Area forecast discussion 
National Weather Service Denver/Boulder Colorado 
252 am MST Sat Nov 22 2014 


Short term...(today through tonight ) 
issued at 252 am MST Sat Nov 22 2014 


Active weather pattern setting up for the short term period and 
continuing into early next week. Current observations show flow 
aloft increasing in the early morning hours in advance of powerful 
150-160 knot upper level jet coming ashore the California/Oregon 
coast. This speed maximum will then drive across the Great Basin 
during the afternoon and evening. Strong upper level divergence 
combined with at least weak but sustained q-g lift and Pacific 
moisture plume is still on track to reach the forecast area late 
this afternoon. Snow will develop first over the mountains of 
western Jackson and grand counties around middle afternoon and then 
spread east across the Front Range mountains during the late 
afternoon/early evening hours. 


Initially...west/southwest flow aloft will keep heavy snow likely 
confined to the mountains of western Jackson/grand counties in 
vicinity of Rabbit Ears Pass and Mount Zirkel Wilderness...but as 
flow turns more west/northwest and stronger cold advection 
arrives late this evening into the overnight hours the heavier 
snow band will shift into the I-70 corridor of the mountains 
including Summit County. This first shot of heavier snowfall is 
expected to produce between 4 and 8 inches over most of the 
mountains by late tonight...with up to a foot from Rabbit Ears 
Pass area northward where the early portions of this storm could 
really pound that area with strong westerly flow. Given the strong 
flow...we do expect some spillover snow to affect the Front Range 
foothills mainly along the peak to peak Highway where a couple 
inches of snow should accumulate. This too already handled well in 
going forecast. Strong winds will produce considerable blowing and 
drifting snow and poor visibilities so earlier issued winter storm 
warnings for elevations above 9000 feet are on track. High 
Mountain valleys including Walden and Kremmling will see lighter 
snow but gusty winds for some blowing snow. At this time...the 
period of more significant snowfall in valley locations is seen to 
be too short and amounts shy of advisory criteria...but will be 
monitored. 


On the plains...there are more indications for a potential weak 
anticyclone to develop tonight just behind frontal passage. That 
would bring a better chance of snow to the plains so have 
increased probability of precipitation just a bit from the Denver metropolitan area 
east/southeast toward Akron and Limon. Warm enough initially in 
the lower elevations for a mix of light rain/snow if we see precipitation 
develop. 


With regard to wind...the Cross Mountain flow increases to around 
35 kts and a rather Strong Mountain top stable layer this morning 
should result in favorable mountain wave profile. Chinook pattern 
in place so stronger and occasional gusts mainly in the 45 to 55 
miles per hour range should stay confined to locations in/right next to the 
foothills. Winds increase further later this afternoon/evening but 
mountain wave structure is expected to break down as mountain top 
stability decreases. 


Temperatures will be quite mild from the foothills down onto the 
plains with warm advection and increasing downslope component. 
Denver metropolitan should see 60f as long as mountain wave clouds dont 
thicken too quickly. Most guidance shows generally thin band of 
mountain wave clouds until afternoon when more widespread cloudiness 
will develop. 


Long term...(sunday through friday) 
issued at 252 am MST Sat Nov 22 2014 


Northwesterly flow aloft will continue on sun as an upper level trough 
deepens over the central and northern US. Cross-sections show moisture 
depth will decrease some in the mountains however lapse rates will be in 
the 7-8 c/km range so orographic snow will continue through the day 
with areas of blowing snow over the higher passes. At lower 
elevations will see a bora type fnt move across the plains early 
with gusty northwesterly winds through the afternoon. Highs will drop back into the 
lower to middle 40s over northestern Colorado. 


For Sun night into Monday northwesterly flow aloft will continue as a few 
disturbances embedded in the flow move across. Cross-sections show 
moisture depth increasing in the mountains by 12z Monday which will continue 
through the afternoon. Lapse rates will remain in the 7-8 c/km range with 
favorable orographic component so will see periods of MDT to heavy 
snow. Winds will remain gusty as well with blowing snow especially 
above 10000 feet. At lower elevations a weak mountain wave may set up late Sun 
night into early Monday morning as component along winds increase to 
around 50 kts. Thus there may be some potential for a marginal high 
wind event in the foothills between 06z and 15z. Otherwise it will 
remain windy over the plains through the afternoon hours with gusty north-northwest 
winds. As far as precipitation there is some potential for a chance of -shsn 
Monday afternoon over northestern Colorado as a disturbance tracks across. Lapse rates 
over northestern Colorado are forecast to be in the 8-9 c/km range. Best chance will 
probably be east of I-25 and over the Palmer Divide as areas near the 
foothills will be fighting strong downslope component. As for highs 
850-700 mb cool a few more degrees so will keep readings in the 
upper 30s to lower 40s. 


By Monday night moisture will begin to decrease in the mountains with 
stability increasing so snow should decrease in both coverage and 
intensity. Meanwhile with mountain top stability increasing into Tuesday 
morning may see another round of stronger winds in the mountains and 
foothills. On Tuesday the flow aloft will remain northwesterly with moisture 
increasing in the mountains lapse rates are only forecast to be in the 4-5 
c/km range so additional snow amounts should be on the light side. 
Over northestern Colorado gusty northwesterly winds will continue over the plains. Highs 
will be in the middle to upper 40s across northestern Colorado. 


For Tuesday night axis of stronger upper level winds in northwesterly flow aloft 
will be over northestern Colorado with some middle level moisture embedded in the 
flow. Thus could see a slight chance of -shsn mainly near the Wyoming-NE 
border. In the mountains expect some lingering light snow Tuesday night due 
to favorable orographics. Once again there will be some potential 
for high winds in the mountains and foothills Tuesday night into Wednesday morning 
as mountain wave intensifies and component along winds increase to 50-55 
kts. On Wednesday will keep in a chance of -shsn in the mountains while over 
northestern Colorado will have a dry forecast with highs in the in the upper 40s 
to lower 50s. Winds will remain gusty at times especially near the 
Wyoming-NE border area. 


For Wednesday night into Thanksgiving the divergence between the European model (ecmwf) and 
GFS continues. The European model (ecmwf) has an upper level ridge building into the 
area with much warmer temperatures in the 60s over northestern Colorado and dry 
conditions. Meanwhile the GFS has northern Colorado in northwesterly flow aloft as a 
cold fnt moves into northestern Colorado by Thursday morning with highs only in the 
30s. There is some moisture behind the fnt which could lead to a 
slight chance of snow if it does move into northestern Colorado as the GFS shows. 
At this point not sure what to believe so will keep readings in the 
upper 40s to lower 50s for now and keep a dry forecast to remain 
consistent with surrounding offices. On Friday the GFS keeps a shallow 
layer of cold air over northestern Colorado which would keep highs mainly in the 
30s over the plains while the European model (ecmwf) has readings in the 60s. As for 
precipitation neither model has much moisture so will keep dry forecast in 
place. 


&& 


Aviation...(for the tafs through 12z Sunday morning) 
issued at 252 am MST Sat Nov 22 2014 


Southwest winds around 10-15 knots at kden and kapa are expected 
to turn more westerly by 20z-23z. However...mountain wave activity 
will keep a chance of light easterly flow at times through the 
day...and also potential for a few westerly gusts to around 25 
kts. Meanwhile...kbjc will likely stronger westerly winds prevail 
with gusts around 30 kts possible throughout the day due to 
mountain wave. For tonight...winds are expected to turn more 
northwesterly toward 06z-10z with frontal passage. Slight chance 
of a passing light rain/snow shower after front especially if 
winds turn more northerly. VFR conditions will prevail with 
gradual thickening of clouds with ceilings lowering from around 
20 thousand feet to briefly as low as 5000-8000 feet 06z-10z 
Sunday. 


&& 


Bou watches/warnings/advisories... 
Winter Storm Warning from 5 PM this afternoon to 5 PM MST Monday 
for coz031-033-034. 


&& 


$$ 


Short term...barjenbruch 
long term...rpk 
aviation...barjenbruch 






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