Area Forecast Discussion
Issued by NWS Grand Junction, CO

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450
FXUS65 KGJT 172052
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
152 PM MST Sun Dec 17 2017

.SHORT TERM...(Tonight through Monday night)
Issued at 152 PM MST Sun Dec 17 2017

Skies have cleared up nicely across the area with the departure of
the weak shortwave trough, though some lower clouds will linger
across northwest Colorado through the afternoon. The absence of
cloud cover going into the evening hours will enhance radiational
cooling and result in another chilly night. Synoptically speaking,
the closed low will remain situated over northern Mexico while the
upper level flow transitions from northwesterly to westerly across
our forecast area on Monday. As a result, we can expect the dry
and mild weather to continue with just some passing high clouds
here and there.

.LONG TERM...(Tuesday through Sunday)
Issued at 152 PM MST Sun Dec 17 2017

Zonal flow aloft will persist on Tuesday and into Wednesday with
temperatures moderating across the region. Our main weather maker
through the long term period, the strong and impressively cold
closed Pacific low, will begin to elongate over the western CONUS
by Wednesday afternoon. The southwesterly wind gradient will
tighten in response as the storm approaches Utah which will result
in breezy conditions throughout the day, though increased cloud
cover will inhibit some of the stronger gusts from mixing down to
the surface.

Good model consistency persists with the onset of precipitation
set to arrive Wednesday evening ahead of a strong cold front. By
daybreak Thursday scattered to numerous showers will have
developed as the front treks across the region. The influx of cold
air with the front will allow 700mb temperatures to plummet
considerably and snow levels to drop to valley floors area-wide.
As the previous forecaster mentioned, model guidance projects the
cold front to be through northeast Utah/northwest Colorado by
sunrise, near the I-70 corridor around noon, and pushing through
the San Juans by sunset Thursday. Snowfall totals will be hashed
out over the next few shifts but the structure of the closed low
looks promising to produce at least advisory level criteria in
several mountain areas and maybe even light accumulations in some
of the lower valleys.

The closed low is projected to transition to an open wave
Thursday night which will allow showers to diminish from west to
east as the trough lifts into the Plains. Some orographic showers
will continue throughout the day on Friday as the northern half of
our forecast area begins to be influenced by another disturbance
associated with a broad upper level trough that will be
dominating the entire western CONUS as we head into the weekend.
Still not a lot of consistency between the models in regards to
the impacts of this system but, for now, cool and unsettled
weather looks to be the norm in the days leading up to Christmas.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1008 AM MST Sun Dec 17 2017

VFR conditions will prevail at all TAF sites for the next 24
hours. Over the CO northwest plateau, at KCAG, KHDN, KSBS and
KEEO, low stratus associated with a dissipating front will keep
ceilings between 1500 and 3000 feet through about 21z then these
clouds will dissipate.

&&

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

$$

SHORT TERM...MMS
LONG TERM...MMS
AVIATION...CC



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