Area Forecast Discussion
Issued by NWS Grand Junction, CO

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

FXUS65 KGJT 111748

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1148 AM MDT Fri Aug 11 2017

Updated aviation section

Issued at 859 AM MDT Fri Aug 11 2017

Did an update to the probability of precipitation for today with
activity having already begun very early today. The plume of
monsoonal moisture reaching into the Four Corners is bringing rain
to some valleys and into the San Juans. Another area of
instability is across the Uncompahgre and Delta/Montrose areas,
and a third area across NE Utah and NW Colorado where the jet
support aloft is strongest.


.SHORT TERM...(Today through Saturday)
Issued at 303 AM MDT Fri Aug 11 2017

A few showers and thunderstorms persist this evening but they are
very isolated in nature. The convection is thanks to a few
stronger vort maxes moving through the mean flow. Looking to our
west, a few cells also continue for Utah so this trend will likely
continue through the morning hours.

As far as the big picture is concerned, high pressure remains to
our south and a slight shift eastward has caused an increase in
moisture. Nothing too excessive, mind you, but enough to cause an
expected uptick in convection this afternoon and evening. Current
IR satellite also shows plenty of clouds to our south, drifting
northeast. Folks that live from the Grand Valley south will notice
these clouds this morning. The clouds will persist through much
of the day becoming a bit thicker as they day progresses. Even
with the clouds in place, another round of convection is expected
today starting around noon and persisting through the evening
hours. Gusty winds and small hail are possible and some heavier
rainfall is also expected thanks to the increased moisture. The
San Juans and areas south look favored today. Even so, all higher
terrain from the Roan/Tavaputs southward will likely see some
convective development.

Saturday looks to be a bit busier even though the moisture tap
from the south will shut down thanks to flow becoming westerly.
However, a weak trough will move over the area from noon onwards
and with weak upper level jet support remaining in place, the
ingredients look to be in place for an active day. Would not be
surprised to hear of a few minor debris flows thanks to the
heavier rainfall.

Temperatures will remain near normal, give or take a few degrees,
thanks to increased cloud cover and rainfall from time to time.

.LONG TERM...(Saturday night through Thursday)
Issued at 303 AM MDT Fri Aug 11 2017

Moisture lifting north and east ahead of longwave trough pushing
into the Great Basin will keep showers and thunderstorms in the
forecast through early next week. Models insisting on a push of
drier air as southwest to west flow develops in the
Tuesday/Wednesday window. Normally, this would be expected, but
plenty of moisture will be lingering to the south with active
tropics and pushes of moisture from decaying convection in
northern Mexico to continue. Also seeing a far amount of model
spread between the GFS and EC, so not quite ready to pull the plug
on the daily convection across the area. However, there will be
less activity and temps will be climbing back above seasonal norms
through the period. Beyond this extended period, CPC 8 to 14 day
outlook shifting odds back into the dry and warmer arena for at
least a week or so.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1148 AM MDT Fri Aug 11 2017

Active day expected as several features are over the area - jet
aloft is strongest across NE UT and NW CO and monsoonal moisture
is increasing from the southeast into the Four Corners.
Anticipating rain and embedded heavy rainers across SE UT and SW
CO, whereas storms across NE UT and NW CO will be more organized
and longer lasting but less coverage across the region. ILS
breakpoints could be reached in heavier storms, with even the
chance for MVFR at times if stronger storms reach the airports.
Instability continues after 00z over the San Juans and in the Four
Corners region allowing showers and thunderstorms to continue into
the nighttime hours.




AVIATION...JAM is the U.S. government's official web portal to all federal, state and local government web resources and services.