the upper 60s and lower 70s. There may be enough mid level
moisture, combined with some instability, to produce isolated to
scattered afternoon showers and storms across the forecast area.

&&

.AVIATION /00Z TAFS through 00Z Saturday/...
Issued at 517 PM MDT Thu Apr 17 2025

North to northeast winds will decrease after 02z with gusts dropping back
to around 20-25 kts aroud 02z followed by a steady north wind around 10-15 kts
after 06z. Cigs will start to develop around 02z then steadily drop into the
IFR to high end LIFR category as snow develops around 06z and continues into
the morning hours.  There could be a break in the snowfall and a period
of slightly higher cigs/vis in the IFR-MVFR category after 16z before cigs drop
and another round of snow spreads in after 19-20z Fri. Snow will continue into
the Friday night period. Snowfall amounts at the terminals will range from
2 to 4 inches through Friday though expect melting on pavement surfaces to
limit accumulations to mainly an inch or two during the colder overnight
periods with the heaviest accumulations at KBJC and KAPA.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MDT Saturday for COZ031-033-
034.

Winter Weather Advisory from 4 AM Friday to 6 AM MDT Saturday
for COZ035-036.

Red Flag Warning until 7 PM MDT this evening for COZ214-216-241-
246-247.

Winter Weather Advisory from 9 AM Friday to 6 AM MDT Saturday
for COZ037.

Winter Weather Advisory from 3 PM Friday to noon MDT Saturday
for COZ041.

&&

$$

SHORT TERM...099
LONG TERM...099
AVIATION...RPK