Area forecast discussion 
National Weather Service Denver/Boulder Colorado 
652 am MST Friday Dec 19 2014 

issued at 648 am MST Friday Dec 19 2014 

Web cams and a spotter report show that light snow is still 
falling in the Winter Park/Berthoud Pass area. Satellite shows 
that the low clouds over Grand County should persist for another 
couple hours. Updated the forecast to add a few more hours of 
light snow in the mountains as well as north and middle Parks. 


Short term...(today through tonight ) 
issued at 422 am MST Friday Dec 19 2014 

Very little in the way of sensible weather is expected today as 
the state will be under gradually rising heights from an 
approaching upper level ridge. Flow aloft will be light-moderate 
and out of the norhwest as the ridge approaches. Temperatures at 
low and middle levels will undergo some modest warming...but 
generally remain similar to yesterday. Temperatures should be 
around seasonal normals except for the northeast corner of the 
state where some lingering snow cover will hold temperatures back 
a few degrees. 

In the mountains...some low level moisture is trapped in the 
valleys which will be held in place by the weak westerly and 
northwesterly flow pattern. This could result in areas of fog this 
morning and cloudiness over windward slopes through the day. 
No precipitation is expected to develop though...since the 
orographic forcing will be so light and a mountain top stable 
layer will limit vertical motions. Thus...partly cloudy skies over 
the mountains and mostly sunny skies on the plains will be the 
main story today. Little additional change to the airmass is 
expected overnight as the ridge axis migrates across the state. 

Long term...(saturday through thursday) 
issued at 422 am MST Friday Dec 19 2014 

Models have fairly weak westerly flow aloft Saturday...with a 
weak upper trough to move across in the afternoon. Strong north- 
northwesterly flow aloft is over Colorado Saturday night well into 
the extended period. The synoptic scale energy for the County Warning Area is 
neutral to weak downward motion Saturday through Sunday night. The 
boundary layer flow looks to be dominated by downsloping... 
especially Saturday night and Sunday. Models have a cold front 
come in around 12z Monday morning. For moisture...there is a 
gradual increase Saturday in the mountains. Moisture continues to 
increase in the mountains Saturday night...getting pretty deep 
by 12z Sunday morning continuing into the extended period. The 
moisture over the plains increases especially in the middle and upper 
levels Sunday night. The Western Plains are drier with the 
downsloping. The quantitative precipitation forecast fields show a tad of measurable snow in the 
northwestern County Warning Area mountains Saturday afternoon. There is a bit over 
all the high country Saturday night...increasing somewhat Sunday 
and Sunday night. The models have a tad over the plains Sunday 
night. For mountain probability of precipitation...will go with "chances" after midnight 
Saturday night...then increase them to 60-80%s Sunday through 
Sunday night. The prognosticated wind speeds and directions will provide 
decent orographic enhancement. The moisture is pretty good too. 
Will up the going probability of precipitation and quantitative precipitation forecast/snowfall amounts in the mountains. 
Highlights may be needed in later shifts. For the plains...10-20%s 
look good Sunday night. Downsloping near the foothills will keep 
those areas drier for sure. For temperatures...saturday's highs 
are 0-2.5 c warmer than today's. Sunday's highs are 1-3 c warmer 
than saturday's. For the later days...Monday through Thursday... 
very strong north-northwesterly flow aloft continues over the County Warning Area 
Monday well into Tuesday night. There are a couple of jet 
maximums prognosticated through that time...with speeds up to 140 knots. 
By Wednesday into Wednesday evening a weakening/flattening upper 
ridge moves across with more gentle northwesterly...then westerly 
flow aloft. By Thursday...west-southwesterly flow aloft is on the 
increase as an upper trough/closed low moves our way. It over 
Utah by 00z Thursday afternoon late. Monday and Tuesday are fairly 
cold...Wednesday warms up...then a cold front with upslope behind 
it moves in Thursday afternoon. Alpine probability of precipitation will be pretty high 
Monday and Monday night with good orographics and moisture. It 
dries out considerably Tuesday through Wednesday night...then 
moisture increases again Thursday and Thursday night. 


Aviation...(for the tafs through 12z Saturday morning) 
issued at 422 am MST Friday Dec 19 2014 

Some haziness or patchy fog will persist around the Denver Airport 
through about middle morning. I do not expect to get any thicker than 
the present 4 mile visibility. Satellite imagery over the Denver 
area does not show any stratus cloud formation...although there is 
a patch of low clouds evident over eastern El Paso County. 

Skies will be mostly sunny through today with light south to 
southwest winds due to the weak pressure gradients across 
northeast Colorado. 


Bou watches/warnings/advisories... 


short term...dankers 
long term...rjk 

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