Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 181023
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
423 AM MDT WED MAY 18 2016

.SHORT TERM...(Today through Thursday)
Issued at 423 AM MDT Wed May 18 2016

The storm center which has continued to bring unsettled weather to
the area moved to south-central Arizona overnight as models had
predicted. Latest radar and surface observations indicated that
showers had diminished over the area overnight, though it`s likely
that a few showers went undetected below the radar beam in the San
Juan, La Sal, and Abajo mountains.

The low begins to fill, evolving into an open wave as it shifts to
northwest New Mexico later today. Divergence aloft favors the
south and expect the bulk of the activity there as depicted by
models. Daytime warming will destabilize the airmass as in past
days, so expect thunderstorms to redevelop during the afternoon.
Though models appeared to be on track with this system they
continued to over forecast snow in the mountains with both GFS20
and NAM12 generating upwards of 18 inches of new snow by Thursday
evening. This hasn`t verified in earlier forecasts and am left to
conclude that convective influence is overdone while temperatures
haven`t been properly taken into account. Suspect 4 to 8 inches
with locally higher amounts are possible above 11,000 feet, but
impacts to roadways over the passes will be minimal. Consequently,
will not be issuing highlights for snow with this issuance.

Latest guidance showed showers largely diminishing overnight
tonight, then redeveloping Thursday afternoon. Showers and
thunderstorms will be fueled by residual moisture and instability
with little dynamic input.

Temperatures are expected to rise a few degrees in response to
weak mid-level warming today. However, temperatures will rise more
noticeably Thursday as 7h temperatures rise from near 4 degrees
celsius to around 8 degrees. As a result, Thursday`s highs should
return to normal, or a few degrees above seasonal norms.
Meanwhile, persistence best describes tonight`s forecast lows
which is right around normal for this time of year.

.LONG TERM...(Thursday night through Tuesday)
Issued at 423 AM MDT Wed May 18 2016

A ridge will build over the region Thursday night into Friday but
residual moisture expected to be sufficient to fuel afternoon and
evening showers and thunderstorms.

Meanwhile, a deep area of low pressure will drop down into the
Pacific northwest before becoming quasi-stationary. Models
continued to struggle with the positioning of the low so
confidence reduced. One thing that has remained consistent is
that this low will tighten the pressure gradient considerably
resulting in a breezy southwest winds across much of the Great
Basin. Eastern Utah and western Colorado can expect winds to pick
up Friday afternoon and to redevelop each afternoon through
Sunday. The best upper level support for this system looks to
stay to our north so expect some showers at times through Tuesday
but nothing too widespread.

Temperatures will rise to near, or a little above normal Friday
and Saturday before dropping a few degrees below seasonal norms
Sunday and into early next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 423 AM MDT Wed May 18 2016

Low pressure to the west continues to pump moisture on southerly
winds into eastern Utah and western Colorado. The influx of
moisture will stay focused over southern portions of CO/UT over
the next 24 hours as the low drops into Arizona then lifts into
southeast Colorado. Therefore, showers and thunderstorms will
continue across the region and could impact flight operation over
a majority of the forecast terminals. MVFR/IFR ceilings and
visibility from passing showers will be a temporary threat along
with the threat of lightning and small hail during the afternoon.
Widespread terrain obscuration will also continue into the
evening. As the storm finally departs, drier air will move over
the region bringing an end to most shower activity after midnight.

&&

.HYDROLOGY...
Issued at 423 AM MDT Wed May 18 2016

Wet weather through midweek combined with rising temperatures
toward the end of the week are expected to drive river levels
gradually higher. In fact, over the next few weeks increased flows
will primarily be the result of melting snowpack. This will cause
rivers and streams to swell causing some streams to reach
bankfull. Use caution in and near swift currents.

&&

.GJT Watches/Warnings/Advisories...

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

&&

$$

SHORT TERM...NL
LONG TERM...NL/TGR
AVIATION...NL/15
HYDROLOGY...TGJT



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