Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 281149
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
549 AM MDT Fri Apr 28 2017

.SHORT TERM...(Today through Saturday)
Issued at 415 AM MDT Fri Apr 28 2017

A broad trough of low pressure formed over the northern and
central Rockies over the past 24 hours. A closed low was in the
process of forming along the border of northwest CO and WY.
Meanwhile, the Polar Jet was sweeping eastward south of Colorado`s
southern border. Residual moisture, instability and weak,
unfocused lift continued to bring some scattered light showers to
the area with snow reaching valley floors in the north.

The southward flowing Polar Jet situated on the western edge of
the trough system is expected to impel the low center southward
across western Colorado during the day. Having the cold core of
the system directly overhead will further steepen lapse rates
resulting in increased convective showers and a few thunderstorms
this afternoon. Meanwhile, classic Carlson model extratropical
cyclone precipitation pattern sets up favoring showers along the
border areas of northeast UT and Northwest CO. Model snow output
not all that impressive so will not be issuing any snow related
highlights with this package.

The storm system continues to shift south tonight with the low
center settling over west-central NM by 12Z Saturday. Warming
aloft will cause lapse rates to ease causing showers to decrease
in both areal coverage and intensity. However, the moisture
wrapped system will continue to generate areas of precipitation
over the region overnight, with the system`s influence shifting
south with the low center late tonight. Overnight lows are
expected to continue to be problematic for west-central Colorado`s
lower valleys as 7H temperatures over the region remain in the -8
to -12 deg C range. Lighter winds coupled with periods of clearing
could bring another round of freezing temperatures to Uncompahgre
River and Grand Valleys. Therefore, have hoisted another Freeze
Watch tonight.

The low finally shifts east over east-central NM as the jet
discussed previously enters, then pushes through the base of the
trough. However, moisture wrapping around the low center is
expected to continue to bring scattered snow showers to the
central and southern Colorado mountains favoring peaks along the
Continental Divide. Outside of these areas, drying and partial
sunshine will allow temperatures to moderate, though afternoon
highs are still expected to be well below normal for this time of
year.

.LONG TERM...(Saturday night through Thursday)
Issued at 415 AM MDT Fri Apr 28 2017

The storm will drop farther over the southern Plains on Saturday
night, shifting shower activity to the San Juans and along the
Divide. Northwesterly flow will set up behind the departing system
and finally allow the clouds to part as we go into the second
half of the weekend and into early next week. An exception to this
will be up north where lingering moisture and instability will
keep orographic showers in the forecast through as late as
midweek.

Wednesday and beyond, high pressure will build in from the west
bringing a return to drier conditions and also near seasonal
temperatures. Extended models differ on strength and duration of
this ridge with the ECMWF being much more optimistic than the GFS
which quickly shifts the ridge east by the end of next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 549 AM MDT Fri Apr 28 2017

Scattered to numerous showers, mainly over the mountains will
continue today as a storm system slides slowly southward over the
area. There is some potential for showers at area TAF sites,
though chances are relatively low. More likely are periods when
CIGS fall below ILS breakpoints at KRIL, KEGE, and KASE.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Freeze Watch from late tonight through Saturday morning for
     COZ006-011.

     Freeze Warning until 9 AM MDT this morning for COZ006-011.

UT...None.

&&

$$

SHORT TERM...NL
LONG TERM...MMS
AVIATION...NL



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