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Forecast Discussion for Phoenix, AZ

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000
FXUS65 KPSR 020600
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1100 PM MST Fri Jul 1 2022

.UPDATE...
Updated Discussion and Aviation sections.

&&

.SYNOPSIS...

Although there is still a minor risk for gusty outflow winds
across lower elevations today, chances for showers and
thunderstorms will decrease and shift more east and southeast
through the weekend. For Saturday and Sunday, most areas will see
little to no rain chances, though a slight resurgence in moisture
is possible for Monday and Tuesday. Temperatures will remain near
normal through the holiday weekend, then trend up later next week.

&&

.DISCUSSION...
Several outflows moved through all or part of the metro area this
evening due to storms originating from Pima, Gila, southeast
Yavapai, and southwest Maricopa Counties. If there had been a
little more moisture, and in turn instability, there likely would
have been a lot more storm activity. Instead, some isolated weak
showers developed on a westward moving outflow. Echoes have
dwindled and storm activity is not anticipated to develop
overnight. One caveat is that an embedded disturbance is slowly
moving northward from southeast AZ. For Saturday, hi-res guidance
is reluctant to develop storms over the lower elevations once
again. This is plausible due to the nearby moisture gradient
(drier air) and some stabilizing that has happened tonight.

&&

.PREVIOUS DISCUSSION...
Convection developed early today across AZ, before 10 AM. GOES
upper-level WV this afternoon shows a stream of deeper moisture
concentrated mainly in southeast AZ and into NM while drier mid
and upper tropospheric air has pushed into the rest of the state
with deeper southwesterly flow southeast . This is noted in well
in the 24-hr change in the sounding profiles from aircraft in
Phoenix and with Flagstaff`s 12Z sounding. There are at least a
couple perturbation waves within the southwest flow. One of those
small waves is moving through northern AZ, helping invigorate
convection over the higher terrain with steeper mid- level lapse
rates.

The 12Z HREF so far has been reliable showing the focus of
the convection along the Rim and in southeast AZ. This includes
Southern Gila, where some strong storms have already developed.
Steering flow is only 5-10 kts out of the southwest and as is
already being seen, storms are experiencing some erratic motions
based on outflow boundaries. Still it is possible for storms to
pulse up locally over an area, especially over terrain features
and with outflow collisions. Localized flash flooding will be the
primary concern for eastern AZ this afternoon. Rain rates have
already been observed in excess of 1"/hr in southeast AZ. Runoff
can be exacerbated by burn scars, especially with more recent
scars with low thresholds like the 2021 Telegraph around the Pinal
mountains south of Globe.

Mesoanalysis is showing low DCAPE values within the axis of deeper
moisture with increasing magnitudes to the west, up to around
1500 J/kg in western Pinal and Maricopa counties. Downbursts in
southeast AZ have already produced strong gusts upwards of 30-40
mph and stronger gusts will be possible further west in the drier
environment with the greater evaporative cooling. Stronger
downburst winds in the areas mentioned could also generate blowing
dust. However, the drier environment in the lower deserts of south-
central AZ may also be a detriment to convection. The environment
is better capped and buoyancy is lower. So, outflows may not be as
efficient at generating new convection the further into this area
they push. This seems to be reflected in the 12Z HREF which again
keeps the convection focused mostly through eastern and southern
Pinal county, for the lower deserts. Still anticipate some
convection to flare up in the Table Top area of southern Maricopa
county, which could produce impacts in the I-8 corridor between
Gila Bend and Casa Grande. Outflows into the Valley cannot be
completely discounted this afternoon, though the potential for
measurable rain or any thunderstorms will be quite low (5-10%).
Convection should remain primarily diurnal and dissipate with the
loss of heating after sundown.

Deeper moisture will drift a little further east and southeast
heading into the weekend and perhaps the most noticeable decrease
in convection will be across northern AZ. Storms are still likely
but with greater focus in the White Mountains, with some extension
into southern Gila county, and down through Southeast AZ.

Some moisture may slosh back into the eastern ~1/3 of our CWA on
Monday/4th of July, seemingly in response to a shortwave lifting
SW to NE through the Great Basin. This could bring about more low
elevation outflows with a low (10-20%) chance for isolated
thunderstorm development - something to watch more closely given
outdoor festivities. By Tuesday the drier air just to the west
appears to win out again and pushes the moisture back east.

Increasing evidence that we`ll be heading into a period of very
hot weather towards the end of next week. GEFS/EPS ensemble mean
height fields are already forecasting values in the 95-99th or
higher percentile (7-10 days out) as the upper level low off the
West Coast weakens/retrogrades and a very broad and strong anti-
cyclone envelopes the Western US. H5 heights may exceed 600 dm for
a broad area as local boundary layer temperatures (850 mb) are
likely to climb toward 30-32C. NBM-based probability of max
temperatures AOA 110F for the lower deserts climb above 0%
Wednesday and reach 40-80% by Friday. CPC is highlighting almost
the entire CWA with a moderate risk for excessive heat (defined by
CPC as exceeding the 85th percentile) July 8-10 in their 8-14 Day
Hazards Outlook. Thus, we may be in store for another round of
very dangerous heat. The heat may also allow the broader regional
circulation to develop a more typical monsoonal flow with richer
moisture returning from the southwest thereafter (CPC is
highlighting much of Arizona with a slight risk of heavy
precipitation July 11-14).

&&

.AVIATION...Updated at 0600Z.

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

Storm activity has finished up for the night. One caveat is that a
weak embedded disturbance could possibly generate weak isolated
showers overnight. Otherwise, thick mainly high clouds will slowly
decrease but linger well past sunrise. Anticipate storm activity
Saturday afternoon and evening will once again be outside of the
metro area but outflow winds may still move through during the
evening. The rest of the night and into morning, easterly winds
will prevail. Expect a transition to westerly winds by
midday/early afternoon.


Southeast California/Southwest Arizona including KIPL and KBLH:

Gusty southwest and west winds are weakening and will continue to
do so over the next few hours. Southerly winds are anticipated to
begin toward sunrise at KBLH (late morning at KIPL) with gustiness
(gusts 20-25kts) at KBLH by midday. Anticipate another sundowner
at KIPL beginning around 00Z. Otherwise, clear skies.

&&

.FIRE WEATHER...
Shower and thunderstorm potential will be shifting into far eastern
Arizona through the weekend with with a slight rebound into Gila
County by Monday/Tuesday. With temperatures hovering not far from
the seasonal normal, humidity values will generally trend lower
with afternoon values falling closer to 10-20% as storm activity
decreases. Overnight recovery should mostly range from 25-40%
except somewhat higher over mountainous areas. Southwesterly winds
will also increase in strength through the weekend particularly
across southeast California and southwest Arizona though all areas
will remain below critical thresholds. Downsloping winds across
western Imperial county, including the Imperial Valley, during
the next few evenings may create a few hours of elevated fire
weather conditions.

&&

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

$$

DISCUSSION...Benedict/Iniguez
AVIATION...AJ
FIRE WEATHER...Benedict/Iniguez

Previous Forecast Discussions may be found at
NWS Phoenix, AZ (PSR) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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