Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 180534
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1134 PM MDT Sat Jun 17 2017

.UPDATE...
Issued at 454 PM MDT Sat Jun 17 2017

Have updated the forecast to begin the Excessive Heat Watch on
Monday. The reasoning behind this change is that forecast models
have been consistent on this expected warm up. However, there
remains some uncertainty on how quickly the temperatures will warm
up on Monday. In addition, experimental NWS Potential Heat Risks
guidance does indicate a moderate risk of heat related health
issues on Monday before elevating to areas of high risk beginning
Tuesday. Therefore, have decided to update the Excessive Heat
Watch to include Monday.

&&

.SHORT TERM...(Tonight through Sunday night)
Issued at 155 PM MDT Sat Jun 17 2017

Weak wave brushing NE Utah and NW Colorado blew through pretty
quickly today and will keep general winds out of the northwest for
about 24 hours. H7 temps decrease slightly over the region on
Sunday, which indicates max temperatures will likely be a couple of
degrees cooler.

.LONG TERM...(Monday through Saturday)
Issued at 155 PM MDT Sat Jun 17 2017

High pressure begins to really strengthen across the southwestern US
Sunday night into Monday and shift eastward to bring its center over
the Four Corners by Tuesday. This is the point at which the
temperatures will begin to exceed the 100s - especially Tuesday,
Wednesday and Thursday when H7 temps get into the 20C range (That`s
68 degrees at about 10,000 feet!). We will be challenging records in
many spots beginning Tuesday...so decided to push the Excessive Heat
Watch back a day since Monday will not be necessarily "excessive"
yet. Something interesting on the NAM today is that it is bringing
0.65 inch PWATs over eastern Utah on Tuesday which differs by 0.10
to 0.20 inch from the GFS and SREF mean. This higher moisture seems
unlikely due to the big ridge over the region...and think that about
a half inch PWAT is still closer to actual. This, as mentioned in
our last few discussions, will allow for a few drifting cumulus
clouds and maybe even a shower or thunderstorm over the highest
terrain each afternoon. Wednesday through Saturday look to be the
most likely day to see afternoon activity over the higher terrain as
weak pieces of energy pass by the WY/UT/CO border. Conditions may
become breezy mid to late week as the pressure gradient tightens
with cooler air masses to our north passing by.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1134 PM MDT Sat Jun 17 2017

VFR conditions will prevail over the next 24 hours with light,
terrain driven wind patterns overnight through Sunday morning.
Winds will be breezy at times Sunday afternoon, but overall much
less than seen in previous days due to a ridge of high pressure
building over the region. Some cumulus development may occur
Sunday afternoon over favored higher terrain, with dry and warm
conditions.

&&

.HYDROLOGY...
Issued at 155 PM MDT Sat Jun 17 2017

A number of streams and creeks continue to run strong, cold and
high and should continue to do so through this weekend. The Green
River near Jensen remains near bankfull and CBRFC forecasts
indicated that high flows there will continue. Meanwhile, tunnel
closures are expected to cause the Roaring Fork in Aspen to
remain near bankfull for several days. Where water is running
high, river banks may become saturated and unstable and lowlands
along the rivers may become inundated. Remember if you are going
to raft, kayak or tube on the rivers be sure to always wear a life
jacket.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Excessive Heat Watch from Monday afternoon through Friday
     afternoon for COZ006.

UT...Excessive Heat Watch from Monday afternoon through Friday
     afternoon for UTZ022-027-029.

&&

$$

UPDATE...Larry
SHORT TERM...JAM
LONG TERM...JAM
AVIATION...MDA
HYDROLOGY...TGJT



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