Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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984
FXUS65 KBOU 150424
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
924 PM MST Sat Dec 14 2019

.UPDATE...
Issued at 921 PM MST Sat Dec 14 2019

With cloud cover disappearing over the urban corridor and parts
of the plains, areas of fog have developed. Some stratus over the
northeastern plains is slowly moving west, not expecting it to
make it all the way into the urban corridor, at least into the
Denver area as winds should return to drainage and then the
northern push expected later today should bring in drier air to
dissipate the stratus and fog.

UPDATE Issued at 620 PM MST Sat Dec 14 2019

Have decreased PoPs quicker this evening, especially over the
plains, and decreased the coverage after midnight. May need to
remove PoPs completely from the forecast area tomorrow morning as
the next system is still digging into California. Most models have
no precipitation in our forecast area until after noon - with
little if any reaching the metro area...except for perhaps the
southern sections but not until Sunday evening. Will wait for the
00z models to come in and see if the later trend continues.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 134 PM MST Sat Dec 14 2019

For this afternoon, moderate to heavy snow continues in the
mountains with enhanced bands of locally heavy snow spreading out
across the urban corridor and adjacent plains in the eastern
Larimer, Morgan and Weld counties. Issued a snow squall warning to
account for this with accumulating snowfall evident on highway
cams. Expect much of this to diminish by this evening. No changes
regarding the timing of the heavy snow through this evening. Most
of the models show the snow intensity decreasing significantly
after midnight. There should be another break in the weather late
tonight into early Sunday. Latest models runs continue to drag the
last part of this system further south during the day Sunday. The
upper level jet will shift to the east of the state with a weaker
zonal flow aloft. Another area of enhanced snowfall is progged to
lift south to north into the forecast area mid morning Sunday and
continue into afternoon. Snow for the Denver area continues to
trend towards decreasing forecast amounts. Several runs do not
even forecast snow in the Denver area. Best chance will be south
of Interstate 70. Some concern of moderate snowfall for Park
County however. Will issues a Winter Weather Advisory for South
Park Sunday through Sunday evening.

.LONG TERM...(Sunday night through Saturday)
Issued at 134 PM MST Sat Dec 14 2019

By Sunday evening the upper trough will be closing in on the four
corners region with flow turning more southwesterly over Colorado.
Drier air will be moving in decreasing snow chances from the North
to the South. Areas south of I-70 will continue to see light snow
into the early morning hours on Monday as the upper trough and
better jet dynamics push southeast. There is little respite as a
weak shortwave embedded in the upper level WNW flow will push in
during the day Monday bringing another round of light snow to the
northern and central mountains. This will be more orographic-based
as there is no jet support with it. Amounts will be on the lighter
side with just an additional 1-3 inches across the higher elevations
by Monday evening. The plains will remain dry with only a slight
chance of light snow for areas south of I-70 along the Palmer Divide
with weak upslope and minimal moisture. An additional trace to 1
inch is possible for those areas. Conditions will remain cool with
highs staying right around freezing on the plains and teens to
in the high country.

On Tuesday, upper level flow will turn more northerly and dry air
will push in bringing snow to an end across the region. With the
clearing Monday night into Tuesday lows will drop into the single
digits across the lower elevations with below zero for the higher
terrain and mountain valleys. Tuesday will be a slow warm up with
the cold air inversions in place, but highs are expected to climb
into the upper 30s to lower 40s under mostly sunny skies.

By mid-week an upper level ridge will build in bringing dry
conditions Wednesday with temperatures warming into the upper 40s
and possibly 50s. For Thursday, models start to diverge on the speed
of an upper level trough that is forecasted to move onshore into
California by Wednesday morning. The GFS has the system moving much
faster than the EC and the low center further north. Both models
show minimal moisture so will maintain a slight chance of snow for
the higher mountains Thursday. The plains should remain dry but with
some CAA temperatures will be a tad cooler than Wednesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 620 PM MST Sat Dec 14 2019

Most shower activity is expected to be done over the airports,
with some isolated showers further east and north along the state
border. At this time, expecting VFR conditions, however low
ceilings are expected to start moving in to the northeastern
plains. Most models have it staying out, but just northeast of the
TAF terminals, with some having it curl into BJC. So it could
require close monitoring overnight. If it does make it in,
ceilings of 200-400 feet will prevail with some patchy fog.
Drainage winds should keep it out of the terminals however. Otherwise,
a dry northerly surge will move down the plains after 10z to
clear out the fog and stratus. Winds will veer around to the
northeast through Sunday morning and afternoon, with another
chance of snow moving in from the south late afternoon to
evening, but expect accumulating snowfall to stay south of I-70.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 8 AM Sunday to midnight MST Sunday
night for COZ037.

Winter Storm Warning until 11 PM MST this evening for COZ031-033-
034.

&&

$$

UPDATE...Kriederman
SHORT TERM...Cooper
LONG TERM...Bowen
AVIATION...Kriederman



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