368
FXUS65 KPSR 152020
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
120 PM MST Sat Nov 15 2025

.KEY MESSAGES...

- The first in a series of weather systems will affect the region
this weekend bringing widespread light to moderate rain, but
limited overall impacts.

- A trailing weather disturbance will bring the next opportunity for
scattered showers to the area Tuesday and Wednesday.

- Temperatures will cool below normal next week with readings
substantially below the daily normals during the middle of the week.

&&

.SHORT TERM /Today through Monday/...
Deep negative height anomalies continue to hover off the southern
California coast with several pivoting vorticity centers causing the
larger circulation to wobble only slowly eastward. The slow forward
progression has kept more robust height falls centered along the
coast range with WV imagery indicating the bulk of stronger dynamics
lifting north rather than surging eastward. Nevertheless, attendant
moisture with this system remains seasonally anomalous with total
column PWATs nearing 1.50" aligning along the California coast.
While a fair proportion of this moisture will be trapped on the
windward side of the coastal range, sufficient inland southerly sfc-
H8 winds have provided moderate flux of higher theta-e through the
lower Colorado River valley. In fact, objective analysis suggests
boundary layer mixing ratios 8-10 g/kg have advected into parts of
the western CWA ahead of an advancing cold front and organized
ascent.

HREF members remain in excellent agreement showing this moisture
flux combined with vorticity forced ascent and frontal forcing along
a narrow cold front producing numerous showers through the western
CWA through this evening. Given the expansive thick clouds, midlevel
cold core lingering offshore, and poor lapse rates, inland
instability has been significantly limited with MLCape/SBCape capped
around 500 J/kg. As a result while the majority of rain accumulation
should occur with lower rainfall rates, embedded convective elements
and locally higher rainfall rates may impact some locations along
the Colorado River this afternoon. At this time with enhanced H7-H3
steering flow, forward progression of individual elements should
preclude widespread instances of higher rainfall amounts, however
unidirectional flow and moisture flux vectors aligning along the
mean flow may result in periods of smaller Corfidi vectors and some
training higher reflectivity echoes. Only the most aggressive 12Z
HREF output indicates notable amounts over 1.00" in any given
location though a recent convective band likely deposited a narrow
swath of 1" amounts. Regardless, the larger preponderance of high
resolution output forecasts rainfall totals under 0.25" with higher
amounts relegated to orographically favored locations where moist
SSW flow best aligns orthogonally to ridge tops and mountain peaks.

As the entire wave structure shifts northeast into NV/UT Sunday,
another better defined vorticity center will rotate through the
trough base bringing a steep cold front and associated forcing
mechanisms through south-central Arizona during the morning hours.
Forecast confidence is very good that at least a broken line of
showers will quickly sweep through the metro with activity lifting
into higher terrain areas during the afternoon. While rainfall
amounts 0.25" or greater will be favored in foothills and mountains
north and east of Phoenix, lower elevations amounts should largely
fall below 0.25" with some locations possibly not even reaching
0.10". A few showers could linger over mountains Sunday afternoon,
however a pronounced midlevel subsidence inversion combined with a
drier post frontal airmass should rapidly cutoff rainfall chances
and result in partial clearing from Phoenix westward.

Subsidence and drier weather may be short lived Monday as a
negatively tilted Pacific shortwaves quickly digs towards the void
left by the initial exiting wave in an increasingly blocked western
hemisphere flow pattern. With lingering moisture and stregthening
jet energy downstream from the appraoching shortwave, theta-e
advection and weak isentropic ascent could support a few pockets of
elevated showers ahead of a reinforcing, stronger cold front surging
into the southern California coast. NBM POPs appeared too aggressive
and widespread (both temporally and areally) with unusually high
values given the pattern, and have pared back this forecast somewhat
with activity more likely to produce minor impacts Tuesday night.
Otherwise, temperatures will tumble next week behind the frontal
passages - initially falling slightly below normal Sunday and Monday
(3F-6F below normal), then plummeting further during the middle of
the week.

&&

.LONG TERM /Tuesday through Saturday/...
Within broader troughing remaining in place across the Western
Conus, a second shortwave will dive into the Southwest early next
week. Guidance is now showing better agreement with the progression
of this second system with a closed low first developing across
California on Monday before tracking south southeastward into our
region on Tuesday. There is still some slight timing and position
differences within the ensemble members, so that in turn means there
is uncertainty with the rainfall totals and exactly when the peak
rain will occur. Some showers may begin to develop late Monday and
Monday night, especially across higher terrain areas before more
widespread rain is likely to occur on Tuesday.

This system should bring better dynamics and forcing, potentially
allowing for a more organized rain event. Forecast moisture levels
will be lower than this weekend`s system, but given the Tuesday
system will be colder that should compensate for the lower available
moisture. Potential rainfall amounts are still fairly uncertain, but
the higher end of potential shows upwards of an inch possible across
south-central Arizona to 0.25-0.5" across the southeast California
lower deserts. As of right now, we are going with a more
conservative 0.1-0.25" for SE CA and around 0.5" for the south-
central Arizona lower deserts. Higher terrain areas north and east
of Phoenix may end up getting another 0.75-1.25" by the time the
rain ends either Tuesday night or early Wednesday.

The active weather period is expected to continue through the rest
of next week with a third somewhat cold system quickly moving from
off the Pacific Northwest on Thursday into our region around Friday
or Saturday. Model uncertainty is even higher with this third
system, but it could end up being the best precip maker. There are
around 30% of the ensemble members that show a more progressive
system which would not provide much additional precipitation, but
another 30-50% show a much slower closed off low which may stick
around for a couple of days.

Temperatures next week will be fairly chilly all week with highs
mostly staying below 70 degrees each day. As of right now, Wednesday
may end up being the coldest day with highs only in the lower 60s
for some lower deserts locations. The persistent higher boundary
layer moisture and clouds should at least keep overnight lows fairly
close to normal readings most nights.

&&

.AVIATION...Updated at 1800Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main aviation concerns during the TAF period will be the
introduction of VFR CIGS (6-8k ft) this afternoon and evening and
SHRA activity Sunday morning. In the short term, no major impacts
are expected with light winds and quiet conditions. The typical
W`rly wind shift may take longer than usual to become established
with some terminals potentially observing more of a S`rly component
through this evening.

By Sunday morning (likely between 11-13Z based on current trends) a
more pronounced W`rly component will take hold with perhaps a few
gusts around 15-20 kts. The best chance to see rainfall activity
over the terminals will also concur with this switch which could
result in some brief reductions in VIS. Even though the chances for
MVFR conditions exist in conjunction with any SHRA activity,
confidence is too low to warrant any mention of impactful CIGs and
VIS in the TAFs at this time. A rogue shower also cannot be
completely ruled out in the vicinity of the terminals from this
evening through early Sunday.


Southeast California/Southwest Arizona including KIPL and KBLH:
The main aviation concern during the next 24 hours will be -SHRA
activity through this evening that could lead to periods of MVFR
VIS. These reductions should be relatively brief in nature before
the region fully drys out by early tonight. Even though chances for
MVFR CIGs are too low to include in the TAFs at this time, they
cannot be completely ruled out through the evening timeframe.
Winds with the associated shower activity will contain a S`rly
component before a W/SW`rly shift takes place once the rainfall
coverage begins to diminish. Some periodic gusts 20-25 kts may be
observed through this afternoon.

&&

.FIRE WEATHER...
A large weather system will slowly move through the region this
weekend bringing cooler temperatures, increased humidities, and
fairly widespread rainfall. Rain chances will peak across the
western districts during the daytime hours today and during the
first half of Sunday for the eastern districts. A few isolated
thunderstorms will be possible, which may produce locally heavier
rainfall amounts. MinRHs today will range from 25-30% over the
eastern districts to 50-70% for the western districts. Sunday will
bring MinRHs of 40-60% areawide. Expect periodic breeziness over the
weekend. The active weather will continue through next week with
another weather system affecting the area by Tuesday and another
later in the week. Expect below normal temperatures and elevated
humidities for all of next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Flood Watch through this evening for CAZ560-568.

&&

$$

SHORT TERM...18
LONG TERM...Kuhlman
AVIATION...RW
FIRE WEATHER...Kuhlman