Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 270503
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1103 PM MDT Sun Mar 26 2017

.UPDATE...
Issued at 1102 PM MDT Sun Mar 26 2017

Confidence on our next late season winter storm`s track has
improved after looking at the latest 00Z model runs. Moderate to
heavy snowfall is expected to fall in most mountain areas
beginning late Monday afternoon/early evening timeframe,
continuing through at least midmorning Sunday. As a result, have
gone ahead and hoisted Winter Weather Advisories for the eastern
Uinta and La Sal mountains in eastern Utah, as well as for the San
Juans and most of the Central Colorado mountains. This event will
be impact based with the highest accumulations and impacts
anticipated above 9000ft. The eastern Uintas will be favored at
the beginning of this storm with the passage of the cold front
early on with favorable northwesterly flow setting up behind it on
Monday afternoon. The San Juans will also be favored as the
cutoff low tracks near the Four Corners on Tuesday afternoon and
evening, generating impressive wraparound moisture and favorable
orographics. While roads may be wet during the daytime hours,
impacts are still expected over high elevation roadways,
especially HWY 550 over Molas and Red Mountain Pass as well as
Lizard Head Pass on HWY 145. These areas will see slick and
snowpacked conditions as well as the potential for blowing snow
and reduced visibilities.

&&

.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 arrive...in 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 06Z TAFS through 06Z Monday night)
Issued at 1102 PM MDT Sun Mar 26 2017

VFR conditions will continue to prevail overnight but our next
storm is already beginning to impact the area with an increase in
high cirrus over the last few hours, as seen on the latest
satellite imagery. Precipitation with this storm could begin as
early as 18Z over the higher terrain with coverage becoming more
scattered and then more numerous and spreading into the valleys by
00Z as the storm works through the region. Cigs will drop below
ILS breakpoints at several TAF sites including TEX, ASE, and EGE,
during heavier showers. Mountains will become obscured in snow
showers by tomorrow evening.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory from 6 PM Monday to noon MDT Wednesday
     for COZ009-010-012-013-018-019.

UT...Winter Weather Advisory from 3 PM Monday to 9 AM MDT Wednesday
     for UTZ023.

     Winter Weather Advisory from 6 PM Monday to 9 AM MDT Wednesday
     for UTZ028.

&&

$$

UPDATE...TGJT
SHORT TERM...MAC
LONG TERM...MAC/MPM
AVIATION...MMS



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