Mobile, Arizona Weather Forecast Discussion

179
FXUS65 KPSR 212020
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
120 PM MST Sun Sep 21 2025
.KEY MESSAGES...
- Rain chances will be heightened through Monday before decreasing
during the middle of the week.
- Temperatures hovering around the seasonal normal will warm
slightly towards the middle of the week, then likely cool below
normal over the weekend.
- A low pressure system will move through the region towards the end
of the week resulting in returning shower and thunderstorm chances.
&&
.SHORT TERM /Today through Tuesday/...
Afternoon WV satellite imagery depicts an upper level low migrating
south off the California coastline in the initial stages of cutting
off from the northern stream flow and larger scale synoptic
troughing. The attendant jet streak associated with this feature has
transported a deep plume of midlevel moisture in the H7-H5 layer with
total column PWATs rising near 1.50". The combination of boundary
layer mixing ratios falling near 10-11 g/kg, deteriorating midlevel
lapse rates, and compromised insolation have resulted in limited
MLCape. However, vorticity advection and forced ascent have
supported a few showers, and enough elevated MUCape still exists
within a layer of marginal midlevel lapse rates for isolated
thunderstorm development. The preponderance of HREF membership is
not particularly enthusiastic about any convective sustenance
anywhere in the forecast area, rather focusing better rainfall
opportunities on the stream of thicker midlevel moisture through SE
California/western Arizona, as well as SE Arizona where better
instability has been realized.
Recent GEFS membership remains an outlier versus other modeling
depicting more expansive convection and outflow boundaries impacting
south-central AZ this evening and overnight. This seems more
unlikely versus other global and high resolution models, though
given the total atmospheric moisture content, scattered showers and
locally gusty winds would not be completely unexpected before
forcing mechanisms exit into northern Arizona and slightly drier air
aloft advects into the region Monday afternoon. This will also
herald the beginning of a western Conus omega block with negative
height anomalies positioned off the southern California coast and
central Rockies respectively. Narrow ridging will become established
between these circulation centers over the forecast area with
increasing subsidence and H5 heights building towards a 585-588dm
range. While lingering cloud cover will likely retard insolation
somewhat Monday keeping temperatures near or slightly below normal,
readings will warm several degrees Tuesday pushing lower elevation
highs back above 100F while rainfall chances become slim to none.
&&
.LONG TERM /Wednesday through Saturday/...
The upper level low will remain cutoff from the main jet stream and
meander off the CA coast through midweek. The positioning of the
cutoff low off the CA coast will cause the subtropical ridge to
amplify further across the region resulting in increased subsidence
aloft and decreasing moisture levels. As a result, rain chances
through early Thursday decrease substantially with NBM PoPs at less
than 10% across the lower deserts and 10-20% across the higher
terrain areas of eastern AZ where enough moisture will be present to
spark some isolated afternoon storms. With the ridge amplifying
overhead, ensembles show 500 mb heights peaking near 590dm during
the Wednesday-Thursday timeframe. In response, temperatures should
peak on Wednesday with highs potentially reaching over 105 degrees
in Phoenix, and remaining above 100 degrees on Thursday.
The weather pattern heading into the end of the week and next
weekend becomes much more uncertain as the cutoff low is forecast to
migrate inland through central/southern CA and then into AZ.
However, model guidance continues to differ in terms of the overall
positioning and speed of the low, which will determine how much
moisture gets advected into the region from the south and thus the
rain potential. It may take another couple of days to get a more
definite picture as to what may eventually occur as models
historically have a very difficult time with cutoff lows, with this
one not being the exception. With the low nearby, temperatures by
the end of the week into next weekend are likely to cool off with
the latest NBM showing highs only in the 90s across the lower
deserts.
&&
.AVIATION...Updated at 1738Z.
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.
However periods of NW`rly flow can be expected this afternoon into
this evening alongside some chances for VCSH, but little if any
impacts are anticipated at this time. SCT-BKN thick mid level clouds
will continue through most of the TAF period with bases generally
aoa 10kft.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are anticipated through the TAF
period. Winds will remain north westerly at KIPL and KBLH through
much if not all of the period. Thick mid-lvl cloud cover is expected
through the period with bases mostly aoa 12 kft through this
afternoon lowering to just below 10 kft tonight. Expect periods of
VCSH/SHRA at both terminals through much of the period, but with
little if any impacts.
&&
.FIRE WEATHER...
Moisture will increase through Monday along with increasing rain
chances. Rain chances peak later this evening into Monday morning
with wetting rain chances generally between 10-30%. MinRHs will
bottom out between 20-30% today and 25-40% on Monday with good to
excellent overnight recoveries at between 50-90%. Some modest drying
with MinRHs dropping between 15-25% is expected into midweek. A slow
moving weather system may impact the region by the end of the week
leading to increasing moisture once again and potentially additional
rain chances. Winds will generally remain light with limited
afternoon upslope gusts through the next several days.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
SHORT TERM...18
LONG TERM...Lojero
AVIATION...Kuhlman/Ryan
FIRE WEATHER...Lojero

NWS PSR Office Area Forecast Discussion