Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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286
FXUS65 KBOU 120353
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
853 PM MST Wed Jan 11 2017

.UPDATE...
Issued at 853 PM MST Wed Jan 11 2017

The latest round of heavy snow in the mountains is starting to
wind down, but web cams show snow is still coming down along the
I-70 corridor and at several ski area snow stakes. An additional 3
to 6 inches of snow has fallen so far this evening. Satellite
imagery shows there is still a slightly unstable area of moisture
moving into the northwest quarter of the state, which will be
moving over the north-central mountains for the next several
hours. The KGJT raob at 00z showed the moisture extending up to
400 mb and nearly moist adiabatic. The precipitable water value
was still 0.38 inches. With snow still occurring over the
mountains and a few more hours still to come, will let the
current warnings continue through midnight. Will be able to bring
the warnings down when we see a decrease in snow coverage.

Looks like the break for the mountains will be short lived, as
another weather disturbance will be moving into the state by
tomorrow afternoon.

No other changes to the forecast are necessary as the shower
activity over the mountains has been dissipating after moving away
from the foothill ridges. Temperatures will be cold overnight in
the cool post-frontal airmass that moved into the region this
afternoon.



&&

.SHORT TERM...(This evening through Thursday)
Issued at 244 PM MST Wed Jan 11 2017

Main concerns center around heavy snowfall across the northern
mountains this afternoon and tonight and gusty winds over the
mountain passes. Observations and radar imagery showing heavier
banded precip developing over Western Colorado and more convective
showers across central and western Utah early this afternoon. All
this will spell for increase snowfall over Northern mountains
through the rest of the afternoon and evening. Even some lightning
has been reported across the Great Basin with this trof. Could
see heavier snowfall rates up to 2 inches/hour with the banded
and convective snowfall as the strong jet core over central
Colorado moves across along with steep lapse rates and strong
orographic flow. Have already extended the winter storm warnings
in the mountains through midnight to account for the heavier snow.
In addition, mountain top winds may gust in the 40-60 mph range
with blowing and drifting snow. Snow expected to decrease later
tonight as the trow moves East of the area.

Across lower elevations...surface cold front has advected further
West and South than expected resulting in colder temperatures this
afternoon and readings only in the 20s/30s on the northeast
plains. Secondary cold front will push into all of Northeast
Colorado on Thursday morning with more colder air and increase in
low level moisture during the afternoon hours. The flow aloft will
shift more Southwest on Thursday while an additional jet streak
pushes into far Northern Colorado during the afternoon. This will
increase snowfall in the mountains again and even a chance of snow
over the urban corridor, given the shallow upslope flow present.
Not expecting the heavy snowfall in the mountains with this next
system as the southwest flow will be not be as conducive for the
strong orographic snowfall. Temperatures will be colder over the
urban corridor on Thursday with readings only in the 30s.

.LONG TERM...(Thursday night through Wednesday)
Issued at 244 PM MST Wed Jan 11 2017

Light to moderate snow will continue over the mountains Thursday
night. Over the plains, a few areas of snow near the urban
corridor may still be occurring with little to no accumulation.
NAM Forecast soundings show drier air moving in before midnight,
but then low level moisture increasing, leading to possible areas
of fog or low stratus. With the GFS not showing the influx of
moisture and cloud cover expected around, did not add this into
the forecast but bears watching.

Southwest flow aloft will continue over the state Friday with
decreasing speeds and decreasing moisture. Expect lighter snow
over the mountains and cloudy and cool conditions over the plains.

An upper low over the Baja on Saturday morning will transition
east into the western panhandle of Texas by Sunday morning,
weakening the southwest flow aloft and concentrating the moisture
to the south of the area. Expecting only a chance of snow for the
mountains along and south of I70 in this pattern. Southerly flow
as the system digs to the south will bring a chance of showers to
the southeastern plains during the day. As the upper low pushes
into the Texas panhandle, southerly flow ahead of it will likely
spread showers further north into the state while colder air will
push south. There may be a brief period of mixed precipitation
over the plains overnight and into the early morning, but being
this far out with some model inconsistencies - do not want to add
that much detail. Snow will likely impact the forecast area Sunday
into Monday morning with accumulations likely.

Model trends have pushed the system out of the area by Monday
night with drier northwesterly flow aloft for Tuesday. Another
system is progged to push down over the state for Wednesday for
another round of snow for the mountains.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 853 PM MST Wed Jan 11 2017

Minimal aviation impacts are expected through tonight and tomorrow
as low clouds have cleared out and the cool, stable airmass has
settled across the Denver area. Winds will be southwesterly for
a couple more hours and then become southerly overnight. East to
northeast winds are expected tomorrow, ahead of a weather
disturbance that will be moving out of the mountains tomorrow
evening. No precipitation is expected before 4 PM.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until midnight MST tonight for COZ031-033-
034.

&&

$$

UPDATE...Dankers
SHORT TERM...Entrekin
LONG TERM...Kriederman
AVIATION...Dankers



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