Area Forecast Discussion

FXUS65 KGJT 201743
Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1143 AM MDT Tue Mar 20 2018
.SHORT TERM...(Today through Wednesday)
Issued at 440 AM MDT Tue Mar 20 2018
A weak disturbance moving over the northern Colorado mountains 
brought light snow to the area early this morning as confirmed by
KSBS and an area webcam. Steep lapse rates, modest Pacific 
moisture and orographic lift provided by favorable northwest flow 
will continue to bring light snow to the Elkhead, Flat Top, Park 
and Gore mountains today. Small perturbations in the 120-130 kt 
jet over northwest Colorado will also play a role. Accumulations 
are expected to be light and generally less than 2 inches. 
Elsewhere, dry conditions will prevail with mostly cloudy skies 
across the north giving way to mostly sunny conditions across the 
southern part of the forecast area. Weak warm air advection (WAA) 
combined with sunshine will cause temperatures to warm relative to
Monday with afternoon highs approaching normal for most 
Snow showers will continue tonight across those northern 
locations outlined previously, but will become more scattered and 
lighter as WAA causes lapse rates to become less steep. Meanwhile,
clouds will increase during the night as mid and upper level 
moisture begins to move over the area from the southwest. This 
moisture will fuel isolated to scattered showers over the northern
and central mountains on Wednesday, with slight chances over the 
southern mountains. Continued WAA will result in snow levels 
ranging from near 9500 feet in the south to around 8500 in the 
north by late afternoon. Despite clouds and shower activity, 
temperatures will continue to trend upward with highs expected to
climb to low to mid 60s in the lower valleys, with 50s in the 
higher valleys, and 40s in the mountains. 
.LONG TERM...(Wednesday night through Monday)
Issued at 440 AM MDT Tue Mar 20 2018
The 500mb ridge axis is forecast to pass through western Colorado
after midnight on Thursday morning. As it does, clouds will 
overspread the entire Western Slope ahead of our next storm 
system. Despite the cloud cover, the warmest day of the week is 
expected on Thursday with highs running 10 degrees above average.
Despite the abundant moisture stream originating in the tropical 
Pacific with the approaching storm system, the Western Slope will
remain relatively dry on Thursday, even in the mountains. 
Guidance has shifted a bit farther west with the overall track of 
the precipitable water plume, and most of this moisture will track
northward over Utah on Thursday, rather than from the Four 
Corners through Colorado. That being said, a large trough finally 
pushes residual moisture eastward later on Thursday night into 
Friday morning. Expect precipitation to begin in the mountains 
late Thursday evening, and last for around a 24-hour period ending
by midnight Saturday. Temperatures will be a key factor with this
event. Guidance currently depicts 700 mb temps of around +2 to 
+5 C when precipitation begins Thursday night. This would result 
in snow levels above 10,000 feet to start. Eventually,
temperatures at this level drop to around 0 C by noon Friday as a
cold front swings eastward across Utah and Colorado. The front 
reaches the Continental Divide by sunset Friday, however by that 
time much of the moisture with this storm system will have moved 
eastward. The bottom line for the Thursday night through Friday 
timeframe will be a relatively warm event with snow in the higher 
terrain, rain changing to snow in areas from 7 kft to 10 kft, and
mostly light rain showers below 7 kft. 
A dry day is in the forecast for early Saturday before our next 
trough drops in from the Pacific Northwest on Saturday evening. The 
most recent deterministic run of the GFS hinted at a slight 
southward shift with this system which would bring some light 
mountain snowfall to all mountain ranges on Sunday. Will hold off
on biting on this solution for now, as the ECMWF remains slower 
and to the west, and both EPS and GEFS ensemble guidance show only
a marginal trough skirting the Rockies at this time.
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1143 AM MDT Tue Mar 20 2018
Winds will become a little breezy this afternoon at most TAF sites
with scattered to broken skies. Broken to overcast skies will be
more prevalent across the south and the north, affecting KCNY,
KDRO and KTEX down well as KHDN, KASE, KEGE and KRIL up
north. CIGS may fall below ILS breakpoints at times throughout the
day at KHDN, KASE and KEGE in off and on light snow showers and
lower clouds due to a weak passing disturbance. Mid and high level
clouds will increase after midnight into Wednesday morning across
much of the region with light drainage winds overnight.