Toltec, Arizona Weather Forecast Discussion

159
FXUS65 KPSR 261151
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
451 AM MST Fri Sep 26 2025
.UPDATE...12Z Aviation Discussion.
&&
.KEY MESSAGES...
- Thunderstorms and rainfall will become more widespread across
  South Central and Eastern Arizona today. A few strong to severe
  storms will be possible along with locally heavy rainfall that
  could result in flash flooding.
- Lingering chances for showers and storms will exist this
  weekend, particularly on Saturday across Southwest Arizona and
  Southeast California, where the chances for a few strong storms
  and locally heavy rainfall have increased.
- Temperatures will fall into a below normal range today through
  the weekend before gradually warming to near normal by the
  middle of next week.
&&
.SHORT TERM /TODAY THROUGH SATURDAY/...
A rather potent upper level low is seen in current mid level wv
imagery shifting southeastward over SoCal, where guidance has
remained in good agreement that it will stall just north of the
International border later today and remain through Saturday. As
this low shifts into position, numerous showers and thunderstorms
continue to generate in a region of ascent over East-Central AZ.
Excellent upper level divergence is present over this region and
this, coupled with a deep southerly fetch of subtropical moisture,
has allowed a continuous generation of showers and storms from
Thursday afternoon through the overnight hours, expected to continue
through much of the morning. As the low continues to approach the
forecast area and deepens over SoCal, there will be a window late
this morning through the afternoon where the Marginal risk for
severe weather is maximized across South-Central AZ. HREF mean
SBCAPE values increase to upwards of 1000-1500 J/kg by midday
juxtaposed with SFC-6 km shear values of 25-35 kts, supportive of
some organized convection for areas from the Phoenix Metro east and
southeast. These factors along with cooling midlevel temperatures
thanks to the low (500 mb temps around -10C) will be supportive of
some cells producing severe (1"+ diameter) hail and strong to severe
wind gusts. However, guidance indicates dry air intrusion mid to
late afternoon, eroding moisture and instability from west to east
and likely precluding the chance for showers and storms over the
Phoenix Metro Area by the early evening.
In addition to severe weather potential, the potential for flash
flooding will also be a concern. A Flood Watch will be in effect
from 8 AM MST this morning through this evening for the Phoenix
Metro Area, eastern Maricopa County, much of Pinal County, and
Southern Gila County. The greatest threat for heavy rainfall remains
across eastern portions of Maricopa and Pinal Counties and into
southern Gila County where training thunderstorms are most likely to
occur. Areas east of the Valley are also likely to experience the
greatest residence time of moderate instability, deep subtropical
moisture advection, and some level of orographic enhancement, and so
these areas will be most favored for flooding impacts. However,
thunderstorms forming along any westward propagating outflow
boundaries could produce training echoes over portions of the
Phoenix Metro, and so we cannot rule out localized flash flooding
over the Metro and have maintained the Flood Watch here.
Saturday, guidance depicts the upper low weakening and remaining
nearly stationary over far Southern CA. Lingering shower and
thunderstorm chances will exist across the forecast area, though the
latest Hi-Res guidance hones in on SW AZ and SE CA for the main
focus for convective activity Saturday afternoon, as the low draws
moisture around its northern flank from the east and shallow low
level moisture creeps into the area from the south (Dewpoints likely
climbing back into the 60s across the western deserts). Though
moisture profiles will be quite meager compared to what one might
expect during the heart of the monsoon season, forcing from
proximity of the low and cooler midlevel temperatures will allow for
rapid destabilization, with HREF and GFS CAPE values upwards of 500
J/kg and locally as high as 1000 J/kg over portions of SW AZ.
Showers and thunderstorms over the western CWA could produce locally
heavy rainfall and strong gusty winds, and the closer to the center
of the low they are, the more stationary they will be. Those nearly
stationary cells could drop 1.0-1.5" quickly enough to present a
localized flash flood threat. Across South-Central AZ, activity is
likely to be more isolated and be focused mostly east/northeast of
the Phoenix Area on Saturday.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Ensembles continue to advertise the upper low lifting northeast
of the area during the day Sunday. Lingering moisture and
favorable (albeit less robust) dynamics ahead of the low are
expected to allow for continued scattered showers and isolated
afternoon thunderstorms, though likely focused over the AZ high
terrain.
By Sunday night into Monday, our region will transition more into
zonal flow to weak ridging as a deep Pacific low moves southward to
off the Pacific Northwest coast. This will help to usher in dry air
across the region ending any rain chances by Sunday night.
Temperatures will take a dive today into the weekend with the help
of the cut-off low and the rain cooled air. Forecast highs this
weekend are currently only in the upper 80s across the bulk of the
lower deserts, or 5-8 degrees below normal. Once we start to see
weak ridging back into our region early next week, highs should
creep up into the low to mid 90s by Monday or Tuesday.
&&
.AVIATION...Updated at 1150Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Multiple weather hazards will impact aviation operations through
this evening including VCTS/TSRA which will be accompanied by
strong, gusty winds and periods of MVFR to IFR cigs and vsby.
Starting off this morning, we will begin to see the development
of BKN cigs around 5 kft at all metro terminals. Winds are
expected to shift from SE to S by 16Z with gusts reaching 20-25
kts at times. Models still indicate that winds will not fully
shift out of the W this afternoon.
Heading into this afternoon, high-res model guidance continues
to indicate convection erupting INVOF all terminals as early as
19Z-20Z. The bulk of the thunderstorm activity will likely be
between 20Z-01Z when the highest impacts are anticipated. During
this timeframe, winds are likely to be quite strong out of the
E-NE with a high likelihood (>70% chance) of wind gusts exceeding
35 kt. Any direct impacts from TSRA would likely result in periods
of MVFR (or lower) flight categories. Storms should finally push
east of the metro terminals around 02-03Z.
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation impacts are anticipated at the SE California terminals
through tonight. Winds will remain primarily westerly at KIPL and
southerly at KBLH through much of the period. There will likely be
a N-NE wind shift at KBLH late tonight. Skies will remain mostly
clear at KIPL with mid-lvl clouds increasing at KBLH late tonight.
&&
.FIRE WEATHER...
Expect fairly widespread showers and thunderstorms across the
eastern districts today with strong outflow winds, hail, and
heavy rainfall likely in some areas. MinRHs will range from 25-45%
through the weekend. Outside of thunderstorm impacts, winds will
be breezy at times with occasional gusts around 20-25 mph today.
The slow-moving low pressure system impacting the region should
continue to bring chances for wetting rains areawide on Saturday
before drying conditions begin Sunday into early next week. Below
normal temperatures will persist through at least Monday.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch from 8 AM MST this morning through this evening for
     AZZ537-540>553-555>558-560>563.
CA...None.
&&
$$
SHORT TERM...Whittock
LONG TERM...Whittock
AVIATION...Salerno
FIRE WEATHER...Whittock/Smith

NWS PSR Office Area Forecast Discussion