Area Forecast Discussion
Issued by NWS Grand Junction, CO

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950
FXUS65 KGJT 240537
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1137 PM MDT Sun Sep 23 2018

.SHORT TERM...(Tonight through Monday night)
Issued at 355 PM MDT Sun Sep 23 2018

The trough and associated cold front continues to dig into the
Great Basin this afternoon, resulting in breezy southwesterly
winds across eastern Utah and western Colorado. Clouds are
increasing ahead of the front, especially across the far northern
portion of the forecast area. This has allowed relative humidity
across the area to increase slightly with current values sitting 5
to 10% higher than this time yesterday. Radar has been relatively
quiet thus far with some light returns only now developing over
the higher terrain of northwest Colorado.

Shower and thunderstorm chances will increase this evening as the
front continues to approach from the northwest. Activity will
generally be confined to areas north of I-70 overnight before
spreading to the central and southern mountains by sunrise Monday
as the trough passes. Drier air will quickly filter into northeast
Utah and northwest Colorado Monday morning as precipitable water
values drop back down to around a quarter of an inch. Breezy
conditions will continue through Monday evening as a ~60 knot
jetstreak sits overhead. As a result, a Red Flag Warning was
issued for much of northeast Utah and northwest Colorado for
Monday. More on that in the Fire Weather discussion below.
Isolated to scattered showers and storms will persist along the
Continental Divide before diminishing by midnight as the drier air
progresses to the south. This will result in impressive
radiational cooling overnight Monday with some of the northern
valleys dropping below freezing.

.LONG TERM...(Tuesday through Sunday)
Issued at 355 PM MDT Sun Sep 23 2018

The majority of the work week will be dominated by northwesterly
flow aloft as the upper level trough sits over the central and
eastern CONUS and as high pressure rebuilds over the southwest.
This will result in dry, and occasionally breezy, conditions
across eastern Utah and western Colorado, though a weak
disturbance will allow for afternoon showers and thunderstorms
over the San Juans both Tuesday and Wednesday. Temperatures will
remain seasonal Tuesday and Wednesday before rebounding back to
above normal Thursday onwards.

The ridge over the southwestern U.S. will break down this weekend
as a Pacific trough quickly progresses inland across California.
Flow will turn to the southwest ahead of this storm with moisture
potentially increasing over eastern Utah and western Colorado on
Sunday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1133 PM MDT Sun Sep 23 2018

Widespread broken to overcast skies are being reported across the
area thanks to an approaching cold front. A few showers have also
been reported but they are spotty in nature. Did include VCSH for
a few TAF sites as the front moves through but do not expect
conditions to drop below VFR. ILS breakpoints might be met briefly
for our higher elevation TAF sites but this should be relatively
short-lived. The surface cold front will be moving through
tomorrow morning and once it passes, a quick jump to high broken
skies is expected before clearing out later in the day. Gusty
northwest winds are expected for much of the area with values
ranging form 20 to 30kts at times from 18Z onwards.

&&

.FIRE WEATHER...
Issued at 355 PM MDT Sun Sep 23 2018

Though localized critical fire weather conditions are possible
through this evening under gusty southwesterly winds, relative
humidity values up north will continue to slowly increase in
response to clouds moving overhead as a cold front approaches. The
front will quickly progress out of northeast Utah and northwest
Colorado by daybreak Monday, allowing for drier air to filter into
the region from the northwest. Post-frontal winds will remain
breezy as a ~60 knot jet sits aloft. Mostly sunny skies will allow
for those stronger winds to mix down to the surface, resulting in
west-northwesterly gusts up to 30 MPH. The combination of the
return of low relative humidity, gusty winds, and the continued
dry vegetation will result in critical fire weather conditions. As
a result, a Red Flag Warning has been issued for much of
northeast Utah and northwest Colorado for Monday afternoon and
evening.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Red Flag Warning from noon to 8 PM MDT Monday for COZ200-202.

UT...Red Flag Warning from noon to 8 PM MDT Monday for UTZ486-487.

&&

$$

SHORT TERM...MMS
LONG TERM...MMS
AVIATION...TGR
FIRE WEATHER...MMS



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