Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 201721
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1121 AM MDT Fri Apr 20 2018

.SHORT TERM...(Today through Saturday)
Issued at 258 AM MDT Fri Apr 20 2018

A deep closed 500 mb low centered over SW UT early this morning
will gradually move east and slowly weaken today through Saturday.
This storm will cover all of UT and CO as well as portions of WY,
AZ and NM for the next 36 to 48 hours. Uplift ahead of the low
center is obvious on IR satellite showing a classically divergence
pattern and cooling tops. As the low moves east cooling aloft will
provide more instability and allow a broader area of precipitation
to spread from west to east across the area. Snow levels that area
relatively high this morning will lower as well, allowing more
snow accumulation in the mountains. Much of the precipitation will
be associated with a TROWAL developing over the northern and
northwest quadrants of the storm and is already evident in
satellite imagery and theta-e fields.

A distinct dry slot will complicate the forecast a bit today as
precipitation over SE UT and central and SW CO will experience a
lull in clouds and precipitation during the day today, while
northern UT and CO continue beneath the TROWAL area, receiving
more steady precipitation and dense cloud cover.

By sunset this evening the upper low center should be east of the
Continental Divide with northeast through northwest flow aloft
over the area. The heaviest and most persistent precipitation
should be focused over the northern halves of western CO and
eastern UT beneath moisture wrapping around the low within the
TROWAL.

.LONG TERM...(Saturday night through Thursday)
Issued at 258 AM MDT Fri Apr 20 2018

Shower remnants from the Friday/Saturday storm will shift east of
the area early Saturday evening as a shallow ridge aloft forms
over the area. Despite the ridge, the GFS, and to a lesser extent,
the ECMWF and NAM, indicated instability showers and embedded
thunderstorms over the mountains of the Continental Divide Sunday
afternoon. This activity doesn`t appear very impactful given the
lack of dynamic forcing beneath the ridge, but some shower
activity could linger into the evening, though models are split
on this.

An open wave trough moves over the Intermountain North late Sunday
night and Monday with the bulk of the energy associated with this
system well to the north of the forecast area. However, daytime
warming combined with a weak influence from this system is
expected to bring another round of afternoon and evening
showers/thunderstorms Monday afternoon and evening. The system
will be east of the area on Tuesday, but isolated showers are
again possible along the Divide during the afternoon/evening. In
fact, models suggest unsettled/disorganized weather will develop
again on Wednesday and Thursday.

During this period temperatures will begin near normal on Saturday
before rising above seasonal norms and staying there during the
remainder of the weekend through the middle of the coming week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1117 AM MDT Fri Apr 20 2018

Plenty of low and midlevel clouds across the forecast area this
morning and expect the same this evening and overnight. MVFR has
been reported at KTEX, KHDN, and KEGE while KASE is in IFR at the
moment. These TAF sites along with KGUC and KRIL will likely drop
up and down between brief IFR, into MVFR and VFR as the system
moves through. ILS breakpoints will continue to be met, or will be
met, for KASE, KEGE, KRIL, KHDN, and KTEX. Conditions will start
improving towards 12Z and beyond as the wraparound moisture ends.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Storm Warning until 6 AM MDT Saturday for COZ010-012-018-
     019.

     Winter Weather Advisory until 6 AM MDT Saturday for COZ004-013.

UT...Winter Weather Advisory until 6 AM MDT Saturday for UTZ023.

&&

$$

SHORT TERM...CC
LONG TERM...NL
AVIATION...TGR



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