Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 240327
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
827 PM MST Fri Feb 23 2018

.UPDATE...
Issued at 826 PM MST Fri Feb 23 2018

Band of heavy snow formed over Larimer, Boulder and western Weld
counties this evening. Snowfall rates of up to 2 inches per hour
were observed. Radar shows this area of snow is weakening and
should dissipate by midnight. Models indicate a second area of
snow will form over eastern Colorado late this evening and after
midnight. IR Satellite imagery showing cooling cloud tops over
south central and southeast Colorado. This appears to be the
beginning of the next round of snow. A few snow showers will
remain possible in the Denver area, however accumulations for
Denver should be light. Removed the mention of freezing drizzle
from the forecast over the eastern plains. Airmass next to the
surface has a ways to go to saturate. By the time the airmass
saturates, the snow lifting from southern Colorado should be over
the area. By 12Z Saturday, expect a few mountain snow showers and
an area of snow over the northeast plains.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 317 PM MST Fri Feb 23 2018

Active weather in the short term with positively tilted 500 mb
trough moving out of southern Nevada and across the four corners
region tonight. Southwest flow bringing plenty of moisture into
the region, with this morning`s clear skies clouding over. Upper
trough becomes more north/south oriented as it becomes centered
over Colorado by 12z Saturday morning, then progresses east during
the day. Departing 250 mb jet this evening puts the region in the
right rear quadrant. Combination of jet dynamics and approaching
trough produce good amount of synoptic lift, with widespread snow
forecast. Have upped snowfall amounts tonight mainly in the
northern urban corridor region where potential for snow band
development this afternoon up to about midnight. Could pick up a
quick 3 inches through early evening, causing difficult travel
problems. As a result have extended winter weather advisory
further west to encompass Weld and eastern Larimer counties for
heavy snowfall tonight.

Freezing drizzle threat still exists in northeast CO tonight.
Mainly at the onset before snow moves in, however potential for
freezing drizzle to linger Saturday morning as moisture moves out
but temperatures remain cold. Ice growth zone dries out, while
cold low levels keep supercooled cloud droplets in contact with
still frozen ground. Something to watch.

As upper and surface low depart on Saturday precip ends west to
east, although will linger in the high mountains where terrain
wrings out the last of the moisture. Strong gradient winds behind
the front will cause gusty west winds, up to 40-50 mph winds in
the mountains and front range, and gusts to 20-30 out on the
plains.

.LONG TERM...(Saturday night through Friday)
Issued at 317 PM MST Fri Feb 23 2018

Precip lull for most of the CWA Saturday evening with gusty west-
northwest winds blowing down off the Front Range and subsiding zonal
flow aloft. Gusts overnight in the 35-50 mph range ridgetops and
east slope of the Front Range. Gusty northwest winds up along the t
Cheyenne Ridge early evening expected to subside through the evening
with boundary layer decoupling. Overnight, shortwave energy and
moisture progged to swing over the state from the west, with much of
this moisture piling up against the west side of Continental Divide.
Guidance 6-hr snow totals ending 12z/Sun in the 3 to 7 inch range,
heavier amounts in the Park and Gore Ranges, high valley snow
amounts generally 2 inches or less. Could see snow blowing off the
ridges and onto the high foothills for an inch or so of wind blown
snow there by morning. Nothing on the plains. High country snowfall
expected to wrap up Sunday morning with the departing shortwave and
its moisture. Although the GFS shows areas of light snowfall
continuing on the west slopes Sunday until 18z/Sunday. Any
additional accumulation based on the GFS would be light and
confined to higher windward slopes and passes.

Sunday looks quite windy with subsident northwest flow and CAA in
the wake of the trough. Cross sections show the 80-100kt speed max
up around 450 mbs translating downward through the day with
increasing mtn top static stability. Should see these Bora winds
spreading out across the plains by late morning or early afternoon
with strongest winds up along the Wyoming border and across the
northeast corner of the state during the afternoon and early evening
hours. Same goes for the Front Range and foothills, although the
strong and gusty winds are expected to continue through early monday
morning when models show the mtn top flow turning southwesterly and
WAA kicks in at mid-levels with passage of the weak shortwave
ridge.

The warmer southwest flow aloft and lower PW air tethered the
passing flat shortwave ridge will help warm sfc temperatures
everywhere on Monday. High temps Monday should come close the norms
for the date with upper 40s in the Denver area, and mid 40s to lower
50s on the plains. High country temps actually quite mild for the
date with 30s as a rule.

Later in the week starting with Tuesday, the upper ridge shifts east
of the state and during the day models show a weak cold front
slipping south over nern Colorado. Front appears dry, but just
enough cool air behind it to shave high temps back 4-6 degs. Tuesday
night into Wednesday, another Pacific weather system in the form of
an open wave trough is forecast to come across Colorado. Models show
the trough closing off over Arizona Tuesday night. Some show this
low tracking way south of Colorado on Wednesday, while the GFS shows
the trough opening up and lifting over Colorado on Wednesday. The
GFS solution would end up generating more snow and colder
temperatures across the CWA. While other solutions not as wet or as
cold. Still Wed temps below average.

Thursday and Friday, shortwave ridging would bring dry and warmer
conditions to the region with only a slight chance of the snow
northern mtns thu night and Friday. Temperatures are forecasted to
be near to slightly above average. Looks reasonable the passing
ridge.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 826 PM MST Fri Feb 23 2018

Low clouds with HZ/BR will continue at the Denver airports through
most of the night. Ceilings will remain less than 1500 feet and
may fall to around 500 feet at times. Snow showers will remain
possible at the Denver airport through 09Z-11Z. However the best
chance for snow later tonight will be to the east of Denver as a
second area of snow forms.

Conditions improve to VFR after 12z Saturday with gusty west-
northwest winds developing. Gusts to 30 knots will be possible
16-22Z.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM MST Saturday for COZ038-
042>044-048>051.

&&

$$

UPDATE...Meier
SHORT TERM...Hanson
LONG TERM...Baker
AVIATION...Meier



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