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Area forecast discussion 
National Weather Service Grand Junction Colorado
301 am MDT sun Aug 28 2016

Short term...(today through monday)
issued at 243 am MDT sun Aug 28 2016

The radar mosaic this morning is clearly showing cyclonic rotation
around the closed low that looks to be over central Arizona. Both
the NAM and GFS initialized well and just about nailing this
location. A few showers and storms have popped up over Arizona at
this hour which is to be expected thanks to the lift supplied by
the low pressure itself. Models agree that this low will shift
eastward through the day straddling the New Mexico and Colorado
border as it does so. For today then, models continue to put
showers and storms over the usual areas: San Juans, Continental
Divide and bookcliffs. The forecast follows suit. Infrared satellite is
showing some cloud cover over the forecast area but not as much as
yesterday. If this remains the case, convection will get going
around noon unlike Saturday where stratified clouds really
hindered any significant convective development. Heavy rain and
gusty winds will be the main concerns.

By Monday, the low pressure will still be over northern New Mexico
but it will have shifted far enough to the east that our upper
level winds will also be northeasterly to easterly. When this
happens, afternoon convection usually starts to diminish as
moisture stops advecting into the area while favorable orographics
will stay over the Front Range. Even so, the location of the low
pressure will provide some lift so some showers and storms remain
possible. Interestingly, models are favoring San Juans, which
makes sense due to that low pressure, but they are also favoring
the central mountains and even the bookcliffs to a lesser extent.
Models are not showing any upper level support while qg forcing is
nonexistent though some midlevel instability remains and looks to be
enough for convection to get going.

Temperatures on both days will be right about where they should be
for this time of year.

Long term...(monday night through saturday)
issued at 243 PM MDT Sat Aug 27 2016

A low pressure trough will move inland over the West Coast
starting Monday night with the first piece of energy ejecting
through the intermountain west. This will cause the ridge of high
pressure to move slightly eastward late Tuesday, allowing for
moisture to increase from the southwest. A slight increase in
thunderstorm coverage is expected Tuesday, with the western
Colorado mountains being favored. The trough will move further
inland with the flow shifting more to a southwest to northeast
oriented pattern on Wednesday into Thursday. Precipitable water
values increase to 0.75 to an inch plus by Thursday with a
stronger shortwave moving through the flow. This trough is not as
amplified as model runs 24 hours ago depicted, so we end up seeing
a southwest flow instead of a more direct southerly tap which
would bring in more moisture. However, sufficient jet support with
our County Warning Area in the right entrance region as well as forcing associated
with the shortwave will lead to a more active day on Thursday with
more scattered to numerous shower and thunderstorm coverage.
Therefore, increased pops in coordination with neighboring
offices. A third impulse is seen tracking across on Saturday.
While details could vary on timing of these shortwaves, it looks
like a more active and unsettled pattern will be in place from the
middle to the end of next week.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 243 am MDT sun Aug 28 2016

A low pressure system centered over northern Arizona this early
morning will track south of The Four Corners by this evening. After
18z, scattered thunderstorms will form mainly over the Colorado
mountains with a 20 percent chance of -tsra at kgjt kril kmtj kdro
and a 40 percent chance at ktex kase kege. Impacts include MVFR
cigs, lightning, and outflow winds of 25 to 40 mph. Mountain tops
may be briefly obscured mainly near the southern Continental
Divide. VFR conditions prevail at eastern Utah taf sites kcny


Gjt watches/warnings/advisories...



Short term...tgr
long term...mda

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