Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 182226
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
326 PM MST Sun Feb 18 2018

.SHORT TERM...(This evening through Monday)
Issued at 326 PM MST Sun Feb 18 2018

Breezy conditions across the plains this afternoon have been
accompanied by very warm temperatures and low relative humidities.
The Red Flag Warning on the Palmer Divide will remain in effect
until 5 PM. Winds will diminish through the evening and the fire
weather danger levels will ease.

Cold Canadian air is in place over Wyoming this afternoon and will
be moving into northeast Colorado after midnight. The cold air
will initially be shallow as it spreads over the plains. Areas of
fog and possibly some freezing drizzle will develop. Cross
sections and model soundings show the cold air will be quite
shallow and the upslope flow will be weak, so the primary threat
from the change in airmass should be fog. Freezing drizzle can not
be ruled out, so it will be mentioned along with the fog. Through
tomorrow, southwesterly flow aloft will continue with more
moisture moving over the region from the south. By afternoon, the
main upper level jet will be in place over the state, providing
a lifting mechanism for the moistening airmass. Snow should spread
across the mountains through the day and start to move out onto
the plains late in the day. The bulk of this approaching system
will have its impact tomorrow night as the upper jet remains over
the state. Mountain areas could see a few inches of snow by
evening. Temperatures are going to be the other big story tomorrow
as highs on the plains will only be in the 20s. Mountain areas
will not be as cold as on the plains due to the limited depth of
the Canadian airmass.

.LONG TERM...(Monday night through Sunday)
Issued at 326 PM MST Sun Feb 18 2018

The broad upper level trough will push east across the Great Basin
Monday night, while a 120+ kt jet max ahead of this feature races
north across the forecast area. There is weak to moderate Q-G
ascent ahead of the trough, and we`ll be getting into the right
rear entrance region of the upper level jet. Cross sections show
Conditional Symmetric Instability (CSI) so there is a strong
potential for heavy banded precipitation. At this time, it appears
this heavier band will most likely shift northeast across the
mountains and nearby adjacent plains through the course of Monday
evening. We see potential snowfall rates of an inch per hour or
more in this band. At this time, the band may just clip the Denver
area, but would favor locations in Larimer/NW Weld counties as
southeasterly 800-650 mb flow may also develop in that area for
added upslope component. For now, the Winter Weather Advisory will
cover the Fort Collins/Loveland area, and will watch for
progression of heavier band to see if any eastward expansion would
be warranted.

The snow is expected to gradually decrease overnight Monday night
into early Tuesday morning as Q-G ascent decreases and upper level
speed max exits the region. We could still see some light snow
linger, but mainly near the Front Range Mountains and Foothills
with weak upslope flow. Temperatures will be sharply colder Monday
night with lows dropping into the single digits on the plains, and
only recovering into the teens for Tuesday. Tuesday night
temperatures may plunge below zero if skies clear sufficiently
with fresh snow cover.

Weak troughiness will remain over the area Wednesday into
Thursday, and a weak wave may bring a few snow showers back into
the forecast area. Temperatures will gradually moderate but stay
below normal.

There is potential for another disturbance or two Friday into
Sunday, keeping some snow showers in the forecast for the
mountains. Temperatures should average below normal for this
period as well.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 326 PM MST Sun Feb 18 2018

Westerly and northwesterly winds will continue through the early
evening across the Denver area. During the evening, surface winds
will de-couple from the mid-level flow and return to drainage
winds for several hours. A Canadian cold front will move through
the area around 2 AM with a wind shift to the northeast. Low
clouds and fog will develop as a shallow airmass moves in behind
the front. Some freezing drizzle may also develop for a few hours.
Additional moisture moving over the state through the afternoon
will deepen the moist airmass late in the day. This will allow
light snow to begin falling. IFR ceilings and visibilities will be
the main aviation impact, starting around 3 AM and continuing
through the day.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 5 PM MST this afternoon for COZ241-246-
247.

Winter Weather Advisory from 4 PM Monday to 5 AM MST Tuesday for
COZ038.

Winter Weather Advisory from noon Monday to 5 AM MST Tuesday for
COZ032-034-035.

Winter Weather Advisory from 5 AM Monday to 5 AM MST Tuesday for
COZ030-031-033.

&&

$$

SHORT TERM...Dankers
LONG TERM...Barjenbruch
AVIATION...Dankers



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