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FXUS65 KGJT 182343

Area Forecast Discussion
National Weather Service Grand Junction CO
443 PM MST Mon Nov 18 2019

.SHORT TERM...(Tonight through Tuesday night)
Issued at 244 PM MST Mon Nov 18 2019

Mid/high level clouds continue to thicken and move across the 
forecast area this afternoon. Even so, high temperatures today
remain similar to or just a couple degrees above yesterday. With
increasing clouds just before sunrise tomorrow morning
(foretelling the coming weather), we'll see low temperatures just
a bit warmer than they were this morning. These clouds continue 
to increase through the day but much of the forecast area will see
one more day of well above normal temperatures Tuesday before the
approaching disturbances bring in some colder air.

Speaking of those disturbances, the first will slide northeast
from the Baja Peninsula. The second digs southeast just off the 
west coast before ejecting the first system to the northeast and 
absorbing it into the flow. This one-two punch will set the
forecast area up 48 hours of on/off precipitation in the valleys
with fairly consistent snowfall in the mountains. Models are in
pretty good agreement in the precipitation starting Tuesday 
evening in southeast Utah/southwest Colorado. Snow levels will
start out around 9,000 feet.

.LONG TERM...(Wednesday through Monday)
Issued at 244 PM MST Mon Nov 18 2019

By Wednesday morning, snowfall rates increase as the southwest 
winds advect plenty of moisture up and into the mountains. Thus,
this southwest flow favors the southern slopes, giving the San
Juans the best chance for upwards of a foot of new snow. The
influence of the first shortwave will move to the east of our area
by Wednesday evening. However, the second, large scale trough 
will begin lifting into our forecast area by early Thursday 
morning. So, given the continued southwesterly flow, some southern
slopes will see snowfall continue between these two forcing 
maximums just due to orographics. With the colder air moving in 
with second system, snow levels will drop but still expect the 
vast majority of the area to keep snow above 7500 feet throughout 
the heaviest snowfall. At any rate, the heaviest snowfall 
accumulations are expected during the day on Wednesday with the 
first push and again on Thursday morning with the second push.

One point of disagreement between the ECMWF and GFS deterministic
solutions is how fast the second system will move out of the area.
The GFS suggests that the best forcing will already be in eastern
Colorado on Friday evening just when the ECMWF has the best 
forcing over southwestern Colorado. Even with this uncertainty,
storm total snowfall still ranges from 10-20 inches with up to 30
inches in the San Juans with lesser amounts as you look further

The ensembles trend toward dry, northwesterly flow starting
Saturday in the wake of this second system. As such, temperatures
will remain below normal through the remainder of the long term


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 443 PM MST Mon Nov 18 2019

VFR conditions will persist over the next 24 hours as mid and high
level cloudiness increases ahead of the next system. Valley winds
will remain light though mid afternoon after which some afternoon
gustiness may develop. Conditions will deteriorate late Tuesday
evening through early Friday. 


CO...Winter Storm Warning from 11 PM Tuesday to 11 PM MST Thursday 
     for COZ018-019.

     Winter Storm Watch from Tuesday evening through Thursday evening 
     for COZ009-012.

     Winter Storm Watch from late Tuesday night through Thursday 
     afternoon for COZ013.

UT...Winter Storm Watch from Tuesday evening through Thursday evening 
     for UTZ028.

     Winter Storm Watch from late Tuesday night through Thursday 
     afternoon for UTZ023.



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