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000
FXUS65 KGJT 270541
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1141 PM MDT MON SEP 26 2016

.SHORT TERM...(Tonight through Tuesday night)
Issued at 252 PM MDT Mon Sep 26 2016

Current weather pattern shows a rex block with high pressure over
the Great Basin and a closed low pressure system spinning over the
Baja Peninsula near the old Mexico-Arizona border. Our CWA is
largely being influenced by this high pressure area, providing
sunny skies and dry conditions with weak winds aloft. Temperatures
are continuing the warming trend seen the last two days, nudging
towards normal levels today and above normal Tuesday. Some high
level clouds may seep into the southern reaches of our CWA late
Tuesday as the low over the Baja gets pushed northward into
Arizona, but overall dry conditions will prevail.

.LONG TERM...(Wednesday through Monday)
Issued at 252 PM MDT Mon Sep 26 2016

The rex block over the region will break down Wednesday as a low
pressure system over the Gulf of Alaska drops down the British
Columbia coastline and settles into the Pacific Northwest by
Thursday. This will cause the high pressure over Texas to amplify
over the Great Plains and in turn draw up sub-tropical moisture in
southerly flow. Mid and high level clouds will increase throughout
the day on Wednesday, as the low pressure system that was located
over the Old Mexico-Arizona border elongates and becomes absorbed
into the southerly flow. In addition to sub-tropical moisture, it
appears that some moisture from the remnants of Tropical Storm
Roslyn, currently located southwest of the Baja coast over the
Pacific, gets entrained into the southerly flow. Both the GFS and
ECMWF are in better agreement with this scenario, whereas the NAM
takes T.S. Roslyn out to sea. Leaning more towards the GFS and EC
solution given the NAM`s poor track record so far this season and
since the NAM appears to be the outlier. Precipitable Water (PW)
values increase to 0.6 inches on Wednesday with 0.75 to 1 inch on
Thursday and Friday (the inch values are over the Four Corners
region). Specific humidity values also increase with values in the
range of 6 to 8 g/kg. This low becomes an open wave and ejects
across the area Thursday into Friday, with moisture remnants of
T.S. Roslyn moving over the area on Friday. There are timing
differences in the models but overall trends seem to indicate the
chance for showers and storms increasing on Thursday into Friday
for more active weather. This system is fairly mild with snow
levels expected to be around 12,500 feet. The latest model trends
seem to be coming in slower with timing of the moisture and
precipitation chances so will be something to keep an eye on for
future model runs as timing may change.

Saturday looks drier but enough moisture still remains for
scattered storms to develop in the afternoon over higher terrain
in southwest flow. By Sunday, the Pacific Northwest trough
progresses inland across the northern Rockies, with precipitation
chances increasing Sunday afternoon into the evening. A cold front
associated with this system will also move through the region
Sunday evening, with H7 temperatures dropping down to the 4C to
7C range Sunday afternoon and down to 1C across the north by
Sunday night. This will in turn lower snow levels on Sunday, with
snow levels around 11,000 feet Sunday afternoon, dropping down to
9,000 feet by Sunday night as the cold front moves through. This
could have some impacts for the mountains and passes, as the
heaviest precip is expected along the cold front. However, this
is still about a week out, so models may change but will be
something to keep in mind for future shifts.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1131 PM MDT Mon Sep 26 2016

VFR pattern remains in place over terminal locations through
Tuesday night. There will be an increase high clouds after 18z
Tuesday with some cumulus cloud development expected over the San
Juan Mountains in southwest Colorado. The development of these
clouds may enhance wind gusts over these mountains through late
afternoon with speeds up to 20 mph possible. Otherwise, winds will
remain light and generally terrain driven. There is a less than 10
percent chance for showers developing over the San Juan Mountains
between 21z and 03z Tuesday evening.

&&

.GJT Watches/Warnings/Advisories...
CO...None.
UT...None.
&&

$$

SHORT TERM...MDA
LONG TERM...MDA
AVIATION...JDC