Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 192026
AFDGJT

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

.UPDATE...
Issued at 120 PM MST Mon Feb 19 2018

Snow has started tapering off across northeast Utah this afternoon
with the strong cold front starting to push into the I-70
corridor. Have issued Winter Weather Advisories for the stretch
from Debeque east to Vail as we expect rain to quickly flip over
to snow just in time for the evening commute. This will result in
significant impacts to travel as conditions ice up. Still picking
up lightning throughout the area with graupel showers being
reported by some spotters. The fun continues for several more
hours as we see this potent winter storm work through the area.

UPDATE Issued at 1042 AM MST Mon Feb 19 2018

Impressive snowfall rates coming in from spotters in and around
Vernal, Utah this morning with up to 2 inches per hour being
reported. Bands of heavier snow continue to work north across the
Basin and have upgraded the winter weather advisory to a winter
storm warning. New snowfall amounts could total up to 6 inches
with these bands and travel will remain difficult through this
afternoon. Very strong winds also mixing down with gusts to 101
mph over the San Juans at the remote Eagle sensor with widespread
gusts into the 40-50 mph range coming in across the valleys.

UPDATE Issued at 930 AM MST Mon Feb 19 2018

Strong southwest flow remains in place this morning with strong
surface cold front sitting north of the Bookcliffs (or basically
I-70) this morning. Heavy snow is falling across northeast Utah
with reports of 8+ inches already near Flaming Gorge Reservoir.
Have upgraded the Eastern Uinta Mountains in northeast Utah to a
winter storm warning and have added the Uintah Basin into a Winter
Weather advisory for another 2 to 4 inches of snow today and
tonight. Storm remains dynamic and plenty of adjustments will need
to be made as we deal with these convective bands. Some lightning
also expected today with a few CG strikes already observed near
Rangely. Expect very heavy snowfall under these bands with some
thundersnow possible to make things even more interesting. Of
course the banding also means one spot gets hammered and 2 to 3
miles away there will be no joy. Stay safe if traveling with winds
gusting to 60 mph possible and sudden "near whiteout" conditions
possible under the stronger bands of snow.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 331 AM MST Mon Feb 19 2018

Can`t really say this storm is starting off with a bang...unless
it is your screen door getting torn of the hinges because of the
wind. GOES16 water vapor products showed the narrow fire hose of
Pacific moisture spreading across the 4 Corners earlier when the
San Juans started to pick up some snow showers. Now this imagery
is showing the dry conveyor belt rounding the trough and extending
from SoCal into South with convection blossoming on the nose of
this over western Colorado. Not only will this feature associated
with the jet core help instability through the day...models
continue to indicate a fairly distance dry slot from SE.Utah into
NW.Colorado. Showers likely to pop in this area but more concerned
with the instability helping to tap into the stronger winds aloft
and decided to expand our wind advisory. The cold (arctic) front
has dropped into NE.Utah far NW.Colorado where it is producing
light snow at Craig this morning. With the strong southerly flow
in place model want to stall or even retreat this front back
northward today before it rushes southward overnight as the upper
trough approaches. This feature will be important to watch as this
should be where heavier precipitation will focus. The southerly
flow will be good for orographics but instability will win again
today. Models are favoring the E.San Juans for capturing the best
precipitation the next 24 hours though any south facing higher
slope could do well. The streaky convective precipitation pattern
expected today will be hard to pinpoint other areas that will do
well. Therefore no confidence in changing winter highlights just
yet but can`t help but feel this storm will be under performing
earlier expectations. Convection has proven me wrong many times
though. Moisture is all but erased by late tonight as the trough
moves overhead and we are left with orographics...instability and
cold advection. Still a good combo for making some decent snow but
trends have really dropped off for widespread precipitation
lasting through tomorrow. Many spots may have seen their high
early this morning as we remain mild with the winds. Cooler air
moving in this afternoon should hold things fairly steady. Much
colder air filters in tonight and highs tomorrow will feel more
like winter.

.LONG TERM...(Tuesday night through Sunday)
Issued at 331 AM MST Mon Feb 19 2018

The large trough over the western US will leave temperatures about
10 degrees below normal for this time of year throughout the week
after the strong cold front comes through tomorrow. These cooler
temperatures will be more noticeable during the nighttime hours,
as bright sunshine will accompany this cooler airmass until the
latter part of the week. The first post- cold front disturbance is
still progged late Wednesday night in southwesterly flow bringing
moisture in WAA to southwest facing slopes through Thursday.
Precipitable water values don`t get much higher than two tenths of
an inch in this southwest flow, so this is not anticipated to be
a big precipitation maker. This system Wednesday night through
Thursday is a precursor to a much larger trough moving into the
Great Basin late next week in the Thursday/Friday timeframe. This
late week trough is on track to move through the UT/CO border late
Friday through Saturday - similar timing as previous forecast
runs.

The progressive pattern anticipated over the next week looks to
continue in the longer term, with the 8-14 day outlook indicating
odds of slightly wetter than usual conditions across the Great
Basin into early March.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1003 AM MST Mon Feb 19 2018

A passing cold front producing low clouds, variable precipitation,
gusty winds will all combine to create variable flight conditions.
The precipitation will be very showery which means VFR conditions
could quickly become LIFR as snow showers pass by or settle in.
Winds will be impacting not only landing and takeoff operations
but mountain turbulence should again be present. Expect widespread
terrain obscuration as well. Conditions not likely to improve
until later in the day on Tuesday as this storm winds down.

&&

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

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

     Wind Advisory until 5 PM MST this afternoon for COZ006-007-011-
     020-021.

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

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

     Wind Advisory until 5 PM MST this afternoon for UTZ022-027>029.

&&

$$

UPDATE...JDC
SHORT TERM...15
LONG TERM...JAM
AVIATION...CC



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