Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 171743
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1143 AM MDT Wed May 17 2017

.SHORT TERM...(Today through Thursday)
Issued at 445 AM MDT Wed May 17 2017

The current satellite water vapor image is showing a storm system
centered along the Oregon Idaho border this morning. Infrared
satellite imagery is showing high clouds moving across eastern
Utah into Western Colorado ahead of an approaching front that is
associated with this storm system.

According to the 0600Z GFS20 this front will begin to impact
eastern portions of the CWA later this morning increasing the
possibility of precipitation for our area. Isolated thunderstorms
will also be a possibility this afternoon and evening as heating
of the day destabilizes the atmosphere ahead of the front. This
is a cold storm system so mountain snows are expected and winter
weather advisories remain in place over the Uintahs and the
mountains of the Western slope of Colorado.

Currently the freezing level is running between 9,000 and 10,000
feet, however snow levels will drop to between 5500 and 6500 feet
overnight tonight. In fact the 0600Z GFS20 is showing 700mb
temperatures forecast to fall to around -7C overnight. This will
translate to near freezing to slightly below freezing temperatures
for many valley locations tonight into Thursday morning. A Freeze
Watch remains in effect for many low elevation areas in the CWA.
This watch will most likely be upgraded to a Freeze Warning with
the afternoon forecast package.

The 0000Z ECMWF and 0600Z GFS20 have initialized well with the
late season winter storm and remain in good agreement sliding the
storm system over the forecast area during the next 24 hours. By
Thursday the storm system will be centered over the CWA placing
the forecast area in a seasonally cool and showery weather regime,
with continued mountain snows. Afternoon and evening thunderstorms
will also be a possibility with daytime heating destabilizing the
atmosphere.

.LONG TERM...(Thursday night through Tuesday)
Issued at 445 AM MDT Wed May 17 2017

With a cold airmass in place chilly temperatures are expected once
again Thursday night with the potential for another Freeze Warning
Thursday night into Friday morning. Forecast models remain in good
agreement through the weekend and move the storm system into the
Great Plains by Friday evening. With this in mind expect unsettled
weather to persist across the forecast area into the evening hours
of Friday.

Dry weather returns to the area on Saturday along with a nice
warming trend as weak high pressure builds over the area. The
warming trend sticks around on Sunday and Monday however weak
cyclonic flow positioned over the area will support a possibility
of afternoon showers and thunderstorms both days.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1053 AM MDT Wed May 17 2017

As of 17z, surface obs and GJX radar velocity data indicate a
frontal boundary positioned from the Craig area down through far
western Mesa county, extending southwestward to Moab. As this
boundary pushes eastward this afternoon, expect temporary
lowering of ceiling heights and visibility. Mainly VFR conditions
will transition to MVFR in heavier precip along the front. Winds
will shift to a more westerly component behind the boundary and
temperatures will drop, with some snow developing later this
afternoon at the higher elevation terminals with IFR possible.
Aviation conditions will continue to be poor overnight.

&&

.HYDROLOGY...
Issued at 0930 AM MDT Tue May 16 2017

Above normal temperatures, especially temperatures staying
above freezing at night, have allowed the remaining snowpack
at high elevations to melt at an accelerated rate.

With cooler temperatures arriving with the next storm system,
melting of the snowpack will slow. The response will be seen over
the next 24 hours as rivers levels and flows slowly decline.

A few of the rivers still being closely monitored include: the
the North Fork of the Gunnison at Hotchkiss the Green River at
Jensen and the Mancos River near Mancos. It should be noted that,
at this time, rivers across eastern Utah and western Colorado are
not forecast to reach flood stage but rather just approach or
reach bankfull conditions.

Increases in river stages lead to much higher river flows making
for swift and unpredictable currents. Debris in the river
could create numerous snags. Water temperatures will be quite
cold with the introduction of the snowmelt. If recreating or
working in or near high flow waterways, use appropriate safety
gear. Unstable banks along fast moving waterways may quickly
give way and should be avoided.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Freeze Watch from late tonight through Thursday morning for
     COZ006-007-011-020-021.

     Winter Weather Advisory until 6 PM MDT Friday for COZ004-009-010-
     012-013-017>019.

UT...Freeze Watch from late tonight through Thursday morning for
     UTZ024.

     Winter Weather Advisory until 6 PM MDT Friday for UTZ023.

&&

$$

SHORT TERM...Larry
LONG TERM...Larry
AVIATION...MAC
HYDROLOGY...TGJT



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