Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 211756
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1156 AM MDT Tue Mar 21 2017

Updated aviation section

.SHORT TERM...(Today through Wednesday)
Issued at 343 AM MDT Tue Mar 21 2017

The 500 mb ridgeline will pass overhead today opening up the area
to increasing southwest flow aloft and at the surface. Today will
be a degree or two warmer than Monday due to less cloud cover and
slight warm advection ahead of the thermal ridge. Only isolated
showers and thunderstorms should form over the higher mountains
this afternoon and evening.

Wednesday will see the southwest flow continuing to increase increase
through the afternoon, along with increasing high clouds. All this
is ahead of the next Pacific storm. A 110 kt jet will spread over the
Four Corners by Wednesday evening, with mountain top winds
increasing to 40 to 50 kts ahead of this system.

The increasing winds and continued warm and dry conditions will
cause an increased awareness of fire weather conditions.

.LONG TERM...(Wednesday night through Monday)
Issued at 310 PM MDT Mon Mar 20 2017

Forecast models are in better agreement on the timing and
placement of this system impacting the area Wednesday evening
through Friday morning. Showers may develop in the southwest flow
ahead of this system by late Wednesday afternoon over the higher
terrain, but the better chances for precipitation will come
Wednesday night into Thursday. Abundant moisture is available as
Precipitable Water (PW) values increase to between 0.4 and 0.6
inches Wednesday evening into Thursday, with specific humidity
values in the 4 to 5 g/kg range. This is well above the normal
values for this time of year.

Warmer temperatures also mean high snow levels to start, with
snow levels mainly between 8000 and 9000 ft MSL during the day on
Thursday. The cold front looks to move through later than earlier
forecast model runs indicated, with current timing sometime
Thursday afternoon and evening. H7 temps will lower to -5C to -3C
post-frontal Thursday night into Friday morning, with snow levels
lowering to around 6000 to 7000 ft MSL.

The potential exists for 5 to 10 inches of snow in the mountains
and rain in the lower elevations at this time. The best chance for
the lower valleys to see snowfall will be after midnight Thursday
night into Friday morning as the colder air moves in with some
mixing of precipitation, but accumulations look limited. Decent
rainfall amounts however are possible in the valleys on Thursday
with potential for thunderstorms as well given the steep lapse
rates, instability and convective nature of this storm. The
southern and central mountains look favored for best snowfall
accumulations given the proximity of the low. Some wraparound
moisture is evident Thursday afternoon and evening on the north
side of the low with Q vector convergence over the central
mountains, as well as a TROWAL signature by Thursday evening in
that wraparound flow.

This system will move across our southern border as a closed low,
with the low strengthening and becoming vertically stacked by
Friday morning over the western OK panhandle and SE Colorado
border. This will take most of the energy to our east over the
Plains and Front Range by Friday morning with a drying trend
Friday afternoon from west to east. Some snowfall will linger
through Friday morning over the western Colorado divide mountains
with north-facing slopes being favored as the flow shifts from
the west-southwest Thursday afternoon towards northerly by
Thursday evening. This setup looks prime for the Uncompahgre
Gorge in the NW San Juans to see the potential for enhanced
snowfall Thursday night into Friday morning, so something to keep
an eye on. Will continue the Special Weather Statement and update
wording to reflect this potential. Still a little too early for
any winter weather highlites but this will be something for later
shifts to consider as details come into greater focus on snow
levels and amounts.

Models are in good agreement in showing a shortwave ridge of high
pressure building back into the region by Friday afternoon through
Saturday for mostly dry weather. Clouds and southwest flow will
increase on Saturday ahead of yet another storm system set to move
through the region on Sunday. The weather pattern looks unsettled
into next week as a series of systems move through the region
bringing potential for more precipitation.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1156 AM MDT Tue Mar 21 2017

VFR conditions will prevail over the next 24 hours, but winds will
pick up as a trough begins to interact with ridging in place.
Virga will develop over the higher mountains after 18Z, but not
expecting any measurable rain to the region. The virga will
produce erratic wind gusts late this afternoon and this evening,
so covered these in the tempos seen in the 18z tafs.

&&

.FIRE WEATHER...
Issued at 310 PM MDT Mon Mar 20 2017

Well above normal high temperatures and dry weather will continue
today. Relative humidities are again expected to drop into the 15
to 25 percent range this afternoon. The gustiest winds will occur
after 3 pm with wind gusts of 20 to 25 mph at lower elevations.
The gusty winds combined with warm temperatures, low humidity and
still dormant or dry vegetation will require a heightened fire
weather awareness. Check the latest forecast before attempting any
burning through as conditions can change rapidly. The potential
for near critical fire weather conditions will be greatest for
elevations below 8000 feet.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

SHORT TERM...CC
LONG TERM...MDA
AVIATION...JAM



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