Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 210551
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1051 PM MST Sat Jan 20 2018

.UPDATE...Updated Aviation discussion.

&&

.SYNOPSIS...
A storm system will move across the region today, bringing much
cooler temperatures, an increase in winds, and chances for light
rain. Temperatures will be well below normal through Sunday, with
over night lows in the deserts dropping into the 30s. A slow
warming trend will occur throughout next week, prior to another
strong but dry storm system affecting the Southwest.

&&

.DISCUSSION...
Satellite trends from this afternoon show weak convection
developing across western Arizona, in the wake of a broad area of
cloudiness over central Arizona. Diurnal heating has allowed for
steepening low-level lapse rates to become juxtaposed with cold
temperatures aloft, allowing for modest destabilization. Would not
be surprised to see a few small low-topped storms develop out of
these, and brief small hail cannot be ruled out. Trends suggest
the most favorable area will remain over Yuma/La Paz Counties and
western Maricopa County through the late afternoon, before the
loss of diurnal heating results in a downward trend in convection.
Otherwise, light showers continue to develop within a narrow
moisture plume aloft. Measurable rainfall has been confined to
the northern and eastern portions of Maricopa County, with gauges
generally observing less than one tenth of an inch.

Still could see a few showers linger into the late evening across
south-central Arizona as the primary vort max rotates across the
northern half of the state. As the storm system exits the region
into Sunday, one more day of well below-normal temperatures can be
expected with high temperatures in the upper 50s and lower 60s.
May still some breezes linger as high pressure builds to the
north, but speeds should be a bit weaker than observed today.

The pattern remains low-amplitude throughout next week, with a
gradual warming trend taking hold. Another strong upper trough
will develop across the western U.S. later in the week, but much
of the Southwest will be situated within drier air aloft. The most
significant impact could be increasing wind speeds on Thursday and
Friday, and a return of cooler temperatures.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
Trough axis has moved east of the area, with a more subsident air
mass overspreading the Phoenix area. Precipitation across the
higher terrain north and east of Phoenix will continue to
dissipate late this evening, followed by a clearing trend across
central Arizona. Otherwise, latest guidance indicates that winds
will remain out of the west at Phoenix with speeds generally less
than 10 kt through Sunday.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather impacts expected. Clear skies and light
diurnal winds will prevail in the wake of the low pressure system
east of the area.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday:
A warming trend can be expected Monday through Thursday with lower
deserts highs climbing well into the 70s again Wed-Thu. Humidities
trend down early in the workweek but overnight recovery remains
good. Winds will generally be light and favor north and
northeasterly directions with some local breeziness Tuesday. A dry
weather system moves through late in the workweek for breezy
conditions (starting Thursday) and cooler temperatures by Friday.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

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DISCUSSION...Rogers
AVIATION...Hirsch
FIRE WEATHER...AJ



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