Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 202100

Area Forecast Discussion
National Weather Service Phoenix AZ
Issued by National Weather Service TUCSON AZ
200 PM MST Tue Feb 20 2018

Expect dry conditions with daytime temperatures well below seasonal
normals through Thursday. A storm system will then bring a chance of
showers mainly north and east of Phoenix on Friday. Cool
temperatures will continue Saturday followed by dry conditions and a
warming trend early next week.


Clear skies prevail across much of southwest Arizona and southeast
California early this afternoon. The exception was across the higher
terrain east of Phoenix where scattered to broken cumuloform clouds
prevail. Temperatures around the Phoenix metro area valid 1 pm MST
were generally in the mid 50s, and these temperatures were about 15-
20 degrees or so below seasonal normals. Expect clearing skies east
of Phoenix this evening followed by clear skies area-wide later

The upper level pattern through about Friday will generally be
characterized with a deep trough over the western CONUS, an upper
ridge over the eastern states, and an upper ridge well west of the
west Coast with ridge axis near 150W. For this forecast issuance,
the 20/12Z ECMWF was unavailable via AWIPS or other sources.

However, the 20/12Z GFS remained similar versus previous GFS
solutions with regard to depicting a digging upper low to move
southeastward across the Great Basin on Friday. This upper low is
then progged to move eastward across northern Arizona Friday night
and into the central/southern Rockies Saturday. The GFS was markedly
more robust versus the 20/00Z ECMWF as well as the 20/12Z NAM12
regarding precip potential for Friday and Friday night.

At any rate, for this forecast issuance have maintained dry
conditions across this forecast area Wednesday into Thursday night.
Thereafter, given the model differences, opted to make only very
minor adjustments to the inherited gridded data PoPs for Friday and
Friday night. Thus, the official forecast continues Friday with a
chance of showers across the higher terrain north-to-east of
Phoenix, and a slight chance of showers for the Phoenix metro area.

Precip-free conditions should continue Friday further west across
far southwest Arizona and southeast California. As the mid-level
trough axis moves east of the area, precip chances will decrease
Friday night. However, residual moisture will maintain a slight
chance of showers across higher terrain east of Phoenix Friday
night. Dry conditions will return area-wide Saturday as the western
CONUS upper trough becomes less amplified, then dry conditions to
continue Sunday into next Tuesday.

Daytime temperatures Wednesday through Saturday will remain about 10-
15 degrees or so below seasonal normals. A warming trend is on tap
Sunday into Monday followed by no significant change in daytime
temps next Tuesday. The current official forecast reflects high
temps Monday and Tuesday mostly within a few degrees of normal.


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

There are no significant aviation weather concerns through
tonight. The clouds have mostly left the terminal area with the
thickest decks well south and east of the Phoenix. The winds this
afternoon will be a little stronger, near 10 kts, with a few
stronger gusts possible. Otherwise, the winds will remain westerly
through this evening before becoming easterly during the
overnight hours.

Southeast California/Southwest Arizona including KIPL and KBLH:

There are no significant aviation weather concerns through
tonight. The winds will become more westerly this afternoon and
follow typical diurnal patterns thereafter. The winds will be
fairly light except for some stronger gusts along the Colorado
River area, including KBLH.

Aviation Discussion not updated for amended TAFs.


Thursday through Monday:
A series of low pressure systems will move through the Desert
Southwest through at least Friday. This will help to reinforce the
well below normal temperatures across the region and will keep
conditions a bit unsettled with the main precipitation threat
across south central Arizona Friday and Friday night. Humidity
will stay elevated Thursday into Friday with minimum RH mostly
between 20 and 30 percent over the deserts. Drier westerly flow
aloft returns Saturday although high temperatures stay below
normal. Continued dry weather with a modest warming trend is
expected Sunday into Monday as minimum RH values drop into a range
mostly between mid teens and low 20s. Expect breezy to locally
windy conditions Thursday and Friday with winds favoring the west;
strongest winds are likely to be over far southeast California
and in the favored higher terrain locations. Rather light winds
are on tap for the weekend and into early next week.


Spotters should follow standard reporting procedures.





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