Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 252332

Area Forecast Discussion
National Weather Service Grand Junction CO
532 PM MDT Sat May 25 2019

.SHORT TERM...(Tonight through Sunday night)
Issued at 212 PM MDT Sat May 25 2019

What is this bright orb in the sky? We have missed you! It`s kind
of nice to see the sun making a return after much of last week
was shrouded in clouds and moisture...although the moisture is
still welcome. Some cumulus clouds seen forming over the ridges
from the bookcliffs northward but overall, mostly sunny skies were
the rule today. Temperatures warmed up quite nicely as expected
with 70s for a change in the lower central and southern valleys.
Skies will be clear overnight but freeze potential will be very
minimal to not expected due to continued warm air advection aloft.

Warm southwest flow will continue on Sunday as a deep cold core low
dives down the Pacific coastline with a southern destination of the
Desert Southwest in mind by Sunday night. Expect a mostly dry day on
Sunday with H7 temps in the +7C to +11C range. What this means is
70s for pretty much all valley locations with some low 80s
potentially creeping into the canyon country in southeast Utah.
Models are beginning to come into better agreement in regards to a
weak shortwave ejecting out ahead of this western low from the
southwest late in the day on Sunday. This will allow for isolated
thunderstorms to form over the higher terrain of the western
Colorado late Sunday afternoon into the evening, favoring the
southern and central Colorado mountains closer to the divide. Storms
are expected to be high-based with gusty winds and very little in
the way of precipitation as models are not showing much QPF, with
the GFS coming around to the much drier NAM. Winds may be a bit
breezy Sunday afternoon though due to this faster flow aloft, also
leading to a pretty warm day with highs closer to normal for this
time of year and mostly dry conditions. Decided to hold off on
wind advisories with this package but something for later shifts
to consider for the Four Corners area on Sunday as it remains
close to reaching criteria.

.LONG TERM...(Monday through Saturday)
Issued at 212 PM MDT Sat May 25 2019

The low pressure system out west will begin making its progression
eastward through the southern Great Basin with the center of the
closed low arriving over the Four Corners region by late Monday
afternoon/early evening. Moisture will increase across eastern Utah
Monday morning and spread into western Colorado by afternoon with
convection developing over the high terrain. Expect high snow levels
to start (10k to 12k feet) as H7 temps remain fairly mild ahead of
this system (+2C to +6C on average in most model solutions) but snow
levels should lower to between 7k and 8k feet Monday evening as the
cold core low tracks across the San Juans and arrives over northeast
Colorado by Tuesday morning. H7 temps will lower to the -2C to -4C
range with passage of this low. Although the -4C center tracks
across the San Juans into the West Elks, the cooler air will affect
all mountain areas Monday night into Tuesday morning. Temperatures
warm up quite a bit across the southern and central tier by Tuesday
afternoon as snow levels rise but cooler air remains across the
north where moisture will wraparound the low in northwest flow,
allowing snow to continue unabated for elevations above 8000 to 9000

There are some timing and placement differences between the GFS and
NAM with the NAM a bit more progressive and keeping the precip
focused more across the northern mountains during the day on
Tuesday, while the GFS extends these chances down to the central
Colorado mountains as well. The interesting thing with this system
is that the moisture content actually increases in the wraparound
moisture post-frontal after the low has moved east of the divide on
Tuesday. Standard precipitable water anomalies actually show drier
air working into the Four Corners under the center of this low
Monday evening with lower specific humidity, which could act to
undercut snow potential in the San Juans. The PWAT anomalies
increase Tuesday morning into the afternoon though as the low picks
up a little Gulf connection to the moisture and wraps this back
around the low into our northern and central Colorado mountains.
Specific humidity values take a ride up towards 5 to 6 g/kg by
Tuesday. It does appear though that winter weather highlites may be
needed for this late May storm system over the mountain areas with
the northern and central Colorado mountains looking favored for the
higher snow totals above 8000 feet. Conditions dry out finally by
Tuesday evening as northerly flow takes hold with the low pulling
further away from the area towards the northern High Plains and
upper Midwest.

Shortwave ridging takes hold for Wednesday with some convection
possible in the afternoon over the higher terrain but overall a
drier and milder day as warm air advection returns. Lower confidence
exists in the long term from Wednesday onwards as model solutions
differ with run to run variability. General weak troughing remains
out west with weak ridging across the Plains, leaving us in this
weak southwest flow with a few weak disturbances moving through time
to time. This will mostly lead to a warming trend as H7 temps rise
once again, pulling us back to where we started before the Monday-
Tuesday low. Isolated to scattered thunderstorms look possible each
afternoon through this period due to enough instability, lift and
remnant moisture with activity favoring the high terrain.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 532 PM MDT Sat May 25 2019

VFR conditions expected the next 24 hours with limited moisture
for making lower cloud decks. The main concern will be gusty
southerly winds that will be developing ahead of the next
approaching storm system to the West. Areas of LLWS are likely
along with ridgetop and mountain wave turbulence. As heating takes
place on Sunday expect most TAF sites to see gusts over 25 mph in
the afternoon.




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