Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 061037
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
337 AM MST Tue Dec 6 2016

.SHORT TERM...(Today and tonight)
Issued at 336 AM MST Tue Dec 6 2016

Mostly clear skies are found over the state this morning as the
next system approaches from the west. Some moisture in the
orographic flow is bringing a few isolated areas of light snow
over the mountains, but overall the overnight snow has ended.
Models have trended to slow the upcoming system down, and so far
observations of it coming onshore over the Pacific Northwest look
to verify this. Have backed off on PoPs due to this, as well as
delayed some of the highlights. Hires models do not show much
precipitation reaching into the mountains until noon or after.
With some accumulation still expected for the mountains, have
changed the Winter Storm Watch for the mountains to a Winter
Weather Advisory for amounts of 4 to 10 inches with a few
locations seeing up to a foot. The advisory will begin at 2pm,
with the heaviest snow expected between 6pm and 6am. Have delayed
the start time of the advisories for the foothills and urban
corridor until 6pm as well to account for the slower system. It
may be late enough to miss the bulk of the evening rush hour
travel time...though will still urge caution to adjust travel
times if possible. As for amounts, differences in the models are
mainly in the form of the heavier snowfall towards the northern
state border as the NAM shows, or the band of heavier snowfall
further south stretching from the Denver area east to the Kansas
border. Believe the NAM jet is progged to far north and the
amount of cold air that will push in from a strong high pressure
out of Canada should override the drying southerly winds progged
at the surface and 700mb. Have trended the forecast to favor the
GFS solution with slightly more accumulation over the Denver area
and east, and slightly less over the northern areas. Temperatures
today will likely only warm into the mid to upper 20s over the
plains and in the teens for the mountains.

Snowfall rates may increase after midnight, especially over the
plains and foothills, as another surge of cold air pushes in to
enforce upslope flow and upward QG motion increases overhead. Lows
overnight will dip into the single digits over the plains while
the mountains will see readings below zero. The northeasterly
winds from the cold surge will likely be blowing between 10-20 mph
over the plains, which will create windchill temperatures below
zero.

.LONG TERM...(Wednesday through Monday)
Issued at 336 AM MST Tue Dec 6 2016

Light snow will continue into Wednesday morning with weak upslope
flow in place, departing Q-G lift, and another expected surge of
arctic air. Have raised PoPs for this period with another inch or
so of snow expected on the plains and another couple inches
possible in the Front Range foothills/mountains. Temperatures may
briefly warm depending on arrival time of next arctic surge but
overall expect readings to be steady or slowly falling through
most of the day as arctic high pressure builds southward across
the High Plains. So, expect teens for early day highs but if
surge is earlier then some spots may not get out of the single
digits all day. Northerly winds will drop wind chill readings
below zero nearly the entire day. The light snow will decrease to
a few showers by afternoon as Q-G lift pushes off to the southeast
and drier northwest flow develops just above the arctic airmass.

By Wednesday night, clearing skies, lighter winds, and fresh snow
cover all points to low temperatures below zero over the entire
forecast area. A few colder spots on the plains should reach
teens below zero while 20 below zero or colder temps are possible
in the high mountain valleys if there`s sufficient clearing.

For Thursday, a stronger but dry northwest flow aloft will be
over the forecast area. Temperatures should begin to moderate but
think models are overdoing it a bit as cold arctic high still
resides to our east/northeast. There may be some high clouds as
well which in combination with fresh snow cover it would be hard
to erode the arctic air. Have dropped highs a couple more degrees
based on these factors.

By late Thursday night and Friday, another Pacific jet stream
should get the orographic snow machine cranking up across the
mountains again. Should see at least several inches additional
snowfall and blowing snow with the strong flow aloft.

A richer Pacific moisture plume is then advertised by the medium
range models to reach the Central Rockies Saturday into early
Sunday. This storm would have potential to bring heavy mountain
snowfall and strong winds. Enough moisture may spill over the
Front Range for a few showers in the lower elevations as well.
Otherwise windy conditions expected with the passage of these
disturbances.

The weather pattern may remain active in the mountains into next
week, while occasional bouts of wind would be the main weather
feature for the lower elevations with the strong westerly flow
aloft holding in place. Temperatures should average closer to
normal for the Friday to Monday period but a few shots of colder
air still possible in this weather pattern.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 336 AM MST Tue Dec 6 2016

VFR conditions are expected through 21z with generally
southeasterly winds at the local terminals. Low level moisture and
increasing lift after 21z then the cigs will drop as easterly flow
increases. Showers are not expected to develop until after 00Z
Tuesday aftn. Should see ILS and some MVFR cigs restrictions
developing at that time then IFR cig and vsby restrictions after
03z as moderate snow develops. Winds will continue
east/southeasterly through Tuesday evening with light to moderate
snow.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to noon MST
Wednesday for COZ035-036-038>041.

Winter Weather Advisory from 2 PM this afternoon to noon MST
Wednesday for COZ031-033-034.

&&

$$

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


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