Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 031750

Area Forecast Discussion
National Weather Service Phoenix AZ
1050 AM MST Mon Aug 3 2020

.UPDATE...Updated Aviation Discussion.


High pressure will persist across the Desert Southwest this week,
resulting in a continuation of the well-above normal temperatures
and dry conditions. Daily high temperatures across the lower
deserts will mostly range from 108 to 112 degrees for the bulk of
the week. The only realistic rain chances will remain across far
eastern Arizona falling mostly on Wednesday and Thursday.


The unusually dry conditions across much of the Desert Southwest
are expected to continue for the foreseeable future. Like the last
several days, the main forecast concern for today and likely for
Tuesday will be the strong high pressure over the region and a
continuation of the heat wave. However, the lofted smoke from the
Apple wildfire east of Los Angeles is likely to influence daytime
insolation across much of the area. Forecast temperatures for
today and Tuesday have been lowered a couple degrees from previous
forecasts due to the layer of smoke located at around 20K feet
above the surface, but confidence in the forecast is much lower
than usual. At least for today, the very weak and mostly westerly
flow aloft should continue to bring lofted smoke eastward through
southeast California into Arizona while much of the smoke from
yesterday still remains aloft due to very little dispersion.
Forecast highs today of 110 to 114 degrees are still likely too
high if the lofted smoke remains thick like yesterday, but if it
does thin out or get dispersed more we could still realize or even
slightly exceed the forecast temperatures. Night time
temperatures will also remain very warm through Tuesday,
especially in the Phoenix area. The Excessive Heat Warning is
still in effect for the El Centro and Yuma areas through this
evening and through Tuesday for the bulk of Maricopa County and
western Pinal County.

Rain chances look pretty grim for much of the region this week
with the best chances falling on Wednesday and Thursday across
eastern Arizona. The last few model runs have been backing off on
what was supposed to be a modest moisture return for Wednesday,
so it seems any chances for Wednesday and Thursday will be quite
marginal and mostly east of a Globe to Tucson line. Outside of
Wednesday and Thursday, any rain chances will be confined to far
southeast Arizona. As of right now, long range models do not
indicate any rain chances for the lower deserts over the next 10

A gradual cool down is still expected starting mid week as a large
trough approaches the California coast Tuesday into early
Wednesday. The trough will push the high pressure ridge currently
over our region southeastward into the Southern Plains and
northern Mexico. The trough is then forecast to mostly stall out
over the Great Basin area later this week keeping the Desert
Southwest under dry southwesterly flow aloft. The lowering
heights aloft due to the trough will at least drop daytime highs a
few degrees with daily highs Wednesday through Sunday mostly
between 108-111 degrees. A drying of the boundary layer will also
occur starting mid week, but especially for Friday into the
coming weekend. This will allow overnight lows to drop to a bit
more comfortable temperature range of mid 70s to lower 80s.


.AVIATION...Updated at 1750Z.

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

Smoke from the Apple Fire will continue to stream into the area
leading to SCT-BKN coverage near 20 kft. In general, SCT-BKN
coverage is expected to continue through today. Winds are expected
to veer toward a west/southwest component early this afternoon,
with some gustiness up to 20 mph possible by mid-afternoon. Still
a low chance that a southerly outflow could push its way up
towards the Phoenix area this afternoon, but more likely is that
if this scenario occurs it will weaken and stall to the south
before affecting TAF sites. Regardless, a low confidence
situation overall. Otherwise, any thunderstorm buildups should
remain well removed across the higher terrain.

Southeast California/Southwest Arizona including KIPL and KBLH:

Smoke from the Apple Fire will continue to lead to SCT-BKN coverage
in the 15-20 kft range near KBLH. Some smoke may also begin to
move into the KIPL area but the coverage should remain FEW to SCT.
Winds at KIPL will favor a southeasterly component through the
morning before transitioning to a westerly component this
afternoon. At KBLH, winds will continue to favor a south to
southwest component through the next 24 hours. A few gusts into
the teens will be possible at both TAF sites going into this


Wednesday through Sunday:
High pressure will continue across Arizona, resulting in
relatively dry conditions and above normal temperatures. Wetting
rains are generally not anticipated most days, but the threat of
isolated/scattered storms will be possible mainly over high
terrain areas on Wednesday and Thursday. Min RHs will generally
fall into the teens each afternoon with single digit values over
portions of the lower western deserts. Overnight max RH should
range around 25-45 percent with locally higher values possible
across southern Gila County. Winds will be mostly light and
diurnal each day along with afternoon breezes.


Spotters should follow standard reporting procedures.


AZ...Excessive Heat Warning until 8 PM MST Tuesday for AZZ534-537>544-

     Excessive Heat Warning until 8 PM MST this evening for AZZ532.

CA...Excessive Heat Warning until 8 PM PDT this evening for CAZ562-



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