Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 221704
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1104 AM MDT THU SEP 22 2016

.SHORT TERM...(Tonight through Friday night)
Issued at 213 AM MDT Thu Sep 22 2016

The current satellite water vapor image is showing a storm system
centered over the Oregon California border this morning with
plenty of moisture pushing through the Great Basin states ahead of
the storm system. Currently the IR satellite image is showing mid
to upper level clouds passing over Eastern Utah and Western
Colorado. Although no lightning has been observed over the past
few hours many of these clouds are probably producing some light
showers.

The 0000Z NAM12, GFS20 and ECMWF have initialized well with the
current synoptic weather pattern and slide the previously
mentioned storm system southeast into Nevada today, placing Utah
and Western Colorado in moist unstable flow. In fact the 0000Z
NAM12 is showing some hefty Cape values over Eastern Utah and
Western Colorado. These values are expected to range between 600
and 900 J/KG today with lifted indices between -4 and -6C. This
instability coupled with plenty of divergence aloft provided by a
100 kt jet will support some strong thunderstorms today, many of
which may be severe. These storms will be moving fast so the main
threat will be hail and strong gusty outflow winds along with
frequent lightning.

Another impact of the approaching storm system will be strong
gusty southerly winds ahead of the storm system. These strong
gusty winds are expected to produce gusts to 58 mph in the
mountains and valleys. These strong gusts have prompted a High
Wind Warning for a majority of our valley locations and a Wind
Advisory for the mountain locations beginning later this morning
and lasting into early hours of Friday morning.

.LONG TERM...(Friday through Wednesday)
Issued at 347 PM MDT Wed Sep 21 2016

The upper trough will approach on Fri with the main low center
ejecting to the northeast. The trough axis is progged to pass Fri
evening with a secondary lobe keeping energy over the area through
Sat as the low center slowly moves into the northern plains. There
continues to be some uncertainty in the timing details, but there
is good agreement that Fri will continue to be unsettled. The
north will be favored for precipitation, and much cooler
temperatures are expected area-wide. Behind the through the
northwest flow will keep showers ongoing over the favored northern
slopes through Sat. Snow levels could drop to around 8000 feet Fri
night...the lowest so far this season. Mountain passes may be
impacted.

The drying trend will continue on Sunday with a warming trend
beginning as high pressure builds to our west. While temperatures
will warm through next midweek...they will remain below normal for
late September. There will be little to no chance of precipitation
in this dry pattern.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1104 AM MDT Thu Sep 22 2016

Stream of deep moisture directed from the Desert SW into NE Utah
where moderate to heavy rainfall has dropped KVEL into LIFR
conditions at times. This line of moisture/showers will slowly
migrate eastward while additional showers and storms begin to form
over the terrain of western Colorado. KVEL and possibly KCNY will
have the highest probability of seeing aviation impacts of mvfr or
lower conditions through the first 6 hours of the 22/18z forecast.
Confidence is lower at other sites however wind gusts over 25 mph
will be likely at all the forecast sites this afternoon ahead of
an approaching cold front. This front pushes across the region
overnight and impacts to flight conditions are likely.

&&

.GJT Watches/Warnings/Advisories...
CO...Wind Advisory until 5 AM MDT Friday for COZ003-009-012-013-
     017>019.

     High Wind Warning until 5 AM MDT Friday for COZ001-002-006-007-
     011-020>023.

     Wind Advisory from 3 PM this afternoon to 5 AM MDT Friday for
     COZ004-010.

     High Wind Warning from 3 PM this afternoon to 6 AM MDT Friday
     for COZ008.

UT...Wind Advisory until 5 AM MDT Friday for UTZ023-025-028.

     High Wind Warning until 5 AM MDT Friday for UTZ022-024-027-029.

&&

$$

SHORT TERM...Larry
LONG TERM...EH
AVIATION...15


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