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Area forecast discussion
National Weather Service Denver/Boulder Colorado
742 PM MST Wed Nov 20 2019

Update...
issued at 738 PM MST Wed Nov 20 2019

Have updated to include areas of freezing fog in the foothills
with patchy coverage along the I-25 corridor overnight. Areas of
fog were observed toward Bergen Park this evening. Locally dense
fog could be an issue with visibilities dropping to less than a
quarter mile in spots. Will leave the remainder of the grids as
is.

Update issued at 643 PM MST Wed Nov 20 2019

Highway cams and radar showing generally light snow at best in the
high country at this time, with minimal additional impact expected
on the roadways. Therefore the Winter Weather Advisory for the
north central mountains has been cancelled. For the remainder of
the forecast area, there will continue to be a gradual improvement
from west to east the remainder of the evening. As a result, have
adjusted the timing of the pops as well. Snowfall along the urban
corridor should wrap up by 8 PM or so.

&&

Short term...(this evening through thursday)
issued at 221 PM MST Wed Nov 20 2019

Complex weather pattern will prevail over the central rockies
through Friday. A large upper level low over California will
slowly track eastward tonight and Thursday and slowly weaken. A
short wave trough embedded in the southwest flow ahead of the main
upper level low will bring a period of rain and snow this
afternoon and evening as it track northeast across Colorado.

Due to mild temperatures, precipitation will begin as rain across
the lower elevations. The change to snow is expected to be slow
this afternoon into early evening. Even though the cold front
passed, the colder air has been slow to arrive. Temperatures have
finally started to slowly fall, however lower 30 temperatures are
still well to the north over northeast Wyoming and western South
Dakota. Eventually, there should be enough cooling to have all the
precipitation fall as snow. This is expected to be a little after
00z. Because of the mild temperatures this evening, not expecting
much impact to the roads. On grassy surfaces, up to 2 inches of
snow will be possible. For the mountains, snow tapers off this
evening, but roads should become snow covered and slippery in
spots. Therefore, will leave the Winter Weather Advisory in
effect.

Subsidence moves behind the exiting trough late tonight and helps
to dry the mid levels. A layer of moisture will remain at the
lower levels and will result in low clouds. Models indicate enough
drying near the surface to prevent freezing drizzle and fog from
forming. Best chance at seeing fog and freezing drizzle will be in
the lower foothills where the clouds intersect the ground.

Thursday will be a cloudy and chilly day. Low levels remain moist
and low clouds persist through the day. The upper level low off
to the west will slowly be weakening. Even though there will be
some moisture around, lift will be weak through the day. There is
some diffluent flow aloft which may help produce occasional light
snow. The best chance for this light snow will be over the
mountains where up to 3 inches of snow will be possible.

Long term...(thursday night through wednesday)
issued at 221 PM MST Wed Nov 20 2019

Chances for light snow continue early in the long term period as
upper low and associated cold pool move across the forecast area.
Weak upward vertical motion in the mid layers depicted in qg fields
and BUFKIT soundings, and combined with saturated soundings will
continue light snow. Best moisture, snow growth zones, and ascent
don't quite line up, so little additional accumulations of a few
inches in the mountains, 1-2 inches in the foothills, and an inch or
less along the I-25 corridor.

Trough shifts to eastern US for the weekend with ridging over the
west, and northwest flow over Colorado. Dry forecast for the weekend
with seasonable temperatures.

Early next week low pressure moves out of Pacific northwest early Monday
and carves out a trough over Colorado on Tuesday. Differences in GFS
& European model (ecmwf) noted by previous shift have come together at the surface
with cold front moving across the eastern plains. Differences
remain at 500 mb, and while timing of the trough passage is about
the same GFS is deeper with a closed low, and European model (ecmwf) showing an open
wave. Nevertheless Max temps on Monday about 10 degrees cooler than
the weekend, and chances for snow showers begin in the northern
mountains Sunday and spread east during the day Monday. Snow will
mix with rain during the day Monday on the plains as low level
temperatures warm above freezing. Light snow showers will continue
into Tuesday with cold pool aloft, mixing with rain again Tuesday
afternoon on the plains. Temperatures remain cool Wednesday despite
building ridge and some sunshine.

&&

Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 643 PM MST Wed Nov 20 2019

Low clouds are expected to persist through tonight and into
Thursday with ceilings of 500 to 1500 feet. Some flurries will be
possible through 03z, with improving visibilities overnight and
the snowfall comes to an end. Little if any additional
snow accumulation expected.



&&

Bou watches/warnings/advisories...
none.
&&

$$

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