Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171124
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
424 AM MST Sat Nov 17 2018

.SHORT TERM...(Today and tonight)
Issued at 424 AM MST Sat Nov 17 2018

The forecast is generally on track. Raised Pops quite a bit with
pretty good certainty now, raised QPF/snow slightly, and slowed
the departure of the system tonight.

Drizzle is developing across northeastern Colorado at this hour
as expected. There are a few light snow showers moving over the
top of the low cloud deck, but the main area of snow is still
north of Laramie and Vernal, so we will have several hours of
mostly drizzle even along the northern border, and much of the day
from I-70 southward. The cooling has been a bit less than
expected overnight, so much of the area is still a little above
freezing which will help conditions through the first part of the
morning. There should be a steady slow cooling though, so freezing
on elevated surfaces and bridges should still be a problem. With
the warmer temperatures the main impacts from freezing drizzle may
be in the foothills and north of highway 34.

The area of lift and deeper moisture will move into northern
border areas and probably the Front Range cities by midday, though
the south edge of it may be slow to push south of I-70. I nudged
QPF up a little bit mainly due to the increased certainty of a
6-12 hour period of steady light snow. Models are producing a bit
more away from the upslope areas now, especially in the northeast
corner where the NAM has a solid 4 inches of snow this afternoon
and evening. Added the far northeast corner to our existing
advisory. For now we`ve kept the advisory timing simple, but the
snow will likely be ending in Fort Collins/Greeley sometime this
evening and could linger into the early morning hours near the
eastern border. The midnight timing is probably not bad for
Denver. Road conditions will be aided by warm ground and temps
starting near freezing this morning, so the worst conditions may
be this evening as light snow continues and the temperature drops
into the teens.

.LONG TERM...(Sunday through Friday)
Issued at 424 AM MST Sat Nov 17 2018

An upper level ridge over the west will allow for warmer and
drier weather to move back into the region through mid-week. The
ridge axis moves over the state on Wednesday. On Thursday, the
models show a short wave trough moving across the state late
Thursday afternoon and Thursday night. This system will bring
a chance of snow to the high country. Over the northeast plains,
dry and mild for Thursday as well, with lee side surface trough
over eastern Colorado. The models show a short wave ridge on
Friday, with a moderate to strong west/southwesterly flow aloft.
This should allow for mainly orographic precipitation in the high
country, with dry conditions over the northeast plains. Outcomes
among the extended models does vary in the latter part of the
week so overall confidence in the outcome is low at that time.
The Canadian shows a short wave trough moving across the state by
12z Saturday, while the GFS/ECMWF has this system further west
over Idaho/eastern UT. Will continue with the best chance of snow
in the mountains for Thursday afternoon through Saturday, with
isolated to scattered pops possible over the northeast plains by
Saturday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 424 AM MST Sat Nov 17 2018

IFR conditions in light freezing drizzle and snow will become
widespread by 14z, with precipitation changing to all snow between
18z and 21z and continuing through this evening. Precipitation
will end between 06z and 10z with ceilings improving quickly after
that. Ice accumulations this morning will be limited by
relatively warm ground and air temperatures. Snow accumulation of
1 to 3 inches is expected at KDEN/KAPA with around 3 inches at
KBJC. VFR conditions are expected for Sunday morning, though
there may still be a ceiling above 4000 ft for the first few
hours.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight MST tonight for COZ035-
036-038>046-048>051.

Winter Weather Advisory from 8 AM this morning to midnight MST
tonight for COZ031-033.

&&

$$

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


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