Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 131034

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
334 AM MST Wed Dec 13 2017

.SHORT TERM...(Today through Thursday)
Issued at 334 AM MST Wed Dec 13 2017

Water vapor imagery is showing a decent wave dropping through the
Dakotas early this morning which is spreading some higher clouds
back over our region. The more interesting feature however is the
darkening in the H2O over the PacNW coast. This wave not quite as
visually impressive as the Plains system but it will have the
support of the upper jet and tap into the only moisture source
around. Models have consistently trended westward with the upper
jet and therefor the moisture over the past 24 to 36 hours of
runs. It now looks a lot more favorable for snow to move across
the northern and central mountains tonight through early Thursday.
Unfortunately the southern mountains...except for some of the high
peaks in the northern San Juans...will again be on the outside
looking in with this storm. According to GQ indicators the
strongest ascent arrives mid evening through the early morning
hours. This corresponds with moisture moving in via the 300k
surface and should be the period of best coverage and snow rates.
X-Sections show minimal EPV nor favorable theta-e lapse rates for
an added convective component in the dendritic zone. Orographic
and CAA will play a role to bring widespread amounts in the 2 to 5
inch range mid mountain to pass level. Higher amounts likely above
timberline in the Park down to the West Elk Ranges and mainly 1 to
3 in the populated higher mountain valleys and portions of the
Yampa River Basin. Should be done by mid day Thursday as the dry
air mixes the dendritic layer clean of moisture. Temperatures
today nearly similar to the past several days though the high clouds
may have some impact. Cooler conditions on Thursday especially in
the north as this system will be pushing a surface frontal
boundary through as well.

.LONG TERM...(Thursday night through Tuesday)
Issued at 334 AM MST Wed Dec 13 2017

We will not have to wait as long between system as the next one
looks to arrive by the weekend. Thursday night through sunrise on
Saturday will be dry as the next upstream system approaches. The
models have been fairly aligned with this larger trough moving
through on Saturday...however there are still some glaring
differences showing up. The EURO/GEM split the energy in the
trough and both of these drop the western split as a closed low
down the vicinity of the Left Coast. The GFS keeps the energy in
one piece and therefore has a much more organized and stronger low
that organizes over the Great Basin and 4 Corners Saturday evening
into Sunday. This solution could be much better for us
precipitation-wise but it is not in phase with what the atmosphere
has been doing lately. So for now it looks like lower pops in the
extended until confidence increases. Either way it looks like some
cooler temperatures will be moving in behind this second trough
and we could end up on the low side of normal which is what the
extended outlooks for December suggest.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 334 AM MST Wed Dec 13 2017

High cloudiness has invaded the area but should not pose any
threat to lower flight criteria through the daylight hours. The
next system arrives tonight and has trended westward and a bit
stronger. As a result precipitation is expected to spread into
northern Utah and Colorado after sunset and expand south and
eastward through midnight. Mountain obscuration will become
widespread on the northern and central mountains of E.Utah and
W.Colorado. As snow spreads in coverage expect MVFR to IFR
conditions will be increasing with KASE most likely impacted by
14/06Z. High probability of ILS break points also being met at
KRIL and KEGE and KTEX through the early morning hours. Otherwise
VFR conditions are expected.




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