Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 160447

Area Forecast Discussion
National Weather Service Grand Junction CO
1047 PM MDT Mon Oct 15 2018

.SHORT TERM...(Tonight through Tuesday night)
Issued at 320 PM MDT Mon Oct 15 2018

Essentially a blue bird day across eastern Utah and western
Colorado this afternoon with just a few fair weather cumulus
clouds throwing a wrench in that otherwise perfect descriptor.
After the widespread season ending freeze this morning, daytime
highs have struggled to recover, even under the abundant sunshine.
The cold airmass that was left overhead in the wake of Sunday`s
cold front has kept temperatures around 20 degrees below normal
across the board today.

The cutoff low pressure system is just beginning to close off over
southeast California and western Arizona this afternoon. The
center will shift further east into central Arizona overnight with
clouds and showers wrapping around it cyclonically. The southern
tier of our forecast area, generally extending from San Juan
County, Utah over to Hinsdale County, Colorado, will see an
increase in low- and mid-level clouds overnight. As a result,
overnight lows will rebound some 3 to 6 degrees. Elsewhere, expect
another chilly night with minimum temperatures in the teens for
the mountains and in the mid to upper 20s for the northern and
central valleys. After breaking today`s low temperature record of
28 degrees by hitting 27 degrees this morning, Grand Junction
could set or tie another record low tonight. The current record is
27 degrees, set in 2017.

From daybreak Tuesday through midnight Wednesday the center of
the low will have progressed north into the Four Corners. As the
storm travels north we can expect isolated showers to become
scattered in coverage down south before reaching the Tavaputs
Plateau during the overnight hours. To ensure continuity, will go
ahead and defer the finer details, and main concerns, in regards
to this storm to the Long Term discussion below.

.LONG TERM...(Wednesday through Monday)
Issued at 320 PM MDT Mon Oct 15 2018

Have decided not to issue any Winter Weather Highlights at this
time in regards to the closed low that is set to impact the Four
Corners area late Tuesday and Wednesday. Not only is there a
considerable model spread in storm total snowfall accumulations
for the southern mountains, but there are also two primary
concerns in regards to the storm`s origin and the resulting
flow aloft over western Colorado. First, to tackle the storm`s

The area of low pressure that is currently situated over Arizona
originated from the broad, positively tilted Pacific trough that
dove from the Canadian Rockies this past weekend. So, from a
significantly cooler region that brought us 700 mb temperatures
ranging from -4 to -8 degrees Celsius south of I-70 and as low
as -14 degrees further north. However, now that the low has
cutoff over the Desert Southwest, much warmer air will be
introduced into it as it lifts north on Wednesday and Thursday. So
while this system will still retain a cold core, with 700 mb
temperatures ranging from -2 to -4 degrees Celsius Wednesday
afternoon, the warmer air originating from down south could wreck
havoc on snow levels. Next, let`s discuss the resulting flow aloft
as the low lifts north.

From the Tuesday night to Wednesday afternoon timeframe, southwest
Colorado will be siting under easterly or at least southeasterly
flow. The San Juan Mountains typically do not do well in this
flow, which is another cause for hesitation on issuing any
highlights. By the time the low`s center reaches southern Utah on
Wednesday night, and flow finally shifts to the a more favorable
southwesterly, the peak amount of available moisture will have
passed. Finally, as stated earlier, significant accumulation
discrepancies exist with this afternoon`s models. Here`s a
breakdown of storm total projections for the San Juans (through 6
PM MDT Wednesday)...NAM12: 15 to 20 inches, NAM40: 12 to 16
inches, GFS: 3 to 6 inches, and the Euro: Maybe 2 inches at the
most. The drastic model spread is impacting the southern valleys
as well with the NAM12 projecting 7 inches in the town of Durango!

Needless to say, there`s a lot of variables in play. However, we
will certainly keep monitoring the situation because the potential
for heavy snow is still there. As for the rest of the extended
forecast, the closed low looks to transition to an open wave on
Thursday with the trough quickly lifting to the northeast on
Friday as a strong ridge of high pressure moves in from the west.
Temperatures will gradually warm through the weekend under mostly
sunny skies.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1031 PM MDT Mon Oct 15 2018

Mid and high clouds expected to slowly spread north into
southeast UT and southwest CO. Then showers developing after
about 00Z Tuesday into southeast UT and southwest CO, with
scattered snow showers over Mountains down to about 8000 foot
level resulting in areas of MVFR and local IFR cigs/vsbys. Clear
skies expected to continue through the period along and north of




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