Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 152344
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
544 PM MDT Sun Apr 15 2018

.SHORT TERM...(Tonight through Monday night)
Issued at 308 PM MDT Sun Apr 15 2018

The focus for the short term is on very windy, dry and warm
conditions Monday and Monday night ahead of a strong upper level
trough and associated cold front set to move through the region
early Tuesday. As the upper level ridge over the area today moves
east Monday, the pressure gradient will tighten considerably
Monday ahead of the trough. A 100+ knot upper level jet will also
be translating eastward on the front side of the trough. Maximum
winds aloft move over eastern UT and western CO after 5 pm Monday,
so the winds aloft max and deepest mixing are not exactly synced.
Despite that, still expect winds 25 to 45 mph with gust 50 to 60
mph in a swath of the area from the Four Corners northeast over
the lower Colorado and Gunnison River Valleys, Tavaputs and
Northwest Plateau of CO Monday afternoon through evening.
Temperatures will also be a good 5 to 10 degrees above normal
ahead of the front.

.LONG TERM...(Tuesday through Sunday)
Issued at 308 PM MDT Sun Apr 15 2018

As the upper level trough and surface cold front cross the region
during the day Tuesday, a dramatic change in the sensible weather
will occur. Many areas will have their daytime max temps reached
in the early morning or will have very little rise during the day
as 700mb temps above zero Celsius in the morning crash to the -6
to -10C range by early afternoon. While the pre-frontal airmass
is dry, the post-frontal air will be moist and unstable. This
surge of moisture and instability coincident with orographic
forcing in the west to northwest flow will result in scattered to
numerous showers...falling as snow generally above 6500 feet.
Areas most likely to see accumulations of 1 to 5 inches will be
north of Hwy 50, including the central and northern mountains.
Models agree on a period of high moisture content in the dendritic
growth zone over these areas for 12-18 hours behind the front.
The San Juan mountains will have more scattered activity and
lighter accumulations. Tuesday will also be breezy to windy, but
sub-advisory levels. So, all-in-all a raw day.

Moisture in the orographic northwesterly flow dries up Tuesday
night and the sky will clear for most areas. Concern then turns to
sub-freezing temperatures for many lower valley areas that have
spring growth underway. If current forecasts remain on track, freeze
watches will be posted on Monday for Wednesday morning.

Temperatures slowly moderate Wednesday and Thursday as we set the
table to do this all over again late in the week. There is
moderately high confidence, based on general model agreement, on a
deep upper level low moving over the Great Basin Thursday. Once
again, eastern UT and western CO will be in the dry, warm, and
windy sector ahead of this system on Thursday. By midday Friday,
there is good agreement in the center of the upper level low being
within 100 miles of the Four Corners and much of UT and CO under
a shield of warm and cold conveyer belt precipitation. A dry slot
nosing around the southern and eastern sides of the center will be
in play to reduce precipitation for some areas. All of these
details, including the eventual path and intensity of this storm,
will be watched closely this week. This anomalously cold storm
does have the potential to provide the higher elevations with a
significant amount of snow and cause travel impacts Friday - and
into Saturday if the system slows down as many closed low pressure
systems do.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 535 PM MDT Sun Apr 15 2018

VFR conditions will prevail over the next 24 hours. Mid and high
clouds will remain scattered to broken over the area with some
partial clearing expected Monday afternoon and evening ahead of a
strong cold front set to move into the area Tuesday. Winds will
pick up from the southwest late Monday morning into the afternoon
with gusts up to 45 mph or greater in eastern Utah and some
western Colorado valleys. Strong winds aloft will create areas of
mountain turbulence with some low level wind shear possible in
some valleys overnight tonight through Monday morning before
stronger winds mix to the surface.

&&

.FIRE WEATHER...
Issued at 308 PM MDT Sun Apr 15 2018

Windy to very windy conditions still on track for Monday
afternoon and evening across much of eastern Utah and western
Colorado with RH values tumbling below 15 percent for several
hours. In areas where fuels have been deemed critical, Red Flag
Warnings are in effect (Colorado zones 207, 290, 295 and 203
below 6k). The windy conditions will persist into the late evening
hours Monday with a strong cold front passing through Tuesday
morning. Another dry, warm and windy day is likely on Thursday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Wind Advisory from noon to 10 PM MDT Monday for COZ001>003-006-
     007-011-020-021.

     Red Flag Warning from noon to 10 PM MDT Monday for COZ203-207-
     290-295.

UT...Wind Advisory from noon to 10 PM MDT Monday for UTZ022-025-
     027>029.

&&

$$

SHORT TERM...BM
LONG TERM...BM
AVIATION...MDA
FIRE WEATHER...BM/JDC



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