Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 262107

Area Forecast Discussion
National Weather Service Grand Junction CO
307 PM MDT Sun Mar 26 2017

.SHORT TERM...(Tonight through Monday night)
Issued at 300 PM MDT Sun Mar 26 2017

As our most recent storm system continues to head eastward into
the high plains, weak ridging aloft has begun over the western
slope this afternoon. Despite rising heights, lingering low level
moisture and cooler air aloft has resulted in a few scattered snow
showers in the central and southern Colorado mountains. These
showers should quickly diminish once surface heating ends toward
sunset. A mainly dry overnight is forecast as the ridge axis
passes east of the divide around sunrise.

Clouds will thicken early on Monday as our next storm moves in
from the west. Monday high temperatures continue to be a bit
problematic with significant differences in forecast guidance.
Have opted to nudge temperatures upward by a degree or two in
this forecast package favoring the warmer MET guidance, given
strong mixing and warmer southerly flow portrayed in several
forecast soundings across the region. Still thinking that cloud
cover and eventually precipitation, especially in western and
northern zones, will ultimately limit temperatures from reaching
their full potential portrayed by the warmest guidance.

Precipitation will begin in the eastern Uinta mountains around
noon Monday, and will spread into the western Colorado high
country during the afternoon. Forecast soundings do indicate a
small amount of instability during the afternoon hours Monday.
Would not be surprised to see some convective showers and some
thunder in locations along and south of the I-70 corridor. Snow
levels will be high to start, above 8000 feet, but will steadily
drop through the event.

.LONG TERM...(Tuesday through Sunday)
Issued at 300 PM MDT Sun Mar 26 2017

The 500mb trough will slowly cut off across the Four Corners
after midnight on Tuesday morning. Forecast guidance continues to
show quite a range of solutions regarding precipitation totals
for this event. For the mountains of Colorado west of the divide,
liquid equivalent totals from the GFS, NAM, ECMWF, and GEM
deterministic models range anywhere from 0.5 to over 1 inch. With
snow ratios around 10:1, this would lead to anywhere from 5 to 12+
inches of snowfall. The 12z GFS showed particularly heavy
precipitation totals, and is the highest outlier at this point.
700mb temperatures are cooler, but not particularly cold, when
the best lift and dynamics the -3 to -5 range on
average from the New Mexico to Wyoming border. Despite this,
relatively mild air in the lowest portion of the atmosphere will
contribute to higher lapse rates and some convective potential
again during the day Tuesday. The potential for convective
snowfall, and briefly heavier precipitation rates, further
complicates the total precipitation forecast. Due to the continued
uncertainty in QPF totals, have opted to wait another forecast
cycle to determine the best course of action regarding highlights
for this event.

As the upper level cutoff low shifts east, lee cyclogenesis will
commence over the southern plains on Tuesday afternoon. This will
shift dynamic support for snowfall to the front range and points
eastward. Despite the loss of dynamics, lingering moisture and
northwesterly upslope flow will result in mountain snow showers
through the night and into Wednesday morning. The ECMWF and NAM
end precipitation in the mountains around noon, with the GFS
holding on to a few snow showers in the Elk, Gore, and Sawach
ranges through 6pm.

The storm system will move east across the High Plains on
Wednesday night bringing an end to the precipitation to all
mountain locations. A transient ridge will provide a short break
as the next storm system drops into the Great Basin region on
Thursday. Both the GFS and the EC take this closed low to a
position near the Four Corners region on Friday and slowly move
the storm east near the Colorado/New Mexico state line on
Saturday. The EC takes a faster and more progressive solution
moving the storm out of our area by Saturday as a quick moving
shortwave drops southeast into New Mexico by Monday. Run to run
consistency has been fairly low with this storm so confidence is
low regarding details of the storm. However, this storm is quite
cold and fairly wet so depending on its exact track, the
possibility exists for significant snowfall in some mountain
locations late Thursday into the weekend.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1216 AM MDT Sun Mar 26 2017

Impacts from the last night`s storm continued over eastern Utah
and western Colorado through the early part of day. Showers were
more limited and confined to the higher terrain. This trend will
continue through the afternoon so do not expect showers to occur
over TAF sites. However, residual low level moisture and
instability is expected to keep CIGS below ILS breakpoints for
much of the afternoon over KEGE and KASE. Clouds will be
diminishing this evening as the atmosphere stabilizes so expect
TAF sites will see a return to VFR conditions region wide.




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