Calipatria, California Weather Forecast Discussion

983
FXUS65 KPSR 210532
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
1032 PM MST Sat Sep 20 2025
.UPDATE...06Z Aviation Discussion...
&&
.KEY MESSAGES...
- Temperatures not far from the climatological normal will be common
  across the area through at least the middle of next week.
- Chances for showers and thunderstorms will return Sunday and
  Monday with periodic opportunities later in the week.
&&
.SHORT TERM /Today through Sunday/...
Early afternoon objective analysis indicates rising midtropospheric
heights with H5 levels above 588dm enveloping the entire forecast
area inducing widespread subsidence under building anti-cyclonic
flow. This ridge amplification regime is being forced by deepening
negative height anomalies along the central California coast and
downstream strengthening of subtropical jet energy. Regional WV
imagery shows these combined features beginning to access a larger
reservoir of thick midlevel moisture which will be ingested into the
strengthening flow and transported inland across the SW Conus over
the next 36 hours.
Despite the overall subsident flow and lack of forcing mechanisms, a
few isolated showers and storms will be possible across the most
favored terrain features through late afternoon given maintenance of
a large pool of 11-12 g/kg mixing ratios. Loss of daytime heating
will preclude further convective development beyond late afternoon.
Otherwise, a deep 600mb-400mb saturated layer will surge into
southeast California Sunday morning, spreading across the forecast
area throughout the day. While total column PWATs near or above
1.50" will be common, boundary layer moisture will not improve (and
likely even deteriorate) while midlevel lapse rates suffer due to
the expansive saturated layer. Sheared vorticity within the
approaching jet streak should be sufficient to support elevated
showers, much of which will be in the form of virga, however
relative humidity below the cloud deck should be high enough to
allow some showers to reach the surface in accumulating fashion.
Forecast uncertainty deteriorates fairly rapidly Sunday night/Monday
morning as expansive southwest flow from the East Pacific continues
to tap an impressive elevated moist layer. One key to the forecast
appears to be the magnitude and positioning of vorticity advection
and forced midlevel ascent. HREF membership depicts little to no
reflection in forecast reflectivities and rainfall amounts, while
coarse global models parameterize notable QPF in an apparent
response to additional sheared vorticity forcing ascent in a very
weakly unstable layer aloft (MUCape potentially 500 J/kg). Other
than PWATS increasing closer to 1.75", forecast BUFR soundings do
not look particularly impressive, but any distinct ascent mechanism
could certainly support a few showers.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
Monday morning may be the peak for rainfall chances with NBM PoPs of
20-40% fairly widespread across the area. These PoPs could be
underdone as this may end up being a somewhat larger area of
rainfall resulting in most locations receiving light amounts of a
few hundredths of an inch to upwards of a 0.25". Even lower forecast
confidence exists through the rest of Monday into Tuesday as
guidance tries to mostly end rain chances, but keeps a cut-off low
just off the southern California coast. This position may still
allow for chances for isolated showers and thunderstorms, despite
the NBM drastically lowering PoPs down to around 10%. Even if rain
chances do continue into Tuesday, most locations may not see much if
any rainfall as ensemble mean PWATs are forecast to lower to around
1.1-1.3" by later Tuesday. Given the higher than normal forecast
uncertainty, don`t be surprised if the forecast shifts during this
time.
Temperatures early this week are likely to start out near normal
with highs mostly in the upper 90s across the lower deserts, but
that may change going into the middle part of the week. Forecast
temperature spread has improved enough to provide for fairly high
confidence in warmer temperatures by next Tuesday or Wednesday.
The latest NBM shows highs likely reaching 100 degrees by Tuesday
with some potential for Phoenix to reach 105 degrees on Wednesday.
We are not likely to get rid of the cut-off low very quickly as
guidance shows the low first drifting a bit to the north across
southern/central California before potentially turning eastward at
some point around next Thursday or Friday. It is unknown at this
time if this shift will actually occur and how far it will venture
to the east as the ensembles try to move it into western Arizona by
next weekend. If the low does fully move into our region later next
week it may bring a return of better rain chances and cooling
temperatures, but that is a big if as cut-off lows are very hard for
models to forecast.
&&
.AVIATION...Updated at 0530Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected through the
forecast period. Winds will continue to follow typical diurnal
tendencies with periods of variability overnight. The easterly
shift will occur later than usual by 09Z at KIWA and 12Z at KPHX.
Thick mid-lvl clouds will arrive Sunday morning with bases aoa 15
kft. There could be a period of SHRA/VCSH during the late
afternoon, but no impacts are anticipated at this time.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are anticipated through the TAF
period. Winds will remain westerly at KIPL and southwesterly at
KBLH overnight before shifting more out of the northwest at both
terminals on Sunday morning. A steady increase in mid-lvl cloud
cover is anticipated early Sunday morning with periods of
VCSH/SHRA developing at both terminals by late morning into the
early afternoon.
&&
.FIRE WEATHER...
Modest drying will occur today with better moisture returning to the
region Sunday into Monday. Rain chances will also return on Sunday
with the best chances likely Sunday night into early Monday with
wetting rain chances between 20-30%. Minimum humidity levels will
generally fall into a 25-30% range following good to excellent
overnight recovery of 50-90%. Winds will remain rather light with
limited upslope gusts. A slow moving weather system may impact
portions of the region during the rest of next week keeping
humidities a bit elevated and potentially additional rain chances.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
SHORT TERM...18
LONG TERM...Kuhlman
AVIATION...Salerno
FIRE WEATHER...Kuhlman

NWS PSR Office Area Forecast Discussion