Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210339
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
839 PM MST Tue Feb 20 2018

.UPDATE...
Issued at 832 PM MST Tue Feb 20 2018

Minor adjustments to the grids this evening. Some area already
colder than forecast this evening so have dropped the overnight
temperatures by 2-3 degrees across the Urban Corridor and
northeast plains. Areas of light snow over the Palmer Divide
spreading north into the southern part of Denver/ Still expect
along a brief period of light snow this evening with little if any
snow accumulation.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 317 PM MST Tue Feb 20 2018

Southwest flow aloft continues as the main upper trough stretches
from central Canada down southwest into the western states. A
shortwave trough over Utah is pushing into the state with another,
yet much weaker than yesterday, convective and slight banding
snow event this afternoon and evening. Based on upstream satellite
and radar observations and hires model trends, have increased the
chance of snow across the I70 corridor and over northern Grand and
southern Jackson counties in the high country, as well as into
lower Larimer County and over the urban corridor down to the
Palmer Divide. Overall, amounts of up to 2 inches are expected
late this afternoon into this evening.

The shortwave trough will pass overhead around midnight, shutting
off the chance of snow and allow for clearing skies. Decreased the
minimum temperature forecast below guidance due to today`s lower
than guidance readings as well and the expected clearing over the
snow covered ground. Winds over the plains should be light enough
to not require a Wind Chill Advisory tonight. The clearing may
also allow for fog to form across the plains, especially along the
South Platte River valley.

On Wednesday, shortwave ridging will allow for mostly clear skies
to begin with and temperatures to climb into the 20s and near 30.
Yet another shortwave will push in from the west to bring some
light snow showers by late afternoon over the mountains.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 317 PM MST Tue Feb 20 2018

Models continue to show a slowly evolving weather pattern across
the country for the rest of this week. A strong upper ridge off
the southeast coast is going to remain in place while a broad
upper trough holds in place over the western United States.
Colorado will be under southwesterly flow, downstream from the
base of the trough. A high amplitude ridge will also remain in
place over the Gulf of Alaska. At lower levels, a dome of surface
high pressure over the northern plains will help to keep a cool
airmass in place over eastern Colorado. This will keep
temperatures below normal into this weekend, although there will
be a gradual warming trend through the forecast period.

Through the week, pieces of energy will rotate through the base of
the trough at times and move across Colorado. This will produce
periods of light snow, mainly in the mountains. Light snow will be
possible in the mountains from Wednesday night through Friday, but
accumulations are expected to be very light. There will also be
a slight chance of snow out across the plains Thursday night.

Early in the weekend, there are indications that the main upper
trough will eject from its position over Nevada and move eastward
across Utah and Colorado. This should bring unsettled weather to
the forecast area Friday night and Saturday. Mountain snow showers
should be expected along with some showers on the plains Saturday
morning. After that, another trough is forecast to develop over
Colorado. The westerly flow ahead of this developing trough should
be enough to replace the cool airmass with some warmer
temperatures for the start of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 832 PM MST Tue Feb 20 2018

MVFR ceilings possible over the next 1 to 2 hours light snow
moving from south to north across the terminals. Partial clearing
expected after 06z, with possible fog forming over the plains,
with a chance to affect BJC and DEN with a weak Denver Cyclone to
form after 09z. Clear skies and light winds expected Wednesday.

&&

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

$$

UPDATE...Cooper
SHORT TERM...Kriederman
LONG TERM...Dankers
AVIATION...Cooper



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