Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 212103
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
303 PM MDT Sat Oct 21 2017

.SHORT TERM...(This evening through Sunday)
Issued at 302 PM MDT Sat Oct 21 2017

Moderate to strong west/northwest flow aloft will remain across
the area through Sunday. Surface gradients are relaxing, so gusty
winds across most of the forecast area will diminish quickly this
evening with the loss of daytime heating and mixing. The dry
airmass and mostly clear skies on the plains should allow for
strong radiational cooling, so lowered tonight`s low temperatures
a few degrees. Some clouds in the mountains should help keep
temperatures from plummeting in the normally cold spots, but still
cold nonetheless. Most of the light flurries in the mountains have
ended.

Cross sections show a mountain top stable layer developing
tonight and favorable setup for a mountain wave. Cross sections
show about 40 knot cross mountain flow which should result in peak
gusts near 60 mph over the higher mountains and exposed ridges.
The gusty winds will attempt to spread down the Front Range
Foothills through Sunday, but will encounter more stable air so
bulk of winds should stay confined to locations in/right next to
the foothills. Some mountain wave cloudiness expected Sunday,
which could hold temperatures back a few degrees north of Denver.
Otherwise forecast on track for warmer temperatures given warm
advection and downslope flow.

.LONG TERM...(Sunday night through Saturday)
Issued at 302 PM MDT Sat Oct 21 2017

A quick moving jet max moving down along the Northern Rockies
Sunday night may provide enough of a disturbance to bring very
light snow to the northern mountains late Sunday night into Monday
morning. Otherwise, a dry cold front will backdoor into the plains
Monday for cooler temperatures, about 5 to 10 degrees compared to
Sunday.

An upper ridge builds over the Great Basin Tuesday before a
weather system digs down out of western Canada Wednesday, turning
northwest winds aloft to westerly by Wednesday. This will result
in continued dry weather for both days and a warming trend, with
readings near 15 degrees above average for the date. Expect mid
70s over the plains and 40s to 60s over the high terrain.

The big weather change is slated for Thursday. The latest 12z EC
has now lost its Four Corner low solution and looks more similarly
to the open GFS and CMC solutions. A positively tilted upper
trough dropping out of Canada will likely push a cold front into
the state during the afternoon with a quick hit of moisture.
Modeled wet bulb zero heights have snowlevels dropping down to
the urban corridor in the afternoon, except the CMC which waits
until the evening - will side with the colder solution. Again,
moisture with this system looks really quick hitting, but will
likely focus over the Front Range mountains, foothills, urban
corridor and Palmer Divide with upslope flow. As the area of
moisture moves south overnight, the upper trough holds back,
keeping cold temperatures over the area for Friday before it moves
east. Warmer temperatures and dry weather should return for the
weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 302 PM MDT Sat Oct 21 2017

Gusty west/northwest winds will decrease quickly by 00-01Z as
airmass stabilizes. Then winds may become variable for a couple
hours 01Z-03Z before switching to normal south/southwest winds
6-12 knots 03Z-18Z. KBJC may be prone to mountain wave gusty west
winds to around 30 knots toward 12Z, with a better chance of those
gusty winds developing there through the day tomorrow. KDEN may
also switch to a westerly during peak heating/mixing after 18Z-20Z
Sunday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

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



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