423
FXUS65 KPSR 301802
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1102 AM MST Sun Jun 30 2024

.UPDATE...Updated 18Z Aviation Discussion.

&&

.SYNOPSIS...
Monsoon shower and thunderstorm activity will increase today
across much of southern Arizona with the best chances for rain
from Phoenix and areas to the east and southeast of Phoenix.
Daily chances for scattered showers and isolated thunderstorms
should then persist through Wednesday with the activity focused
more over higher terrain locations. Drier conditions are
anticipated late this week with rain chances mostly ending
starting Thursday. Above normal temperatures are forecast for the
entire week with excessive heat conditions impacting portions of
southeast California and the Lower Colorado River Valley.

&&

.DISCUSSION...
As forecast, a large MCS developed last evening across New Mexico
and another in Sonora Mexico before moving into southeast Arizona
over the past several hours. Convection is still ongoing across
southeast Arizona, now moving into southern Pinal County, but it
is now generally elevated in nature and gradually dissipating.
Additional west northwestward propagating showers will remain
possible through sunrise, potentially reaching portions of the
Phoenix area. However, the bulk of the activity seems likely to
mostly bypass Phoenix to the south, moving through the Gila Bend
area before slowly dying out as it moves into Yuma County around
sunrise. A remnant MCV may end up positioned somewhere just east
or southeast of Yuma later this morning while having little
impact on any further development later today.

The 00Z HREF and the latest HRRR runs generally all point toward a
busy monsoon day today across southeast Arizona into the higher
terrain and then over portions of the south-central Arizona lower
deserts this evening and tonight. Moisture will continue to
stream into southern and central Arizona this morning and
afternoon boosting area PWATs to around 1.75", while low level
mixing ratios rise from the current 9 g/kg to 11 g/kg. Given the
sufficient moisture and likely good insolation over much of the
area by mid morning, instability should be more than adequate for
shower and thunderstorm development this afternoon.

The HREF indicates the best instability with MUCAPEs of around
1000 J/kg will exist across far southeast Arizona northward to
around southern Gila Co. where some strong to possibly severe
storms could occur. Less instability with MUCAPEs of maybe 500-750
J/kg is forecast over western Pinal into Maricopa Counties where
at least some minimal CIN will also be in place. However, this
area will also host much higher DCAPEs, on the order of around
1500 J/kg which will likely provide for good chances for strong
outflow winds this evening. The higher terrain convection east of
Phoenix mid to late afternoon may send an westward propagating
outflow, but hi-res CAMs give a better shot at a strong outflow
moving northwestward into Pinal County by early evening from the
convection near Tucson. This outflow will likely be enough to
trigger additional convective development as it progresses through
Pinal into Maricopa County later in the evening. Strong gusty
winds and the potential for blowing dust will likely be the main
storm impacts late this afternoon and evening as the HREF shows
upwards of a 90% probability of 30+ kt winds and a 10% probability
of 50+ kt winds across central Pinal Co. The strong outflow winds
should then progress through most if not all of the Phoenix area
with a 50-70% probability of 30+ kt winds. Localized rainfall
amounts upwards of an inch or more will be possible, especially
within Pinal Co. By late evening into the early overnight hours,
the CAMs show some further redevelopment of showers and storms
within the Phoenix area through northwest Maricopa County to as
far west as eastern La Paz County.

After the expected busy day today, Monday could up being fairly
quiet but that is far from certain. Light southwesterly flow is
forecast to develop by Monday morning over at least southwest
Arizona and likely into south-central Arizona and this should
begin to bring some drier air into the area. Despite the
southwesterly drying flow, guidance still indicates plenty of
instability and overall minimal CIN across south-central and
eastern Arizona. A likely remnant MCV from this evening`s
convection should move north of Phoenix Monday morning/afternoon
likely providing subsidence just to the north and east of Phoenix.
However, more favorable conditions should be seen across southern
Maricopa County which the HRRR shows as an area of development by
mid afternoon. Given a weak southwesterly steering flow, some of
this convection could very well make its way into the Phoenix area
during the late afternoon/early evening. DCAPEs will not be as
high on Monday, but with MUCAPEs potentially around 1000 J/kg we
can`t rule out a few strong storms. The southwesterly drying flow
is likely to persist into Tuesday, but ensemble mean PWATs still
remain high at 1.5-1.7" while generally staying there through
Wednesday. Forecast confidence for both Tuesday and Wednesday is
not all that high as convection is likely to be conditional due to
the lack of any organized forcing. There will definitely be some
higher terrain afternoon convection, but with an overall weak
southwesterly flow any convective development across the lower
deserts will likely be dependent on colliding outflows.

The synoptic pattern will begin to shift starting Wednesday as a
very strong high pressure ridge develops off the California coast
before likely shifting into at least western portions of the
Desert Southwest by Thursday. The positioning of the high should
result in dry northerly flow across our region starting Wednesday
night and lasting through at least Friday. This northerly flow is
not likely to completely scour out the lower boundary layer
moisture, but it will bring in markedly drier air aloft which will
easily be enough to squash most if not all of convective
development starting Thursday. NBM PoPs for Thursday and Friday
are at most 10-15% over higher terrain areas to around 5% over the
lower deserts. Eventually, guidance shows some moisture beginning
to seep back into the region from the east next weekend.

Forecast temperatures this week remain largely unchanged and
really do not change much day to day. Expect lower desert highs
ranging from 107-112 degrees across south-central Arizona to
upwards of 110-115 degrees for the lower deserts of southeast
California into far southwest Arizona. Overnight lows will also
run very warm this week with readings mainly in the low to mid
80s over the rural deserts to the upper 80s and lower 90s within
the metro areas.

&&

.AVIATION...Updated at 1755Z.

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

Main weather concerns heading into this evening will be
thunderstorm activity and gusty winds from outflows. In the
meantime, westerly winds are expected to prevail through this
afternoon with speeds generally aob 10 kts, although a few
occasional gusts in the mid to upper teens will be possible.
Attention then turns to a complex of thunderstorms expected to
develop across southeast AZ and migrating its way northwestward
into south-central AZ by early this evening. The initial hazard
will be a surging outflow, which will shift the winds from the SE
with gusts increasing into the 25-40 kt range potentially. The
timing of the outflow at this time looks to be between 02-04z.
Accompanying the outflow will be the potential for blowing dust as
well causing a significant reduction in visibility. Scattered
thunderstorm activity will be possible across the terminals into
the overnight period. There is still quite a bit of uncertainty on
the overall coverage and thus at this time only VCTS have been
introduced in the latest TAF package. AMDs to the TAF package will
likely be needed once confidence increases on the overall
convective evolution this evening. Thunderstorm activity is
expected to exit the region between the 10-12z timeframe Monday
morning.


Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation aviation weather concerns expected through the
TAF period. Winds will generally be out of the southeast at KIPL
and out of the south at KBLH. Winds are expected to gust upwards
of 20-25 kts this afternoon and early evening, especially at KBLH.
FEW-SCT passing high clouds are expected through tonight.

&&

.FIRE WEATHER...
Moisture levels and storm chances will increase today with good
chances for showers, scattered storms and strong outflow winds
late this afternoon and evening across south-central AZ. MinRHs
today will still see upper teens over much of the lower deserts
and 25-30% in higher terrain areas before improving another 5% on
Monday. Overnight recoveries will be good over much of the area
tonight with 40-50% RHs over much of the eastern districts to
20-35% over the western districts. Outside of thunderstorm
activity, winds will follow fairly typical diurnal trends but
with more of a south southwesterly dominant direction, especially
across the western districts. Daily monsoon storm chances should
persist Monday through Wednesday across south-central Arizona, but
coverage is likely to be fairly limited while favoring higher
terrain areas. MinRHs of 20-25% across the lower deserts to
upwards of 35-40% over the eastern Arizona high terrain can be
expected through Wednesday with drying conditions and rain
chances mostly ending starting Thursday. Temperatures will remain
several degrees above normal each day this week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530.

     Blowing Dust Advisory from 4 PM this afternoon to 10 PM MST this
     evening for AZZ553.

CA...Excessive Heat Warning until 8 PM PDT Friday for CAZ562-566-567-
     569-570.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Lojero
FIRE WEATHER...Kuhlman