Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 171855
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1155 AM MST Sat Feb 17 2018

.SHORT TERM...(Today through Sunday)
Issued at 438 AM MST Sat Feb 17 2018

00Z H500 hand analysis map shows a strong ridge over the Aleutians
wit most of NOAM under the influence of the large gyre of low
pressure centered over Hudson Bay. A ridge over the high latitudes
of the E.Pac can only mean one thing...cold and unsettled weather
settling into the West. However this will not be during the short
term as the next system is still organizing North of the Canadian
border. Warm conditions will settle in ahead of this system with
conditions becoming breezy to windy Sunday as our flow turns turns
southwesterly. This will create somewhat of a challenge to the
temperature forecast as we melt the snowpack up in the Yampa
valley which has been holding temperatures down. For now have
settled on the colder side of guidance up there. There is a
moderate tap to Pacific moisture feeding into the jet stream but
much of this will be hitting upstream mountains before finally
shifting southward late on Sunday. There will likely be some
isolated showers developing later in the day across the high
peaks but the best action will be saved for Sunday night into
early next week.

.LONG TERM...(Sunday night through Friday)
Issued at 438 AM MST Sat Feb 17 2018

A deep and broad upper level Pacific trough will continue to
elongate as it begins to progress across the western CONUS Sunday
night. Southwesterly flow will increase over eastern Utah and
western Colorado throughout the night as the trough dives into
the Great Basin and the 120-knot jetstreak rounds the base of the
low. This will allow for showers to increase across the forecast
area with the peak coverage occurring Monday afternoon and early
evening as a cold front pushes through the region. Scattered to
numerous showers will persist overnight before coverage begins to
be confined to the higher terrain on Tuesday.

Snow levels will be high at the onset of the event Sunday night in
response to the mild southwesterly flow ahead of the storm.
However, as cold air filters into the region with the progression
of the cold front, snow levels will drop down to valley floors by
late Monday afternoon. Current projected storm total snowfall
and the strong winds aloft could make this a rather significant
storm and have decided to push out Watches early this morning. The
lower elevations of southeast Utah and southwest Colorado could
see anywhere from a few tenths to maybe an inch or two. Naturally,
forecast snowfall will continue to be tweaked over the next few
shifts to adjust for the latest model trends. Stay tuned.

Model discrepancy increases on Tuesday with the progression of the
trough as the Euro still lags behind the GFS by a good 6 to 12
hours. And now there`s even greater discrepancy in the potential
for a closed So-Cal low to develop mid to late next week. Given
the lack of consistency with the models, forecast confidence
decreases from midweek onwards. However, we can expect
temperatures to cool down close to seasonal norms behind the cold
front on Tuesday before gradually moderating as clouds and showers
decrease.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1155 AM MST Sat Feb 17 2018

Expect VFR conditions and CIGS above ILS breakpoints through the
next 24 hours. Winds will be light and terrain driven this
afternoon and overnight.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Storm Watch from Sunday afternoon through Tuesday morning
     for COZ004-009-010-012-013-018-019.

UT...Winter Storm Watch from Sunday afternoon through Tuesday morning
     for UTZ023.

&&

$$

SHORT TERM...15
LONG TERM...MMS
AVIATION...NL



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