National Weather Service Forecast Discussion

000
FXUS65 KBOU 161603
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
903 AM MST Sat Feb 16 2019

.UPDATE...
Issued at 903 AM MST Sat Feb 16 2019

Satellite showing a large area of lift and snow across western
Colorado at this time being produced by a trough over Utah. This
will shift east into the central mountains later this morning and
early afternoon. The first wave of snow brought 1 to 4 inches of
snow through mid morning across the mountains. This caused roads
to quickly become snow covered and slippery. Road conditions have
improved with daylight, increased traffic, and lighter snow.
Expect road conditions to worsen again as snow picks. Plan on
extending the Winter Weather Advisory into mid afternoon for this
next round of snow. For the Front Range and eastern plains, the
cold front associated with the trough moving across Utah and
Colorado will push through late this morning and early afternoon
bringing gusty northwest winds. Still on track for some snow
showers, mainly south of I-70. Little to no accumulations are
expected with this.

&&

.SHORT TERM...(Today and tonight)
Issued at 500 AM MST Sat Feb 16 2019

Forecast for today looks on track, just a couple hours slower than
our previous forecast. There`s a band of moderate to heavy snow
showers that will move across our mountains between now and about
9 am. This should produce most of the snow for this event, with a
quick 2-4 inches of snow. Unfortunately, this is well timed to
meet the morning ski traffic. After that, light snow showers
should continue in the mountains the rest of the day. For the
plains, as usual, the forecast is complicated. The initial shower
band will likely die on the downslope westerly winds accompanying
it as it moves off the mountains. The cold front should drop down
across the plains around noon. This airmass is colder and almost
saturated, and by that time there will be deep instability with
500 mb temperature down around -30C. So a chance of afternoon snow
showers with the north winds into the Palmer Divide looks
reasonable. However, there will still likely be a westerly
component just off the ground that will probably keep there from
being much upslope into the foothills. That`s the plan anyway--we
will have lower PoPs in the Denver area in case the wind turns
into the terrain a bit more than expected. This too should be just
for a few hours--probably just scattered quick showers, but even
if it blows up unexpectedly not more than a couple inches in the
late afternoon. Most places should have a midday high with colder
temperatures in the afternoon.

We did add some isolated snow showers this evening as another
surge of cooler air drops across the plains. Low level flow should
be going more northwesterly, but also not as strong so unsure
which effect will win. Still probably a better chance of these
light showers away from the Front Range. Light mountain showers
will gradually diminish as the moisture layer thins, but may not
completely go away until near morning.

Only minor changes to the forecast temperatures, with cooler highs
on the eastern plains where the warm air shouldn`t get to. Then a
little cooler tonight with stronger cold advection.

.LONG TERM...(Sunday through Friday)
Issued at 500 AM MST Sat Feb 16 2019

Models have a mean upper trough over, at least, much of the
western United States Sunday through Monday night. There is
downward synoptic scale energy for the CWA most of Sunday, then
upward motion is progged Sunday night through Monday. It is
strongest later Monday night. The low level winds will be
dominated by east and northeasterly upslope flow Sunday into
Monday, then they become east-southeasterly the rest of Monday.
Fairly brisk southeasterlies winds are progged Monday night. A lot
of upslope those four periods. Looking at moisture, Sunday starts
out pretty dry but there is an increase on Sunday afternoon. The
GFS and NAM differ considerably through mid afternoon Sunday, with
the NAM much drier. Moisture is pretty widespread and deep all of
Sunday night through Monday night. The QPF fields have a bit of
measurable snowfall over the northwestern CWA Sunday morning. This
area expands to cover the mountains and eastern half of the
plains by Sunday evening. By 12Z Monday continuing through Monday
night, there is some minor measurable snowfall over most of the
CWA on the QPF fields of one model or another. For pops, will go
with "chance"s over the mountains on Sunday. By Sunday night
through Monday night, will go with "likely" pops in the mountains.
For the plains, will go with 20-60% pops Sunday night through
Monday night, the highest values over the CWA`s western and
southern plains. The snow will mainly be light over the CWA with
a pretty cold airmass in place. Accumulations will not be
significant. For temperatures, Sunday`s highs will be 4-8 C colder
than this afternoon`s readings. Monday`s highs will cool another
2-5 C from Sunday`s. For the later days, Tuesday through Friday,
models basically keep an upper trough in place over Colorado all
week. There may be some short wave ridging briefly Wednesday
night. Overall the airmass should remain colder than normal all
four days. For moisture, there is some on Tuesday, then it dries
out quite a bit Wednesday into Thursday. Moisture increases
somewhat late Thursday and Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 903 AM MST Sat Feb 16 2019

A cold front will push through around 18Z. Behind it, northwest
winds to 30 knots are expected. Winds may anti-cyclone and turn a
north or northeast direction behind the front this afternoon.
Scattered snow showers will be possible behind the front as well.
These will be short lived, with no accumulation expected. Ceilings
may lower to 3000 to 6000 feet with the snow showers, otherwise
ceilings are expected to stay above 6000 feet. Clouds are expected
to scattered out tonight. Low clouds may form over far eastern
Colorado tonight, but should remain east of the Denver area.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MST today for COZ031-033-034.

&&

$$

UPDATE...Meier
SHORT TERM...Gimmestad
LONG TERM...RJK
AVIATION...Meier

NWS BOU Office Area Forecast Discussion