Calexico, California Weather Forecast Discussion

475
FXUS65 KPSR 231904
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
1204 PM MST Tue Sep 23 2025
.KEY MESSAGES...
- Warmer-than-nomral temperatures along with dry and tranquil
  conditions can be expected across the region through midweek
- An area of low pressure will bring a noticeable shift in
  conditions for the latter portion of the week and into the
  weekend with increasing shower and thunderstorm chances and
  cooling temperatures
&&
.SHORT TERM /TODAY THROUGH THURSDAY/...
Current 500mb analysis and WV imagery reveals the Desert
Southwest caught between to areas of low pressure, one over
Colorado, and the other spinning just off the California Coast.
The gap between these two systems will be filled with the early
stages of upper-level ridging, setting up an omega blocking
pattern that will be in place through the middle portion of the
week. What this means for us will be the return of warmer than
normal temperatures through this timeframe with lower desert high
temperatures hovering right around the triple digit mark this
afternoon. For Wednesday, temperatures are expected to tick a few
more degrees rising to around 100-105 degrees for the lower
elevations. This will be a good 5-8 degrees above normal for this
time of year and will result in widespread moderate with localized
areas of major HeatRisk around the Phoenix metro. These areas of
major HeatRisk are likely an artifact of decreasing daily normals
(now in the upper 90s) and are less to do with how abnormal
expected temperatures will be given the fact that observations
over the past three to four months have, at times, far exceeded
what we will see over the next few days. With that being said,
heat precautions should continue to be taken into account if you
work outdoors or plan to be outside for extended periods of time
during the hottest period of the day.
The overall pattern will begin to shift heading into Thursday as the
aforementioned Pacific Low will begin to slowly meander east toward
our forecast area. Once is moves inland over central California,
guidance has it diving further south before the center of
circulation settles near the San Diego area. There are some slight
spatial discrepancies amongst the global models regarding exactly
where the low will position itself, but regardless of where it
does, our area will be under favorable conditions for an increase
in shower and thunderstorm activity. Increasing moisture and
upper-level diffluence inducing rising motion will promote
convection over the Arizona high terrain Thursday afternoon and
evening. The main concerns with potential activity will be strong
outflow winds, heavy downpours, and frequent lightning. Over the
lower deserts, convective activity is likely to be limited due to
a capping inversion in place. However, a few storms cannot be
completely ruled out but they will heavily reliant on outflows
approaching from the high terrain to the east and north. The ridge
will not be completely removed from the picture but its influence
will begin to shift as the closed low begins to shove it off to
the east. Temps over South-central and Southwestern Arizona will
once again hover near 100-105 degrees, while further west over
Southeast California, readings will be slightly cooler due to the
proximity to the approaching disturbance.
&&
.LONG TERM /Friday through Monday/...
Model guidance has come into better agreement for Friday on the
track of the upper-level low, with the center likely to set up
near San Diego, yielding to a somewhat higher confidence forecast.
With the upper-level low setting up near San Diego, strong
moisture advection is expected during the day on Friday with
mixing ratios forecast to reach 12-13 g/kg, helping to yield
strong instability with the latest forecast soundings in Phoenix
showing CAPE values in excess of 1000-1500 J/KG. In addition, the
region will be located along the left exit region of an upper-
level jet streak, yielding strong divergence aloft and thus good
upper-level ascent. Combining these factors along with strong mid-
level flow yielding 0-6 km shear values in excess of 25-30 kts,
the recipe will be there for strong to potentially severe
thunderstorms to materialize across portions of south-central and
southeast AZ during the day of Friday. With the decent moisture
levels in place, these thunderstorms are likely to be very
efficient heavy rain producers, thus increasing the potential for
flash flooding. Given the increased potential for flooding, WPC
has placed much of eastern AZ in a slight risk for excessive
rainfall leading to flash flooding. Keep in mind that we are still
about three days out and things could still shift, especially
with the track of the upper-level low. However, if the current
model projections are correct, Friday looks to be a highly
impactful weather day across much of south-central and southeast
AZ.
Heading into the weekend, model guidance does diverge somewhat on
the trajectory of the upper-level low but still does maintain the
center to the west of the region. Thus, rain chances will likely
continue, especially on Saturday when there will still be decent
moisture and instability in place to potentially yield additional
thunderstorm activity. Thereafter, there are signs that by next
Sunday and Monday the upper-level low will be weakening and move
eastward, with drier air moving in and rain chances decreasing.
Temperatures starting on Friday and through the upcoming weekend
will cool off to below normal levels under decreasing heights
aloft from the approaching upper-level low as well as under the
influence of clouds and potential rainfall. Latest NBM shows
afternoon highs across much of the lower deserts only topping out
in the lower 90s, however, if the clouds and rainfall prove to be
more abundant then there is the potential for high temperatures
to be stuck in the 80s. Along with the cooler daytime highs,
overnight and early morning low temperatures will also cool down
with most areas bottoming out in the low to mid 70s, with some of
the cooler rural areas potentially dipping down into the 60s.
&&
.AVIATION...Updated at 1712Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation impacts are expected through at least Wednesday
afternoon. Winds will remain light (aob 8 kt) through the period
mostly following diurnal trends with periods of near calm winds
during transitions. Expect clear skies to persist through the
period.
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are anticipated through the next 24
hours. Very light winds (aob 7 kt) will prevail at both terminals
through the TAF period with prolonged periods of VRB. Winds will
favor the E through much of today before switching to the W this
evening. At KBLH, extended VRB winds are expected to give way to
NNW winds later this evening. Expect clear skies to persist
through the period.
&&
.FIRE WEATHER...
Dry conditions along with warming temperatures to above normal
levels will prevail through midweek. MinRHs today will be in the
20-30% range, before dropping into the 15-25% range on Wednesday
with fair to good overnight recoveries in the 30-60% range.
Heading towards the end of the week and into next weekend, a
slow-moving low pressure system will impact the region leading to
increasing moisture levels and rain chances with enhanced
probabilities of wetting rainfall, particularly across south-
central AZ. Winds will remain relatively light during the next
couple of days with some modest afternoon upslope gusts.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
SHORT TERM...Lojero
LONG TERM...Lojero
AVIATION...Smith/Kuhlman
FIRE WEATHER...Lojero

NWS PSR Office Area Forecast Discussion