San Luis, Arizona 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

180
FXUS65 KPSR 312210
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
310 PM MST Sat May 31 2025

.KEY MESSAGES...

- An influx of tropical moisture will spread over the region
  tonight into Sunday allowing for widespread showers and
  scattered thunderstorms to develop on Sunday.

- A few strong thunderstorms with gusty winds, small hail, and
  localized heavy rainfall are possible on Sunday.

- Temperatures will drop below normal with highs in the nineties
  for several days starting Sunday, though temperatures will warm
  each day after that resulting in a return to above normal
  temperatures by the end of the workweek.

&&

.DISCUSSION...
The forecast for an unusually wet early June weather system to
pass over the area tomorrow remains mostly on track. A closed
upper low is centered west of Baja California, resulting in
southeasterly flow aloft. Meanwhile, Tropical Storm Alvin moved
over cooler waters and an environment with stronger vertical wind
shear thanks in part to the low off the Baja, and thus has decayed
into a post-tropical remnant low early this morning as it
approaches the southern tip of the Baja Peninsula. This remnant
low, though it will remain far to the south, will serve as the
primary source of moisture for the upcoming wet weather, with the
closed low to our southwest drawing moisture northward. An
increase in moisture, particularly in the mid levels, is already
apparent, with latest RAP analysis showing a tongue of >1" PWATs
beginning to spread into SW AZ and SE CA. NAEFS/EFS ensembles
continue to advertise mean PWATs increasing over the area through
tomorrow morning for SE CA and SW AZ and through tomorrow
afternoon for South-Central AZ, with values peaking briefly around
1.5", which is in excess of the 99th percentile for the time of
year, near the climatological maximum.


The latest HREF goes through 12Z Monday, capturing the bulk of
the precipitation expected from this event. Though precise
rainfall amounts remain uncertain due to the hit-or-miss nature of
thunderstorms and some possible gaps in the widespread shower
activity, the overall evolution of the event has come into better
focus. We may see some scattered light showers develop as early as
this evening mainly across southeast California and southwest
Arizona, but little if any accumulation is expected. We should see
shower activity really blossom around sunrise across SW AZ into
SE CA. As the low ejects northeastward toward the area, this
shield of precipitation, likely developing some embedded
thunderstorms as the day goes on, will shift into South-Central AZ
by mid-late afternoon. With these showers, expect average
accumulations on the order of a few tenths of an inch across SW
AZ, 0.25-0.5" across South-Central AZ, with locally higher amounts
of 0.5"+ in thunderstorms. Totals upwards of 1" with any training
of storms over the same spot will be possible. During the
afternoon, as the core of the low moves over SoCal, CAPE values up
to around 1000 J/kg will materialize over Southeast California,
presenting the greatest concern for strong storms over the
forecast area. Several CAMs show thunderstorms developing over the
spine of Baja and even over the San Diego Mountains before moving
off to the northeast, potentially impacting Imperial and Eastern
Riverside Counties. With any storms that do develop in this
environment during the late afternoon, there is a 30- 50% chance
of gusty outflows in excess of 30 kts.

The shower and isolated thunderstorm activity is likely (50% PoPs
for Phoenix and up to 80% over the high terrain north/east) to
continue through Sunday evening into the overnight hours, but
coverage is expected to decrease with time. With the low
continuing eastward, the area with the greatest instability
(albeit elevated during the overnight hours) will shift over
South-Central AZ, presenting a conditional thunderstorm threat if
this instability is realized during the overnight hours into
Monday morning. Lingering moisture on Monday will present lower
chances (20-40%) for showers and isolated storms over the
foothills, with much better odds over Northern AZ, as a strong
subsidence inversion sets up over much of the area during the
afternoon in the wake of the upper low. Any leftover moisture is
expected to come into play for Tuesday as a second upper level low
is forecast to quickly swing through the area from the west
northwest. The NBM has been slow to introduce rain chances for
this second system, but confidence is starting to increase for at
least some slight chances for showers and a few isolated
thunderstorms mainly Tuesday afternoon. We have increased PoPs
during this time to mainly give higher terrain areas at least a
mention of rain chances. The lack of good moisture will be the
main limiting factor as the system actually looks like it will
bring a brief period of good forcing with cold air aloft.

Temperatures will drop well below normal tomorrow thanks to
abundant clouds, fairly widespread rainfall, and the cold core of
the closed low moving directly overhead. Expect Sunday to be the
coolest of the next 7 days, with afternoon highs around 10F below
normal, ranging from the middle 80s to the lower 90s. Temperatures
will warm each day following Sunday through the workweek, with
highs eventually topping 100F again around Thursday across the
lower deserts. Latest NBM seems to be favoring an upper level
pattern by late week into next weekend where a subtropical ridge
influences the region and positive height anomalies creep into the
area from the southeast. While the 75th percentile of the NBM
distribution shows highs around 110 next Saturday and Sunday,
there is still a fair amount of spread, with IQRs >=5F next
Saturday onward.

&&

.AVIATION...Updated at 1710Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
Low confidence in wind trends will be the greatest weather issue
through Sunday afternoon under periods of thick mid/high cloud
decks. West winds should quickly settle over the area with some
gusts 15-20kt possible during the late afternoon/early evening, then
persisting longer than usual into the overnight. The traditional
morning easterly component may not completely become established
Sunday with some variability before quickly reverting to a west
component by late morning. While cloud decks will thicken and lower
through the day with some passing -SHRA possible, the better odds
for cigs falling below 10K ft AGL and more concentrated SHRA should
not arrive until late Sunday afternoon/evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
Lowering cigs, increasing chances for SHRA, and erratic wind
directions will all be weather issues through Sunday afternoon.
Confidence is good that a southerly wind component will prevail
through this evening with some oscillation between SE and SW and
occasional gusts 20-25kt through mid evening. Cloud decks should
thicken and lower - especially overnight with bands of SHRA moving
into the area Sunday morning. Have added some VCSH mention in this
package, and while not explicitly mentioned in the TAF, SHRA could
yield erratic wind directions and gustiness. More expansive SHRA
with scattered TSRA may be possible Sunday afternoon with more
notable impacts.

&&

.FIRE WEATHER...
An unseasonably wet weather system will track through the area
Sunday bringing widespread wetting rain chances of 50-80% and
chances for thunderstorms (15-30% chance). Afternoon minRHs will
rise to 20-35% areawide Sunday, with similar values anticipated
Monday. Periods of showers and isolated thunderstorms are
expected starting Sunday morning over the western deserts,
spreading eastward over the day and lasting through the overnight
hours Sunday night. The elevated humidities Sunday-Monday will
begin to lower starting Tuesday, but MinRHs should mostly stay
above 15% through the middle of the upcoming workweek. A drier
weather system is likely to move through the region on Tuesday
possibly bringing some isolated showers and a few thunderstorms
focused over higher terrain areas. Hotter and seasonably dry
conditions are likely to return later next week.

&&

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

$$

DISCUSSION...Whittock
AVIATION...18
FIRE WEATHER...Whittock/Kuhlman