Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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434
FXUS65 KBOU 160434
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
934 PM MST Thu Feb 15 2018

.UPDATE...
Issued at 847 PM MST Thu Feb 15 2018

The snow bands keep developing this evening. At times there is
moderate snowfall under some of them. Cheyenne`s radar is showing
a back edge to it all pushing southeastward. Current GFE grids
are pretty accurate showing the best snow/pops. Will make a few
minor adjustments.

&&

.SHORT TERM...(This evening through Friday)
Issued at 306 PM MST Thu Feb 15 2018

Snow is occurring over most of the mountains this afternoon,
although the heaviest convective band appeared to break down as it
moved into the I-70 corridor this afternoon. At the same time,
showers were rapidly developing across the plains as the airmass
sufficiently destabilized.

The convection on the plains should become more widespread as a
cold front pushes southward with shallow upslope flow developing
behind it. This environment is favorable for locally heavy
showers, so the ongoing idea of up to 3" of snow on the plains
mainly along and south of a Denver to Akron line appears to be a
good start. Will have to watch this closely through the course of
the evening however, as these convective situations can produce
heavier snow amounts in a short period of time. Temperatures
should drop rather quickly into the 20s behind the front, so we
may see some impact on roads toward mid evening.

In the mountains, the Winter Storm Warning continues through 6
PM. Moisture depth and instability decrease rather quickly after
that time, but still some potential for a couple hour extension
before more significant drying and stabilization come in.

Precipitation will be diminishing in most areas toward midnight
as the stronger QG descent moves across the forecast area,
although a few light showers could still linger over the higher
mountains and Palmer Divide. Skies will clear later in the night
through early Friday morning. Temperatures should hit the teens
with even a few single digits for lows on the plains, while single
digits and even a couple below zero readings expected in the high
country.

Dry conditions will prevail Friday, and mostly sunny skies should
allow temps to warm back into the 40s on the plains, with 20s and
30s mountains. Winds increase across the high country late in the
day but strongest winds hold off til Friday night.

.LONG TERM...(Friday night through Thursday)
Issued at 306 PM MST Thu Feb 15 2018

An upper trough will push over the state Friday night bringing
snow to the high mountains. Expect 1 to 5 inches, with highest
amounts north of Rabbit Ears Pass. This system will also be
increasing winds, especially over the mountains and high
foothills. Model cross sections show 50-70 kt winds moving into
the mountains, with a decrease in speed near 300 mb. This combined
with downward QG motion on the backside of the trough will force
the strong winds down the east slopes of the Front Range mountains
and foothills. Gust speeds may get as high as 65 to 85 mph in the
wind prone areas. Have increased wind gust speeds in the forecast
grids to show a greater chance for the higher speeds. At this
point, local Sangster wind models do not have enough pressure
gradients to push much out into the adjacent western urban
corridor area, but could still see gusty winds reaching into the
30 to 40 mph. These strong winds will moderate minimum
temperatures along the foothills and urban corridor, increased
readings in these areas for this reason.

On Saturday, an upper ridge will push overhead with drier
conditions and warmer air pushing in aloft. This will create more
stability while another wind max pushes into the mountains. Winds
look slightly stronger, especially going into the nighttime. Once
again, will be expecting wind gusts of 65 to 85 mph possible
Saturday night. Due to the possibility of winds over 75 mph Friday
night and Saturday night, will issue a High Wind Watch stretching
across these times. Winds will subside during the morning and
early afternoon hours during Saturday, but and will mention this
in the highlight.

Sunday will be another warm day, with readings in the 60s over the
plains in the upper 30s to mid 40s in the mountains. Clouds will
be increasing through the day as the next system from the Pacific
pushes in to the Upper Great Basin. Should start to see snow
pushing into the northern mountains by Sunday night and become
widespread. A northeast push of winds will enter over the
northeastern plains due to a surface low deepening over southern
Colorado. However the actual cold front isn`t expected to push
into the plains until Monday morning to bring snow to the plains.

The upper trough will slowly transition over the state Monday with
drier air moving in for Tuesday, though temperatures will remain
cold due to a surface high pressure sliding down into the Great
Plains. Flow aloft will become southwesterly Wednesday and
Thursday to allow for drier and warmer conditions.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 847 PM MST Thu Feb 15 2018

Winds have been a bit pesky at DIA with the showers around but
the east-northeasterly component has been in place shortly after
00Z. Models bring the winds around to southeast then drainage by
12Z Friday morning. It seems reasonable. Will keep a TEMPO group
in for snow until 06Z. Ceilings issues should be done around 09Z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from late Friday night through Sunday morning
for COZ033>036.

&&

$$

UPDATE...RJK
SHORT TERM...Barjenbruch
LONG TERM...Kriederman
AVIATION...RJK



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