Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 221102
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
402 AM MST Sun Jan 22 2017

.SHORT TERM...(Today and tonight)
Issued at 402 AM MST Sun Jan 22 2017

Flow aloft will increase out of the northwest as a ridge moves in
from the west. Associated subsidence will help diminish the light
snow over the mountains by noon. Clearing skies over the plains
and gusty northwest surface winds mixing down will allow for
temperatures to be slightly warmer than yesterday. The gusty winds
in the high country and foothills will be decreasing slightly this
morning as gradients relax, though gusts to 35 mph may still occur
through early afternoon.

Flow aloft will then turn west-southwesterly and increase tonight
as a jet streak helps dig a trough along the west coast. The
initial moisture will push into the mountain this evening as the
ridge axis is over eastern Colorado, with very weak QG lift in
southwesterly flow at mountain top. This will result in light
snow through midnight, with accumulations only around an inch or
less. After midnight, the jet will push into northwestern Colorado
to increase snowfall over the mountains, though our position
relative to the jet isn`t favored yet for heavier snowfall, so
expecting another 1 to 3 inches by morning. However, with the jet
overhead, isolated areas could see some banding bringing local
amounts higher. The plains will remain dry with downsloping flow.

.LONG TERM...(Monday through Saturday)
Issued at 402 AM MST Sun Jan 22 2017

Upper trough will shift across the Rockies Monday with a new low
forming over the Dakotas on Tuesday. There are only subtle
differences in the models which are generally too far north for
much precipitation on the plains. There are a few model runs that
show enhanced precipitation over the mountains Monday night with a
snow band on the plains Tuesday morning from coupling of a jet
streak and the convergence and upslope on the north side of a
surface low. Most models either lack this, or show it further
north across southeast Wyoming. However, this minority of models
does show substantial amounts of snow in this band (up to a foot
across Denver in the NAM is the extreme example). While the threat
of that much snow looks pretty low, the jet streak is agreed on
and the chance of a little snow on the plains might be higher than
one would first assume from the low position. Again, this would
probably only be a quick shot as the jet streak comes through and
the low level flow is briefly north-northeast. So we will leave
the PoPs on the plains in the late Monday night into Tuesday time
frame.

For the mountains this looks to be mainly a light-moderate
orographic snowfall. Winds are stronger Monday but in a fairly
stable airmass. For Monday night and Tuesday there is some cooling
aloft but the winds are much lighter. Best shot at significant
snow is with the above mentioned jet streak Monday night, but the
location and strength of that remain uncertain. Advisories may be
needed for the peak of the event, especially for zone 31, but the
snow should not be significant until at least Monday morning.

For Wednesday and beyond, we will be sitting in the colder air for
a couple of days. A trough will drop down from the north bringing
a better chance of light snow to the mountains about Thursday,
then we will have drier and warmer air in place for the weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 402 AM MST Sun Jan 22 2017

VFR conditions are expected through Monday morning as an upper
ridge moves across the region. Skies are expected to be mostly
clear this morning increasing to mostly cloudy tonight, but
ceilings are expected to remain above 120,00 feet. Drainage winds
this morning, then northwest winds gusting over the northeastern
plains may mix down into the area airports, then a Longmont
Anticyclone may form to bring southeasterly winds late this
afternoon before drainage winds again tonight.


&&

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

$$

SHORT TERM...Kriederman
LONG TERM...Gimmestad
AVIATION...Kriederman


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