Area Forecast Discussion
Issued by NWS Grand Junction, CO

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072
FXUS65 KGJT 191737
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1037 AM MST Fri Jan 19 2018

.SHORT TERM...(Today through Saturday)
Issued at 409 AM MST Fri Jan 19 2018

Southwest flow aloft will increase throughout today continuing the
warmer than normal high temperatures. A strong Pacific storm will
move into the western Great Basin this morning and into northwest
Utah late this afternoon. Its surface cold front will move across
the eastern Uinta mountains after about 4 pm this afternoon and
reach extreme northwest Colorado this evening.

Have issued a Winter Storm Watch starting at midnight tonight for
the Eastern Uintah Mountains. The cold front stalls over central
Utah tonight and Saturday morning so unsure how much snow will
fall over NE Utah until the front passes. The potential is there
for heavy snow after the front passes, and the total snow
accumulation will depend on when that occurs, and there is some of
uncertainty in that timing through Saturday morning.

Saturday afternoon it looks like the upper trough will start
moving more steadily east, which should push the cold front into
extreme western CO late Saturday afternoon. Valley rain and
mountains snowfall should begin west of a line connecting highway
550, Grand Junction and Maybell by sunset.

.LONG TERM...(Saturday night through Thursday)
Issued at 409 AM MST Fri Jan 19 2018

Have issued a Winter Storm Watch for the San Juan mountains for
late Saturday afternoon through Sunday morning. The warm phase of
the storm will be yielding to a strong cold front Saturday
evening as the main upper level low/trough nudges eastward out of
the Great Basin and across our forecast area. This will shift the
focus of the heavier precipitation from the south and southwest
facing slopes to the northwest and north facing slopes as the
front passes. Snow levels will be dropping to the valley floors
with widespread light accumulations anticipated. Model generated
snowfall for the lower valleys generally running in the 1 to 3
inch range, although locally higher amounts are expected.

Favored valley locations include the Northwest Plateau from
Dinosaur east through Craig and Hayden and over our higher ridges
across our southwest valleys. Reasoning differs for both locations
as the northern valleys will be seeing the colder air arrive a
little sooner with some expected overrunning of moisture above the
deepening cold pool. Southern valleys will be seeing a sliver
of drier air riding in aloft, helping to destabilize conditions
Saturday evening out ahead of the front. Convective element will
drive snow levels down and result in brief heavy precipitation
should this thing hold together. Higher ridges between Mesa Verde
National Park east to the Durango West area and over to the region
north of Bayfield have the potential to see enhanced precipitation
for a few hours Saturday evening just ahead of the front. Moisture
profiles stands back up (moisture levels improve again), after
midnight with areas of light snow expected to persist through
early Sunday morning.

As for the mountains, this is looking like a solid advisory level
storm for all of our mountains with generally 6 to 12 inches
anticipated, the potential for heavier snow exists over the
eastern Uintas and the San Juans. Still seeing some timing issues
between the models and specific humidities tally off rather
quickly as the low shifts east Saturday night. Duration of the
event will also limit potential for widespread heavy snowfall in
excess of a foot, so will be holding off on watches in other
mountains zones.

This system lifts will become a distant memory by Sunday evening.
Next wave arrives late Monday and Tuesday. Models have been
trending weaker with this system with scattered showers across our
northern and central mountain zones. Looks like a third in this
series of storms will be tracking into the region late in the
week. Models are not in great agreement with arrival of this
stronger system running between late Wednesday night (Canadian),
Thursday afternoon (GFS) or Thursday evening (EC). Confidence this
far out is marginal for now, but expect timing issues to improve
over the next few runs.

Expect a cooler week overall with temperatures falling to more
seasonal normals throughout the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1037 AM MST Fri Jan 19 2018

Mid and high level cloudiness will continue to stream overhead on
strong southwesterly flow ahead of the next system. Mountain wave
turbulence could be an issue overhead while down at the surface
lighter winds are not expected to be an issue most areas.
Tailwinds leading to into KASE this morning are forecast to
become more southerly through the day. CIGS will lower on Saturday
morning but the only impact at this time will be at KVEL where the
snow will developing after sunrise and MVFR conditions are
expected to develop.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Storm Watch from Saturday afternoon through Sunday
     afternoon for COZ018-019.

UT...Winter Storm Watch from late tonight through late Saturday night
     for UTZ023.

&&

$$

SHORT TERM...CC
LONG TERM...JDC
AVIATION...TGJT



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