Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 181055
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
355 AM MST Sun Feb 18 2018

.SHORT TERM...(Today through Monday)
Issued at 355 AM MST Sun Feb 18 2018

Well here we are again. Another robust open trough swinging across
the West with a prolonged period of strong...unstable SW flow
pointed at us. It`s like groundhog day except I am the guy who
keeps stepping off the curb into the frozen pothole of slush.
This system is eerily similar to last weeks early week storm with
a downstream jet remaining overhead as the upstream trough digs
over the West. Models have slowed this trough down a bit with the
main axis push now delayed until well into Tuesday. So a
warm...mainly dry and breezy to windy day is in store for today
and added some advisories across E.Utah where gradients are the
tightest under the core of stronger winds. As we moving into
tonight and Monday...instability parameters (EPV/Lapse rates)
suggest precipitation patterns will again be streaky along with a
constant SW orographic component smashing into our mountains. It`s
looking good for the southern and central mountains to erase some
more of the huge deficit in the SWE/snowpack as there should be
some places measuring snow in feet. SW facing aspects farther
north will do well also along with unpredictable heavy snow bands
hitting many areas. So again low level thermal profiles will be
driving the precipitation type in the lower elevations. Where a
heavier convective band sets up expect snow...otherwise things
will be wavering in the lower valleys of central and southwest
CWA. Snow should be the dominant ptype in the southern valleys
tonight with some accumulations of a few inches by morning...but
then temperatures should rebound in the afternoon with snow levels
pushing back into the foothills. All together this storm could
bring some 3 to 8 inches near the foothills from PSO to DRO but
this appears to be in pieces so holding off on winter headlines
this morning. The colder air will be backing in to our NE tonight
and looks to stall near our northern border much of Monday as the
upper flow dominates. The other front to our West should not make
much progress either which means our N.Utah mountains into the
Manilla area should do good also. This colder air should begin to
make some progress southward later in the day on Monday and this
will bring the snow threat to the higher valleys of NW Colorado.
Winds will make this a nasty storm and expect plenty of travel
issues with new whiteout conditions over many mountain roadways.

.LONG TERM...(Monday night through Saturday)
Issued at 355 AM MST Sun Feb 18 2018

Snow will continue Monday evening as the surface cold front will
be just to the west of Steamboat Springs and draped down to the
Book Cliffs and Tavaputs. The NAM, and to a lesser extent the GFS,
indicate some moderate to heavy snowfall over the central and
southern mountains which is also when the best divergence aloft
looks to move overhead. This divergence should increase lift
causing an uptick in snow production. We shall see. Either way,
snowfall associated with the front will continue through daybreak
Tuesday. As is usually the case after frontal passage for the
mountains, much colder air will drop down causing instability
showers and some convective bands to form. All models show this
occurring and this follows from what we usually experience. The
tricky part will be forecasting where these bands set up. A quick
couple of inches, possibly more, are always possible if a band
sets up and remains fairly stationary allowing a relatively small
area to get lots of precipitation. By Tuesday evening, all the
action will end though a few stray showers may be possible over
higher terrain. High temperatures Tuesday will be noticeably
cooler than they have been dropping anywhere from 10 to 15 degrees
below normal.

Wednesday will be relatively calm as another system starts digging
down from the northwest. Southerly flow ahead of this system may
bring a few showers to the area as early as Thursday as weak
impulses move through. The GFS is painting fairly widespread
precip from Thursday evening onwards in a warm front-like
environment. Precip continues through late Friday night as a cold
front and upper level front, much like the one we`ll see on
Monday/Tuesday, move through. The EC is getting more on-board with
this solution though timing differences do continue to remain.
Chances are increasing that another round of much needed precipitation
is on its way.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 355 AM MST Sun Feb 18 2018

Concerns around the first half of the 18/12Z forecast will center
around winds as VFR conditions will be dominating. Increasing SW
flow ahead of the next Western trough will bring widespread wind
gusts over 25 mph to many TAF sites by early afternoon. Strong
winds over the terrain will also create areas mountain wave
turbulence and localized low level wind shear in protected
valleys. As moisture increases late expect obscuration of more
terrain and by sunrise on Monday several TAF sites will be
impacted by weather...with KHDN...KASE and KTEX the most probable.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory from 5 PM this afternoon to 8 AM MST
     Tuesday for COZ001>005-010-017.

     Wind Advisory from 11 AM this morning to 5 PM MST this afternoon
     for COZ001>003.

     Winter Storm Warning from 5 PM this afternoon to 8 AM MST
     Tuesday for COZ009-012-013-018-019.

UT...Winter Weather Advisory from 5 PM this afternoon to 8 AM MST
     Tuesday for UTZ023-025-028.

     Wind Advisory from 11 AM this morning to 5 PM MST this afternoon
     for UTZ027-029.

&&

$$

SHORT TERM...15
LONG TERM...TGR
AVIATION...TGJT



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