Ocotillo, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

009
FXUS65 KPSR 292202
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
302 PM MST Thu May 29 2025

.KEY MESSAGES...

-Temperatures peak Friday, with forecast highs around 100-105
across the lower deserts leading to localized areas of Moderate
HeatRisk.

- An influx of tropical moisture over the weekend will bring
widespread chances for showers and isolated thunderstorms, with
the best chances focused on Sunday into Sunday night.

- Below normal temperatures with highs around 95 degrees across the
lower deserts are expected from Sunday through at least the middle
of next week.

&&

.DISCUSSION...
The pieces are coming together late this week for an unusually wet
late May/early June weather system to influence the region this
weekend. Current mid-level wv imagery reveals an upper low that has
settled west of the Baja Peninsula (and is expected to meander there
for a few days), and further north, a somewhat disjointed upper
level ridge axis stretches from just off the West Coast through the
Intermountain West and up into Central Canada. Meanwhile, the source
of moisture for our upcoming wet weather has become the first named
tropical cyclone of the Eastern North Pacific season, Alvin, and is
approaching 15N/107W at this hour. Do not be concerned about direct
impacts from Alvin, as the storm will weaken and become a remnant
low as it approaches the Southern Baja Peninsula. However, the
moisture associated with the remnants of Alvin will then be pulled
northward into Southern AZ over the weekend thanks to the cyclonic
flow around the aforementioned cutoff low west of the Baja.

In the near term, expect the region to fall under the influence of
the aforementioned upper level ridge centered to our north, with
strong positive height anomalies shown building over the Interior
West and ensemble mean H5 heights approaching 587-589 dam Friday,
tempered somewhat by the proximity of the cutoff low to our
southwest. Despite the latest HREF output indicating abundant high
level clouds continuing to overspread the region tomorrow as they
are today, NBM temperatures still reflect the impact of the ridge
strength peaking tomorrow, with afternoon highs between 100-105F
across the lower deserts Friday. This will likely (>60% chance) be
the hottest day until at least next Friday for our forecast area.

Ensembles have consistently advertised PWATS increasing from around
0.5" Friday to around 1" by late Saturday and upwards of 1.25" late
Sunday. When these values peak, they will be in excess of the
99th percentile of climatology. PoPs become introduced to the area
Saturday, though the lifting mechanism to produce some light,
high-based showers will be weak disturbances lifting to the
northeast of the cutoff low. Once the main low center nears our
area on Sunday, rain chances will increase quickly by the
afternoon with widespread chances of 50-80%. Instability should
also increase enough to bring thunderstorm chances into the
picture by late Sunday morning, likely lasting through around
midnight Sunday. Forecast MUCAPE is not all that impressive, but
it seems plausible we will see a swath of 500-1000 J/kg of CAPE
traversing the area just ahead of the low center later on Sunday
providing chances for some storms. Model soundings also show
enough shear for a few strong thunderstorms Sunday evening.
Rainfall will vary quite a bit with some areas barely seeing
anything (especially portions of SE CA) to some localized spots
possibly (10%) seeing an inch or so. The latest WPC QPF shows
amounts averaging around 0.1" or so along the CO River Valley,
0.2-0.3" over the south-central Arizona lower deserts, to as high
as 0.5-0.75" over the higher terrain. The threat for any flooding
is likely to be quite small as the instability should be limited
and the steering flow will average 10-20 kts. As the cutoff low
continues to track across Arizona during the overnight hours
Sunday night into Monday morning, it is forecast to quickly weaken
before tracking into New Mexico by noon Monday. A strong
subsidence inversion is shown developing in GFS bufr soundings
Monday in its wake, especially by the afternoon, precluding the
chance for lingering shower activity except perhaps over prominent
high terrain to the north/east of Phoenix.

For some perspective, Phoenix Sky Harbor has only seen measurable
rainfall on 38 separate days during the last week of May and the
first week of June since 1896. The last few times Phoenix recorded
measurable rainfall during this period was in 2015, 2008, 1994, and
1992. The highest amount recorded during this period was 0.41" on
June 3, 1915. For June 1st, Phoenix has only seen measurable
rainfall one time (1914). It is even more unusual for Yuma to see
any rainfall in the last week of May or in the first week of June as
it has only occurred on 11 separate days.

Drier conditions are expected to move in behind the weather system
on Monday, but there now looks to be a second potential disturbance
diving southward off the coast of California during this time.
Guidance is still somewhat uncertain with the eventual track of this
second system, but it`s looking more likely (55% of ensemble members
comprise WPC clusters that depict a separate, second disturbance
separate from a broader trough moving through the Western US) to
move directly through our region at some point next Tuesday or
Wednesday. However, even if it does move through moisture levels are
likely to be quite limited which may preclude any additional rain
chances.

Forecast temperatures for Sunday through the middle of next week are
still quite uncertain due to the unsettled weather pattern.
The latest NBM now shows highs between 90-96 on Sunday with readings
somewhere in the low to mid 90s through around next Wednesday or
Thursday (overall, near to below normal looking at probabilistic NBM
distributions.) The uncertainty in temperatures for Sunday is mainly
from the expected cloud cover and rain developing, while the
uncertainty into the middle part of next week is due to the
potential track differences with the second system. Either way it
seems we will mostly likely see several days of below normal
temperatures for the start of June.

&&

.AVIATION...Updated at 1728Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
No aviation weather concerns are expected through the TAF period.
Light and variable winds will be favored through the rest of the
morning before seeing an increasing S-SW component going into this
afternoon. Winds will continue to veer toward a westerly component
by late afternoon and continue into tonight. Light and variable
winds are expected at times, particularly during diurnal
transitions, with speeds mostly remaining below 10 kts through the
TAF period. SCT-BKN mid and high clouds will continue with
periods of virga possible.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are anticipated through the next 24
hours. Winds at KIPL will predominantly favor the E-SE, while
directions at KBLH will favor the S. Expect periods of light and
variable winds to occur throughout the TAF cycle. Otherwise,
expect SCT-BKN mid and high clouds through the TAF period with
virga possible at times.

&&

.FIRE WEATHER...
An unseasonably wet weather system will track through the area
Sunday, bringing 50-80% chances for wetting rain to the eastern
districts of South-Central Arizona and 15-50% chances in the
vicinity of the Lower Colorado River Valley and over Southwest
Arizona. Until then, seasonably hot and dry conditions will
prevail. Afternoon MinRHs will increase from 8-15% Friday to
10-20% Saturday and peak Sunday at 25-30% areawide. Overnight
recoveries will also improve each night, from 20-40% tonight to
60-80% areawide by Sunday night. Winds will favor typical diurnal
tendencies with periodic afternoon gusts to around 15 mph through
Friday. South southwesterly winds are likely to be more dominant
over the weekend with afternoon gusts to around 20 mph. After
Sunday, expect humidities to decrease, returning more typical
levels by the latter half of the upcoming workweek.

&&

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

$$

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