Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 190034

Area Forecast Discussion
National Weather Service Phoenix AZ
534 PM MST Thu Apr 18 2019

.UPDATE...Updated Aviation Discussion.


Temperatures will be notably warmer through Friday as high
pressure builds over the region. Lower elevation communities will
approach the century mark Friday afternoon. A dry weather system
will move through Saturday, first bringing some breezy weather
then slightly cooler temperatures following on Sunday and Monday.
Heading into next week, a return to warmer weather is likely with
another run at triple digit temperatures possible Wednesday.


The forecast for Southwest Arizona and Southeast California will
remain rather tame the next week, outside warm daytime temperatures
Friday, and near critical fire weather conditions this weekend. The
overall pattern is defined by a strong ridge of high pressure
building into the Desert Southwest (with a ridge axis extending from
Yuma to Las Vegas) and an upper low spinning in the Eastern Pacific
(near 28.0N/129.7W).

Significant warming was evident on the 12Z KTWC upper-air sounding
this morning...associated with the leading edge of the upper ridge.
Although the ridge axis will be positioned east of the forecast area
(along the Arizona/New Mexico border) Friday afternoon, warm air in
its wake will mix to the surface, resulting in daytime temperatures
in the Phoenix Metro nudging in the upper 90s. A few locales may hit
the century mark for the first time this year tomorrow. In any
event, the heat Friday will be the main weather story.

Restating the previous forecast discussion; "These warm temperatures
will bring a Moderate HeatRisk to a few locations, primarily in the
hot spots of the Imperial, Lower Colorado River, Lower Gila River,
and Salt River valleys. This would include El Centro, Yuma, Parker,
and Phoenix. While temperatures this warm are not unheard of, they
are approaching record levels. Data from county and state level
health partners have shown an increases in heat-related illnesses
with temperatures such as these coming up. Folks are encouraged to
make sure they are properly hydrating and seeking relief from the

As the ridge tracks east, the southern periphery of the dry upper
low in the Eastern Pacific will push into SW CA/NW AZ this weekend.
Although the dry airmass in place will prevent any precipitation,
this system will tighten pressure gradients enough for some gusty
conditions Saturday and Sunday. Winds should stay below the critical
fire weather thresholds, it may be possible for a few locations to
briefly hit Red Flag criteria. At this time, critical conditions are
not expected to be widespread or long-lived for a Fire Weather

As we move into the first half of next week, an upper low from the
NW will move into the Great Basin. Southeast California/Southwest
Arizona will again be on the southern periphery of this system and
will not be impacted by precipitation. It will however result in
some breezy conditions from the north to northwest Monday and


.AVIATION...Updated at 0025 UTC.

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

With no aviation concerns during the period expect light and
variable to light winds favoring diurnal trends through early
Friday morning. Wind speeds will be mostly under 8kt with
isolated periods of higher speeds near 9 kt. For Friday afternoon
expect atypical wind directions favoring southeasterly to
southerly directions. Skies will be partly cloudy with SCT-BKN
cirrus this evening with decreasing high clouds by later tonight

Southeast California/Southwest Arizona including KIPL and KBLH:

There are no aviation weather concerns during the period. Expect
light winds with diurnal tendencies along with periods of light
and variable winds during the period. Otherwise skies will be
mostly clear with occasional FEW-SCT cirrus passing through the

Aviation Discussion not updated for amended TAFs.


Saturday through Wednesday: There will be elevated fire weather
concerns this weekend as low humidity values combine with breezy
conditions. The strongest winds will spread across Southeast
California and the mountains north and east of Phoenix, including
the Tonto NF, on Saturday. 20-foot winds will range from 15-20 mph
in those ares with stronger gusts. Sunday the strongest winds are
expected in Tonto National Forest with similar speeds to Saturday.
Both days, afternoon humidity values will bottom out in the 10-20
percent range with overnight recovery generally 30-50 percent. After
the weekend, the winds will decrease and follow more typical diurnal
tendencies, but daytime humidity values will remain between 10-20

Spotter activation is not expected for the next 7 days.




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