Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 130242

Area Forecast Discussion
National Weather Service Denver/Boulder CO
742 PM MST Fri Jan 12 2018

Issued at 732 PM MST Fri Jan 12 2018

Main changes to evening forecast was to increase cloud cover over
portions of the northeast plains for this evening in wake of this
afternoons disturbance and cold front. Latest satellite imagery
and observations showing widespread stratus over the far northeast
plains while another swath of stratus has developed from Longmont
and stretch southeast through Centennial and down across the
Palmer Divide. This will likely erode away towards midnight with
strong downslope flow and increased drainage winds from the south
and southwest. Radar still also showing some isolated snow showers
over the plains with approach of upper level jet streak.

There is still some ongoing light snow over the higher mountains
but additional accumulations will be 1-2 inches mainly over higher
areas. Later tonight moisture depth will become more shallow with
only a few flurries by later tonight.

UPDATE Issued at 501 PM MST Fri Jan 12 2018

Quick update as showers continue over sections in and east of the
Denver area. There has been some mix of rain and snow but no
accumulation. showers should be ending by 7 pm.


.SHORT TERM...(This evening through Saturday)
Issued at 328 PM MST Fri Jan 12 2018

Upper level trough will move south of the area this afternoon.
Drying and subsidence behind it will bring showers to an end over
eastern Colorado. The showers over eastern Colorado were mainly
rain and light. Will have pops decreasing this afternoon over the
plains with the chance for showers ending by 00Z. Web cameras
indicating snow is decreasing and ending in the mountains in many
locations. Models want to keep light snow going over the favored
west facing slopes. Will have likely pops for the west facing
slopes tonight with additional accumulation up to 3 inches.
Elsewhere, if there is any additional snowfall, it will be light.
Plan on canceling the Winter Weather Advisory in the mountains
within the next hour since snow has decreased/ended and road
conditions are improving. However, wet roads may refreeze this
evening creating slick conditions.

For Saturday, appears there will be enough moisture in the
northwest flow aloft to keep areas west of the Continental Divide
cloudy. There may be a few areas of flurries or light snow with
this, but no accumulation is expected. For the Front Range and
eastern plains, partly cloudy skies and dry conditions are
expected. Temperatures will be near normal with highs in the 40s
to lower 50s.

.LONG TERM...(Saturday night through Thursday)
Issued at 328 PM MST Fri Jan 12 2018

Warmer and drier air will move across Colorado in northwest flow
aloft on Sunday. There will be a little shortwave that will likely
produce some clouds over northern and eastern sections. Then a
stronger wave will drop from central Canada into the central and
eastern U.S. on Monday. The models have been trending a bit more
vigorous with this wave which seems correct given the sharp
temperature gradient. This means the cold air should make it back
to Denver, and there`s a good chance of light snow as the
shortwave passes early Monday. Model variations are mainly minor
timing differences and maybe 100 miles in position which results
in a 10 degree temperature difference for Denver Monday/Tuesday depending
on how hard the cold air is forced westward. Temperatures will
likely be mainly in the 20s over the plains during the day Monday,
and could get near or below zero Monday night, though the low
level winds in Denver will likely be coming around to southerly
and keep us a bit warmer.

Still good agreement on the ridge rebuilding behind the shortwave
on Tuesday, with drying and recovering temperatures but how much
depends on how deep the cold air intrusion was.

The forecast quickly gets to be a mess from Wednesday on. There`s
a little better agreement on energy from the jet over the Pacific
plowing east into the ridge at our latitude. Middle of the road
forecast is still a weak to moderate strength open wave that could
bring light snow to the mountains. However, about half of the GFS
members and the last couple runs of the ECMWF model have a
stronger system that closes off as it drops either over Colorado
or near the four corners. Pretty good chance this will be a
transitory system, but that could provide a better chance of rain
or snow at lower elevations Wednesday or Wednesday night. Probably
working with dry low levels though, so those solutions may not be
as promising as they look at first.

Better agreement on ridging behind the Wednesday system, then the
next and probably stronger wave coming out of the jet for next
weekend. We could see stronger southwest flow aloft for a pretty
mild day or two Thursday/Friday, then the moisture arrives. Way to
early to tell if it will be something that closes off over or
south of us, or just a good stream of moisture for mountain snows beginning
Friday night or Saturday. It does seem to be heading toward mild
temperatures and a wetter (at least for the mountains) pattern.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 732 PM MST Fri Jan 12 2018

Tricky forecast with the low clouds this evening with a narrow
swath of stratus from Longmont and extending southeast through
BKF, while APA is on the edge with stratus. Denver is more
complicated with some thin stratus through the area but is
fighting the southerly downslope flow. Have added a tempo for
some stratus through midnight with low confidence.




LONG TERM...Gimmestad
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