Area Forecast Discussion
Issued by NWS Grand Junction, CO

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723
FXUS65 KGJT 190533
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1033 PM MST Fri Jan 18 2019

.UPDATE...
Issued at 900 PM MST Fri Jan 18 2019

Well...9pm MDT has arrived, and snow continues to fall across the
Grand Mesa, northern San Juans, Vail Pass, and the Flat Tops. In
fact, webcams on the Grand Mesa, Vail, Ouray, and even Steamboat
indicate an inch or two of fresh snow accumulation in the past
three hours. GOES nighttime microphysics imagery continues to
indicate expansive low-level upslope cloud cover throughout much
of the favored northern slopes. Only in the last 20 minutes or so
has there been any indication of dry air entrainment into this
cloud/precipitation deck...so we will push the current Winter
Storm Warnings/Advisories another three hours to midnight.

UPDATE Issued at 555 PM MST Fri Jan 18 2019

All remaining winter weather headlines will be extended three
hours until 9pm this evening. Saturation in the lowest levels
continues to support lingering light to moderate snow over the
Grand Mesa and northern San Juan Mountains. Additionally, snowfall
resulting in reduced visibility continues to affect I-70 on Vail
Pass, as well as on CO 13 in the Meeker area. Shallow, moist,
post-frontal upslope flow can be tricky to time...and many
northern-favored slopes may be getting more than they bargained
for on the back end of this storm this evening. The latest high-
resolution guidance supports at least another 1-3 hours of
snowfall in all of the aforementioned zones. Things *should*
diminish by 9pm MDT...

UPDATE Issued at 452 PM MST Fri Jan 18 2019

Satellite, radar, and surface observations indicate that snowfall
is coming to an end across western Colorado. Have taken down
several winter weather headlines in accordance with these trends.

Two particular areas will need to be watched for possible
extensions, however. Low level upslope flow over the Grand and
Battlement Mesas continue, and webcams show continued
accumulations at this hour. Additionally, a few recent runs of
the HRRR hint at the potential for a gorge convergence event in
the northern San Juans along US 550 from Ridgway through Ouray
and Red Mountain Pass. Wind vectors do support this scenario...the
question will be if enough low level moisture remains in the
northmen San Juans. We will see if these model trend become
reality in the next hour or so.

&&

.SHORT TERM...(Tonight through Saturday night)
Issued at 402 PM MST Fri Jan 18 2019

It`s called favored flow for a reason, right? Northwesterly flow
left in the wake of the cold front this morning has resulted in
heavy snowfall accumulations for northwest Colorado. Are you ready
for this? 8 to 12 inches for the Central Yampa River Basin
(including a report of 11.5 inches in the town of Craig), 10 to
12 inches in the Upper Yampa River Basin, and 25 inches at
Steamboat Ski Resort! Favorable upper level support paired with
the abundance of moisture provided by the atmospheric river
allowed the San Juan River Basin and the San Juan Mountains to
receive some good snowfall totals as well with 6 to 10 and 8 to 13
inches so far, respectively. Of course the Grand Valley missed
out on the action last night with temperatures staying too warm
yesterday evening and only briefly dropping to 31 degrees early
this morning behind the cold front, making me public enemy number
one I`m sure. Light orographic snow showers will continue along
the Continental Divide late this afternoon and into the early
evening hours with the remaining ongoing winter weather highlights
still on track to expire at 6 PM MST. The Elkhead, Park, and Gore
ranges in northwest Colorado will continue to see isolated
showers overnight and into Saturday as northwesterly flow persists
aloft, though accumulations will be light. Elsewhere, heavier
cloud cover will continue to dissipate as high pressure builds to
the southwest tonight and Saturday. These clearing skies will
enhance radiational cooling overnight with lows dropping an
additional 10 degrees or so to what was experienced Thursday
night. Additionally, residual low level moisture paired with fresh
snowfall will allow for areas of fog to redevelop across some of
the valleys overnight. High temperatures on Saturday will only
fluctuate slightly from what was experienced today, though I did
trend several degrees below model guidance to account for the
return of the valley inversions. Expect another quiet night for
Saturday.

.LONG TERM...(Sunday through Friday)
Issued at 402 PM MST Fri Jan 18 2019

The ridge will remain in place through midday Sunday before the
arrival of the next Pacific trough on the west coast quickly
flattens it. Upper level flow will once again shift to the
southwest over eastern Utah and western Colorado as the trough
digs into the Great Basin Sunday night. Moisture will spill out
ahead of this feature and the associated cold front into our
region Monday morning with showers increasing throughout the day
as a result. Plenty of cold air with this system with 700mb
temperatures dropping from -3 to -6 degrees C Monday morning to -9
to -14 degrees C Monday night. For right now the trough looks to
pass across the entirety of the forecast area with most locations
on track to receive some precipitation. Additionally, a ~115 knot
jetstreak is set to move over the central and southern portions
of the region Monday afternoon which would provide some enhanced
snowfall rates. The trough will progress east into the Plains on
Tuesday with drier north-northwesterly flow setting up in its wake
as a strong ridge amplifies off the west coast. A quick moving
shortwave trough is still anticipated to ride the ridge axis and
drop right into the Intermountain West during the Wednesday
night/Thursday timeframe. The ridge then looks to migrate eastward
during the latter half of the week, drying things out a bit for
us here in eastern Utah and western Colorado.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1020 PM MST Fri Jan 18 2019

Aviation conditions will continue to improve overnight at sites
still seeing lingering low clouds. ASE, EGE, HDN and TEX all
should clear out over the next few hours. VFR conditions will
prevail throughout the entire day on Saturday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Storm Warning until midnight MST tonight for COZ009-013-
     018.

     Winter Weather Advisory until midnight MST tonight for COZ010.

UT...None.
&&

$$

UPDATE...MAC
SHORT TERM...MMS
LONG TERM...MMS
AVIATION...MAC



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