Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 271132

Area Forecast Discussion
National Weather Service Phoenix AZ
432 AM MST THU OCT 27 2016

.UPDATE...Updated Aviation and Fire Weather Discussion.


Strong high pressure over the region will lead near record
temperatures today. A weather system moving through California on
Friday will bring a chance of showers to southeast California along
with slightly cooler temperatures. High temperatures this weekend
will remain well above normal, but a gradual cool down will occur
through the middle of next week. Near to slightly above normal
temperatures are likely for much of next week with the mostly dry
weather continuing.


An unseasonably strong ridge of high pressure over the Desert
Southwest has led to 500mb heights reaching 590dm (97-99% of climo)
and 850mb of 22-24C over south-central and southeast Arizona. Looking
upstream, a fast moving upper level low approaches California. Upper
level moisture ahead of this system along with some moisture being
stripped away from the rapidly decaying Hurricane Seymour (located
800 miles west of southern tip of Baja) has led to increasing high
cirrus into our region. The cirrus should stay thin enough not to
impact temperatures today across the eastern half of Arizona, but
may keep temperatures a degree or two cooler than previously
forecast across southeast California and southwest Arizona. A
forecast high of 98 degrees at KPHX still holds which would tie the
previous record.

As the Pacific low comes ashore across central California early
Friday, moisture advection will be underway into southeast
California. This available moisture along with dynamical support
aloft should give rise to some showers over portions of southeast
California mainly during the daytime hours Friday. Heights aloft will
drop across the Desert Southwest as the trough passes through
California leading to a cooler day on Friday. Cloud cover may also
influence temperatures somewhat, but the boundary layer warmth will
mostly remain in place leading to highs mainly in a 90-95 degree
range over the deserts.

Dry southwesterly flow aloft will be in place for this weekend with
500mb heights remaining quite high over Arizona. A deep upper low
will shift into the Great Basin on Sunday which should give us a
slight dip in temperatures, but highs should still be 4-7 degrees
above normal. Another Pacific low is forecast to dip further south
early next week, possibly moving into southern California Tuesday
night and then Arizona for Wednesday. Model ensembles show an open
wave moving through the Desert Southwest on Wednesday with little
moisture associated with the system, but the 00Z operational GFS and
European are a bit more optimistic. For now we have held off on
including much in the way of any rain chances, but a more dramatic
cool down seem plausible. Starting Monday highs should mostly be in
the 80s across the lower deserts and this should persist at least
through the middle of the week.


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

No aviation concerns through the TAF period. Winds will be light and
primarily out of the east...with a few hours of very light north to
northwesterly winds possible. Skies will remain mostly clear, with
few to scattered mid- and high- level clouds passing over terminals.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns through the TAF period. AT KIPL, winds will be
light and out of the west/northwest. At KBLH, winds will be light and out
of the west for the remainder of the morning, before switching to the
northeast late this morning through early this evening. Skies will
remain mostly clear with few to scattered mid- and high- level
clouds passing overhead. Although rain is not anticipated during this
TAF period, want to note that rain chances will be on the increase
starting around 12Z tomorrow and a few daytime showers over portions
of southeast California are possible.

Aviation discussion not updated for amended TAFs.


Saturday through Wednesday...

High temperatures this weekend will remain well above normal, then a
gradual cool down is expected through the middle of next week as a
a low pressure system moves across southern California Tuesday night
and into Arizona Wednesday. As of now, little moisture is expected to
accompany this system, and the greatest impacts will be the slight
cool down in temperatures.

Minimum humidities will remain near the 20 to 30 percent range each
day with good overnight recoveries. Winds will remain light and
follow normal diurnal headings through the entire period, except for
some periods of afternoon breeziness up to 20 to 25 mph in southeast
California Sunday.


Spotter activation will not be needed this week.




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