FXUS65 KPSR 192205

Area Forecast Discussion
National Weather Service Phoenix AZ
305 PM MST Thu Oct 19 2017

Updated Aviation and Fire Weather sections.


A weak upper disturbance will shift eastward out of Arizona this
evening, with drier air overspreading the region from west to
east. Winds will increase as a cold front moves eastward tonight
and tomorrow, bringing cooler temperatures this weekend. High
pressure will rebuild over the region into early next week
leading to well above normal temperatures.


Satellite imagery from this afternoon shows a narrow band of
ascent focused over Gila County into east-central Arizona,
accompanying a weak shortwave disturbance moving through the
region. Showers and a few thunderstorms have been observed since
early this morning, but with the leading edge of drier air aloft
spreading eastward, should continue to see rapid west-east clearing
through this evening.

A weak cold front will move through the region tomorrow afternoon,
resulting in increasing westerly winds across the entire area.
Sustained speeds around 15-20 mph, with some gusts to 30 mph,
across the lower deserts of south-central and southwest Arizona
will be possible. Even stronger winds are expected locally across
parts of southeast California, and a Wind Advisory has been
issued for southwest Imperial County (including a segment of I-8)
beginning this evening through late Friday evening. Patchy blowing
sand and blowing dust will also be possible mainly across
Imperial County tomorrow afternoon. Winds will weaken into
Saturday while turning out of the north across the lower Colorado
River Valley, as high pressure builds over the Great Basin.
Locally gusty winds will still be possible here, while even drier
low-level air continues to spread into the Southwest.

The other more pleasant effect on our weather will be the modest
cooling trend that will take place, as high temperatures in the
upper 80s to lower 90s are likely tomorrow, and mid-80s for high
temperatures on Saturday. Unfortunately, this will be short-lived,
as pattern amplification occurs in response to a very strong ridge
of high pressure building just east of the Pacific Coast. Well
above-normal temperatures will return by Monday, approaching
record levels on Tuesday. The heat will moderate slightly later
in the week in response to northern Rockies upper trough, but
highs will still remain in the 90s at most lower desert locations.



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

Surface winds will favor southeast directions until 23Z-00Z before
southwesterly directions prevail this evening. Some portions of
metro Phoenix may maintain surface wind directions in the
southeast quadrant. Otherwise, surface winds return to
southeasterly after 06Z. Aloft however, southwest and west winds
will slowly strengthen overnight. Not strong enough in the lower
levels to reach LLWS criteria. Anticipate earlier than normal
development of southwesterly surface winds Friday (before 18Z)
along with some gustiness after 21Z. No significant clouds, just
some cirrus.

Southeast California/Southwest Arizona including KIPL and KBLH:

Southwest and west winds will become more prevalent through 00Z
before beginning to weaken after 03Z. Surface winds will be
strongest over central, and especially western, portions of
Imperial County with gusts to 25 kts common through early evening.
There will be some weakening of the surface winds by late evening
but winds in the lower levels above the surface will remain
strong. Some places could flirt with LLWS criteria until the
inversion breaks after 16Z Friday. Gusty surface winds resume by
midday Friday. No significant ceilings, just cirrus.


Sunday through Wednesday:
A warming trend begins Sunday with temperatures rebounding close
to 10F above normal on Monday and Tuesday. Minimum humidities will
remain below 15% (even at higher terrain locations) and overnight
recovery will be fair to good (at best). Winds will be light
overall (favoring north and northwest directions during the
daytime) except for breezy easterly winds on Wednesday.


Spotters should follow standard reporting procedures.


CA...Wind Advisory until 11 PM PDT Friday for CAZ562.



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