Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 282347
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
547 PM MDT Wed Jun 28 2017

Updated aviation discussion

.SHORT TERM...(Tonight through Thursday night)
Issued at 330 PM MDT Wed Jun 28 2017

The shortwave which passed over the region last night drove a cool
front across northeast Utah and northwest Colorado overnight. The
East-west oriented stationary front straddling the forecast area
has moved little during the day and is expected to stay put
overnight. Meanwhile, the forecast area will continue to be
impacted by a deep low centered over western Canada in the short
term.

Breezy west to southwest winds will decrease and give way to
normal drainage flows this evening as the atmosphere decouples.
Despite another weak shortwave trough brushing the northernmost
portions of the CWFA overnight, the stabilizing effects of cooling
and limited moisture will bring an end to isolated showers and
thunderstorms over the northern mountains this evening. This
activity is not expected to deliver much in terms of measurable
precipitation, but will be capable of producing strong outflow
winds to 50 MPH. Overnight lows should be a bit cooler north of
the front described in the previous paragraph, while near
persistence lows are more likely to its south.

Another breezy afternoon/evening is in store Thursday as the
height gradient aloft tightens ahead of the next shortwave moving
through the base of the Canadian system. Deep mixing will aid
momentum transfer from mid-levels of the atmosphere to the
surface. The airmass is expected to remain dry, so except for
isolated showers/thunderstorms over the northern mountains, dry
weather will prevail. Temperatures are indicated to be cooler,
especially north of the stationary front where highs will be near
normal. Fire weather concerns linger due continued breeziness and
low relative humidity. See the fire weather discussion for
details.

The last shortwave, described previously, will drive the
stationary front south of the area late Thursday night with
clearing occurring in its wake. Understandably, overnight lows
will be cooler, dipping by about 5 degrees at most locations
relative to tonight`s forecast lows.

.LONG TERM...(Friday through Wednesday)
Issued at 330 PM MDT Wed Jun 28 2017

Northwest flow on the back side of the northern states trough will
re- enforce the relatively cool air over our CWA on Friday. The
bulk of the low level moisture will be found east of the divide in
the upslope pattern behind the front. Steep lapse rates associated
with the cooler air aloft may try and pop some mountain showers
in the wake of the trough but moisture remains very limited...and
measurable precipitation isolated. Isolated afternoon convection
remains in the picture over the weekend as a few Pacific waves
progress through the Westerlies located across the Northern
Rockies. The westerlies retreat northward going into next week
as the subtropical ridge strengthens over the Desert Southwest and
Southern Rockies. This subsident ridge will help cap the
atmosphere and expect mainly sunny skies and strong warming to
commence through the upcoming Holiday. Some low level moisture may
be trying to invade from the south allowing afternoon humidity
levels to ease upward. This and lighter winds aloft should help
limit the extreme fire conditions. Temperatures will be well above
normal as well.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 547 PM MDT Wed Jun 28 2017

Breezy conditions and occasional LLWS possible over the next 24
hours as a jet streak crosses the region tonight with continuing
elevated upper level support on Thursday as well. High ceilings
and good visibility are expected with VFR conditions.

&&

.FIRE WEATHER...
Issued at 330 PM MDT Wed Jun 28 2017

Red Flag Warning remains in effect until 8 PM today for all fire
weather zones with the exception of UTZ485. Cooling temperatures
and decreased wind during the latter part of the evening will
bring a cessation in critical fire weather conditions through
Thursday morning.

The jet remains overhead on Thursday so more wind is expected than
earlier forecast. Though temperatures will be cooler, especially
north of the I-70 corridor, RH is still expected to fall below 15
percent for several hours Thursday afternoon/evening. Therefore,
will hoist Red Flag Warnings for much of the region once again.
Held out UT zone 485, and Colorado zones 201 and 205 along with
elevations above 9000 feet in zones 291, 293 and 295 where RH
expected to be a bit higher.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Red Flag Warning until 8 PM MDT this evening for COZ200>203-205-
     207-290>295.

     Red Flag Warning from noon to 8 PM MDT Thursday for COZ200-202-
     203-207-290>295.

UT...Red Flag Warning until 8 PM MDT this evening for UTZ486-487-490-
     491.

     Red Flag Warning from noon to 8 PM MDT Thursday for UTZ486-487-
     490-491.

&&

$$

SHORT TERM...NL
LONG TERM...NL/15
AVIATION...JAM
FIRE WEATHER...TGJT



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