Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 302129

Area Forecast Discussion
National Weather Service Phoenix AZ
229 PM MST Thu Mar 30 2017

Updated Aviation section.


A strong low pressure system will produce windy conditions this
evening along with much cooler temperatures Friday. Isolated
precipitation is possible across the higher terrain of eastern
Arizona Saturday as the storm lingers. Warmer conditions will then
return Sunday and into early next week as high pressure again builds
across the region.



Remainder of this Afternoon and Tonight...

A very powerful and dynamic Pacific weather system was approaching
AZ, and should intensify further as it tracks rapidly south into
northern AZ by late tonight.  However since most of the
intensification and upward vertical motion will develop over land,
and without any renewed Pacific influence, it will be relatively
moisture starved as it muscles its way into AZ. Additionally, as a
rule of thumb, fast southward moving weather systems always
intensify due to rapid loss in planetary vorticity or rapid
latitudinal change.

Strongest 500 mb height falls of 200 meters occur between 5 pm and
midnight along the Colorado River and parts of southwest AZ, which
is a wind signature to us and very foreboding. 500 mb height falls
are even stronger in northern AZ and represent the vertical motion
part of this weather system, suggesting a chance of showers and
thunderstorms generally from Flagstaff northward, especially between
the Grand Canyon and Page AZ just before midnight. Additionally,
because of how cold and dense the airmass will become following the
cold front from the north, powerful wind gusts are expected across
portions of southeast CA and southwest AZ this evening, i.e. gusts
to 50 mph possible.  At noon winds were already gusting to 35 mph at
Blythe CA along the Colorado River.  Wind and blowing dust
advisories are currently posted for our portions of southeast CA and
southwest AZ including the Colorado River through about midnight.

Friday and Friday night...

Lighter winds, but still breezy, from the north and northwest will
continue on Friday, along with a dramatic cool down in the aftermath
of the cold front. Mostly clear skies are also forecast over our
area. The former Pacific low pressure system will have settled over
northern AZ Friday afternoon as a cutoff low will become nearly
stationary into early Saturday.

Saturday and Saturday night...

Models forecast the northern AZ cutoff low to slowly drift into
western New Mexico by Friday afternoon. Some of the coldest air
aloft, with afternoon instability, will brush by our mountainous
zone 24, southern Gila County. There is a slight chance of a shower
or afternoon thunderstorm Saturday afternoon in zone 24 from
Globe/Miami eastward, particularly over the highest terrain of the
San Carlos Apache Indian Reservation bordering the White Mountains.
Clearing Saturday night. A relatively cool afternoon is expected in
south central AZ Saturday, but starting to warm significantly over
the southeast CA and southwest AZ deserts.

Sunday through next Thursday...

Except for another fast moving disturbance across Utah and far
northern AZ on Monday, our forecast area will remain mostly clear
with above normal temperatures. In fact a strong warm-up is forecast
Wednesday and Thursday as an unseasonably strong high pressure
system builds over the region.


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

A cold front, located roughly along a SLC-LAS-LAX line at 21Z,
will continue moving eastward reaching PHX by around 04Z-05Z.
This will lead to southwest and west wind gusts of 30-40 kts over
far southeast California and southwest Arizona along with areas
of blowing dust (vsbys 5-10SM; locally 1SM) through about 06Z.
Winds over south-central AZ will not be quite as strong - gusting
25-30 kts after 23Z. Precip expected to stay north of Riverside-La
Paz-Maricopa counties (may see some shallow sct-bkn layers at
7-9 kft north of 1-10). Winds weaken after 07Z.

Aviation discussion not updated for amended TAFs.


Saturday through Wednesday: After below normal temperatures on
Friday, highs will rebound on Saturday to near normal. Breezy
winds are expected once again in SE California and far western
Arizona as the low pressure system that will bring us windy
conditions today finally exits our area. Thereafter, high pressure
will follow for Sunday, resulting in a warming trend and a return to
above normal temperatures with relatively light winds. Another
passing dry low pressure system may affect our area Monday/Tuesday
which should bring another round of breezy winds although no
precipitation is expected. Its trajectory will be further north so
we are not expecting winds to be anywhere near as strong as what we
will see for today. A ridge builds in on Wednesday bringing warming
conditions and relatively light winds.


Spotters should follow standard reporting procedures this week.


AZ...Red Flag Warning until 8 PM MST this evening for AZZ131-132.

     Blowing Dust Advisory until 11 PM MST this evening for AZZ020-

     Wind Advisory until 11 PM MST this evening for AZZ020-021-025-

CA...Red Flag Warning until 8 PM PDT this evening for CAZ231.

     Blowing Dust Advisory until 11 PM PDT this evening for

     Wind Advisory until 11 PM PDT this evening for CAZ030>033.



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