Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 240459
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1059 PM MDT FRI SEP 23 2016

.UPDATE...
Issued at 633 PM MDT Fri Sep 23 2016

Still seeing good precipitation across the area with a few
embedded thunderstorms early this evening. The only area that
seems to be left out is southeast UT. Therefore upped pops/clouds
quite a bit over a good portion of the area for the next few
hours. Satellite images indicate that there continues to be
additional energy on the backside of the low that will rotate into
the area later tonight. Therefore, after the present bout of
activity winds down a little later this evening, we can expect to
see precipitation again pick up shortly after midnight. The
favored area will then be over the northern portion, but have
stretched pops farther south than the previous forecast indicated
with isolated in the central valleys and chance in the central
mountains.

&&

.SHORT TERM...(Tonight through Saturday night)
Issued at 324 PM MDT Fri Sep 23 2016

At 21Z it appears the front has arrived to the Divide and is
leaking over. Snow was quite abundant with the front earlier today
with accumulations down to at low as 8000 feet and temporary
impacts to the roadways above 10000 feet. Though a period of snow
is likely to continue over our eastern mountains road and ambient
air temperatures should limit the accumulations. Convection of
course can render that last statement as false but do not
anticipate a need for winter highlights this evening. Water vapor
is showing the main system driving this front spinning back over
the UT/ID/WY interface. A dry punch and subsidence should allow
for clearing across much of the region before a backside spoke of
energy rotates around the low as it shifts farther into Wyoming
overnight. Dynamics are not overly impressive as QG progs show the
greatest up lift well north near and north of the upper low
center. Instability is marginal but weak ascent and moist
orographics should lead to snow falling over the northern
mountains of Utah and Colorado Saturday morning. Impacts will be
the greatest above 9000 feet where generally 2 to 5 inches should
accumulate. Therefore have issued an early season winter weather
advisory for the snowfall. Temperature guidance has come in a bit
warmer with added moisture and cloud cover. The Gunnison Valley
could see some sub freezing temperatures near sunrise otherwise
confidence not to high for freeze headlines. This looks more
certain by Sunday morning as drier air moves in and skies clear.
Many of the higher valleys could push below the freezing mark.
Precipitation will linger across the northern mountains of
Colorado through early afternoon Saturday...with snow becoming
less of a factor as temperatures warm in the afternoon.
Temperatures will be a bit warmer tomorrow expect in the high
eastern mountains where prefrontal temperatures were allowed to
warm today.

.LONG TERM...(Sunday through Friday)
Issued at 324 PM MDT Fri Sep 23 2016

Dry weather is expected to return to the forecast area Sunday and
Monday. The storm which brought wind, heavy rain, and mountain
snow splits Saturday night with the bulk of the energy moving to
the northeast. However, a portion of the jet digs southward
carving out a closed low over central New Mexico. The moisture
wrapped system to the south will retrograde west-southwestward
across northern Mexico to the Gulf of California by Monday
evening. During this period, a dry northeast flow Sunday will
give way to dry easterlies on Monday. Forecast highs Sunday will
remain below average, though temperate in the valleys with cool,
crisp fall conditions in the mountains. Continued sunshine on
Monday will bring afternoon temperatures back to near normal
levels.

From Monday night into Tuesday the closed low will move from the
northern Baja region to southwest Arizona. Models indicated a
weak lobe of vorticity moving northward along the eastern edge of
the low could bring some light showers to the San Juan Mountains
during the afternoon/early evening. Chances improve Tuesday and
Tuesday night as the low lifts across Arizona and becomes
entrained in the prevailing continental flow. Confidence is very
good up to this point as both the ECMWF and GFS were in solid
agreement. However, Thursday`s weather is less clear as the GFS
becomes more progressive and dryer, in stark contrast to the ECMWF
which indicated showery and cool conditions will persist. Given
model differences am forced to accept the blended solution which
features a little of both. By Friday however, both models were
back in agreement over eastern Utah and western Colorado with
moisture in southwest flow feeding localized moist convection
during the afternoon. Except for some cooling Wednesday resulting
from cloudy/showery conditions in response to the passage of the
low, temperatures are expected to hover right around normal for
the last days of September.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1037 PM MDT Fri Sep 23 2016

A northwest flow will continue to spread across the area during
the next few hours. This will bring a secondary wave across the
northern half of the area late tonight and into the morning. As a
result precipitation with snow above 7500-8000 feet will increase
for a period early Sat morning. The main areas of concern will be
in the mountains along and north of Interstate 70 that will be
favored for precipitation. In addition other mountains along
the Continental Divide and some higher valleys may see areas of
fog. At times mountains will be obscured. KASE...KEGE and KVEL at
times may see MVFR or brief IFR conditions in showers and low
clouds. Conditions will begin a slow improvement by late morning
and through midday on Sat with VRF conditions area-wide. Drier
conditions are then expected through Sat evening.


&&

.GJT Watches/Warnings/Advisories...
CO...Winter Weather Advisory until 11 AM MDT Saturday for COZ004-013.

UT...Winter Weather Advisory until 9 AM MDT Saturday for UTZ023.

&&

$$

UPDATE...EH
SHORT TERM...15
LONG TERM...NL
AVIATION...EH



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