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Area forecast discussion 
National Weather Service Phoenix Arizona
815 PM MST Sat Sep 20 2014

Synopsis...
lingering moisture across the region and low pressure approaching
from the west will keep at least slight chances for showers and
thunderstorms for today. Drier air will gradually filter
into the region Sunday and Monday for a decline in storm chances.
Slight chances for showers and thunderstorms will be confined to the
higher mountains of south-central Arizona during the middle of next
week with slightly above normal temperatures. An approaching
Pacific weather system late next week will lead to an increase in
storm chances.

&&

Discussion...
a very vigorous Pacific shortwave that moved into central and
Southern California Saturday provided weak upper level support across
central Arizona for a few strong heat of the day thunderstorms near
Phoenix given the rich moisture supply. For the remainder of the
evening only a slight chance of showers and thunderstorms can be
expected through midnight in the absence of surface heating and
outflow boundaries. Clearing skies are expected after midnight
across the entire forecast area.

As the Pacific trough moves farther north and away from Arizona...into
central Nevada...a more dynamically stable atmosphere is expected
Sunday afternoon and evening. A thinning of boundary layer moisture
is also expected from the west. Only a slight chance of thunder-
storms are forecast over the mountains of southern Gila County zone
24 east of Phoenix on Sunday.

Updates were made to diminish the chance of shower/thunderstorm activity over
south central Arizona the remainder of the evening. Otherwise...no
additional updates are expected. Previous discussion still applies.



Previous discussion...340 PM MST...
precipitable water values hovering around 1.5 inches across the
lower deserts and a very broad difluent middle-layer stretching
north-northwest through the Great Basin allowed for convective
development in south central Arizona Saturday afternoon.

Storm chances will be on the decline through Monday before coming to
a quiet holding pattern through the week. Monsoon moisture looks to
hang around this week but mainly across eastern Arizona. The upper
level disturbance is prognosticated to move north through the Great Basin
by Monday and will allow a westerly flow to settle in place over the
southwest deserts as well as a drying trend. Will keep slight chance
mention in zone 24 for the higher terrain locations. Temperatures
will have little day to day change...remaining at or a few degrees
above seasonal normal with high pressure dominating the region
through middle week.

Thursday through Saturday...attention then turns to a possible
seasonal transition system for late week into next weekend.
Confidence is still not very high on the specifics of the system but
the 00z operational models have come in closer agreement that a deep
Pacific trough will slide through California on Friday and possibly
as far south as Arizona sometime next weekend. Widespread slight
chance probability of precipitation are in the forecast for Friday. Either way it is fairly
likely this low will user in cooler and much drier air...and
potentially end our monsoon season.

&&

Aviation...
south-central and southwest Arizona including kphx...kiwa...ksdl...
convective chances over the greater Phoenix area have ended. Scattered-broken
clouds at or above 10 thousand above ground level are expected through 08z sun...along with light
wind under 8 knots. From 08z sun to 21z sun...mostly clear skies
and light wind.

Southeast California including kipl...and kblh...
through 21z sun...mostly clear skies and light wind.



Aviation discussion not updated for amended tafs.

&&

Fire weather...
Tuesday through Saturday...
moisture retreat due to westerly flow will keep storm chances
minimal through Thursday and limited to the higher mountains of
south-central Arizona. Meanwhile...temperatures nudge upward a few
degrees above normal. Humidities on the lower deserts drop below 15
percent though maximum humidities remain fair. No strong winds are
expected during this time frame. On Friday...a Pacific weather
system will pull moisture northward over the region for a return of
storm chances into next weekend...mainly east of the lower Colorado
River valley. In addition...cooler temperatures and breezy to
locally windy conditions can be expected as well.

&&

Psr watches/warnings/advisories...

Arizona...none.

California...none.

&&

$$

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Discussion...vasquez/Dewey
aviation...vasquez
fire weather...Meyers/aj

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