Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 202343

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
543 PM MDT Sun Aug 20 2017

.SHORT TERM...(Tonight through Monday night)
Issued at 345 PM MDT Sun Aug 20 2017

Southerly moisture has increased throughout the day across the
southern half of our forecast area which has led to an uptick in
clouds as well as orographic showers this afternoon. Still,
available moisture is relatively high based with this morning`s
upper air sounding boasting a PWAT only a tenth of an inch higher
than 12Z yesterday. With that being said, gusty outflow winds will
continue to be the primary threat with storms this afternoon and
evening as opposed to heavy wetting rains, though some brief locally
heavy rain is still possible with "juicier" storms. As has been the
trend the past couple of days, most convection will end after
sunset. Overnight lows this evening will be slightly warmer in
response to increased cloud cover.

The area of low pressure will remain well situated over southern
California on Monday with high pressure to our east over the
southern Plains. As a result of this continued weather pattern we
should not expect much change to our forecast on Monday with another
round of diurnal scattered showers and thunderstorms over the higher
terrain. Mid and high level clouds will prevail with overall sky
cover increasing from north to south. Given this the best viewing
locations for the eclipse on Monday afternoon will be further
north across portions of northeast Utah and northwest Colorado
where only some benign and thin cirrus are expected. Anticipate
another quiet night for Monday with hardly any fluctuation in
overnight lows.

.LONG TERM...(Tuesday through Sunday)
Issued at 345 PM MDT Sun Aug 20 2017

Tuesday will see the upper level ridge axis shifting further
westward and beginning to build over our forecast area. The SoCal
low will drift back towards the Pacific coast in response. As
mentioned previously, it`ll be a messy transition with not much in
the way of substantial drying but also not much of a surge of
monsoonal moisture. Even so, given the presence of residual
moisture, orographics, and daytime heating we can expect scattered
showers and thunderstorms during the afternoon and evening hours.
The same is now true for Wednesday as extended models appear to have
slowed a bit in the arrival of the deep low situated over the Gulf
of Alaska which will be the driving force to usher the persistent
SoCal low inland and through the Great Basin. The position of the
upper level ridge axis will be crucial for the forecast through
midweek as that will dictate how much monsoonal moisture is able to
be advected into our region.

The aforementioned Gulf of Alaska low will dig deeper off the coast
of the Pacific Northwest towards the latter half of the work week,
finally kicking the SoCal low out of its rather stationary state.
Extended models have this feature becoming an open wave trough as it
progresses into the Great Basin, shifting the ridge axis and
allowing for a more substantial surge of moisture to set up over the
forecast area. Better coverage of showers and thunderstorms should
develop in response to this increased moisture around or after the
midweek point.

Drier northwesterly flow looks to set up behind this trough as high
pressure rebuilds over the Great Basin, initiating a drying and
warming trend.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 539 PM MDT Sun Aug 20 2017

Plenty of clouds can be found across the forecast area this
evening with most ceilings hovering around 10K feet or so. Some
convection also continues at this hour but is already waning so
not much concern for any TAF sites to have thunderstorm issues
over the next few hours. Clouds will remain overnight and vary
from scattered up north to more broken down south. Again, cloud
heights should remain well above ILS breakpoints so no TAF
concerns then. For tomorrow, expect another round of showers and
storms firing over the higher terrain before moving into valleys.
Did not include VCTS at this time as confidence not high enough
yet as to which airports will be affected. KDRO and KTEX look to
be the most vulnerable for now.




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