Area forecast discussion 
National Weather Service Denver/Boulder Colorado 
940 PM MST Thu Dec 8 2016 

issued at 935 PM MST Thu Dec 8 2016 

Snowfall now underway in the high Country. West-northwest winds 
of 30-40 mph also producing some blowing snow. Weather spotter 
reported momentary white out conditions while driving over 
Berthoud Pass in the past hour. Regional radars indicate light to 
moderate snowfall up along the Continental Divide with passage of 
a weak upper air disturbance in moderate northwest flow aloft. 
However...water vapor satellite imagery shows a break in the 
moisture immediately upstream from Colorado. Consequently could 
see a modest drop off in snow intensity next couple of hours but 
not necessarily a drop off in wind speeds. Actually models 
indicate an increase in the cross mtn flow with an increase in mtn 
top stability. It's after midnight when the high country should 
see a notable increase in snowfall rates with the arrival of the 
next wave of moisture and qg forcing marked by the wide area of 
precipitation indicated on radar over sern Idaho...swrn Wyoming 
and northern Utah at this time. Higher west-northwest facing mtn 
slopes and passes could see 1-2 inch per hour snowfall rates 
during the pre-dawn hours with the passage of this disturbance. 
Blowing snow also a good bet esply on the passes. A Winter Weather 
Advisory is in effect for mtn zones 33..34 and 31 now until 5 PM 
MST tomorrow. Orographically favored northwest slopes could end up 
with close to a foot of powder by afternoon. As for the 
plains...dry conditions will prevail next 24 hours but wouldn't 
rule out occasional bursts of very light snow or flurries blowing 
down off the higher foothills. Still no accumulation for lower 

Update issued at 518 PM MST Thu Dec 8 2016 

Zone and point forecasts were updated and sent out a short time 
ago. Adjusted a handful of the weather and sky cover grids starting 
Saturday out through Wednesday night. Removed any mention of rain 
in the high mtn valleys and went with a rain/snow mix during the 
day light hours Saturday and Sunday in the Front Range foothills 
to coincide better with the wetbulb freeze level. Also added a bit 
more sky cover in areas with pops 20 percent and greater. 


Short term...(this afternoon through friday) 
issued at 330 PM MST Thu Dec 8 2016 

Moderately strong northwesterly flow aloft will continue over the 
forecast area tonight and Friday. The synoptic scale energy is 
benign tonight and Friday. Normal diurnal wind patterns are 
progged for the plains and drainage winds are progged overnight. 
Foothills tonight and Friday. The higher mountains can expected 
west and northwesterlies strong enough for some blowing snow. 
Models have moisture increasing and getting pretty deep for the 
mountains and current satellite pictures concur with this. The quantitative precipitation forecast 
fields show fairly decent precipitation/snowfall amounts in the 
mountains tonight and Friday. Snow Advisory criteria looks fine in 
the mountains with the moisture and orographic enhancement. Will 
leave highlights as is. For temperatures, friday's highs will be 8 
to 13 c warmer than today's highs. 

Long term...(friday night through wednesday) 
issued at 255 PM MST Thu Dec 8 2016 

Moist flow from the northwest will continue into the extended generating 
more orographic snow in the mountains. Snow fall will wind down a 
bit Friday night into Saturday with some light snow still expected 
with continued orographic influence. The plains will remain dry on 
Saturday with a Lee side low near the base of the foothills keeping 
winds downsloping onto the plains warming temperatures into the 50s 
for Saturday. The strong west-northwest flow will bring increased wind gusts to 
the mountains but with little shear near mountain top and 
subsequent stable layer do not expect the winds to make it down 
the foothills. Winds of 35 to 40 in the mountain valleys to speeds 
up to 60 near mountain top will be possible through the day 
Saturday creating blowing and drifting snow and potential 
hazardous driving conditions for weekend travelers. 

Saturday night into Sunday models have the upper jet dropping south 
into the northern mountains combining with a conveyer belt of 
Pacific moisture to increase snowfall over the mountains Saturday 
night through Sunday. Looking at 700 mb...temperature values are 
higher then with the previous storm with the influence of warm air advection from 
westerly flow aloft. Therefore expect a lower snow to liquid ratio 
with this storm and heavier more wet snow. Current quantitative precipitation forecast models 12 
hour accumulations from 0.30 to 0.60 with the higher amounts over 
west facing slopes. This could equate to snowfall amounts of 4.5 to 
9 inches and combined with continued wind gusts up to 50 mph an 
advisory may be needed. A cold front will move into the northern 
plains from Wyoming bringing slightly cooler air. The increased NE 
flow on the plains behind the front will have to compete with the 
strengthening surface low close to the foothills in achieving 
desired upslope. Will keep a slight chance on the plains Sunday 
morning but confidence is low for much precipitation on the plains. 
Temperatures will only be slightly cooler then Saturday with highs 
in the 40s. 

For next week the upper level pattern will continue to be strong 
from the west-northwest. Models are coming into better consensus with an 
Arctic push of cold air from the north bringing temperatures on 
the plains back to the teens and 20s and possibly below zero 
overnight by mid week. The only model that keeps it further east 
is the ec so will do an average of temps for that period with more 
emphasis to the cooler side. Snow will continue in the mountains 
with the only difference through the week being intensity. This 
will change as the days go on seeing where models put jet 
placement and the best lift. Temperatures for next week will hover 
around normal with the drop by mid week then back above freezing 
by Thursday. 


Aviation...(for the 06z tafs through 06z Friday night) 
issued at 935 PM MST Thu Dec 8 2016 

Light and variable winds in the Denver Metro area at present time 
still expected to become predominantly a drainage flow in the 
next hour or two. Speeds will generally be light...under 10 kts. 
Otherwise it will stay dry with cigs at or above 12k feet for the 
next 24 hours. 


Bou watches/warnings/advisories... 
Winter Weather Advisory until 5 PM MST Friday for coz031-033-034. 



short term...rjk 
long term...Bowen 

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