Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 111633
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
933 AM MST Wed Jan 11 2017

.UPDATE...
Issued at 908 AM MST Wed Jan 11 2017

Latest radar imagery showing snowfall increasing again across
Western Colorado and this trend will continue this afternoon over
northern mountains. Even some lightning strikes over Nevada this
morning so airmass will become unstable this afternoon. This could
result in some heavier bursts of snow in the mountains with
snowfall rates of 1-2 inches per hour in the heavier snow. Cross
sections still show this moisture into this evening with strong
orographic flow so may need to extend the winter storm warnings in
the mountains through this evening. Hi resolution models however
start to decrease qpf amounts this evening. Will watch trends this
afternoon for a final decision on this.

Surface cold front pushing through the plains now as front through
Fort Morgan and even some stratus/light fog over the far ne
plains. Given temperatures only in the teens/20s will need to
lower temperatures even more for this afternoon. Front stalls late
this morning before getting into the Denver area as it meets the
stronger SW flow coming off the Palmer Divide and foothills. Best
pressure falls are now moving into Southern Nebraska so don`t
think there will be much further westward push. However, latest
model runs due bring the front a bit further west than previous
model solutions.

&&

.SHORT TERM...(Today and tonight)
Issued at 408 AM MST Wed Jan 11 2017

Moisture in wly flow aloft will continue in the mtns today with
favorable orographics.  Position of upper level jet and improving
lapse rates would suggest heavier bands of snow will be possible
thru the aftn hours.  In addition QG fields show some minor mid lvl
ascent as well.  Thus warnings will stay in place thru the aftn.

At lower levels have seen wind gusts overnight in the 50s and 60s
with a few 70s in a few spots in and nr the foothills.  Overall set
up has been rather marginal so should see most areas remain blo high
wind threshold the rest of the morning.  For later this morning and
aftn sfc low pres will intensify along the front range as an
arctic cold fnt moves across the far nern plains by aftn. There
is some potential for high winds across the palmer divide late
this morning thru the mid aftn as could see a few wind gusts fm 50
to 60 mph across srn areas of Douglas...across Elbert into
Lincoln counties. In addition will see gusty winds dvlp along the
front range as well with gusts in the 30s and 40s fm the wsw.

As far as highs there will be quite a range across nern CO as
readings will rise well into the 50s around Denver while over the
far nern plains readings stay in the 30s. Western extent of fnt
will likely stall nr a New Raymer to Fort Morgan to Last Chance
line by late aftn.

Meanwhile a few showers could move off the higher terrain and
across portions of the front range so will keep in low pops fm
previous fcst.

For tonight snowfall rates should decrease in the mtns as a
disturbance moves east of the area however cross-sections still
show lingering moisture and decent lapse rates. Thus there will be
periods of orographic snow however additional amounts should stay
mainly on the light side.

.LONG TERM...(Thursday through Tuesday)
Issued at 408 AM MST Wed Jan 11 2017

On Thursday...an Upper level trough of low pressure stretches from
central California into the northern Great Basin....with a 100 KT+
jet oriented from southwest to northeast across Colorado. This
pattern combined with plenty of mid and upper level moisture will
result in light snow across the high country. However...a few
locations especially along zone 31 could see periods of moderate snow
due to lift from the upper jet. On the plains...models show a weak
front moving into northeastern Colorado by afternoon. Some weak
upslope combined with plenty of moisture flowing over the mountains
and some lift from the upper level jet could produce scattered
snow showers across the foothills and plains by afternoon. Models
do not show much Equivalent Potential Vorticity to support CSI
banding. However...due to the location of the upper jet...some
CSI banding is not out of the question. Looks like snow showers
should be light...with the possibility of localized heavier snow
showers if banding does occur.

On Friday...the upper low deepens as it moves into southern
California and the northern Baja. Light snow should continue in the
mountains as the moist orographic southwest flow continues. The
plains should be dry and colder with some morning fog possible.

On Saturday...snow decreases across the high country as moisture and
orographic flow diminish. The models show the upper low tracking
across the Desert Southwest over the weekend...but diverge somewhat
in how the system ejects into the Central Plains States. The
Canadian Model is the furthest north and has the upper low over
southeastern Colorado by 00z Monday...over east central Colorado by
06z Monday and over eastern Nebraska by 18z Monday. The GFS is
slower with the system and has the upper low drifting from
southeastern Colorado at 06z Monday into north central Kansas by
12z Tuesday. The ECMWF is the furthest south solution and tracks
the upper low from the Texas/Oklahoma Panhandle 12z Monday into
southwestern Iowa by 12 Tuesday. Models also show a cold front
moving into northeastern Colorado around noon sunday. The
combination of increased moisture and upslope flow behind the
front and QG lift from the upper low could produce accumulating
snow across northeastern Colorado from Sunday into Monday.
However...at this time...there is some uncertainty with the track
of the storm. The ECMWF and over half of the GFS ensembles keep
the upper low too far south to have much of an impact across
northeastern Colorado. Will need to keep an eye on the track of
this storm to see how it will affect northeastern Colorado.

Drier weather is expected by Tuesday as the upper level storm system
exits the region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 908 AM MST Wed Jan 11 2017

Southwest winds increasing at APA and will also become gusty at
BJC/DEN between 17-18z. Surface cold front to the east of the
terminals but at this time not expected to make it this far West,
however models are showing it getting it closer to KDEN than
previous runs so there is low confidence in overall wind
forecasts.

 &&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 5 PM MST this afternoon for COZ031-
033-034.

&&

$$

UPDATE...Entrekin
SHORT TERM...RPK
LONG TERM...Kalina
AVIATION...Entrekin



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