Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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469
FXUS65 KBOU 182200
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
300 PM MST Mon Dec 18 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 205 PM MST Mon Dec 18 2017

The flow aloft will be relatively weak tonight into Tuesday. A
deformation area will be sitting over the state tonight as a
system passes across southern New Mexico. On Tuesday, a short
wave ridge aloft will be over the region. The flow aloft will
transition to more of a westerly component late in the day.
Otherwise the airmass will dry and stable, with high temperatures
similar to today.

.LONG TERM...(Tuesday night through Monday)
Issued at 205 PM MST Mon Dec 18 2017

Tuesday night and Wednesday, the flow aloft will increase and
become more zonal ahead of the next storm system. A lee trough
over eastern Colorado will enhance the downslope along the Front
Range. Not much mountain wave amplification present however on
the NAM12 spatial cross-sections so strongest winds should be
confined to the mountains and higher foothills. Over the
northeast plains, it will be dry and mild with highs around 60,
well above the normal of 42. The fire danger will be elevated due
to the dry conditions, but the wind does not appear to be strong
enough to warrant any fire weather watches at this time. Big
changes late Wednesday night and Thursday, the next system will
usher in much colder temperatures and a good chance of light snow
for the region at that time. The upper trough over Washington
state early Wednesday will dive south into northern UT by 06z
Thursday and into southwest CO by 00Z Friday. Moderate mid level
qg ascent will push across northeast CO Wednesday night into
Thursday morning. The cold front will drop the high temperatures
by 30+ degrees from Wednesday to Thursday, with north to northeast
upslope from the sfc to 700 mb. The best combination of forcing
aloft, moisture and upslope would appear to be 09z-18z Thursday.
Best snowfall will likely occur in and near the foothills, initial
estimates of 3-6 inches possible in the foothills, with 1-3
inches for the Urban Corridor. The system will translate eastward
Thursday night into Friday with mid level subsidence and a short
wave ridge over the state on Friday. Temperatures on Friday will
moderate only slightly as it will be near freezing for the high.
Friday night into Saturday will get even colder as another system
brings a blast of Arctic air into the region. Highs over the
weekend will be stuck in the teens through Sunday, with overnight
lows in Denver at or below zero. A strong upper level jet will be
over the region Friday night and Saturday so banded type snowfall
is also possible. Models generate 24-hr totals from 2-6 inches
over the weekend with potential for localized enhanced banding
under the jetstream. Dry but continued cold Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 205 PM MST Mon Dec 18 2017

VFR conditions will persist through Tuesday. Light northeast winds
will transition to a south/southwest drainage by early this
evening. By Tuesday afternoon, a light east to southeast winds can
be expected.
&&

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

$$

SHORT TERM...Cooper
LONG TERM...Cooper
AVIATION...Cooper



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