Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 161044
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
344 AM MST Wed Jan 16 2019

.SHORT TERM...(Today and tonight)
Issued at 340 AM MST Wed Jan 16 2019

Shortwave trough is currently across Nevada and Utah putting
southwesterly flow across Colorado. Upward QG vertical velocity
is likely peaking across the area currently, and will decrease
then change to downward this afternoon as the trough axis crosses
the state. The extra lift right now is helping to increase cloud
cover across the plains and may be producing isolated areas of
flurries. Forecast soundings show a warm layer just above the
surface, and with some areas below freezing over the plains, could
see isolated areas of freezing rain/drizzle, but not enough to
create an impact. Snow over the mountains this morning will
continue to be limited in nature due to the unfavored
southwesterly flow except over the Park Range, where the Advisory
is in effect for.

Flow will veer to the west as the trough passes today to increase
snowfall over the rest of the mountains. Winds at mountaintop will
be increasing with cross sections showing 60 kts of cross mountain
flow. This will produce areas of blowing snow in the mountains. With
the subsident downward motion expected this afternoon, some of
these winds are expected to move down the foothills with gusts to
45 mph, yet the stability profile is not that great, so while the
western urban corridor may get gusty, speeds should stay below 35
mph. The downsloping and dissipation of some cloud cover just lee
of the mountains will keep temperatures up over the plains.

Tonight, as flow is west-northwest behind the trough, snow will
continue in the favored flow over the mountains with another 1 to
4 inches, with the higher amounts found over the Park Range.

.LONG TERM...(Thursday through Tuesday)
Issued at 340 AM MST Wed Jan 16 2019

By Thursday morning, expect only a few snow showers to be
lingering in the mountains. Those should then give way to partial
clearing over the high country through mid afternoon as a flat
upper level ridge builds over the state. However, clouds will be
on the increase again later in the day with snow spreading back
into the northern Colorado mountains Thursday evening as the next
and stronger Pacific storm system moves across the Great Basin.

A deep moisture plume arrives ahead of this system, with 700-500
mb specific humidity approaching 3 g/kg and integrated water vapor
transport (IVT) around 2 standardized anomalies. While the
moisture is there, the orographic support for more significant
snowfall in the northern mountains will be limited through much
of Thursday night, as southwest flow aloft will effectively block
the northern mountains (except the Park Range). That will be
changing Friday as the upper level trough passes across the state,
switching winds around to the northwest. As a result, we should
see an uptick in snowfall rates across the I-70 Corridor and
Summit County as the favored NW flow develops and cold advection
kicks in. Most of the models have trended a little drier for this
round of precipitation, but ensemble averages still show a good
shot of accumulating snowfall with several inches of snowfall
expected for the mountains through Friday. In addition, gusty
northwest winds are expected to create blowing and drifting snow
to the high mountain passes.

On the plains, we still have favorable factors in place for some
snow. While the latest models are digging the trough a bit more,
we do have a brief period of deep QG lift with the trough and
surface frontal passage Friday afternoon. Winds turn more
northerly behind the front, and a small change in wind direction
could support a period of light snow accumulations. While the
latest operational models generally trended toward a weak
downslope component and thus little if any snow, there are several
ensemble runs showing potential for a brief period of snow. As a
result, we`ll maintain a fairly consistent forecast across the
plains with a chance of snow developing late Friday morning into
the afternoon behind the frontal passage. That chance may linger
into Friday evening (especially on the Palmer Divide where
northerly flow is more favorable), before ending overnight.

Temperatures will turn colder across the plains through Friday
night with a glancing blow of arctic air. However, the latest
models are now suggesting a quicker warmup starting Saturday and
continuing through the weekend.

The next fast moving storm system arrives early next week, likely
bringing another round of mountain snowfall and a chance of snow
and colder temperatures to the plains. The GFS and some of its
ensembles have sped up the arrival of this system, and potential
it could reach our forecast area as early as Monday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 340 AM MST Wed Jan 16 2019

VFR conditions will continue through Thursday morning with
ceilings around 10kft for the next few hours before they raise and
scatter out throughout the day. Current winds are west to
northwesterly, but will soon turn back to southerly drainage. As
the upper trough passes this afternoon and strong winds in the
foothills push down, winds will turn west to northwesterly, with
gusts up to 25 kts near the foothills. Normal nighttime drainage
winds will return after 03z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MST Thursday for COZ031.

&&

$$

SHORT TERM...Kriederman
LONG TERM...Barjenbruch
AVIATION...Kriederman



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