Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 200400

Area Forecast Discussion
National Weather Service Denver/Boulder CO
900 PM MST Fri Jan 19 2018

Issued at 900 PM MST Fri Jan 19 2018

Evening model runs have come in stronger than earlier runs for
Sunday`s storm. The Four Corners circulation will generate strong
upward forcing over eastern Colorado through the day Sunday in the
deformation area downstream of the low. Specific humidity values
show more available moisture early in the storm which will support
an increase in snowfall Sunday morning. Strong surface
cyclogenesis will produce gusty winds across the northeast plains.

Have extended the Winter Storm Watch to cover the remainder of
northeast Colorado, including the Denver Metro Area and I-25
corridor. Difficult travel conditions are expected through the day
Sunday with snowfall not expected to begin tapering off until late
afternoon or evening.


.SHORT TERM...(This evening through Saturday)
Issued at 250 PM MST Fri Jan 19 2018

There is a moderate westerly flow aloft across Colorado this
afternoon along with abundant high level moisture streaming in
ahead of the developing storm system. Expect this moisture to
remain over much of northeast Colorado through tonight, with some
thinning on Saturday as the flow backs more to the southwest as
trof approaches. Main change to forecast for Saturday was to
delay and decrease the mountain pops until Saturday afternoon.
Brunt of moisture will deepen more by Saturday evening. Some light
accumulation`s in zone 31, but anything significant in the rest
of the mountains will hold off until Saturday evening with
unfavored southwest orographic flow.

Across the plains on Saturday will see some slight cooling of
temperatures as surface winds turn more easterly Saturday
afternoon as surface low pressure begins to deepen during the
afternoon hours. Any showers will hold off until Saturday night
period (see below)

.LONG TERM...(Saturday night through Friday)
Issued at 250 PM MST Fri Jan 19 2018

Models continue to converge of a single solution as they show the
closed upper low passing over the Four Corners Saturday night, a
bit later than what earlier model runs indicated. Models also
indicate a later arrival time for the cold front on the plains.
All along, precipitable water amounts given by the models haven`t
been all that great. That said, a deep upper low is still progged
to track east over southeast Colorado during the day Sunday,
positioning the forecast area under a brisk south-southeast mid-
level flow Sunday morning, and an even stronger northeast flow in
the afternoon. Moisture wrapping around this cyclone Sunday
morning, coupled with increased cold air advection and strongest
700-300mb Q-G ascent should generate the greatest snowfall rates
and coverage along and east of the Continental Divide. Sfc-700 mb
deformation axis setting up sometime Sunday morning from about
Elbert County southeast of Denver to Sedgwick County near the
state`s northeast corner will act as a focus for the heaviest
snowfall on the plains during the day. Could see northeasterly
winds gusts to around 40 mph along this axis during afternoon,
namely across Sedgwick, Phillips, Washington, Lincoln and eastern
portions of Adams and Arapahoe Counties. Could see snow totals in
this area anywhere from 4 to 8 inches by evening and with the
gusty winds, areas of blowing snow. Closer to the Front Range,
snow amounts not expected to be as great due in part to an earlier
shut down in snowfall with nwly winds downsloping off the Front
Range during the afternoon. The I-25 corridor may still see
anywhere from 3 to 6 inches by early Sunday afternoon, with the
greater totals in and around the Denver metro area.

As the upper low lifts out across western Kansas Sunday
afternoon, should see snowfall decreasing from west to east
across the forecast area. Mountain valley locations could see
the snow ending by around midday, while northwest facing mtn
slopes and ridges are likely to see snowfall lingering until
nightfall with cold and moist air continuing to wrap around the
departing cyclone.

Highlights issued at this point: A Winter Storm Watch for the
mountain zones 31..33-34. This watch runs from 01z/Sun to 19z/Sun.
A second Winter Storm Watch has been issued for portions of
northeast Colorado and Palmer Divide. This watch runs from 07Z/Sun
to 00z/Mon. Other areas not covered by these watches may also
cover under a Winter Storm Watch or Winter Weather Advisory
depending on later model guidance.

For the remainder of the extended period, airmass drier out and
gradually warms with the upper ridge building to our west. A weak
disturbance in the northwest flow aloft could bring some more snow
and gusty winds to the northern mountain ranges on Monday and
Monday night.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 900 PM MST Fri Jan 19 2018

No aviation impacts this evening or tomorrow morning. Ceilings
should remain well above 6000 feet AGL through Saturday afternoon.
A surface cold front is expected to move through Denver by Sunday
evening. Wind shift to the north will occur during the afternoon
with precipitation develop in the evening. MVFR and IFR conditions
are expected Saturday night.


Winter Storm Watch from late Saturday night through Sunday
afternoon for COZ038>046-048>051.

Winter Storm Watch from Saturday evening through Sunday morning
for COZ031-033>036.



SHORT TERM...Entrekin
AVIATION...Dankers is the U.S. government's official web portal to all federal, state and local government web resources and services.