Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 261816
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1216 PM MDT Sun Mar 26 2017

.UPDATE...
Issued at 905 AM MDT Sun Mar 26 2017

Snow was winding down in the mountains this morning, becoming more
scattered in coverage. Expect additional accumulations will be
light, therefore allowed the Winter Weather Advisory for the San
Juan Mountains above 9500 feet expire.

&&

.SHORT TERM...(Today through Monday)
Issued at 500 AM MDT Sun Mar 26 2017

Upper air hand analysis at 500mb show a fairly blocky flow pattern
across the lower 48. Ensembles suggests the heights along the
mid-Atlantic coast to Great Lakes are slightly anomalous. This
ridge is helping to keep a closed low over the MS valley which is
holding back low pressure over our area from sweeping eastward at
a faster pace. Radar mosaic had cooled off late last evening but
through the early morning hours has blossomed. This is mainly due
to convection as the cold core of the trough is slowly translating
across western Colorado ahead of the back edge of the upper level
channelized vorticity. The echos on radar also show northerly flow
in place with cold air advection now favoring north facing slopes.
Places like Telluride...and the Highway 550 corridor from Ridgway
to Silverton will be favored. Snotels show mainly 3 to 6 inch
totals with a few outliers in the 8 to 10 inch range so advisory
is well on track. Snow is down to at least the 7000 foot mark and
there will be some impacts to roadways in the south including
Highway 160 between Durango and Cortez and 550 as mentioned above.
Satellite imagery suggest this system will be focusing east of the
divide by sunrise as the cyclonic jet slides into SE Colorado and
lowers heights aloft and forces cyclogenesis at the surface.
Drying of the dendritic layer and increasing mid level instability
through the afternoon should leave mainly isolated showers in
place favoring the higher divide mountains to the eastern San
Juans. Transitory ridging overnight means dry conditions overnight
which will preclude decent WAA tomorrow morning in the mid
levels. This WAA will be evident by the increasing mid level cloud
deck from SW to NE across the CWA from sunrise onward Monday
morning. Felt the chances of precipitation in the lower elevations
were a bit too optimistic as the lower portion of the the
sounding will be quite dry. Virga seems more likely through the
late morning into early afternoon in most elevations below 7000
feet. Elevated stability decreases and ascent increases with the
arrival of the next cyclonic jet by mid afternoon and showers
will be expanding across the region. Snow levels start around 9000
feet through influenced by convection could be as low as 7500
feet. Temperatures a bit tricky on Monday with thicker mid level
cloud cover being replaced by more patchy convective clouds in the
afternoon. There is a 13 degree spread in the Max numbers just at
GJT as a result and will not make a big swing either way attm.

.LONG TERM...(Monday night through Saturday)
Issued at 500 AM MDT Sun Mar 26 2017

The pattern across the mid latitudes again favor the early week
system to close off to our west Monday night and dig southeast on
Tuesday before swinging east Tuesday night. Ensembles show this
storm picking a decent amount of Pacific moisture out West but it
will really tap the Gulf as it slides south of the 4 Corners on
Tuesday. This storm will bring widespread precipitation much of it
in the form of snow above 8000 feet. Convection will again play a
big role with steep lapse rates leading to afternoon thunderstorms
in many areas on Tuesday. Model spread still interesting with the
H5 low tracks spread from northeast to south-central New Mexico
Tuesday afternoon. Snow is excess of 6 inches again probable over
many mountain locations above 8500 feet by Wednesday morning. The
southern mountains would have to be favored due the proximity of
the low and upper jet.

Confidence in the speed of the potentially cut-off upper level low
over northern NM moving east is moderate as most such lows move
out slower than models predict. However, the GFS and ECMWF do
agree on moving it east into the Central Plains Wednesday and a
brief building an upper level ridge over the region Wed night and
Thursday. There may still be some remnant scattered showers over
the higher terrain Wednesday on the backside of departing low
pressure. Thursday should be dry and warmer.

Then yet another vigorous upper level trough, which is handled
very similarly in the long range models, will drop southeast over
the Great Basin Thursday, cut off Friday and settle south over
Arizona into early next weekend. Sensible weather affects over
eastern UT and western CO are of moderate confidence due to the
nature of cut-off lows despite good agreement in the models. With
such a dynamic system and strong upper level divergence on its
east side as it drops south, would expect a high probability of
precipitation Thursday night and Friday. However, will remain
cautious with precipitation chances and realize that any deviation
in the path or intensity of this system will result in
significant changes one way or the other. A more eastward path
over UT/CO will mean colder with snow at lower levels. A more
westward path leaves our area warmer and drier.

&&

.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.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

UPDATE...NL
SHORT TERM...15
LONG TERM...15/BM
AVIATION...NL


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