Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 231012 AAA

Area Forecast Discussion
National Weather Service Phoenix AZ
310 AM MST Sat Jun 23 2018

.UPDATE...Updated aviation discussion.

Temperatures closer to seasonal normals can be expected through
Monday as high pressure weakens across the Southwest. Another
warmup is expected Tuesday and Wednesday, with high temperatures
forecast to be near 110 degrees across the lower deserts. A dry
weather pattern will continue through late next week as richer
moisture remains fixed over northern Mexico.


Quiescent weather conditions continue across the Southwest amidst
a benign large-scale weather pattern. Broad west-northwesterly
flow is positioned across the Great Basin, with Arizona positioned
along the southern fringe of the stronger flow aloft. A shortwave
impulse over the northern Rockies will dig southeastward towards
the central High Plains, prompting a weakening of midlevel height
fields across Arizona this weekend. As a result, a minor cooling
trend closer to seasonal normals will commence today, with high
temperatures generally within a couple degrees of 105 this
afternoon across the lower deserts. The minor pattern change will
also support an increase in winds this afternoon, as southerly to
southwesterly winds gust to 20 mph this afternoon across south-
central Arizona, to 30 mph across southwest Arizona and the lower
Colorado River Valley. Also of interest, a very shallow layer of
richer moisture from the Gulf of California is advecting northward
this morning, with 60s dewpoints funneling through the lower
Colorado River Valley and Imperial Valley, and low 50s into south-
central Arizona. While this will have virtually no impact on
sensible weather conditions other than to facilitate a slight
increase in boundary-layer RH, it is at least evidence that low-
level moisture will more easily be able to spread northward once
a more typical Monsoonal pattern takes hold again.

Into next week, a mid-level anticyclone will quickly rebuild in
the wake of the aforementioned shortwave trough, leading to
another minor warming trend. The hottest temperatures of the week
(and perhaps the year, so far) will occur on Tuesday and
Wednesday, with Phoenix forecast to reach 111 degrees on Tuesday.
While current HeatRisk output suggests this will remain just shy
of excessive heat thresholds, these temperatures will still result
in heat-related impacts across the lower deserts.

In what has remained the theme thus far in June, the
climatologically favored anticyclone near the Four Corners that
typically supports prolonged periods of excessive heat, will
instead be short-lived as another upper trough develops over the
western CONUS. This will act to weaken the anticyclone, and bring
temperatures back closer to seasonal normals by late next week,
while amplified ridging (and associated heat) is focused east of
the Rockies. While Monsoonal moisture will struggle to make it
into south-central Arizona with this pattern given the slightly
west of south component to the flow aloft, it will be more likely
to reach New Mexico and far eastern Arizona by late next week.


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

High pressure and dry northwesterly flow aloft to keep skies mainly
clear through the TAF period. Winds to mainly follow normal diurnal
patterns, with some gustiness (up to 15-20 kt gusts) during the
afternoon/early evening hours on Saturday. Minimal aviation concerns
through the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:

High pressure and dry northwesterly flow aloft to keep skies mainly
clear through the TAF period. WInds to remain southerly at KBLH and
southeasterly at KIPL through the taf period. At KIPL, wind gusts up
to 15 to 25 kts will be possible and at KBLH wind gusts up to 20 to
30 kts will be possible during the day on Saturday.

Aviation Discussion not updated for amended TAFs.


Monday through Friday:
A rapid warming trend will spread into the districts early next
week with temperatures easily climbing above seasonal normals by
Tuesday. By the middle of the week, hot and dry conditions will
return with highs near or just above 110 degrees across the lower
deserts. Minimum afternoon humidity values will fall back mostly
into the single digits with a return of poor to fair overnight
recovery. No strong winds are expected next week, although typical
afternoon upslope gustiness will be common around terrain
features. There are still no signs of rain through late next


Spotter activation will not be needed through at least the middle of
next week.




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