Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 260458

Area Forecast Discussion
National Weather Service Phoenix AZ
958 PM MST Tue Jul 25 2017

Drier air moving into the region will result in a much lower
chance of storms for much of the work week. Decreasing cloudiness
and moisture will support a warming trend through Thursday with
near normal highs. An increase in moisture beginning Thursday will
usher in a increased chance of storms from west to east from
Thursday night through the weekend. Similarly, high temperatures
decrease as well...most noticeably over south-central Arizona.


Noticeably more muted afternoon and evening with regards to
Monsoon storm activity across our forecast area as steering, mid
and upper level flow orients out of the southwest. Area of drier
Pacific air has begun to advect into the region, with afternoon
dewpoints dropping down in the upper 30s around Yuma and 40s for
El Centro and Mexicali. Back towards the south-central AZ deserts,
sfc dewpoint conditions are still elevated from the combo of
drying not reaching us just yet and the lingering runoff/puddles
from yesterday`s significant rain event.

Southwest flow does not completely kill off our storm chances (it
hasn`t in years past...Monsoon 2015 stands out as a season where
SW flow produced a few storm event across Phoenix), but the
combination of drier and more broadly forced subsident flow do
draw them down for the next few periods. Only minor updates worked
into tonight`s grid to trend them closer to current sky and other
surface observation parameters.


Operational models and ensembles are in good agreement on the
drying and increased stability through early Thursday with almost
no CAPE expected after this evening. Later this week the south
side of the high pressure system to our east will begin to yield
to several inverted troughs and disturbances along with a return
of increased moisture advection from the south and southeast,
putting an end to the drying trend by sometime Thursday. The
resulting increase in PWAT and mixing ratios will initially
increase POPS, first in the east, and then gradually to the west
beginning Friday afternoon and evening and into the weekend. Then
continued moisture advection through the weekend will support the
return of significant unstable conditions in the lower deserts
beginning Saturday and the return of Monsoon storms chances. The
increased Monsoon moisture this weekend will also be accompanied
by below normal high temps through Monday.


South-Central Arizona including KPHX, KIWA, and KSDL:
Break in the Monsoon storm activity will continue overnight and
into Wednesday. Mostly clear skies may fill with some high level
debris clouds from storms well south of the border. Enough
moisture will linger to develop from FEW to SCT CU fields
tomorrow, especially over the higher terrain N/E of Phoenix.
Surface winds to follow typical diurnal trends, switching to light
easterly overnight and westerly after midday Wednesday.

Southeast California/Southwest Arizona including KIPL and KBLH:
South to southeasterly winds to persist for the terminals with
mostly clear skies through the Wednesday morning hours. Some FEW
to SCT high level layers may develop from any storms that do fire
over the Baja Spine, but with the short window of drying underway
the next few days...even storm coverage may be limited south of
the Border.

Aviation discussion not updated for amended TAFs.


Friday through Tuesday:
Humidities and storm chances begin to increase into this weekend
with chances reaching southeast California by Saturday.
Temperatures will decrease to near to slightly below normal late
this week. Apart from thunderstorms, winds will follow familiar
warm season patterns.


Spotters should follow standard reporting procedures.




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