Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 300956

Area Forecast Discussion
National Weather Service Grand Junction CO
356 AM MDT FRI SEP 30 2016

.SHORT TERM...(Today through Saturday)
Issued at 356 AM MDT Fri Sep 30 2016

Residual energy from T.S. Roslyn continued to push northeastward
across west-central Colorado early this morning, generating a
broad area of showers north and east of a Gunnison-Grand Junction-
30 miles west of Craig line. Moderate lapse rates have precluded
thunderstorm development and showers have been light.

Roslyn`s remnants will continue to produce showers over northern
Colorado through mid-morning. Then, a weaker disturbance moves
over southeast Utah during the latter part of the morning.
Meanwhile, mid-level drying working northeastward across Arizona
will allow surface heating on the flanks of this perturbation to
cause thunderstorms to fire over this area. The drier air
infiltrating the Four Corners region will limit precipitation
chances south of the Abajo and San Juan Mountains. In contrast,
deep moisture over the central portion of the forecast area will
fuel scattered to numerous showers and embedded thunderstorms into
the evening with reduced chances north. Localized heavy rain
remains a threat as the 00Z/Fri sounding at GJT held just over an
inch of precipitable water.

The influx of drier air will continue tonight which, when combined
with diurnal cooling and the development of a short-wave ridge,
will largely bring an end to showers through late Saturday
morning. A few light showers may persist over the central
mountains during this time frame. Residual moisture, diurnal
warming and diffluence aloft will result in scattered showers and
thunderstorms during the late morning and afternoon on Saturday,
mainly over the mountains.

High temperatures today will remain cool in response to cloudy and
cool conditions for most locations. The southernmost zones should
see some sunshine which is expected to raise temperatures 3 to 5
degrees with respect to Thursday. Mild overnight lows follow
tonight with highs near normal on Saturday.

.LONG TERM...(Saturday night through Thursday)
Issued at 356 AM MDT Fri Sep 30 2016

Over the weekend the upper flow turns to a drier SW. Temperatures
recover to near normal and mainly diurnal showers and
thunderstorms will favor the mountains. A colder and stronger West
Coast low develops along the OR-CA coast. Sunday, a strong vort
max digs down the west side of the trough progressing it into the
Great Basin on Monday. Models have good timing agreement but
differ with the strength and position of the passing low. The GFS
has all the energy tightly closed and passing through the southern
half of the forecast area. The EC is more elongated with much of
its energy stretched northward through Wyoming. Both solutions
have strong SW winds developing early Monday as the cold front
passes in the afternoon. These storms may be strong with
increasing instability and a veering and speed shear environment.

Monday night-Tuesday night, the upper flow veers to NW in strong
cold advection. The GFS has a -24 cold core grazing the north
Monday night then after a bit of a lull on Tuesday a second wrap-
around cold core passes Tuesday night. This could bring significant
snowfall to the mountains along the Continental Divide as far
south as the NW San Juans. The EC solution would limit snow
accumulations to NW Colorado. Elsewhere expect below normal
temperatures and freezing Tuesday night temperatures are possible
in the higher valleys. Wednesday, a drying and warming trend


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 356 AM MDT Fri Sep 30 2016

KTEX, KRIL, KEGE and KASE will have CIGS below ILS breakpoints
through roughly 16Z, possibly accompanied by showers at times.
Meanwhile, low clouds over central and north-central Colorado will
obscure mountains. Showers wane during the latter part of the
morning, but will then redevelop along with a few thunderstorms
over the higher terrain toward midday as temperatures rise. The
southern airports have little chance of being impacted by storms
as drier air moves overhead. Elsewhere, airports within roughly a
175 mile swath centered over the I-70 corridor have a good chance
for rain, heavy at times, from 18Z through 03Z/Saturday. Stronger
downpours will be capable of producing MVFR VSBY/CIGS and possibly
brief IFR conditions. North of the area previously delineated
chances for weather impacts at airports is less likely. Showers
and thunderstorms largely diminish in the evening. Partial
clearing occurs overnight but patchy fog is possible in some
central valleys.


.GJT Watches/Warnings/Advisories...




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