Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200941
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
341 AM MDT Mon Mar 20 2017

.SHORT TERM...(Today through Tuesday)
Issued at 315 AM MDT Mon Mar 20 2017

A weak shortwave trough will pass over the area late this
afternoon and evening. It is evident this morning on satellite
entering the western Great Basin. Most of the energy with this
feature will ride north of the forecast area, with a weak
troughline dragging through between 5 pm and midnight then
clearing the area to the east late tonight. The cloudiness with
this system will help hold temperatures down a degree or two and
showers and a slight chance for thunderstorms are expected over
the higher elevation, mainly north of a line from Montrose to
Monticello.

Winds will become gusty again this afternoon and early evening
causing heightened fire weather concerns.

Tuesday should be drier but southwest winds will increase as the
next trough approaches the west coast.

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

Tuesday night will remain dry. 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, with the
main trough passage Sunday afternoon. 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 12Z TAFS through 12Z Tuesday morning)
Issued at 315 AM MDT Mon Mar 20 2017

VFR conditions will continue at all TAF sites for the next 24
hours. Winds will be terrain driven until about 17z then,
become breezy from the southwest through 02Z/Tuesday. Also during
this period, isolated to scattered showers and thunderstorms will
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

Well above normal high temperatures and dry weather will continue
today. Relative humidities are again expected to drop into the 15
to 25 percent range this afternoon. The gustiest winds will occur
after 3 pm with wind gusts of 20-25 mph at lower elevations. 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...CC
LONG TERM...MAC/CC
AVIATION...CC
FIRE WEATHER...TGJT


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