Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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000
FXUS65 KBOU 110413
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
913 PM MST Sat Feb 10 2018

.UPDATE...
Issued at 913 PM MST Sat Feb 10 2018

Snow has continued sagging southward through the evening and has
almost exited the forecast area. Lingering light snow continues in
the Douglas County and the southern Front Range foothills, and
over southern Lincoln County. Over the rest of northeast Colorado,
skies will be clearing out and temperatures will be dropping.
Changes to the forecast this evening have involved dropping
temperatures in the forecast and removing the mention of snowfall.
Low temperatures could drop to zero or a few degrees colder across
the plains. The fresh snow and clearing skies, along with light
winds will be favorable for strong radiational cooling. Tomorrow
looks like a sunny and warmer day as the flow aloft transitions to
westerly and dry air advects into the region.

UPDATE Issued at 513 PM MST Sat Feb 10 2018

The Winter Weather Advisory in the mountains has been allowed to
expire. Snow has ended across most of the mountains with just
scattered light snow showers noted over parts of zone 34. Web
cameras at some mountain locations in the north are showing partly
cloudy skies.

On the plains, the main area of snow is now located over the
Palmer Divide and over the southwestern suburbs of Denver.
Adjusted the forecast to begin clearing the snow from the northern
locations. Will also lower the temperatures, since gradually
clearing skies will allow for good radiational cooling overnight.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 325 PM MST Sat Feb 10 2018

Has been a good snow day in the BOU forecast area with synoptic
scale lift associated with an approaching 500 mb trough in
northwest flow...and a nice 90 to 100 kt jet at 300 mb sagging
north to south across the area. Band of heavier snowfall from Park
county across southern Denver metro and on east onto the plains at
20z. The snow band will continue to drop south this afternoon
associated with movement of the upper jet. Sharp cutoff to the
north, with snow ending across the northern tier of counties.
Expect an additional inch or two mainly south of I-70 the rest of
this afternoon and evening before it ends entirely. Temperatures
have not budged today in low level easterly flow on the plains
reinforcing cold surface air, and cloud cover preventing any
warming.

Cold night in store tonight with sharp clearing line behind the
upper trough. Expect light winds and clear skies by midnight to
allow for excellent radiational cooling. Temperatures in the
single digits above zero, which is 10-15 degrees below normal but
seasonable nonetheless.

For Sunday the region will be under shortwave ridging at 500 mb in
continued northwest flow aloft, and weak high pressure at the
surface. Sunshine and light southerly wind will allow temperatures
warming closer to normal; 40s on the plains and 20s-30s in the
mountains.

.LONG TERM...(Sunday Night through Saturday)
Issued at 325 PM MST Sat Feb 10 2018

Early Monday the mid-level flow goes zonal over Colorado as a
strong Polar Jet carves out a sharply curved upper trough down
the Pacific West Coast. By midday transport flow turns
southwesterly over Colorado as the upper trough makes steady
headway across the Great Basin. Along the way, southerly low-
level flow feeds into the bottom of the trough providing
additional moisture for another round of snowfall for our high
country Monday afternoon through Tuesday morning. This same south-
southwest sfc-700 mb flow less than favorable for orographic snow
production in our northern mtn ranges. So accumulations on west-
southwest facing slopes expected to be no more than 2-4 inches.
On the northeast plains of Colorado, yet another shallow arctic
front is progged to slip south over the area early Monday
morning. Models show the coldest air behind this front being
funneled southward along the I-25 corridor by circulation around
surface low forming along the front southeast of the Denver metro
area. This shallow deck of cold, moist air banked up against the
foothills could again produce snow flurries and possibly some
freezing drizzle over portions of the I-25 corridor during the
late morning through early evening hours. Appears daytime temps
may not climb out of the 20s up against the Front Range and up
near the Wyoming and Nebraska borders. While farther south and
east of the Denver metro area, a dry and warmer southerly wind
should send the mercury up into the upper 30s and lower 40s by
afternoon, assuming skies remain generally clear as the NAM,
ECMWF and Canadian models indicate.

During the day Tuesday the West Coast trough cuts off and pretty
much stalls out over central and southern California. Circulation
around the bottom of the trough feeds a broken stream of moisture
northeastward towards Colorado, although it appears most of this
moisture will be captured by the state`s southwest and west
central mtn ranges. Still enough of this moisture will spread far
enough north for a chance of snow showers in our higher mtn
ranges, mainly before midday. Meanwhile, downslope flow off the
Front Range and Palmer Divide will begin the warm up and dry out
the plains airmass. High temps on the plains for Tuesday in the
mid-40s to lower 50s are expected to warm to the mid-50s and
lower 60s on Wednesday. As usual, coolest readings will be found
across the northeast corner of the state.

Thursday through Saturday, GFS and ECMWF show the West Coast
trough making very slow eastward progress across the Great Basin
and Desert Southwest, with the closed low tracking over Arizona
on Friday and across New Mexico on Saturday. Whereas, the Canadian
model moves the trough and closed low off the California coast,
and not until Saturday does it move this system onshore. During
this period, the Polar jet remains well north of Colorado, which
should keep temperatures on the mild side, but not quite as warm
as Wednesday. A decent sub-tropical jet sitting south of Colorado
could help advect scanty amounts of moisture up into the CWA, for
at least a chance of snow showers in the high country, and
perhaps a stray rain/snow shower or two on the plains. Otherwise,
this period generally looks dry and seasonably mild.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 913 PM MST Sat Feb 10 2018

Snowfall is coming to an end at Denver area airports with just a
single lingering snow flurry at KBJC. With dew points falling
toward zero, the airmass may be too dry for fog or stratus to
develop. This should result in mostly clear skies overnight and
through tomorrow. Winds should be light through the next 24 hours.
No more aviation impacts are expected.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

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



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