Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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679
FXUS65 KBOU 202216
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
316 PM MST Sat Jan 20 2018

.SHORT TERM...(This afternoon through Sunday)
Issued at 1158 AM MST Sat Jan 20 2018

Upcoming weather system is currently digging into the Great Basin
with rain and snow showers spreading across western Colorado and
into Wyoming as upward QG vertical motion increases over the
state. Snow will be increasing across the mountains through
tonight, with upward QG values topping near -40 mb/hr by early
Sunday morning. This is when the mountains will see their heaviest
snowfall rates, between 1 and 2 inches per hour. The moisture will
be spreading east, however low level moisture will push into the
plains this evening first. Viewing forecast soundings over the
plains show this moisture warmer than required for ice nucleation,
therefore will continue to have a mention of freezing drizzle over
the plains. This is most likely to occur between 9pm and 3am,
before additional cooling from the north and deeper moisture
moving east of the mountains will help change the precip over to
snow. The exception will be over the far eastern plains where it
may take longer for a switch over due to the delay in cooling and
deeper moisture. This initial freezing drizzle layer will produce
slick conditions before the expected snowfall tomorrow.

Upslope winds will deepen early tomorrow morning into the late
morning hours along with the increase of upward QG vertical motion for
the eastern slopes of the Front Range mountains and foothills as
well as the urban corridor to see snowfall rates increase. After
noon, the upper low including the 700 mb low will push east into
Kansas, therefore turning mountain top wind more northwesterly to
begin decreasing snow from northwest to southeast. At the same
time the pressure gradient will be increasing and winds across the
area will increase, with gusts in the 35 to 50 mph, highest across
the Palmer Divide and east. This may produce near Blizzard
conditions, but not sure how long they will last. Will keep the
mention of reduced visibilities in the Winter Storm Warning. Will
add an Snow and Blowing Snow Advisory for zone 47, southern
Lincoln County. Only expecting 2-4 inches down there, however
strong winds will create hazardous conditions and low visibility
in blowing snow.

For total snow amounts, increase the forecast just slightly for
the mountains with the strong upward QG and some models coming in
slightly higher in amounts. Also decreased amounts ever so
slightly over the plains due to a slight slowing and weakening of
the storm in all models. Still, the strong upward QG should wring
out a lot of moisture.


.LONG TERM...(Sunday night through Friday)
Issued at 1158 AM MST Sat Jan 20 2018

The upper low will be lifting northeast into Kansas Sunday night
with a diminishment of snowfall from west to east across the
northeast plains. There will still be strong northwest winds over
the plains with gusts in the 40-50 mph range through the evening
so will be holding on to the warnings through 8 pm there. Have
increased winds over the plains for Sunday evening.

For Monday and Tuesday, expect a moderate northwest flow aloft
regime to set in over Colorado in the wake of this weekends storm
system. There appears to be enough moisture and weak ripple in
the flow to keep scattered snow showers going in the mountains
but amounts will be on the light side. Given the mid level flow,
still expect a fair amount of winds over the mountains and east
slopes, mainly in the 30-50kt range.

For Wednesday and early Thursday, high pressure ridge aloft will
build over Colorado, before shifting east of state late Thursday.
Expect a warming with readings back into the 40s and lower 50s by
Wednesday and Thursday. Some of this warming will still depend on
how much snow cover is still lingering.

The next storm system is poised to translate across Colorado
Thursday night through early Saturday time frame as an open wave
with the brunt of the energy from Colorado and northward. Long
range models are similar with the general overall solution but
there are still some differences in amplitude and timing amongst
them. Will keep forecast as is with chance pops and cooler
temperatures, but won`t fiddle much with details this far out.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1158 AM MST Sat Jan 20 2018

Northeast winds continue at all airports with cooler air moving in
and increasing low level moisture. Low clouds with ceilings of
1000 to 3000 feet are expected to form around 03Z. Clouds will
continue to lower through this evening. Eventually, freezing
drizzle is expected to form around 04-06Z with ceilings falling
below 1000 feet. Freezing drizzle will change to snow between 09Z
and 12Z. Snow will then persist through most of Sunday. The
heaviest snow is expected to occur Sunday morning and into the
early afternoon. Total snowfall for the upcoming storm through
Sunday evening for the Denver airports is expected to be in the 5
to 8 inch range.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from midnight tonight to 8 PM MST Sunday
for COZ046-048>051.

Winter Storm Warning from 6 PM this evening to noon MST Sunday
for COZ031-033>036.

Winter Weather Advisory from 6 PM this evening to noon MST
Sunday for COZ030-032.

Winter Storm Warning from midnight tonight to 5 PM MST Sunday
for COZ039>042-044-045.

Winter Storm Warning from midnight tonight to 2 PM MST Sunday
for COZ038-043.

Winter Weather Advisory from 8 AM Sunday to 5 PM MST Sunday
afternoon for COZ047.

&&

$$

SHORT TERM...Kriederman
LONG TERM...Entrekin
AVIATION...Kriederman



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