Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 302056
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
156 PM MST Sat May 30 2020

.SYNOPSIS...
Strong high pressure persisting over the region will lead to
temperatures around 10 degrees above normal across south-central
Arizona. Slightly cooler, but still above average temperatures are
likely early next week as an area of low pressure slowly moves
towards the west coast. Increasing moisture may also bring a
slight chance of thunderstorms to southern Gila County through at
least the middle of next week.

&&

.DISCUSSION...
Current visible satellite shows thunderstorm activity increasing south
of Tucson and over parts of Northern Arizona. Activity is still
quiet for us but latest hi-res guidance and satellite trends
suggest storms may develop over Gila County within the next couple
of hours. Otherwise, temperatures across the Valley are already
in the 104-107 degree range with a few more hours of peak heating
to go. An Excessive Heat Warning remains in effect for south-central
Arizona, including Phoenix.

Farther west, atmospheric heights are falling as a low pressure system
slowly moves onto the California coast. Heights will continue to
fall today and tomorrow ultimately leading to a slight reprieve
from the recent excessive temperatures. Afternoon highs today will
be 5-10 degrees cooler than yesterday across southeast California
and western Arizona but the heat will linger through tomorrow in
south-central Arizona. This afternoon will be a bit on the breezy
side for southeast California and western Arizona with some gusts
approaching 30 mph.

Otherwise, lingering moisture will keep chances for isolated
thunderstorms over the higher terrain across the eastern half of
Arizona. For our forecast area, the mountains east of Phoenix will
have generally 10-20% chance for storms on any given afternoon
over the next several days. Storms are not expected to be prolific
rain producers, but may produce gusty winds, outflows, and
lightning strikes. Distant storms may also send long traveling
outflows and a few may reach the lower desert areas of Pinal and
Maricopa Counties. Convection potential over the lower desert,
including the Phoenix area, is limited given the overall dry
atmospheric profile.

Ensemble guidance remains consistent showing a Pacific trough
deepening off the West Coast late next week. The ensemble spread
on how the trough will progress is varied enough to create
uncertainty in the forecast late next week. For the most part,
trends still favor a gradual cool down through at least the
middle of next week with afternoon highs nearing seasonal normals
by Thursday or Friday.

&&

.AVIATION...Updated at 1800Z.

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

Light winds this morning will continue to become variable at times
before southwesterly winds take hold this afternoon. Afternoon
breeziness with gusts upwards of 18 kts will be possible as daytime
mixing increases. More thunderstorm development is expected this
afternoon mainly to the south and east of the metro over the higher
terrain. Can`t rule out an outflow moving into the metro early this
evening, but confidence is too low to mention in the KPHX, KSDL, and
KDVT TAFs at this time. Have added an outflow in the KIWA TAF since
there is higher confidence of an outflow reaching the site. Latest
CAMs and HREF guidance indicate an outflow from the south/southeast
reaching KIWA around 01Z-02Z with speeds upwards of 10-15 kts
possible. The magnitude, timing, and direction of outflows are
subject to change in later updates. Otherwise, FEW-SCT mid and high
level clouds aoa 12 kft will be possible throughout the TAF
period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at KIPL will favor a westerly component through the next 24
hours, while winds at KBLH will favor a south to southwesterly
direction. Afternoon breeziness will be possible at both sites, with
gusts upwards of 20-25 kts possible at times. Otherwise, mostly
clear skies will persist, aside from some passing high clouds.

&&

.FIRE WEATHER...
Tuesday through Saturday: Moisture may remain ample enough for
isolated afternoon thunderstorms nearly every afternoon and
evening across much of eastern Arizona, including Gila County.
Storms farther west into the lower desert area around Phoenix is
less likely. Storms are not likely to produce much rain, but may
create strong gusty winds, outflows, and lightning strikes.
Otherwise, winds are likely to follow typical diurnal directional
trends with some afternoon breeziness. Minimum humidity values
will drop into the 10-20% range with overnight recoveries rising
into the 20-40% range. Even though these elements remain well
below critical thresholds, the fire danger will remain heightened.

&&

.CLIMATE...

Record highs:

Date        Phoenix          Yuma
---- -------   ----
May 30 114 in 1910 120 in 1910

May 31      109 in 2012    113 in 2012

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ534-537>556-
     559>561.

CA...None.
&&

$$

DISCUSSION...AD
AVIATION...Smith
FIRE WEATHER...AD/CB
CLIMATE...Hodges/MO



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