Area Forecast Discussion
Issued by NWS Grand Junction, CO

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756
FXUS65 KGJT 252158
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
358 PM MDT Tue Apr 25 2017

.SHORT TERM...(Tonight through Wednesday night)
Issued at 358 PM MDT Tue Apr 25 2017

An active afternoon today with plenty of clouds and showers (and
even a few lightning strikes) over the past several hours.
Precipitation will continue this evening but coverage will
gradually decrease as our latest disturbance is kicked to the
southeast. The Winter Weather Advisory is still in effect for the
San Juan Mountains until 9 PM this evening. Although the roads
look fine on webcams down south at the moment, periods of
decreased visibility and additional accumulations are still
expected this evening so will keep the Advisory as is and the
evening shift is welcome to re-evaluate the situation in a few
hours.

Orographic showers will linger in the northwesterly flow overnight
and into Wednesday as the next Pacific trough digs inland. With
such a messy transition between storms, we will not be seeing
clear blue skies, especially north of I-70. Coverage of showers
will quickly increase Wednesday evening, becoming numerous after
midnight. Snow levels will rise to between 8 and 9,000 feet
before quickly dropping to mountain bases by daybreak Thursday.
Models are showing impressive QPF values with this storm during
the overnight hours on Wednesday with significant accumulations
possible in a 6 to 12 hour period for the northern and central
mountains. Generally 6 to 12 inches are expected with locally
higher amounts possible, especially above 9000 feet. As a result,
have gone ahead and hoisted a Winter Storm Watch for these
locations. If the bulk of snow falls from 6 PM Wednesday to 6 AM
Thursday as anticipated, there will be definite impacts to travel,
especially over the higher mountain passes. It is, after all,
late April! Decided to leave the southern mountains out of the
Watch since these areas do not tend to do well in
westerly/northwesterly flow but definitely encourage later shifts
to take a closer look at these areas for potential highlights.

Temperatures will rebound slightly Wednesday afternoon but highs
will still be 5 to 10 degrees below normal. As the previous
forecaster mentioned, subfreezing temperatures will be possible in
some of the lower valleys in west-central Colorado and east-
central Utah tonight. However, widespread impacts are not
anticipated and, if sites do drop below freezing, it will only be
for an hour or so. Warm air advection and an influx of mid and
high level clouds ahead of the next system will allow overnight
lows to moderate Wednesday night and jump several degrees.

.LONG TERM...(Thursday through Tuesday)
Issued at 358 PM MDT Tue Apr 25 2017

Coverage of showers will shift to along the Continental Divide
Thursday afternoon as the shortwave trough lifts into the Plains.
Meanwhile, off the west coast, a well-amplified ridge begins to
set up the latter half of the week. This will push yet another
upper level trough into our forecast area Friday and into Saturday
with extended models even carving out a cutoff low. Details still
need to be worked out with this storm and would definitely prefer
to see some more model consistency. Regardless, the cool,
unsettled weather will continue through at least the end of the
work week. Temperatures will remain below normal through the week
and overnight lows will approach or reach freezing in many valley
locations.

Going even further into the extended, northwesterly flow appears
to set up over the region on Sunday. This will bring a shift
towards drier conditions although lingering moisture will more
than likely keep showers going over the northern mountains into
early next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1133 AM MDT Tue Apr 25 2017

Convection has kicked off across the forecast area with a few
thunderstorms having already formed. VCTS and Tempo -TSRA looks a
safe bet for many TAF sites this afternoon and evening as
convection continues. A stronger cell may drop flight conditions
to MVFR briefly but a return to VFR will occur quickly thereafter.
ILS breakpoints have already been met for most TAF sites and will
stay down through the evening hours. Most precipitation will end
by 03Z as clouds start to lift somewhat overnight.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until 9 PM MDT this evening for COZ018-
     019.

     Winter Storm Watch from Wednesday evening through Thursday
     evening for COZ004-009-010-012-013.

UT...None.
&&

$$

SHORT TERM...MMS
LONG TERM...MMS
AVIATION...TGR



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