Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 210106

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
706 PM MDT Fri Oct 20 2017

Issued at 702 PM MDT Fri Oct 20 2017

Winds continue to decrease across the area this evening with the
loss of daytime heating and deeper mixing. Peak gusts generally
under 30 mph in most areas, although passing showers and
approaching cold front may tick winds back up to near 40 mph later
this evening. Even with the potential uptick in wind gusts, speeds
will still be under advisory criteria. So dropped the wind
advisory an hour early. New gridded forecasts will be out shortly.


.SHORT TERM...(Tonight through Saturday night)
Issued at 342 PM MDT Fri Oct 20 2017

Breezy to windy conditions will continue through this evening
under a pre-frontal southwest flow. Some gusts have already
exceeded 45 mph in northwest Colorado with a gust of 60 mph at
Douglas Pass. Other areas in the wind advisory are flirting with
upper 30s and low 40s but do expect criteria to hit as the
stronger upper level jet works overhead late this afternoon and
early evening across southeast Utah into northwest Colorado. This
sufficient mixing has also resulted in much warmer afternoon temps
so bumped up temperatures a bit above guidance. The wind advisory
will continue until 8 pm MDT this evening, before decoupling
occurs post-frontal and with the setting sun.

A strong cold front will march across the area with a noticeable
wind shift from southwest to northwest this evening and overnight
as it passes through. The front looks to enter northeast Utah
around 6 pm, move across northwest Colorado and be near the
bookcliffs by 9 pm and move through the rest of the forecast area
and be over the San Juans by midnight. This system will also bring
some showers to the region this evening through Saturday morning
with northern and central areas of western Colorado favored. The
northern and central mountains look to pick up about 2 to 4 inches
of snow as much colder air moves in behind this cold front and
trough passage. H7 temps lower to -8C up north with -10C air after
sunrise up north. Expect precip to quickly come to an end after
sunrise Saturday morning as dry air quickly punches in with a 110
kt upper level jet helping to push this system to the east. A few
lingering showers and clouds may remain along the divide through
the morning hours but should clear out as the day wears on. Due
to the quick nature of this system and limited moisture, elected
not to issue any winter weather highlites as the models and
forecast has consistently showed 1 to 4 inches at best, which is
below advisory criteria, even for early season.

The rest of Saturday looks dry and noticeably cooler as northwest
flow sets up behind this system. Breezy conditions may still
remain due to the upper level jet overhead. Daytime highs on
Saturday will be some 20 degrees colder than seen today (Friday)
with highs 10 degrees below normal.

.LONG TERM...(Sunday through Friday)
Issued at 342 PM MDT Fri Oct 20 2017

Northwest flow will remain in the picture Sunday through early
next week as high pressure builds over the Desert Southwest and
begins to amplify across the west coast by mid-week. A slow
warming trend is in store with temps warming back up to above
normal levels by Monday. Some mid and high clouds will move
through across the north on Monday as a trough moves across the
northern High Plains, having little effect on our area other than
some clouds and breezy conditions. The next chance of
precipitation arrives on Thursday as a strong and deep trough of
low pressure moves through the Northern Rockies and down the Front
Range. This system looks much colder than anything seen so far
this fall with H7 temps dropping into the -10C (south) to -16C
(north) range. This would mean precipitation quickly changing over
to snow as the leading edge moves southward throughout the day
and snow levels lowering to all valley floors. Having said that,
snow looks to favor the higher terrain of western Colorado and
higher valleys along the divide, with the Front Range taking the
brunt of this system. Models are in fairly good agreement today on
the timing and track of this system but were not in complete
agreement on how far west to take this system from run to run. The
details are subject to change as we get closer to this event, but
something to watch as this polar airmass encompasses much of the
Intermountain West and Plains Thursday into Friday.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 542 PM MDT Fri Oct 20 2017

Gusty winds out of the west and eventually the northwest will be
the primary aviation hazard through the evening hours at all TAF
sites as a strong cold front moves through the region. Scattered
showers of rain and snow will accompany the front which is
currently situated in northeastern UT. Periods of mountain
obscuration and reduced CIGS/VIS can be expected with heavier
showers. Shower and wind activity will diminish from NE to SE
overnight as significant clearing occurs behind the front. By 12Z
Saturday only some isolated showers will linger along the
Continental Divide with widespread VFR conditions returning
shortly after.




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