Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 101807
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1107 AM MST Tue Jan 10 2017

.UPDATE...
Issued at 1100 AM MST Tue Jan 10 2017

Changes on the way to winter weather highlights for the next 24
hours. First...the high wind watch for the Front Range foothills
zones 35 and 36 has already been upgraded to a high wind warning.
Warning begins at 2 pm MST this afternoon and now runs to 6 AM
MST Wed. Model guidance shows gusty downslope/Chinook winds
developing in the foothills over the next few hours on the nose of
a strong jet diving down from Idaho. Next...the winter weather
advisory for the northern mtn zones 31 and 33 will be upgraded to
a winter storm warning as of 5 PM MST when this same jet is
expected to funnel in a deep ribbon of moisture on strong west-
northwesterly winds. The northern mtns...particularly the Park
Range north of Rabbit Ears Pass and the Rabbit Ears Range will be
most susceptible to this flow. The higher elevations of Summit
and eastern Grand counties will also be under major influence of
this moisture rich flow. Periods of heavy snow...strong winds
causing drifting snow and near white out conditions in blowing
snow at times reasons for the warning upgrade. Farther south in
mtn zone 34 the winter weather advisory will be extended to 5 PM
MST Wed. Northwest flow less conductive for heavy accumulations
in this area except perhaps up around Berthoud Pass and Winter
Park area where snow amounts could be similar to those in the
Park Range. East of the mtns dry and breezy conditions will
prevail through tonight. However by morning could see a few light
rain/snow showers drift east over the adjacent plains...and west
winds could become quite gusty near the base of th4e foothills.

&&

.SHORT TERM...(Today and tonight)
Issued at 356 AM MST Tue Jan 10 2017

Wly flow aloft will continue over the area today and tonight.  Cross-
sections still show decent moisture and favorable lapse rates thru
the aftn in the mtns so will continue to see periods of snow and
gusty winds over the higher passes.  There could be a brief lull
early this morning but it could increase again by late morning into
the aftn especially along along and north of I-70.  Tonight with
lapse rates becoming more stable snowfall may decrease this
evening although gusty winds will continue over the passes.

Over nern CO it will be dry thru the aftn with highs in the mainly
in the upper 40s to lower 50s across the plains.  As for high wind
potential not sure how tings are going to evolve later this aftn and
tonight.  Cross-sections do show lapse rates becoming more stable by
early this evening and continuing overnight with a mtn wave
developing. Component along winds are fcst in the 50-60 kt range
so there is some threat for high winds in the foothills so will
issue a watch. Below 6000 ft not sure if stronger winds will mix
down into zns 38 and 39 so will hold off on a watch at this time.

.LONG TERM...(Wednesday through Monday)
Issued at 356 AM MST Tue Jan 10 2017

A 110-140 knot west-southwesterly jet maximum is over the
forecast area continually Wednesday through Thursday. By Thursday
night, the flow aloft becomes southwesterly but still stays in the
100-120 knot range. For much of the time, the QG Omega fields
have weak upward synoptic scale energy over the forecast area all
four periods. On Wednesday morning, a cold front and some upslope
moves into the northeast corner but it never makes it all the
westward to the foothills. All the models show that. Usually these
airmasses make it across all the planes. Drainage and downsloping
predominated Wednesday night. On Thursday, another cold front
with easterly upslope makes through all the plains into the lower
foothills by midday. The upslope lasts into the evening, then
gives way to normal drainage patterns by midnight. There is a
mountain wave set-up on the cross section again, Thursday morning.
Winds will blow in favored areas but they should not get fierce
in speed. There is decent moisture to continue over the mountains
on Wednesday and by later afternoon, there may be some low level
cloudiness getting into the plains with the upslope. The moisture
deepens in the mountains later Wednesday night and continues
Thursday and Thursday night. There is a bit of mid and upper level
moisture over the plains Wednesday night. There is pretty decent
moisture over the plains on the GFS Thursday and Thursday night,
less on the NAM but more in the lower levels those two periods.
The QPF fields have fairly decent snowfall amounts in the
mountains on Wednesday into the evening. Amounts decrease later
Wednesday night and continue with just a tad Thursday and Thursday
night. The orographic enhancement is poor from Thursday onward
with poor mountain top wind directions and speeds are down too.
There is a tiny bit of measurable precipitation out over some of
the plains Wednesday afternoon and again Thursday afternoon and
evening. For pops in the mountains will go with 60-100%s on
Wednesday, then 30-80%s Wednesday night through Thursday night.
The orographic snow models points to perhaps advisory amounts of
snowfall in the high mountains, at least Zone 31. This could be
addressed after this morning`s Winter Storm Warning expires at
18Z for the mountains. For pops on the plains will go with 0-
10%s Wednesday afternoon, then 0-25%s Thursday afternoon and
night. For temperatures on Wednesday, highs will be similar to
today`s but up to 10 C colder over the far northeast corner.
Thursday`s highs are 6-9 C colder then Wednesday`s. For the later
days, Friday through Monday, models keep the strong southwesterly
flow aloft on Friday and Friday night, then it decreases slowly
Saturday and Saturday night. A weak upper trough moves across
Colorado Sunday and Sunday night. The ECMWF has an upper closed
circulation with this going right across eastern Colorado Sunday
night. the GFS has this feature well south and southeast for the
state during that time. There is weak east and northeasterly winds
aloft on monday. If the ECMWF solution pans out there will be
more clouds and a shot at some scattered light snow for the CWA.
If the GFS is correct, it will be mostly clear.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1100 AM MST Tue Jan 10 2017

South-southwest winds will continue to strengthen through the early
afternoon hours with gusts in the 20-25kt range as a rule. However
near the foothills such as at KBJC...could see west winds gusting
30-45 kts at times by mid to late afternoon. Winds will subside
some at all airports this evening...only to ramp up again after
midnight with the formation of a strong high amplitude mtn wave.
Could see gusts approaching 50 kts near the fthls and 35 kts
farther out onto the plains late tonight. Otherwise continued dry.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 2 PM this afternoon to 6 AM MST Wednesday
for COZ035-036.

Winter Weather Advisory until 5 PM MST Wednesday for COZ034.

Winter Weather Advisory until 5 PM MST this afternoon for COZ031-
033.

Winter Storm Warning from 5 PM this afternoon to 5 PM MST
Wednesday for COZ031-033.

&&

$$

UPDATE...Baker
SHORT TERM...RPK
LONG TERM...RJK
AVIATION...Baker



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