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Forecast Discussion for Phoenix, AZ

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FXUS65 KPSR 261109

Area Forecast Discussion
National Weather Service Phoenix AZ
409 AM MST Thu Apr 26 2018

.UPDATE...Updated Aviation and Fire Weather discussions.


Very warm and dry conditions will continue into the first part of
the weekend as lower desert high temperatures reach into the
middle to upper 90s each day. A slight chance for showers will
exist across southern Gila County Friday and Saturday afternoon as
a weak storm system moves across the area. A cooling trend
starting Sunday will eventually lead to below normal temperatures
starting early next week.


A deep Pacific low off the West Coast will help to build heights a
bit further over the region today leading to highs to around 100
degrees for the warmest desert locations. Further east a cold
front will dive southward through the western Plains states and
the central Rockies. Eventually this cold front will push westward
through New Mexico early tonight and then into far eastern
Arizona by early Friday morning. This cold front will bring a
short period of modestly strong southeasterly low level winds into
eastern Arizona. Low and mid level moisture levels will also increase
behind the front allowing for enough moisture for isolated
showers and maybe a few thunderstorms across the eastern Arizona
high terrain starting Friday afternoon. A southwesterly steering
flow will keep any rain activity over the high terrain, but we
can`t completely rule out the possibility of outflow winds
traveling westward far enough to reach the foothills or lower
deserts in Pinal and eastern Maricopa Counties.

Temperatures Friday will drop a couple degrees from today`s highs
as heights aloft lower from the approaching Pacific trough that
begins to move onshore across northern California and Oregon. This
trough will be slow to progress eastward this weekend as the low
center only reaches Idaho by Sunday night. Shower and thunderstorm
chances will again return across eastern Gila County for the
daytime hours Saturday with better upper level support as the
trough nears the region. Rain chances will however come to an end
Saturday evening as westerly flow increases pushing much drier
air through the region. The trough will remain mostly to the north
of our area this weekend as it slowly drifts eastward, but it
will bring increased breeziness and a cooling trend. Highs
Saturday will still be several degrees above normals, but Sunday`s
readings should drop into the upper 80s to around 90 over the
deserts, or right around normals.

The trough will open up and become more expansive next Monday into
Tuesday while a shortwave trough digs southward down the backside
of the trough. Though there is still some model spread, models
mostly agree another closed low will develop from this diving
shortwave trough. This could result in a closed low moving through
the Desert Southwest sometime during the middle of next week,
most likely on Wednesday. This scenario would bring at least a
slight chance of showers and thunderstorms to the high terrain,
possibly even some high based storms over the deserts in an ideal
situation where moisture levels are high enough and the low
center passes through southern Arizona. Temperatures for next week
should take a decent hit with highs easily falling into the
middle 80s, possibly lower 80s in some lower desert spots.


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

There are no major aviation weather concerns today as winds will
remain light and follow typical diurnal tendencies for the Phoenix
area terminals. Some thick high clouds will filter over the area
but decks should remain at or above 20k feet.

Southeast California/Southwest Arizona including KIPL and KBLH:

Stronger winds will be of concern this afternoon, especially for
KIPL, with gusts up to 20-25 kts. The winds at KBLH will not be as
strong but some afternoon breeziness can be expected. Otherwise,
the wind speeds should settle a bit after sunset.

Aviation Discussion not updated for amended TAFs.


Saturday through Wednesday...
The very warm temperatures will begin to subside on Sunday and
eventually cooling into the mid 80s for lower desert locations
early next week. A very slight chance for thunderstorms exists
Saturday, primarily for Gila County, with a threat for dry
lightning and only a little rainfall. Gusty and erratic winds
from storms are possible. Otherwise, most afternoons will see some
stronger breezes up to 20-25 mph for the higher terrain north and
east of Phoenix, and for the fire districts in southeast
California. Minimum RH values will stay in the 10-20 percent range
with modest overnight recoveries.


Spotters are encouraged to follow standard reporting procedures.





Previous Forecast Discussions may be found at
NWS Phoenix, AZ (PSR) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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