Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 071714

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1014 AM MST Thu Dec 7 2017

Issued at 1013 AM MST Thu Dec 7 2017

Forecast is on track as upper level speed max is generating light
snow already in the northern mountains and southern Wyoming. High
mountain valleys are also getting some light snow given this
upper level support. Most mountain areas are still on track to
get 1-4 inches, with up to 6 inches in favored north/northwest
facing aspects. On the plains, winds are increasing but low level
north/northwest flow means mostly downslope in place along the
Front Range. As a result, should see lots of virga but only a
chance light snow across the plains. Palmer divide should fare
better since that flow is upslope there, so expect some impact for
the evening commute on the I-25 Corridor roughly south of Castle
Rock. Increased PoPs a bit more there with an inch or so possible.


.SHORT TERM...(Today and tonight)
Issued at 333 AM MST Thu Dec 7 2017

Northerly flow aloft will prevail behind a short wave trough over
the Southern Rockies early this morning. The jet turns
northeasterly around the upper level ridge centered over the
Pacific Northwest later today. Colorado will be under the left
exit region of the jet this afternoon and evening, which will
provide lift that is expected to produce light snow across parts
of the area. Moisture is limited with this system so expect
snowfall amounts to be light. North facing mountain slopes should
see the highest totals, up to 6 inches. Expect most mountain
locations to be in the 1 to 4 inch range. For the lower
elevations, downslope northerly flow off the Cheyenne ridge should
prevent snowfall north of the Denver area. From Denver south, the
northerly flow will become upslope and provide some weak
additional lift. If snowfall occurs, it is expected to be light
and less than an inch. Temperatures will remain cool today with
30s expected across northeast Colorado.

The subsident side of the jet shifts over the area late tonight.
Snow will decrease and come to an end overnight. Lows will be in
the 20s across northeast Colorado due to cloud cover and winds
helping to keep temperatures from plummeting.

.LONG TERM...(Friday through Wednesday)
Issued at 333 AM MST Thu Dec 7 2017

Very large blocking upper ridge stretching from off the srn
California coast to up along the Canadian Rockies will remain the
dominate weather maker through nearly the entire extended period.
Models show the ridge at full strength on Friday and Saturday,
deflecting the storm track well up into Canada. Around here,
moderate northwest flow aloft will mix downward from time-to-
time producing gusty nwly winds on the northeast plains. Near the
Front Range, a downslope pressure gradient will produce gusty
Chinook winds at times which will aid in the warm up during this
period. Over the weekend, should see daytime temps running 14-18
deg F above average on the plains. Mtn area temps won`t be too far

Models indicate some weakening in the upper ridge by late the
weekend with a jet max and associated upper air disturbance
cresting the ridge and racing southward along the ern slope of the
Montana and Wyoming Rockies. This moisture starved feature appears
to reach nrn Colorado late Sunday night, cooling temps by several
degs and generating gusty n-nwly winds on the plains Monday, but
no precipitation as it appears now. After the brief cool down
Monday, temps rebound by 2-5 deg F in many areas on Tuesday as
the ridge gains some strength and moves closer to Colorado. Could
again see lower 60s along the Front Range along with gusty
downslope winds for much of the day.

For Tuesday and Wednesday,a gradual westward shift in the upper
ridge will cause day-to-day cooling aloft and at the sfc. The
period should remain dry, although the GFS shows a weak clipper
system brushing ern sections of the CWA late on Wednesday. A quick
increase in clouds and wind with its passage. Whereas the
European model indicates nothing of the sort.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1013 AM MST Thu Dec 7 2017

Moisture and cloud cover will increase with ceilings lowering from
around 7000 feet down to 3000-6000 feet 21Z-06Z. At this time,
expect mostly virga, with only a chance of light snow or flurries
reaching the ground. Cloud cover will decrease after 06Z with
improving ceilings. Winds are turning northerly and should see
gusts to 20-25 knots through the afternoon, before decreasing and
turning more westerly after 02Z.




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