Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 191030

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
430 AM MDT Sat Aug 19 2017

.SHORT TERM...(Today through Sunday)
Issued at 430 AM MDT Sat Aug 19 2017

The weather pattern featured low pressure over southern California
and a broad area of high pressure extending from the southern
Plains west-northwestward across New Mexico to the western Great
Basin. A disorganized mass of clouds were caught up in the weak
deformation between these systems, loosely aligned east-west
across central Nevada and Utah.

Modest moisture levels combined with daytime heating are expected
to fuel isolated to scattered showers and thunderstorms over the
mountains from late morning into the evening. This activity will
be high based judging from evening soundings and Bufr forecast
soundings. Consequently, look for more wind than rain from today`s

The low over southern California erodes the high over the region
to some degree on Sunday. This causes the deformation to become
repositioned over southwest Colorado. According to GFS and NAM
this substantially increases shower and thunderstorm activity over
the San Juan Mountains. EC was less insistent, but not entirely
inconsistent. In any event, appears the region is in store for an
uptick in moist convection Sunday afternoon with storms
transitioning from high based to more efficient rain producers.

Temperatures will run a little bit above normal today with slight
cooling in store Sunday with the anticipated increase in showers
and thunderstorm activity.

.LONG TERM...(Sunday night through Friday)
Issued at 430 AM MDT Sat Aug 19 2017

The GFS remains consistent with initiating a change in conditions
by Sunday night as monsoon moisture increases from the south. A
slow moving old closed low will settle over southern California
and high pressure will consolidate over Texas. The flow between
these two systems will funnel moisture north into southern AZ and
NM. This flow will remain in place through much of the week. The
only change in the GFS to consider is that initially, Sunday
evening through Tuesday, most of the moisture barely clips the SW
portion of the CWA before bending to the east over SE CO, much as
the EC had been doing the last few days. Unfortunately, the
possibility is high for cloud cover to interfere with viewing the
solar eclipse Monday over much of western CO and eastern UT.

Moisture will continue slowly increasing through Tuesday with
incrementally higher precip chance each day, especially between
00z and 06z each evening. Wednesday, especially Wed. evening,
appears to bring the first big surge of monsoon moisture as the
southern CA low moves east and over the forecast area, drawing
substantial moisture with it. The low is projected to pass over
the area Thursday which should bring the greatest areal coverage
of precip. Slightly drier NW flow aloft is expected Friday.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 430 AM MDT Sat Aug 19 2017

Moderate moisture in a westerly flow aloft is expected to generate
isolated to low end scattered thunderstorms over the higher
terrain again this afternoon and evening. There is a slight chance
that thunderstorms could briefly impact KASE, KTEX and KGUC
bringing strong outflow winds to 45 MPH and light rain. However,
it`s unlikely this will cause CIGS to fall below ILS breakpoints
and VFR conditions should continue. The remaining TAF sites will
continue to experience VFR conditions over the next 24 hours.
Outflow gusts aside, winds are expected to be relatively light and
terrain driven.






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