San Luis, Arizona 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

854
FXUS65 KPSR 020545
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1045 PM MST Sun Jun 1 2025

.UPDATE...Updated 06Z Aviation Discussion.

&&

.DISCUSSION...

Key Messages:

- Showers and isolated thunderstorms will sweep across the area
through tonight with some lingering higher terrain shower activity
Monday

- Another round of isolated light showers possible Tuesday night and
Wednesday

- Temperatures falling below normal the next couple days, however
quickly rebounding near to slightly above normal the latter half of
the week

Early afternoon WV imagery reveals a compact, nearly cutoff upper
circulation center spinning along the northern Baja coast while an
elongated, positively tilted trough entering the Pacific NW will
act to dislodge and absorb this cutoff feature over the four corners
area in the next 48 hours. Concurrently, deep moisture profiles
originating from a remnant tropical system continue to be pulled
poleward in a robust meridional tropospheric wind profile with
objective analysis suggesting 9-10 g/kg boundary layer mixing ratios
hovering along the international border. Satellite and objective
analysis also indicates impressive jet level divergence and strong
ascent juxtaposed with this theta-e surge portending numerous rounds
of showers propagating through the forecast area.

While the anomalous moisture flux will support an unusually high POP
forecast for early June, limiting factors for more expansive,
heavier convective based rainfall include poor lapse rates owing to
the tropical nature of the incoming airmass and extensive thick
cloud cover muting insolation. Thus, embedded thunderstorms, while
prevalent, may not be as prolific through much of the area awaiting
the actual passage of the upper cold core this evening and
overnight realizing modest deep layer instability. Potentially, the
more robust thunderstorm activity may be possible in an area arcing
across SE California/SW Arizona late this afternoon and evening
where MLCape/MUCape 500-1000 J/kg have the best odds of being
achieved. Should this outcome materialize, a few stronger storms
would be possible with gusty outflow winds (20-40% chance of 35+ mph
gusts), patchy blowing dust, small hail, and heavy downpours.

Overall, the majority of the CWA should see some accumulating
rainfall with HREF membership only leaving out portions of Riverside
County on the NW side of the upper low where ascent mechanisms are
not nearly as robust. In general, HREF mean output indicates around
0.10" base total with better than 0.50" accumulations under isolated
thunderstorms and in preferred upslope locations. That said, it
wouldn`t be out of the question for some very localized areas to
receive 1.00"+ accumulation, but would likely require training
thunderstorm echoes with odds less than 20% and representing the
upper end of the ensemble spread. The upper low will have lifted
into northern Arizona by Monday morning with strong evidence of only
a few lingering showers rotating about the southern periphery of the
vorticity lobe. Any remaining showers or new development should
migrate almost exclusively to higher terrain locations Monday
afternoon. While automated NBM POPs and QPF are generally acceptable
forecast parameters over the next 18-24 hours, elevated values
persist far too long with model artifacts providing an unrealistic
outlook Monday, thus have trimmed this mandated NBM output to align
closer to HREF output and conceptual thinking.

Models remain consistent in breaking off a vorticity lobe from the
aforementioned Pacific NW trough into a quasi-cutoff feature
traversing the California coast, then ejecting across the Southwest
during the middle of the week. While some low level moisture may
remain available with this system passage, the majority of deep
tropical moisture will have been scoured away resulting in limited
rain chances. There also continues to be substantial ensemble spread
with respect to the depth and forward propagation speed to this
system yielding low forecast confidence to a scenario already
subject to greater uncertainty given the climatological rarity of
this synoptic setup. Have cut back NBM POP magnitudes and areal
expanse during this time frame given the preponderance of ensemble
output along with a recent precedent for egregiously deleterious NBM
POP forecasts.

While some measure of broad troughing will likely hover over the SW
Conus during the latter half of the week, moisture will finally be
completely scoured from the forecast area as subtropical ridging
begins to strengthen over south TX/northern Mexico. The primary
forecast uncertainty will be tied to the amount of retrogression
this ridge will obtain into the Southwest and the magnitude of
midlevel heights advecting into the region. Ensemble means suggest
H5 heights increasing somewhere in a 584-591dm range resulting in
temperatures rebounding back near the seasonal normal. Should
heights solidly above 588dm be realized, then forecasts towards the
upper end of the guidance envelop (several degrees above normal)
would come to fruition yielding a return to widespread moderate
HeatRisk by the end of the week.

&&

.AVIATION...Updated at 0545Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
Rain has ended over the Phoenix Metro. There is a very small
chance (<25%) of any additional shower activity as the low
pressure moves to the north of the Phoenix Metro during the
overnight hours. Winds will generally be southeasterly through
tomorrow morning, but may go light and variable at times. Winds
will then go back westerly/southwesterly early tomorrow morning.
SCT-BKN clouds with bases aoa 7-8 kft will start to scatter out
tomorrow afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds at KBLH will be out of the south through the whole TAF
period. Wind speeds will be in the low teens until 09Z then lower
to aob 8 kt. At KIPL, winds will generally be southeasterly
through early tomorrow evening, but may go light and variable late
tomorrow morning. Winds will then go southwesterly tomorrow
evening. Wind speeds will be in the lower teens until ~10Z then
will generally be aob 8 kt through the rest of the TAF period.
SCT-BKN mid level clouds will scatter out through tomorrow morning
and afternoon.

&&

.FIRE WEATHER...
A very unusual wet, late spring weather disturbance will move
through the districts tonight and Monday yielding better than a 50%
chance of wetting rains. Chances for thunderstorms (10-30% chance)
will also linger into Monday which could produce isolated areas of
heavier rainfall. Additional light showers with lower wetting rain
potential will arrive Tuesday night and Wednesday. Otherwise,
afternoon minRHs will range from 25-40% Monday with temperatures
much below normal. As temperatures warm closer to normal by
Wednesday, minimum RH should fall into the teens, then closer to
single digits by the end of the week as temperatures warm further.
Excellent overnight recovery above 70% Monday will deteriorate into a
poor to fair range of 20-40% by the end of the week. Outside of
erratic, gusty winds near showers and storms early in the week,
winds should be fairly typical for late spring with the usual
afternoon upslope gustiness.

&&

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

$$

DISCUSSION...18/Young
AVIATION...Berislavich
FIRE WEATHER...18