Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 220402

Area Forecast Discussion
National Weather Service Phoenix AZ
902 PM MST FRI OCT 21 2016

Dry weather with mostly clear skies will continue across the Desert
Southwest through Saturday. Temperatures will be unseasonably warm.
By Sunday, a large Pacific low pressure system will move into the
western states. This will draw a considerable amount of subtropical
moisture into the region with threat of showers starting Sunday
afternoon and continuing through Monday night. The best chance of
showers will occur Monday over south central Arizona, with afternoon
thunderstorms possible.


Today`s highs ended up very close to Thursday`s, but low level
moisture levels are already starting to improve. A gradual cooldown
with an uptick in moisture will be the story this weekend with rain
chances coming back into the region as early as Sunday. The forecast
through Saturday still looks to be in good shape, so no adjustments
are needed.



Tonight through Saturday Night...

An unseasonably strong high pressure system will continue to cover
the region through Saturday night, resulting in mostly clear skies
and above normal temperatures. Light winds are also forecast.

Sunday through Monday Night...

A fairly strong Pacific trof is still forecast to move into the
western states Sunday and Monday. Increasing southwest winds aloft
will import a copious amount of mid/high level moisture into AZ
ahead of the trof. Mid/high level clouds will result in possible
light showers or sprinkles due to dry low levels.

Monday is looking very interesting. For days now models have been
forecasting a low level moisture surge into southwest and south
central AZ from Mexico. With each model run, moisture amounts have
increased, leading to more and more convective instability over
southwest and south central AZ Monday afternoon. New model output
now shows low level Mexican moisture to be at monsoon levels, which
is considerable for this incoming airmass. In response modeled
soundings for portions of the southwest and south central AZ deserts
show relatively low convective trigger temperatures, 79 deg F at
Wickenburg, 86 at Phoenix, and 74 in Globe Miami, with C.A.P.E.
values from 300 to 800 j/KG, a bit more than yesterday.
Additionally, check out the forecast Monday afternoon vertical wind
shear profile for Phoenix. A good looking shear profile indicating
the potential for weak organized right moving convective cells.
And, with an upper level shortwave forecast to move into the area,
Mondays forecast could become very interesting.  Precip
probabilities especially south central AZ, including Phoenix, were
raised for Monday.

Tuesday through Thursday...

Drier and more stable westerly flow aloft will preclude shower
activity Tuesday except for the higher terrain of southern Gila
County bordering the White Mountains.  Clear skies and warmer
temperatures will return Wednesday through Friday.


South-Central Arizona including KPHX, KIWA, and KSDL:

No aviation concerns through the TAF period. Light winds following
typical diurnal directional patterns are expected. Skies will remain

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns through the TAF period with light winds and
clear skies.

Aviation discussion not updated for amended TAFs.


Monday through Friday... A low pressure system will affect the
Desert Southwest next week for a continuation of increasing
humidities early next week. There will be a chance of showers and
thunderstorms Monday into Tuesday. Best chances will be Monday.
Temperatures will be significantly cooler as well. Humidities
decrease from west to east Tuesday and Wednesday with little change
Thursday and Friday. Overnight recovery will remain good.
Temperatures slowly increase Wednesday through Friday. Other than
some southerly breeziness Monday in south-central Arizona, no strong
winds are anticipated except for local gustiness associated with


Spotter activation will not be needed this week.




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