Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 252124

Area Forecast Discussion
National Weather Service Phoenix AZ
224 PM MST Mon Sep 25 2017

Under sunny skies, temperatures will slowly warm over the next few
days though readings will remain slightly below average. An area of
low pressure may pull moisture back into eastern Arizona by the
middle and end of the week supporting some late season showers and
storms. Warmer temperatures expected toward the weekend.



Broad level trough situated across the western Lower 48, with the
mid-level trough axis extending from eastern Montana toward
southeast California, continues to bring cooler-than-normal
temperatures to our forecast area. A few mid level clouds are
forming ahead of a weak vort max but nothing of consequence as
this time.

A closed low will develop over the Southwest the next few days,
with the flow on the east side of the low drawing some modest
low/mid level moisture into eastern Arizona. Solutions continue to
differ on the westward extent of the moisture and how unstable the
airmass might get. Comparing SREF, NAEFS, and ECens solutions, the
ensemble means do seem to agree that moisture will work into Globe
and nearby areas but struggle to get much further east. A slight
chance it gets as far as Phoenix. Yuma and El Centro areas will
stay dry. Any showers/storms that do develop will carry off to the
north/northeast in the mean flow. On Thursday, the low will open
up and lift northward, which will sweep the moisture back

Throughout the week, temperatures will be on a gradual climb and
lower elevations may approach the triple digits again by the
weekend. GEFS plumes show H85 temps for Phoenix around 24C or so
which will push temperatures into the upper 90s and possibly AOA
100F Saturday. Worth noting the average (1981-2010) last day of
100+ temps for Phoenix is Oct 3 and Yuma Oct 6.


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

Light diurnal winds through the next 24-36 hours with FEW-SCT
clouds AOA 20kft will cause little impact to area terminals.

Southeast California/Southwest Arizona including KIPL and KBLH:

Northwesterly flow will continue to weaken this afternoon/evening
with more typical diurnal (weak) flow developing for the overnight
hours. Any clouds will remain AOA 20kft.

Aviation Discussion not updated for amended TAFs.


Wednesday through Sunday: A large area of low pressure aloft will
dominate the weather pattern over the desert southwest for the rest
of the work week, keeping temperatures below seasonal normals, and
keeping drier air in place over southeast California and the
southwest Arizona deserts. Expect minimum RH values from the single
digits to low teens over the central deserts Wednesday, slowly
climbing mostly into the teens by the end of the work week.
Southerly flow ahead of the upper low will gradually advect moisture
into south central Arizona by Wednesday, bringing a chance for
afternoon and evening thunderstorms to most areas east of Phoenix.
There will initially be a slight chance for storms into the greater
Phoenix area Wednesday but afterward moisture will retreat slightly
to the east, focusing any chance for storms into the higher terrain
areas east of Phoenix Thursday into the weekend. Minimum RH values
will stay mostly in the mid to upper teens Friday into the weekend,
with values over 30 percent in the higher terrain. As the upper low
weakens this weekend, high temperature climb to around seasonal
normals with warmer deserts into the upper 90s. No strong winds are
expected during the five day period, just some minor and typical
afternoon gustiness favoring north to upslope.


Spotters should follow standard reporting procedures.




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