Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 212200
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
400 PM MDT Thu Sep 21 2017

.SHORT TERM...(Tonight through Friday night)
Issued at 359 PM MDT Thu Sep 21 2017

Windy conditions are occurring in most areas today where gusts 35
to 45 mph are common. Some areas are even gusting to 50 mph or
above, mainly over northwest Colorado valleys. Dry conditions are
in place as well with mostly sunny skies, leading to critical fire
weather conditions in some areas. See the Fire Weather section
below for more details. The storm system developing to our west
responsible for sufficient mixing of these upper level winds with
a 130kt jet parked over Utah. Our CWA remains in the left exit
region of this jet, which is allowing for windier conditions
rather than any precipitation as the atmosphere remains dry. Wind
Advisories remain in effect through 9 pm this evening for much of
southeast Utah, northwest Colorado and west-central Colorado
valleys. This also includes the Paradox valley in southwest
Colorado as well as the Tavaputs Plateau in both east-central Utah
and west-central Colorado.

Breezy conditions will remain overnight as the 130kt upper level
jet shifts eastward over the Four Corners region and across
western Colorado by Friday afternoon as the upper level low drops
into the northern Great Basin from the Pacific Northwest. Plenty
of cloud cover and moisture is associated with this upper level
jet as seen on GOES-16 satellite data today. This mid and high
level moisture is expected to move over the area heading into
Friday with increasing clouds as a result. Daytime temperatures
will lower by some 10 degrees from today. Do not anticipate
needing any additional wind or fire weather highlites for Friday
as relative humidity levels are expected to increase with the
increasing cloud cover and moisture. This cloud cover should also
prevent the stronger upper level winds from reaching the surface
with just breezy conditions expected. Some showers will develop
mainly over the higher terrain of the eastern Uintas and San Juans
overnight, with some development over the rest of the higher
terrain by Friday afternoon. Not expecting much in the way of
precip accumulation as low levels still remain dry, but the best
chances appear to be over the San Juans, with still high snow
levels around 12kft. Not enough to warrant any winter highlites as
light accumulations are expected at the higher peaks. H7 temps
still remain fairly mild as our CWA remains in the warm sector.

.LONG TERM...(Saturday through Thursday)
Issued at 359 PM MDT Thu Sep 21 2017

The upper level trough will continue to amplify on Saturday as the
upper level low shifts southward towards southern Nevada and
southwest Utah and deepens. Even though models are not in
agreement on how far south to take the upper low and deepen the
trough, the models are in good agreement on the overall forecast
trends. Expect better chances of shower and thunderstorm
development on Saturday as better instability and shear exists
with CAPE in the 400 to 600 J/kg range and lapse rates approaching
8 degrees C/km. The better shear over southwest Colorado and the
divide mountains south of I-70 may result in a little better
organization for some stronger storms to develop. Snow levels
still remain high with the highest peaks above 12kft seeing some
snow accumulation, but still remains minimal at this time due to
mild H7 temps around 6 degrees C.

Drier air punches in across the south on Sunday as the upper low
tracks across Utah from southwest to northeast, keeping scattered
convective showers across the north. Colder air finally begins to
move into the region as this upper low tracks across the area. The
coldest air arrives by Sunday night into Monday as H7 temps dip
down to -3C across the north and 0C across the south with some
moderation by Monday afternoon up to 0C across the north and 3C
across the south. Snow levels look to drop down to 7000 feet by
this time. The northern mountains stand the best chance to see
snowfall accumulations but details are not clear at this time.
There is also good potential that some other lower elevations will
see season ending freeze as lows dip to the upper 20s to low 30s
in some areas, mainly the northern and southern valleys, as well
as the valleys along the divide (eastern most portions of the CWA).
Something for future shifts to consider as the time gets closer.

The trough is expected to remain over the region through Wednesday
as another piece of energy dives down the backside of the trough
towards the Four Corners region for an uptick in shower activity.
A ridge of high pressure moves back into the region by Thursday
for a slow warming trend Tuesday through the end of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1133 AM MDT Thu Sep 21 2017

South to southwesterly winds will be gusting across the region
today thanks to a strong jet moving overhead and slowly
approaching cold front. Winds will gust anywhere from 30 to 45 MPH
for most areas though eastern portions of the forecast area should
see lighter gusts. Plenty of sunny skies will keep VFR conditions
in the picture through tomorrow.

&&

.FIRE WEATHER...
Issued at 359 PM MDT Thu Sep 21 2017

Winds will be very gusty ahead of an approaching storm system in
the Great Basin. Southerly winds gusting 35 to 45 mph will be
common over much of eastern Utah and western Colorado through the
rest of this afternoon and evening. Afternoon humidity in the
lower teens will also occur over many of the lower elevations of
southwest Colorado where fuels are critically dry. Therefore the
combination of wind and low humidity will create Red Flag
conditions over far SW Colorado. Red Flag conditions may occur
elsewhere for brief periods of time this afternoon as well.
Regardless, winds will remain strong enough today that control
problems are anticipated on any new or existing fires. Winds look
to remain breezy through the weekend before this system moves
eastward, with moisture levels coming up above critical thresholds.
Southeast UT will avoid critical conditions due to non-critical
fuel conditions.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Wind Advisory until 9 PM MDT this evening for COZ001>003-006>008-
     020.

     Red Flag Warning until 7 PM MDT this evening for COZ207-290.

UT...Wind Advisory until 9 PM MDT this evening for UTZ022-025-027-029.

&&

$$

SHORT TERM...MDA
LONG TERM...MDA
AVIATION...TGR
FIRE WEATHER...TGJT



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