Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 230429

Area Forecast Discussion
National Weather Service Denver/Boulder CO
929 PM MST Wed Feb 22 2017

Issued at 928 PM MST Wed Feb 22 2017

Latest satellite imagery shows upper low spinning slowly east from
the Idaho/Nevada/Utah tri state intersection. Meanwhile, there is
a dry slot working northeast across our forecast area right now,
with better deformation and precipitation stretching out just to
our north, and that should stay that way most of the night.
However, there is moderate to strong Q-G lift so drying should be
filling in again toward daybreak. On the plains, there is a
another frontal surge, this one with more low level moisture,
backing southwest across the Nebraska panhandle and southeast
Wyoming. The increased moisture and cooler temperatures, along
with upslope flow, will bring potential for stratus and fog across
the plains late tonight into Thursday morning. There will also be
a chance of light freezing drizzle with the upslope but not
sufficient moisture depth over the northeast corner for
seeder/feeder interaction early on. Better chance of snow
spreading down into the lower elevations with yet another stronger
frontal surge Thursday afternoon/evening, although points near the
Wyoming/Nebraska border could start picking up accumulating snow
early Thursday morning already. Will still have to watch that area
for possible advisory if things shift slightly southward, but for
now only advisories will remain in the northern tier of mountains
where better orographic forcing begins tomorrow afternoon through
Thursday evening.


.SHORT TERM...(This evening through Thursday)
Issued at 240 PM MST Wed Feb 22 2017

The weather challenge for the period is the timing of snow over
the region. Light snow is moving into western Colorado with the
increasing moisture from an upper level trough over the West. The
increasing moisture ahead of the system will stretch over the
Great Basin and into Colorado with the help of an upper level jet.
This will bring snow to the mountains starting this afternoon and
continue through Thursday evening. A cold front will drop south
out of Wyoming Thursday afternoon but progress will be impeded by
a surface low over the SE portions of the CWA. Various models
indicate this low keeping precipitation to the North closer to the
Wyoming border through most of the day with light snow making it
into Denver and south of I-70 around 6 pm Thursday evening.
Amounts will be higher in the mountains with areas of Rabbit Ears
Pass seeing the highest amounts at 14 inches with lesser amounts
over the divide. For the plains the higher amounts of 2 to 4
inches will be closer to the Wyoming border with trace to 2 inches
elsewhere. Temperatures will drop overnight with lows below
freezing and mid to upper 30s on Thursday. Further south the front
is expected to wash out keeping areas in southern Lincoln county
warmer with highs in the lower 50s.

.LONG TERM...(Thursday night through Wednesday)
Issued at 240 PM MST Wed Feb 22 2017

Upper level low will be centered over the Nebraska panhandle
Thursday evening. It will track east across Nebraska Thursday night
and into Iowa Friday. For north central and northeast Colorado, a
north to northwest flow aloft will prevail. Light snow is expected
across northeast Colorado behind the exiting trough. Over mountains,
orographic lift will produce snow. For Friday, gusty northerly
winds are expected over the eastern plains as a surface high drops
south into Wyoming. Along the Front Range winds turn
northeasterly. This upslope flow may produce light snow in and
near the foothills. Temperatures will be cold Friday with highs
mainly in the 20s. Light snow will be possible in the mountains
due to orographic lift. In general, snowfall amounts are expected
to be light, though roads may become snow covered in places at

For the weekend, westerly flow aloft will prevail. A fast moving
short wave trough will race across the four corners and Southern
Rockies Saturday night and Sunday. This could bring snow to the
mountains along and south of Interstate 70, otherwise dry
conditions are expected. Temperatures will be cool Saturday with
readings in the 30s across northeast Colorado. On Sunday,
temperatures are expected to be near normal.

An upper level trough will move onto the California coast Monday.
Southwest flow ahead of it will bring mild and dry conditions. As
this trough approaches, the chance for snow will increase over
the mountains Monday night. The trough is expected to push across
the Central Rockies Tuesday. The best chance for snow will be
over the mountains. Temperatures will cool to near normal. On
Wednesday, a cool and dry northwest flow aloft will prevail
across Colorado.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 928 PM MST Wed Feb 22 2017

Main concern in the short term is threat of fog and stratus deck
late tonight into Thursday. Frontal push through the Nebraska
panhandle has a pretty good push behind it with 3mb pressure
rises. Low level moisture increases behind the front so some
threat of fog developing on the periphery of a developing Denver
cyclone after 12Z. HRRR and RAP on board with some fog and if it
does develop visibility could drop to 1/4sm through 15Z. Overall
confidence on the fog is low so will go with VCFG in the TAF for
now, but certainly bears watching through Thursday morning. Then
chance of snow showers will increase Thursday afternoon and
evening as a stronger front pushes across the area. Generally
northerly winds expected this evening, turning more northeast with
frontal push toward 10Z-12Z. Then winds may become quite variable
through the day tomorrow depending on progression and development
of Denver cyclone, and finally cold front arrival tomorrow


Winter Weather Advisory until 9 AM MST Friday for COZ031-033.



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