Area Forecast Discussion
Issued by NWS Grand Junction, CO

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184
FXUS65 KGJT 200540
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1140 PM MDT Sun Mar 19 2017

.SHORT TERM...(Tonight through Monday night)
Issued at 300 PM MDT Sun Mar 19 2017

The upper level ridge axis has continued to shift east of the
Rockies this Sunday afternoon. Faster southwesterly flow aloft
will gradually move eastward into the region through the early
portion of this week. Valley locations have been warming quite
efficiently over the past few days with good mixing up to 600mb
or so apparent in regional model and observed soundings. Despite
thin cirrus aloft, afternoon highs this afternoon and on Monday
should run near the top end of available guidance...in this case
the warmer MET. The record high for Grand Junction on Monday is
81...and we should be within a degree or two of that mark.

Monday`s forecast could be complicated by any precipitation that
manages to fall as a weak shortwave passes through during the
afternoon hours. 12z forecast guidance does hint at a very slight
amount of convective potential during the late afternoon hours.
Most of the shower activity will likely be limited to the higher
terrain from central Colorado northward, however associated cloud
cover from diurnally driven precipitation could knock
temperatures down a few degrees. Valley locations from the I-70
corridor on southward will remain mostly dry.

.LONG TERM...(Tuesday through Sunday)
Issued at 300 PM MDT Sun Mar 19 2017

Any precipitation that does fall on Monday evening should rapidly
diminish after midnight as the shortwave quickly exits eastward
into the high plains. Weak ridging will return to eastern Utah and
western Colorado on Tuesday with a mostly dry day forecast. Guidance
has been fairly consistent showing a few showers developing over
the Colorado high country after the ridge axis passes the region
around midnight Wednesday. Southwesterly flow will strengthen
aloft through the day as our next major storm system moves ashore
along the California coastline. All guidance is slower with this
storm system in today`s runs, especially the GFS which keeps the
500mb trough axis offshore until after 6pm Wednesday. The net
effect for significant weather in our region for this forecast
package has been to lower POP chances a bit during the early
afternoon hours Wednesday. In fact, some areas especially in
southwestern Colorado may not see any precipitation at all until
after sunset Wednesday. Due to this shift in model timing,
confidence remains only moderate regarding precipitation onset at
this time. Higher confidence is found in the wind forecast for
Wednesday afternoon and Thursday. A 100-knot jet streak will shift
over the central Rockies by late afternoon Wednesday and into
Thursday morning. Southwesterly winds could become gusty during
this time, with 30-40 mph possible in some of the higher terrain.

Early in the morning on Thursday, a cold front associated with
the large trough over the western CONUS will march eastward
through eastern Utah and western Colorado. Some model differences
remain regarding the timing of this front, with the faster ECMWF
and Canadian moving the front through the Grand Valley prior to
6am Monday. The GFS is more sluggish, with the front about 6
hours slower for now. Regardless of the timing, much cooler air
will filter in behind the front with high temperatures about 15 to
20 degrees cooler on Thursday. There will be a decent amount of
precipitation along and behind this front as well, with guidance
showing around a quarter to a half of an inch of rainfall in the
valleys, and up to an inch or so of liquid for the mountains.
700mb temperatures will fall into the -3 to -5 range behind the
front, resulting in snowfall for the mountains perhaps as low 7500
feet or so. Precipitation will end from west to east on Friday
morning, with a few snow showers lingering in the mountains on
Friday afternoon.

Beyond the mid to late-week storm, guidance remains consistent
showing ridging and dry weather early on Saturday. Models then
diverge on Saturday afternoon with the ECMWF showing showers area-
wide as a new system drops in from the northwest. The GFS keeps
this system to our west until after midnight on Sunday. For what
its worth, the trend has been for systems to end up drier than
modeled at this range lately. Time will tell if that will be the
case with next weekend`s event as well.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1140 PM MDT Sun Mar 19 2017

VFR conditions with CIGS above ILS breakpoints will continue at
all TAF sites across eastern Utah and western Colorado through
the next 24 hours. Winds will be terrain driven, becoming breezy
from the southwest after 18Z and continuing through 02Z/Tuesday.
Also during this period, isolated to scattered showers and
thunderstorms are expected to develop over higher terrain. Shower
activity is not expected to impact TAF sites directly, however
outflow winds associated with high based cells could produce
strong and unpredictable outflow winds during the afternoon and
early evening.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Sun Mar 19 2017

Near-record high temperatures and dry weather will continue into
Monday. Relative humidities are again expected to drop into the
15 to 25 percent range Sunday and Monday afternoon. Mixing will be
greatest during the mid and late afternoon, resulting in some
wind gusts over 20 mph. The gusty winds combined with warm
temperatures, low humidity and still dormant or dry vegetation
will require a heightened fire weather awareness. Check the latest
forecast before attempting any burning through Monday as
conditions can change rapidly. The potential for near critical
fire weather conditions will be greatest for elevations below
8000 feet.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...MAC
LONG TERM...MAC
AVIATION...NL
FIRE WEATHER...TGJT



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