FXUS65 KPSR 222137

Area Forecast Discussion
National Weather Service Phoenix AZ
237 PM MST Sat Sep 22 2018

As drier air continues to move into the region expect a slight
warming trend through today. Daytime highs will reach the low 100s
again today and remain very near these above normal levels through
the coming week with little day to day change expected.
Precipitation and storm chances will remain very low and are
generally not expected through the forecast period with the
occasional slight possibility of very isolated, short-lived
afternoon pop-up showers and storms.


Although today marks the first day of Autumn, Mother Nature
refuses to be rushed into anything different than hot anytime
soon. Early afternoon temperatures have climbed into the upper 90s
to low 100s across the lower deserts and the low to mid 100s over
SE CA. Lower humidity levels than yesterday are being observed
across the deserts with surface dewpoints running 6-9 degrees
lower than yesterday afternoon with readings in the mid 40s to mid
50s. Likewise, boundary layer dewpoints are also registering
lower values. Consequently SPC mesoscale analysis shows more
stability and significantly lower CAPE fields over south-central
deserts at only 100-500j/kg, and falling, amidst the afternoon
dry-air mixing. The early afternoon satellite imagery is showing
scattered areas of towering and fair weather cu from the central
to western deserts and into SE CA along with plenty of cloud free

The operational models and ensembles remain in fairly good agreement
on maintaining the flat upper level ridge in control through the
weekend and early next week centered above and just to our south
with broad troughing and the dry westerly flow just to our north.
This pattern will continue to support hot, above normal temperatures
and mainly dry conditions. Dry westerly flow above H5 continues to
support a general drying trend into the workweek, with H7 and above
joining in during Sunday afternoon. However, models show that
boundary layer, and especially H8-H7 moisture may not be as quick to
dry out quite as much or quite as fast due to occasional relatively
modest moisture advection incursions from NW Mexico into south-
central AZ through early next week.

Expect very little day to day change with hot above normal
temperatures in the low 100s amidst low storm and precipitation
chances through the period. On Tuesday and Tuesday evening a
relatively dry, shallow and weak four-corners trough axis will
move across the region and try to draw some NW Mexican moisture
north, although models show the isolated storm activity associated
with this feature will likely be confined to far SE-E AZ as well
as north-central AZ. For the second half of the week dry
northwesterly flow will be in control followed by a ridge of high
pressure moving into the Intermountain West which will increase H5
heights over south-central deserts to 588-590dam.



South-Central Arizona including KPHX, KIWA, and KSDL and :
Southeast California/Southwest Arizona including KIPL and KBLH:

Deep easterly flow aloft to keep winds going from an easterly
direction at all of the Phx area terminals through the entire TAF
period, with a bit of gustiness again possible during the mid/late-
morning hours on Sunday. Winds at KBLH to mainly follow typical
diurnal trends, while tending to favor a westerly direction at KIPL.
High pressure aloft and a dry airmass to keep cigs down in the FEW-
CLR range, mainly aoa 10k feet at all of the TAF sites.

Aviation Discussion not updated for amended TAFs.


Tuesday through Saturday:
Temperatures will continue to remain 2-4 degrees above seasonal
normals through the entire period. Mainly dry conditions are
expected, except for a very slight chance (<10%) for a few isolated
showers/storms over the higher terrain north and east of Phoenix on
Tuesday, as a bit of moisture is briefly pulled northward into the
region. Minimum humidity levels to remain around 10-15 percent for
the lower deserts and 15-25 percent for the higher terrain north and
east of Phoenix, but with fair to excellent overnight recoveries.
Winds to mainly remain on the light side (except for some afternoon
gustiness, mostly following the usual diurnal trends.


Spotters should follow standard reporting procedures.




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