Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 281142
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
542 AM MDT Fri Jul 28 2017

.SHORT TERM...(Today through Saturday)
Issued at 422 AM MDT Fri Jul 28 2017

Showers and embedded thunderstorms were holding on over
Canyonlands National Park and the Abajo Mountains with another
area of light showers over the southwest San Juan Mountains early
this morning. The activity over east-central and Southeast Utah
appeared to be driven by low level convergence associated with a
surface low over the Grand Flat aided by jet level divergence
associated with a 60 KT jet streak over southern Wyoming.
Ostensibly, the divergence aloft also played a role in sustaining
shower activity over the San Juans as well, but it was less clear
if any lower level dynamic forcing was at work.

Models suggested some of this activity may persist through
daybreak so will hold onto lower end PoPs this morning. Trough
moving inland during the late morning and into the afternoon will
cause high pressure to recenter to the east heralding the
beginning of the next monsoonal surge. Precipitable Water values
over GJT had fallen to 0.70 inches last evening but were still
near an inch or higher over southeast Utah and southwest Colorado
according to model analyses. That moisture will begin to spread
northward during the day, but won`t reach northeast Utah and
northwest Colorado where PW levels will remain relatively low
limiting precipitation chances of precipitation over the lower
elevations. In contrast, deep moisture to the south will generate
scattered to numerous showers and thunderstorms during the
afternoon and evening, initiating over the higher terrain with
some storms moving over adjacent valleys. Light steering winds
will yield slow moving storms, so localized heavy rain a threat
again today. Quasi-stationary jet to the north mentioned
previously will continue to provide some dynamic forcing which
should keep some showers and thunderstorms going late into the
night. Potentially, a weak 5H low center could provide additional
lift late tonight so went with moderate PoPs for the southern,
and portions of the central mountains and adjacent valleys.

Forecast model discrepancies evident Saturday with the weak low
pressure disturbance embedded in the overall pattern. Models
showing the location of this disturbance in vastly different
locations; from just south of the Four Corners to centered over
the Divide and Front Range by afternoon. The San Juans and
Colorado Divide mountains ought to see some juicy thunderstorms
Saturday afternoon with this pattern no matter the solution, but
the actual location of this disturbance will effect where the
strongest storms set up.

Temperatures will be 2 to 4 degrees cooler across the southern and
central zones today in anticipation of increased clouds and
showers associated with northward propagating moisture. Northeast
Utah and northwest Colorado will see little change from
yesterday`s highs. Overnight lows aren`t expected to see much
change, but look for highs on Saturday to continue to trend
cooler.

.LONG TERM...(Saturday through Thursday)
Issued at 220 PM MDT Thu Jul 27 2017

High pressure propagates westward back over the Four Corners early
week through midweek indicating a potential downturn in the
moisture feed into eastern Utah and western Colorado. However,
higher terrain across all of eastern Utah and western Colorado
will see afternoon showers and thunderstorms through much of next
week with a general downturn in precipitation efficiency by
midweek.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 542 AM MDT Fri Jul 28 2017

Areas of showers will linger early this morning, though TAF sites
do not appear to be threatened before noon. An influx of moisture
across southeast Utah and southwest Colorado and portions of
central Colorado will fuel scattered to numerous showers and
thunderstorms with higher terrain favored. However, this activity
is likely to impact KTEX and could result in brief MVFR
visibility. Otherwise, despite activity over surrounding higher
terrain, TAF sites can expect VFR conditions through the next 24
hours.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

SHORT TERM...NL/JAM
LONG TERM...JAM
AVIATION...NL



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