Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200452
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
952 PM MST Sun Feb 19 2017

.UPDATE...
Issued at 602 PM MST Sun Feb 19 2017

The Winter Weather Advisory for the San Juan Mountains has been
allowed to expire. Please keep in mind that lingering snow showers
are anticipated through this evening with locally up to 2 inches
of additional snow fall possible for the San Juans. The Winter
Weather Advisory for the Central Colorado Mountains remains in
effect through 7 AM MST Monday morning.

&&

.SHORT TERM...(Tonight through Monday night)
Issued at 349 PM MST Sun Feb 19 2017

The closed low bringing the clouds, rain and snow continues to
open this afternoon and will become an open wave/trough by later
this evening. There is hardly any change to forecast thinking as
plenty of moisture remains in the atmosphere and continues to be
worked on by the trough as it moves through. Widespread
precipitation is being reported across the CWA with snow at higher
elevations and rain at lower elevations. Snow levels vary across
the area but 9,000 feet still looks good for the going advisories
which continue at this time. The NAM continues to show the trough
syncing up with another wave well to our north later tonight. When
this occurs, winds will become northwesterly and precipitation
will pick up especially over favored northwest facing slopes
ending by daybreak. Do have some concern that advisories for San
Juans may end too soon (6PM) this evening and may need to be
extended as latest guidance does keep some precip going through
tonight. However, HRRR and RAP not too enthusiastic about this
precip. Either way, next shift will need to keep an eye on precip
and where focus sets up. Also, a few lightning strikes were
reported in Cortez which makes sense as instability from the low
pressure aloft caused some low top thunderstorms. Included the
chance of storms for southern valleys through the rest of the
afternoon for the off-chance a few more pop-up.

The rest of the forecast area will see showery precipitation
through this evening and overnight with plenty of clouds hanging
around. These clouds will moderate temps somewhat keeping lows a
little bit warmer than yesterday. Expect some areas of patchy fog
to form overnight in those normally fog-prone areas, too, thanks
to increased moisture from today`s precipitation.

On Monday, clearing conditions will kick in as the trough shifts
well to our east. Partly cloudy skies are expected with partly to
mostly cloudy skies for the mountains. The jet stream then becomes
oriented from the southwest to northeast over the Intermountain
West. Little ripples of energy will work through the jet stream
bringing plenty of rain and snow to central and northern
California up through Nevada and into Idaho while we stay just to
the southeast of this precipitation. A few showers are not out of
the question, especially for the Uintahs and our far northern
zones, but with most support to our northwest, little
precipitation is expected. No big swings in temperature either so
similar highs and lows remain in the forecast.

.LONG TERM...(Tuesday through Saturday night)
Issued at 349 PM MST Sun Feb 19 2017

The jet stream starts dropping southward Monday night into Tuesday
as a trough starts digging down from the Gulf of Alaska. As the
jet starts dropping, some showers are possible over the highest
terrain though no appreciable accumulation is expected. These
showers will start forming Tuesday and persist through Wednesday.
Again, these look to be more nuisance showers than anything of
much consequence. As the base of the trough drops down to central
California, an area of deformation looks to set up over central
Nevada through Utah and into our northern valleys. This
deformation looks to persist Wednesday afternoon through Thursday
morning when the trough finally moves through during the day. Once
it moves through, light precipitation will persist into Friday. As
this is occurring, a deep area of low pressure will be dropping
down the West Coast. As it does so, the low will eject a short
wave that will bring a reinforcing shot of rain and snow for the
central and northern mountains late Friday night into Saturday
morning. Like the last disturbance, once the short wave moves on
showery precip looks to continue through Saturday.

So Monday through Wednesday look to be the nicest days this week
with more widespread precipitation moving in Thursday and beyond.
Temperatures will run warm through the same timeframe and then
dropping to at or below normal to end out the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 945 PM MST Sun Feb 19 2017

The back edge of the shower activity is currently running along a
line from KHDN to KCEZ at this time. Activity will quickly move
southeast and east of the forecast area over the next few hours
with areas of MVFR and Local IFR conditions diminishing through
08z. Once the system moves east coverage will become scattered
with some local areas of fog in low valley locations through 15Z.
VFR is anticipated at all terminals on Monday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until 7 AM MST Monday for COZ009-010-012-
     013.

UT...None.
&&

$$

UPDATE...Larry
SHORT TERM...TGR
LONG TERM...TGR
AVIATION...MPM



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