Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 170356
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
856 PM MST Wed Jan 16 2019

.UPDATE...
Issued at 849 PM MST Wed Jan 16 2019

Although light snow will linger in zone 31 this evening, it
does not appear to be heavy enough to continue with a Winter
Weather Advisory overnight. Therefore have opted to cancel it
this evening as the models all show improving conditions. Highway
cameras this evening show mainly light snow in that area. Light
to moderate snow indicated over Berthoud Pass AWOS but this should
slowly improve as well overnight. Next round of snow should start
to push into the our mountains Thursday afternoon.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 218 PM MST Wed Jan 16 2019

Water vapor imagery shows the shortwave responsible for producing
snow showers over the mountains today moving through far
northeastern Colorado. This feature will exit the state in a few
hours with mid to upper level ridging building in behind it.
Water vapor imagery also shows a stripe of dry air noticeable on
all three WV channels entering northwest Colorado and moving
toward our CWA. This feature will likely reduce snowfall rates in
the mountains to the point where there won`t be much accumulation
shortly after midnight tonight. This will likely allow the Winter
Weather Advisory to be cancelled before the 13Z expiration
tomorrow morning. QPFs were decreased in the mountains between
06-18Z Thursday to account for the dry air moving into the area.

Ridging aloft and weak lee cyclogenesis across the eastern plains
will allow for conditions to be dry and mild across the urban
corridor and eastern plains on Thursday. Western slopes in the
mountains will go through waves of light snow and flurries
tomorrow with minor accumulations during the day.

.LONG TERM...(Thursday night through Wednesday)
Issued at 218 PM MST Wed Jan 16 2019

Two troughs will move across Colorado during this period, Thursday
night and Friday, and again about Monday.

The first system will have a weaker lead trough Thursday night
that will bring increasing moisture to the mountains. There should
be a short period of moderate snowfall in areas favored by
westerly flow, mainly around Rabbit Ears Pass and to a lesser
extent Vail Pass, with lighter snow across the rest of the
mountains. There may also be a few light showers on the plains near
the northern border. The main piece of the trough will come about
Friday afternoon, with another period of moderate mountain snow,
along with a cold front and a chance of snow showers over the
eastern plains. The NAM continues to produce a few inches of snow
from about Denver southward, while every other model is further
south and takes the main area of precipitation across southeastern
Colorado with Denver on the edge of very light snowfall.

Adjustments made at this time were to raise PoPs for the
mountains through this period, and also a little for the plains
late Friday as there`s enough lift for a decent chance of at least
a little snow over the valleys and plains. We made only a small
upward adjustment in amounts to the favored mountain areas. At
this point it looks like two rounds of a few inches snow with a
break in between, so we may not need an advisory. We also
increased the winds on the plains as raw model data and
statistical guidance support higher speeds and the post-front
winds are usually a bit stronger for at least a few hours. We`ll
be showing gusts to around 40 mph, but brief 50 mph gusts would
not be surprising.

The weekend brings ridging and a recovery to mild temperatures,
though there will likely still be some clouds from the west to
southwest flow aloft. There`s reasonable agreement on the timing
of the next system on Monday or Monday night. There has been more
spread on the strength and latitude of the low coming over the
Rockies, but today`s models were converging a bit on the idea of
the low going over Colorado with eastern Colorado cyclogenesis on
Monday. The consensus track right now would be favorable for a
decent snow in northeastern Colorado, possibly mixed with rain at
the start if it`s during the day Monday. The models have between a
quarter and three-quarters of an inch of precipitation. There`s
still a lot of differences between the models and successive runs
though, so it`s nowhere close to a high confidence situation. Half
of the GFS ensembles are still north of us which would probably
keep the plains dry or nearly so. We did raise PoPs a bit over our
model blend. Cool or cold temperatures will then be in place for
the rest of the week, with moderate agreement on a reinforcing
shortwave in northerly flow in the Wednesday/Thursday time frame.
It could be colder than what we`re showing, though it does look
like the coldest air will be east of Colorado.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 849 PM MST Wed Jan 16 2019

VFR conditions expected through tomorrow evening. Light drainage
winds overnight. Lee cyclogenesis across northeast Colorado and
Wyoming will allow winds to turn southerly during the day
tomorrow.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Cooper
SHORT TERM...Danielson
LONG TERM...Gimmestad
AVIATION...Cooper


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