Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 192134

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
334 PM MDT Wed Jul 19 2017

.SHORT TERM...(Tonight through Thursday night)
Issued at 334 PM MDT Wed Jul 19 2017

Classic monsoonal pattern in place featuring a low pressure trough
over the West Coast and high pressure centered over the southern
Plains. Circulation between these two features continues to carry
subtropical moisture northward over the forecast area which has
raised precipitable water values (PW) to over an inch in the 12Z
sounding at KGJT. Deep subtropical moisture combined with daytime
heating will continue to fuel scattered to numerous showers and
thunderstorms late this afternoon and into the evening with
localized flash flooding possible. Consequently, will leave the
Flash Flood Watch in place through midnight.

Diurnal cooling will bring a downturn in shower/thunderstorm
coverage and intensity during the night and into Thursday
morning. However, with very little change in the weather pattern
described above indicated by latest models, expect conditions
Thursday afternoon/evening will be similar to today`s. However,
models indicated a decrease in PW which will translate into fewer
storms and a reduction in heavy rain producing storms. In the
absence of dynamic forcing, expect showers and thunderstorms will
largely diminish late Thursday night as the atmosphere stabilizes
with diurnal cooling.

Night time lows will remain above normal tonight and Thursday
night as clouds and moisture limit radiational cooling.
Conversely, highs on Thursday will remain a bit cooler than normal
due partly to mostly cloudy conditions and scattered to numerous

.LONG TERM...(Friday through Wednesday)
Issued at 334 PM MDT Wed Jul 19 2017

Monsoon moisture will continue to stream across the region from
the southwest on Friday. Both Nam and ECMWF indicated moisture
levels will rise with NAM suggesting PW values near 1.2 inches.
GFS was the outlier with near steady state moisture in the
atmospheric column. Regardless, it seems likely that
afternoon/evening showers and thunderstorms will remain capable of
putting down heavy rain with localized flooding possible. Should
models settle on a solution close to the latest NAM ab additional
Flash Flood Watch may be warranted.

NAM/GFS, and to a lesser extent the EC, indicated high pressure
will again migrate west bringing drier air down from the north
this weekend and into early next week. As a result, there will be
a trend toward decreasing clouds and thunderstorm activity from
Saturday into Sunday. EC and GFS were at odds as to when the next
monsoon surge arrives next week. In the EC solution moisture
returns Monday while the GFS only allows modest moisture back into
the area beginning Tuesday. Given model differences left low end
chance PoPs for Monday with increased chances Tuesday and
Wednesday. Temperatures this weekend through early next week will
be near or a little above normal.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1115 AM MDT Wed Jul 19 2017

Anticipating a stormy day today. Beginning to see cloud tops
increase in the San Juans where clear air has led to increasing
lapse rates. Thunderstorm activity should be fairly widespread
through 03z before shifting interest to NE Utah and NW Colorado
and will bring sites below ILS breakpoints at times. MVFR will be
possible if a TAF site is hit by stronger storms, but is expected
to be short lived. A similar pattern is expected Thursday.



CO...Flash Flood Watch until midnight MDT tonight for COZ001>003-006-

UT...Flash Flood Watch until midnight MDT tonight for UTZ022>025-



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