Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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498
FXUS65 KBOU 160445
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
945 PM MST Wed Nov 15 2017

.UPDATE...
Issued at 945 PM MST Wed Nov 15 2017

High clouds are diminishing under weak short wave ridging as
expected. Only minor changes, mainly slightly cooler lows in most
places.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 247 PM MST Wed Nov 15 2017

Satellite imagery shows a split jet with the polar to the north as
the subtropical jet aligns itself over the Great Basin. A trough
will move into the region by Friday but winds and upper clouds
will increase. For tonight...clouds will move in over the region
as moisture increases. Winds will pick up over the higher terrain
with the incoming upper jet gusting to 30 mph overnight above
timberline. On the plains overnight lows will be mild with lows in
the mid to upper 30s close to the foothills with downsloping from
the westerly jet. Further to the east lows will be cooler in the
20s and low 30s.

For Thursday the upper ridge will be in place ahead of the trough
with increasing upper level westerly flow aloft. Increased
downsloping from a deepening lee side low and warming SW winds
will allow for high temperatures to get 10 to 15 degrees above
normal. We will fall short of the record high of 80 degrees,
however, highs will be an unseasonable low 70 for the Metro area.
Winds will increase through the day as the gradient increases
ahead of the next system. Over the higher terrain wind gusts up
to 50 mph will be possible by max mixing with 30 mph on the
plains. Upper clouds will gradually increase through the day
before the lift and moisture enters Park county by late Thursday.

.LONG TERM...(Thursday night through Wednesday)
Issued at 127 PM MST Wed Nov 15 2017

...Pacific storm system will bring accumulating snowfall and
blowing snow to the mountains Thursday night through Friday night...

A strong pacific jet stream will be moving toward Colorado
Thursday evening. Model solutions show a healthy plume of Pacific
moisture underneath this jet stream, as seen in the Precipitable
Water (PW) and specific humidity fields.  For the mountains, snow
(with rain in valley locations) should begin to develop and
become more widespread overnight. However, the intensity during
this period is in question because of the west/southwest flow
and relatively poor orographic forcing for the north central
mountains and Summit County. Lapse rates are good with values near
6 C/km, and proximity of the upper level jet may lend itself
toward banded precipitation, favoring the northern border area
roughly from Rabbit Ears Pass and Rocky Mountain National Park
northward.

This pattern should remain in place through early Friday, before
significant changes occur during the day and evening. Strong cold
advection arrives in the north toward late morning, and then
toward the I-70 Corridor by evening. As the cold front arrives,
snow levels will rapidly drop to valley floors. The heaviest
precipitation will occur along/just behind the front in cold
advection, and given the rapid cooling we expect mountain road
conditions to deteriorate rapidly from north to south on Friday.
We will issue a Winter Storm Watch for the mountains above 9000
feet starting midnight Thursday night through Friday and Friday
night, and word the watch accordingly for the expected increase
in storm intensity Friday/Friday evening.

On the plains, downslope flow Thursday night will provide for mild
overnight low temperatures, followed by a quick warmup Friday with
highs a good 10-15 degrees above normal. Cold front should arrive
later in the day with falling temperatures late in the afternoon
through Friday evening. Models continue to support a band of
precipitation streaking off the foothills and despite downslope
component can`t argue with that considering the strong upper level
jet in place late Friday afternoon and Friday evening.
Temperatures will turn cold enough to allow for some snow down
onto the plains. However, any accumulation should be limited by
the relatively short duration of precipitation, and the downslope
component.

Things dry out quickly later Friday night into Saturday.
Temperatures will then average near to above normal for the
weekend into early next week in west/northwest flow aloft. Will
have to watch out for backdoor cold fronts during this period, but
those are always difficult to time in this pattern.

Finally, snow could make a return to the high country toward
Tuesday and Wednesday of next week when another batch of moisture
may arrive in the west/northwest flow aloft.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 945 PM MST Wed Nov 15 2017

VFR through Thursday.

&&

.FIRE WEATHER...
Issued at 127 PM MST Wed Nov 15 2017

Thursday will see elevated conditions over the plains and
especially the Palmer Divide and Lincoln county areas. Winds will
pick up with a strong push from the SW helping to bring
temperatures into the upper 60s and low 70s with decreasing RH
values. Speeds will pick up by max heating in the afternoon with
gusting up to 25 possible.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from late Thursday night through late Friday
night for COZ031-033-034.

&&

$$

UPDATE...Gimmestad
SHORT TERM...Bowen
LONG TERM...Barjenbruch
AVIATION...Gimmestad
FIRE WEATHER...Bowen



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