104 
FXUS65 KPSR 240009
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
509 PM MST Tue Sep 23 2025

.UPDATE...Updated Aviation Discussion.

&&

.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 0006Z. 

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: 
Confidence in wind directions through the TAF period is moderate,
but wind speeds through most of the period will be light, at or
below 8 kts. Winds now are favoring NW-N and will trend more to
NE-E by 04-05Z tonight. During the night and early Wednesday
morning winds may shift back to a light westerly component at
KPHX, but confidence in this is low and thus VRB04KT is shown.
Easterly wind speeds will increase to around 10 kt with some gusts
up to 15-20 kt for a period between 15-19Z. Winds should subside
heading into Wednesday afternoon and may go VRB for a couple hours
before shifting westerly. SKC will prevail through most of the TAF
period. 

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are anticipated through the next 24
hours. Very light winds (aob 6 kt) will prevail at both terminals
through the TAF period with prolonged periods of VRB. Wind
components 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...RW
LONG TERM...Lojero 
AVIATION...Benedict/Smith 
FIRE WEATHER...Lojero