Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 221955

Area Forecast Discussion
National Weather Service Phoenix AZ
1255 PM MST Thu Jun 22 2017

.UPDATE...Updated aviation and fire weather discussions.


High temperatures today will not be quite as hot as the past
couple days but still very hot. Humidity will be higher as well.
Anticipate little change in temperatures Friday. Temperatures
increase over the weekend. Storm chances return to the higher
terrain as well. Temperatures start to decline on Monday but still
excessively hot in some areas. Modest additional cooling is
anticipated Tuesday and Wednesday.


A weak Gulf surge evident in the surface obs with dew point
increases brought by southwesterly winds over metro Phoenix (more
south and southeast further west). The first foray of shallow Gulf
moisture was seen Wednesday morning at places like Yuma and El
Centro which had high dew points before mixing out in the
afternoon. In fact, the El Centro area saw dew points rise to the
70s. There will be a larger area affected today with broader
coverage of the more moist air. A decaying MCS over Sonora could
possibly reinforce this process with outflow but Hermosillo obs
didn`t reflect much in the way of outflow. The increase in more
humid air will lead to lower high temperatures today with part of
the insolation going into latent heating. Unfortunately, not
enough cooling to drop the Excessive Heat Warning. The moist
layer is relatively shallow and expect dew points to decline in
the afternoon with mixing. Given the shallow nature of the moist
layer and the close proximity of the high center, there will not
be enough CAPE for storms on the lower deserts. Even the higher
terrain will struggle to see any storms as drier air moves in over
portions of northern and eastern AZ.

Friday through Sunday...
The high will sag southward on Friday and dew points will decline
as well. Anticipate little change in temperatures. Over the
weekend, ridging consolidates over the west and the high
strengthens. Accordingly, temperatures increase at least a few
degrees. Expecting to stay below records but we may be only a few
degrees below the peak values we saw on Tuesday. A complicating
factor will be the return of deeper moisture into Arizona as a
backdoor front pushes against the southern Continental Divide.
However, models are not indicating a major influx that would lead
to widespread storms. Rather, it would be more like what we`ve
seen the past couple days with high-based storms over the favored
higher terrain areas of Arizona sending outflow pretty far afield
to the lower elevations. Unfavorable steering flow will also tend
to prevent storms from getting to the central Arizona deserts
(including metro Phoenix). Anticipate Sunday afternoon/evening
being more active than Saturday.

Monday through Wednesday...
A combination of higher dew points and debris clouds will nudge
temperatures down a bit on Monday. However, a number of locations
will still reach high to very high Heat Risk levels. Thus,
extended the Excessive Heat Warning to Monday for portions of our
forecast area including metro Phoenix. A trough passing to the
north will weaken the ridge leading to a modest cooling trend
Tuesday and Wednesday. Anticipate a decrease in storm activity
over Arizona but not altogether since there will still be some
lingering moisture over the southeast third of the state.


South-Central Arizona including KPHX, KIWA, and KSDL:
West winds occasionally gusting to around 20 kts will continue
through late afternoon, subsiding after sunset. The switch to
easterly winds will occur later than normal, around 10Z at KPHX.
Temperatures will be slightly cooler than previous days, and
should remain critical thresholds. Intermittent high clouds will
continue through tomorrow afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation impacts through Friday morning as skies remain mostly
clear. Winds will favor a southerly direction, especially during the
afternoon and early evening hours. Some afternoon breeziness is
likely at KBLH with gusts near 20 kts.

Aviation discussion not updated for amended TAFs.


Sunday through Thursday:
High pressure will generally remain positioned over the Southwest
through late next week, maintaining above normal temperatures. A
modest increase in moisture will occur next week, but still should
see minimum RH values in the 10-20% range each afternoon. Isolated
thunderstorms are possible each afternoon across the higher
terrain of south-central Arizona, including southern Gila County,
but rainfall amounts will be light. Lightning ignitions remain a
concern given the dry sub-cloud layers, along with gusty outflow
winds. For now, it appears any significant moisture intrusion will
hold off until after the period, maintaining dry fuel conditions



Record highs this week:

Date           Phoenix            Yuma
----           -------            ----
6/22         116 in 1988        115 in 1960
6/23         116 in 1974        116 in 1959
6/24         118 in 1929        120 in 1957
6/25         120 in 1990        119 in 1994
6/26         122 in 1990        122 in 1990


Spotters should follow standard reporting procedures.


AZ...Excessive Heat Warning until 8 PM MST Monday for AZZ530-533-534-

     Excessive Heat Warning until 9 PM MST /9 PM PDT/ Sunday for

     Heat Advisory until 9 PM MST Sunday for AZZ557-558-563.

CA...Excessive Heat Warning until 8 PM PDT Monday for CAZ560-561-563-

     Excessive Heat Warning until 9 PM PDT Sunday for CAZ562-564-565.



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