200
FXUS65 KPSR 271013
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
313 AM MST Tue Oct 27 2026

.KEY MESSAGES...

- Dry and tranquil weather conditions will continue through the
  middle of the week with temperatures within a few degrees of
  daily normals.

- An unsettled weather pattern will return to the region late in
  the week and persist through this weekend resulting in much
  cooler temperatures and chances for widespread rainfall.

- There will also be a possibility of embedded thunderstorms with
  heavier rainfall which could lead to localized minor flooding
  Friday and Sunday.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...
Continued dry west quasi-zonal flow will keep quiet weather
conditions over the region for the next 2-3 days before an
unsettled period of weather begins Friday. Current IR satellite
imagery shows clear skies across the bulk of the Desert Southwest
with the next batch of clouds to eventually move in late tonight
still off the California coast. Expect daytime highs today similar
to yesterday`s mid 80s with overnight lows Wednesday morning a
bit warmer than this morning as the higher clouds move in from the
west. The incoming high clouds will blanket the entire area
during the daytime hours Wednesday, but they should be thin enough
for some dull sunshine throughout the day. A passing weak
shortwave across the Great Basin tonight into early Wednesday
should also lower heights over the western deserts leading to
highs dropping into the lower 80s, while the rest of the lower
deserts holds in the mid 80s for highs.

Going into Thursday, a strong upper low is expected to dive south
southwestward to just off the coast of Washington while a second
shortwave approaches California from the west within the same
large-scale trough. With the polar jet supporting the northern
system and a strengthening subtropical jet supporting the southern
shortwave and eventually a much stronger one by the weekend, the
Western U.S. is shaping up for a busy latter part of the week. For
the Desert Southwest, the deepening trough to our west will also
lead to increased southerly flow on Thursday helping to gradually
advect lower level moisture into southern and central Arizona
leading into Friday. Forecast temperatures for Thursday are very
similar to Wednesday, but expect thicker clouds and a bit warmer
overnight temperatures.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Friday is still looking like a fairly wet day across the bulk of
central Arizona as moisture levels rise to 200-250% of normal and
the area falls under strong difluence aloft due to the incoming
near record strength (for this time of year) subtropical jet.
Guidance continues to heavily favor showers and isolated
thunderstorms developing at some point early Friday morning
centered over south-central Arizona and then expanding northward
and eastward throughout the day on Friday. Rainfall rates are not
anticipated to be all that heavy with the bulk of the rainfall
falling at less than 0.1" per hour, but with embedded heavier
showers or thunderstorms, rates upwards of 0.5-1.0" per hour
should be possible. GEFS and EPS ensemble mean QPF for the Friday
event shows an average of around 0.50"-0.75" from Phoenix and
into the higher terrain north and northeast of Phoenix to
0.10-0.25" over much of the rest of southern and central Arizona.
The higher end of guidance (NBM 75% percentile) still shows
potential for heavy rainfall with amounts of up to around 1.5"
across south-central Arizona. As a result, WPC`s ERO continues to
depict a Slight Risk for excessive rainfall on Friday. Given the
propensity for the NBM to forecast too much QPF for our area in
the mid to long range, we are leaning toward the lower end
amounts. Some higher end amounts of over 1" are expected to fall,
but it is likely to be fairly localized.

As the subtropical jet lifts northeastward later on Friday, the
best ascent will shift out of Arizona leaving only continued
chances for isolated upslope driven shower activity for Friday
night and Saturday. The unsettled weather pattern will persist
over the weekend with an atmospheric river approaching the region
from the southwest later on Saturday and likely arriving during
the day Sunday with the brunt of this expected modest atmospheric
river impacting areas across southern Arizona and northern
Sonora. Model uncertainty remains quite high for this second
weather event with differences in the track and the strength of
the shortwave trough and differences in the amount of moisture.
The EPS continues to show higher moisture levels and QPF amounts
compared than the GEFS, but both have trended lower with QPF over
the past 24 hours. The GEFS`s additional 0.25-0.50" for south-
central Arizona looks to be a bit too low considering the amount
of moisture potential, but the EPS`s 0.75-1.50" may be a bit too
high. The timing with the bulk of the rain likely falling during
the first half of Sunday still looks good, but as stated above how
much rain will fall is still quite uncertain. Considering this
will be the second rain event within 3 days, any additional
moderate to heavy rain could compound any flooding issues that
could occur on Friday. Rain chances may linger through Sunday
night across eastern Arizona, but by Monday much of the area
should be drying out as the system is expected to quickly push
northeast of the area.

Temperatures during this unsettled weather pattern are expected to
fall below normal starting Friday with highs dropping to between
75-80 degrees before bottoming out closer to 70 degree highs for
Sunday and/or Monday. NBM guidance shows fairly large forecast
temperature spread for the first half of next week as the large
scale troughing may linger over the region for a couple more days.
If this happens, highs will very slowly creep upward through the
low to mid 70s, whereas if the ridge takes over we could see
highs closer to 80 degrees by next Tuesday or Wednesday.

&&

.AVIATION...Updated at 0547Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No aviation weather concerns under mostly clear skies expected
through Tuesday. The wind pattern will continue to exhibit
typical diurnal tendencies with speeds mostly aob 6 kts. There
will also be extended periods of light variability to even calm
conditions. A period of light southerly crosswinds is likely early
Tuesday afternoon before the westerly transition by the late
afternoon hours.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns under mostly clear skies expected
through Tuesday. Winds will favor diurnal patterns with light
speeds, mostly below 8 kts, at both terminals. W winds are
expected through sunrise before shifting toward a S-SE direction
by late morning and then back W in the evening/overnight hours.
KBLH will see a NW wind component through most of Tuesday morning
and then shift S by the afternoon. Both terminals will also
experience periods of light variability to even calm conditions.

&&

.FIRE WEATHER...
Warm and dry conditions will persist through at least the middle
part of the week before a much cooler and wetter pattern sets up
Friday into this weekend. Minimum humidity levels will bottom out
today at 15-30% Tuesday before gradual moisture improvement
arrives starting Wednesday. Overnight recoveries will remain good
at 40-65%. Winds will remain light each day favoring typical
diurnal patterns and minimal upslope breeziness.

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Benedict/Lojero
FIRE WEATHER...Kuhlman

NWS Phoenix (PSR) Office