Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 221850
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1150 AM MST Thu Feb 22 2018

.UPDATE...
Issued at 1147 AM MST Thu Feb 22 2018

The Winter Storm Warning for Pagosa Springs and the Winter Weather
Advisory for the southern San Juan Mountains have been expired as
of 10:45 MDT. While some light to moderate snow showers will continue
in the higher terrain, surface temperatures have warmed and
additional accumulations are unlikely through the day.

UPDATE Issued at 1028 AM MST Thu Feb 22 2018

Latest webcams, observations and spotter reports indicate snow has
pretty much ended in the Durango area and points eastward towards
Bayfield. Snowfall accumulations throughout this zone indicate 1
to 3 inches on average with a little less than 4 inches in
Bayfield and up to 6 inches to the east of Bayfield. Not expecting
much additional snowfall accumulation if any does fall, with
satellite showing improving trends to the southwest. So cancelled
the Winter Weather Advisory for COZ022 (Animas River Basin). As
far as the Pagosa Springs area, 6 inches was reported here with
snow continuing to fall, so will let the Winter Storm Warning
continue for COZ023. Will also let the Winter Weather Advisory for
the SW San Juans (COZ019) continue as 5 to 10 inches have already
fallen and snow is still occurring.

Rest of this afternoon looks convective with some of the near term
models showing a few bands setting up. At this time, looks like
an additional inch or two could fall in some areas. It`s hard to
pinpoint exactly where but some models indicate the Grand Valley
and Highway 50 corridor from Delta to Montrose could potentially
see some more light snowfall throughout the day where the bands
look to come off the Uncompahgre Plateau. This will be something
to monitor throughout the day.

Will begin to turn the focus towards the next storm set to move
into the area after midnight tonight and bring more snowfall to
all mountains and some valleys all day Friday into Saturday
morning. High confidence that winter weather highlites will be
needed for this storm. Just a matter of deciding which areas and
to what extent.

&&

.SHORT TERM...(Today through Friday)
Issued at 401 AM MST Thu Feb 22 2018

As models had predicted, a low pressure trough was moving eastward
across western Utah/Arizona early this morning. Ahead of the
trough a broad swath of snow had developed which extended from
southwest Colorado to KHDN in the north, primarily east of a K4V0
to KCNY to KCEZ line. Snotel sites in the southeastern San Juan
Mountains indicated the best accumulations, with estimated
accumulations of 3 to 6 inches or more.

The base of the trough will rotate through with a negative tilt
this morning. Jet divergence, mid-level lift and orographics
continued to favor the southwest San Juan Mountains according to
models. Understandably, models center the best accumulations over
the Pagosa Springs and the San Juan Mountains to the north
through noon. Snow will impact the central, and to a lesser
extend, northern Colorado Mountains and adjacent valleys as well,
but accumulations likely to remain below advisory criteria. During
the afternoon, dynamic forcing becomes less of a factor and
snowfall will become more showery in nature as the 5H cold pool
approaches yielding steep lapse rates.

Poorly organized snow shower activity is expected to continue
tonight and Friday as a second trough makes its way across the
Great Basin. As the system draws closer snow should begin to fill
in, becoming more widespread as the day progresses. This activity
may require additional highlights for Friday and beyond, but
confidence with respect impacts and timing not quite there yet.

Temperatures will remain cooler than normal today as clouds and
snow limit insolation across the region. Little change in readings
were indicated for tonight or Friday.

.LONG TERM...(Friday night through Wednesday)
Issued at 401 AM MST Thu Feb 22 2018

By Friday night, the base of the upper level trough will be over
eastern Utah while the surface reflection of said trough will be
over western Colorado. The heaviest precipitation will be riding
along and just ahead of the cold front with snowfall expected from
the northern mountains southwestward through the Grand Mesa and
down to the La Sal Mountains. Saturday morning, the front will
move moved to the Front Range with only a few orographic showers
to contend with over the Continental Divide. When all is said and
done, total snowfall amounts look to be in the advisory level
range (generally 6 to 12 inches for the mountains) for the higher
elevations of Colorado. The big question, as it has been most of
this season, will be if and where the heavier bands set up. Time
will tell and we`ll be monitoring as usual.

Saturday will bring `a bit` of a break but not much of one as
another piece of the polar front jet brings the next system from
the northwest. A few snowshowers will fall over the northern
mountains with more widespread snow beginning after midnight.
Models really favoring the mountains along the Continental Divide
for snowfall with most valleys staying mostly dry except those
close to mountain bases. This system looks to bring a quick shot
of snowfall with amounts hovering around 6 inches. This will
likely change as we get closer to the event but all in all,
amounts look to be on the lower side.

Monday and Tuesday will be quiet with variable cloudiness.
Temperatures will start to warm up thanks to southwesterly flow
advecting in warmer air. Wednesday onward, another system will be
on our doorstep but not much agreement between the GFS and EC. The
GFS brings a closed low down to the desert southwest and shifts it
eastward bringing us some light, isolated precipitation. The EC
brings a closed low across the Four Corners while also bringing
plenty of precip. With these model discrepancies, expect some
changes over the coming days. Can say this, let`s hope the EC
wins!

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1044 AM MST Thu Feb 22 2018

A challenging aviation forecast on Thursday afternoon with several
instances of convective snow bands producing highly variable
conditions from the Colorado border eastward. These bands have
been capable of dropping visibility to under a mile and lowering
ceiling heights to LIFR levels, however only for short periods of
time. Short term models indicate the best chances for brief spouts
of IFR and below will be at GJT, MTJ, RIL, ASE and HDN through the
afternoon hours. After sunset, generally lighter snowfall will
continue in the mountains with CIGs rising in valley terminals.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

UPDATE...MAC
SHORT TERM...NL
LONG TERM...TGR
AVIATION...MAC



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