Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 180924
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
324 AM MDT Tue Apr 18 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 257 AM MDT Tue Apr 18 2017

Forecast thinking remains the same in the short term period. An
upper level jet will support a cold front at the surface that will
move through the area this evening and overnight. Ahead of the
front, deep mixing that will reach 500mb and an increasing
pressure gradient will both lend themselves in creating a breezy
day. The strongest winds will be felt north of I-70 as gusts reach
over 30 mph at times in the afternoon. Areas south will also see
gusty winds of 25 to 30 mph through the afternoon and evening
hours. These gusty winds will continue until the cold front pushes
through and get noticeably stronger just as the front moves
through so expect a windy night as well. These winds will also
contribute to critical fire conditions as described below. This
southwesterly flow will also allow high temperatures to reach a
few degrees higher than seen yesterday.

As far as the front is concerned, models are progging the front to
enter northeast Utah/northwest Colorado between 6 and 9PM and
having moved across the entire CWA by daybreak Wednesday. The best
forcing still remains north of I-70 where most precipitation is
expected though some showers will occur over the San Juans and
central mountains albeit on the low side, a quarter of an inch or
so. Some thunderstorms are also possible along and just behind the
front with the main concern being some strong downdrafts. Some of
the higher elevations in the northern mountains and Flat Tops may
see 1 to 3 inches of new snow as the front moves through with the
central mountains also possibly seeing an inch or two.

For Thursday, cold air advection at the mid-levels will allow some
instability showers to continue for the northern mountains and
Flat Tops. Remaining areas will see a cloudy start to the day with
clouds lifting as the day progresses. High temperatures will drop
anywhere from 5 to 10 degrees than those seen today.

.LONG TERM...(Wednesday night through Monday)
Issued at 258 PM MDT Mon Apr 17 2017

The forecast models remain in fairly good agreement through Monday
so this is leading to more confidence in the going forecast. The
main story is that a fast and progressive flow will develop off
the Pacific leading to a series of open troughs skirting the area
with ridging in between when looking ahead at the extended. These
systems appear to be trending further north with each run and as
the system gets to be about 24 to 48 hours out so keep in mind
that the exact storm track could change.

Wednesday night will be cooler in the wake of the passing cold
front with a light westerly flow as the gradient relaxes. Thursday
will see an increase in southwest winds as a negatively tilted
trough makes its way onto the Northern California and Pacific NW
coast, tightening the gradient once again. Dry and breezy
conditions ahead of this system and associated cold front may lead
to fire weather concerns on Thursday afternoon and evening. This
negatively tilted trough will allow for increasing instability
with showers and thunderstorms developing Thursday afternoon and
evening, mainly across northeast Utah and northwest Colorado. The
trough will move through the area Thursday evening into Friday
afternoon with the northern and central mountains being favored
for snowfall as H7 temps drop to around -4C to -8C north of I-70.
This system will quickly take its energy out across the Front
Range and Plains as the main upper low slides southeast through
Wyoming into eastern Colorado and Kansas by Friday morning.
Meanwhile, an amplified ridge of high pressure will build across
the west helping force this system quickly eastward on Friday with
showers coming to an end by Friday evening. Temperatures will be
noticeably cooler on Friday and Saturday in the wake of this
system, but should quickly warm back up to above normal levels by
Sunday as the ridge of high pressure moves overhead.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 257 AM MDT Tue Apr 18 2017

An approaching cold front will cause an increase in winds across
the area today. Expect wind gusts of 30+ mph north of I-70 with
gusts of 20 to 30 mph for areas south. The winds will begin right
around 18Z and continue until the cold front moves through later
in the evening. Ceilings and visibilities will remain VFR through
the period though some showers will drop ceilings and
visibilities from time to time. A few thunderstorms are also
possible but confidence not high enough to include for any TAF
sites. By 12Z Wednesday, the front will have moved across the
entire forecast area so conditions are expected to improve after
that.

&&

.FIRE WEATHER...
Issued at 257 AM MDT Tue Apr 18 2017

As mentioned above, winds will pick up today across the forecast
area. Forecast soundings continue to indicate deep mixing which
will allow winds and wind gusts to reach 25 to 35 mph for CO fire
zones 207, 290, 292 and 203 where fuels are critical. Therefore, a
Red Flag Warning remains in effect for this afternoon and evening
to account for these conditions. Important to mention that much
of southeast Utah and northern Colorado will also see these same
conditions but fuels, at this time, are not critical so will hold
off issuing anything for that area.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Red Flag Warning from 1 PM this afternoon to 8 PM MDT this
     evening for COZ203-207-290-292.

UT...None.
&&

$$

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



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