Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200223
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
723 PM MST Mon Feb 19 2018

.UPDATE...
Issued at 722 PM MST Mon Feb 19 2018

Decided to cancel the Wind Advisories that were left as winds have
decreased to well below advisory levels with the setting sun. The
higher mountain passes may see some breezy to windy conditions
continuing with blowing snow this evening, but wind advisory
thresholds are no longer expected to be met. Also, clearing is
becoming evident across southeast Utah and portions of western
Colorado south of I-70, with thick cloud cover in snow showers
continuing across the mountains of western Colorado as well as
all areas north and along I-70. Some low visibilities are being
seen already in fog due to recent precipitation. Dense fog could
become a concern for areas that received significant snowfall,
like Vernal, the Highway 40 corridor from Craig to Steamboat, or
portions of the Gunnison Basin as skies begin to clear later
tonight as the storm moves out of the region. Confidence is not
high enough to issue any Dense Fog Advisories, but this will be
something we continue to monitor throughout the evening.

UPDATE Issued at 516 PM MST Mon Feb 19 2018

A look at webcams and observations across the region indicate
highlites remain on track. Took a look at areas not under any
winter highlites and decided to issue a Winter Weather Advisory
for the Gunnison Basin (COZ014) due to near white out conditions
over the western end of the zone over Cerro Summit and Blue Mesa
Summit where heavy snow and blowing snow are occurring and the
roads remain snow-packed. Convective showers are rolling through
this area so expect bursts of heavier snow at times, even in
Gunnison where the current temperature is 28 in moderate snow and
freezing fog. This is all under a southwest flow, with the flow
expected to shift to a more favorable west flow this evening. The
southern Colorado valleys were another area of concern with
periods of light to moderate snow occurring and even some
lightning activity between Durango and Bayfield. However, webcams
indicate roads remain wet with little accumulation on the grassy
surfaces until you get into the higher elevations near Hesperus
which looks snowpacked and is technically located in COZ019 (the
SW San Juans) and they are already under a Winter Storm Warning.
So, for now, will hold off on issuing any highlites for the
southern valleys as only expecting a few inches at best here and
roads do not appear impacted at the moment. Plus convection is
expected to wind down after sunset this evening with most snow in
the valleys coming to an end after midnight with snow continuing
in the mountains through Tuesday morning, according to the 3km
NAMNest model which seems to handle the convective element fairly
well.

&&

.SHORT TERM...(Tonight through Tuesday night)
Issued at 341 PM MST Mon Feb 19 2018

Another one of those exciting weather days across eastern Utah and
and western Colorado as a strong upper level system and its
associated cold front sweep across the region. Gusty southwest
winds will continue to plague the southern half of the forecast
areas through this evening, basically from Interstate 70 south to
the New Mexico state line. Had gusts clock in over 100 mph over
the higher peaks with 50 to 60 mph gusts elsewhere. Have adjusted
the wind highlights a bit for this evening, dropping them from the
I-70 corridor and shift them south into the southwest valleys
including Pagosa Springs and Durango. Latest LAV guidance
bringing peak gusts to near 50 mph for a few hours this evening.
Add in the bonus convective showers and potential remains high to
see these type of winds into the evening hours. Expect to winds to
diminish behind the strong cold front that is making the rare
push south during the daylight hours with the front likely
accelerating a bit as the sun sets.

Focus then shifts to the snow portion of this strong winter storm.
Latest HiRez models keeping these bands active through late
tonight as we see the upper level jet move in overhead with the
approaching H5 trough axis squeezing in behind later tonight. The
emphasis of our snowfall will also be shifting from the southwest
facing slopes to the west and northwest facing slopes overnight.
This places our central mountains in better position to pick up
heavier snowfall overnight and nudge numbers up closer to a foot
in the Aspen and Snowmass areas with amounts tapering off as we
work northeast toward Vail. Still solid advisory amounts which we
already have in place. Namnest is also showing some decent bands
aligning along the I-70 corridor and advisory were issued for
these areas earlier this afternoon for up to 6 inches of valley
snow.

The northern zones were enjoying some overrunning enhanced
snowfall as the warmer air aloft rode over the top of the
deepening cold pool north of the Bookcliffs. Earlier banding also
brought heavy snow into the Vernal and Flaming Gorge areas with
the band aligned roughly along the Green River. GOES-East picked
that up nicely in a few our our RGB curves. Expect the snow across
the north to become more stratiform as the evening progresses with
snow persisting through the early morning hours before drier
conditions push in from the north.

Pushing back to the south, the strong front will continue to drive
southward this evening, reaching our southernmost zones by
midnight or shortly thereafter. Widespread snow over the San Juans
will persist with southwest slopes losing out once the front
passes, which is good news for the northwest facing slopes.
Overall amounts should still approach a foot plus over most of the
San Juans with higher amounts up above the 12k mark. Looked at the
southern valleys fairly closely for potential winter highlight
level snowfall. Checked model soundings, meteograms and time-
heights across the southern valleys supports amounts in the 1-3
inch range with possibly a bit more along the mid-slopes. So will
stick with the wind products for now and have the evening shift
keep close tabs on these areas.

Temperatures will be down a good 10 to 15 degrees in most
locations on Tuesday with snow showers persisting through the day.
Winds will be lighter as we recover from this wind, rain and snow
event. One last piece, convective potential has fell off
significantly this afternoon and have removed the thunder from the
forecast overnight.

.LONG TERM...(Wednesday through Monday)
Issued at 341 PM MST Mon Feb 19 2018

The next Pacific system will be carving our a long wave trough
over the Western U.S. Wednesday and Thursday with flow shifting
back around to the southwest. Models dragging a bit of moisture
northward in the San Juans and southern Valleys Wednesday night
and Thursday. GFS and NAM generating light to moderate QPF that is
focused over the San Juans and near Pagosa Springs. Have not dove
into this system hard core yet with emphasis today on the current
system. The quick takeaway here is that we should see another
round of snow across the southern zones going into the day on
Thursday.

We are still not done by any means as the long wave trough to our
west is expected to lift out and across the Great Basin later
Thursday and Friday. Strong southwest flow out ahead of it will
keep moisture lifting northward and would expect to see more wind
as we often do moving into the Spring months. WAA showers will
have the potential to bring moderate snowfall to the mountains
with rain/snow showers over the valleys through Friday. Colder air
arrives Friday night and Saturday, which is the period where
snowfall amounts should tick up, especially across the central
mountains and northwest San Juans. Pattern is somewhat repetitive
right now, which is a good thing as we enjoy one of the snowier
February`s in recent memory.

Spring-like roller coaster anticipate with temps with below normal
readings to start off, warming back to more normal levels by
Friday, then dropping off again over the weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 441 PM MST Mon Feb 19 2018

Ongoing winter storm causing mins at some airfields this eve in
heavy snow. Snow showers are winding down across NE Utah and parts
of NW Colorado, though VEL is likely to go down in FG tonight due
to their heavy snow earlier today. This trend will continue
southeastward throughout the evening. As flow becomes
northwesterly, expect conditions to get worse from SBS to ASE now
until about 06z. Low lying stratus will likely persist through the
early morning hours Tuesday bringing persistent mountain
obscurations through 15z Tuesday.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until 8 AM MST Tuesday for COZ001>005-
     007-008-010-014-017.

     Winter Storm Warning until 8 AM MST Tuesday for COZ009-012-013-
     018-019.

UT...Winter Weather Advisory until 8 AM MST Tuesday for UTZ025-028.

     Winter Storm Warning until 8 AM MST Tuesday for UTZ023-024.

&&

$$

UPDATE...MDA
SHORT TERM...JDC
LONG TERM...JDC
AVIATION...JAM



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