Guadalupe, Arizona Weather Forecast Discussion

376
FXUS65 KPSR 230007
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
507 PM MST Mon Sep 22 2025
.UPDATE...Updated Aviation Discussion.
&&
.KEY MESSAGES...
- Mainly dry conditions will prevail through the middle of the
week before a low pressure system brings increased shower and
thunderstorm chances by the end of the week.
- Temperatures will warm into an above normal range during the
middle of the week, but cool below the seasonal normal by the
weekend.
&&
.SHORT TERM /Today through Wednesday/...
Afternoon WV imagery and objective analysis shows a well defined
circulation center west of the California coastline entering a
retrogressive phase, and in the process of cutting off from the main
Conus flow. Moisture entrained in an enhanced jet streak ahead of
this feature combined with sheared vorticity has resulted in a
distinct band of showers/embedded storms streaming into central
Arizona. However, as vorticity advects inland and further wave
retrogression becomes established, shortwave ridging and increasing
subsidence will overspread the region by this evening precluding
additional rainfall chances.
Over the next 36 hours, a well defined omega block will develop over
the western Conus with the east Pacific negative height anomaly only
slowly drifting north, while mirroring troughing enters the central
Rockies. In between, pinched high amplitude ridging will build
through the CWA, and extending into the Great Basin with H5 heights
locally building in excess of 590dm. Numerical guidance spread is
quite narrow resulting in excellent forecast confidence of rapidly
warming conditions, such that by Wednesday, temperatures 4F-8F above
normal will be common. This will yield a short duration period of
widespread moderate HeatRisk with localized areas of major HeatRisk
within the Phoenix metro, albeit only a consequence of the
climatological factoring into the risk calculation. Raw high
temperature forecast depict readings barely breaching 105F in the
typically warmest river valleys after overnight lows in the upper
70s/lower 80s. While certainly not entirely devoid of any health
risk, values of this magnitude are far from levels experience for
much of the past 3 months. Otherwise, as suggested by forecast
sounding data, modest drying will occur in the boundary layer
resulting in almost zero chance of lower elevation rainfall, and
possibly even prohibitive of deep convection over mountains.
&&
.LONG TERM /Thursday through Sunday/...
Heading towards the end of the week, the cut-off low is forecast to
migrate inland through central/southern CA and then into AZ.
However, disagreements continue amongst the model guidance in terms
of the overall track and speed of the low as it migrates inland,
which makes for a low confidence forecast by the end of the week
into next weekend as the overall track and speed will determine the
degree of moisture return and placement of upper-level dynamics. At
this time, rain chances start to increase as early as Thursday
afternoon/evening, mainly across the eastern third of AZ, before
chances extend into the lower deserts heading into Friday due to a
further increase in moisture and upper-level dynamics. Depending on
the speed of the low, rain chances may linger into next weekend.
Given the upper-level dynamics that will be involved with the low,
if enough moisture and instability are present, then there is the
potential for strong thunderstorms and areas of heavy rainfall to
materialize, particularly on Friday. Please stay tuned to the latest
forecast throughout the week for updates.
Temperatures will still remain above normal on Thursday, in the low
to mid 100s, with the subtropical high lingering over the region.
Thereafter, by Friday and into the upcoming weekend with the
approaching low, temperatures are expected to trend downward to
below normal levels with the latest NBM showing highs topping out in
the low to mid 90s and overnight lows in the low to mid 70s across
the lowest deserts.
&&
.AVIATION...Updated at 0006Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Breezy NW winds will subside this evening. Confidence on timing of
the E wind shift at KPHX is low. VRB04KT is favored between 05-10Z
and then E winds may develop between 10-15Z. Winds will remain
light (aob 8 kt) Tuesday and shift westerly around 19-20Z. Skies
will clear this evening and remain mostly clear through Tuesday.
Southeast California/Southwest Arizona including KIPL and KBLH:
Very light winds (aob 6 kt) will prevail at both terminals through
the TAF period with prolonged periods of VRB. Wind components will
still tend to favor an easterly component at KIPL and SE to N at
KBLH. Skies will clear this evening and remain mostly clear
through Tuesday.
&&
.FIRE WEATHER...
Shower activity will linger through this morning, particularly
across the western districts, before conditions dry out areawide
heading into this afternoon. Dry conditions with near zero rain
chances will then prevail through midweek. A slow moving weather
system is likely to impact the region by the end of the week leading
to increasing moisture once again and potentially additional rain
chances. MinRH values will remain elevated in the 25-35% range today
before dropping into the 15-25% range through midweek with good to
excellent overnight recoveries. 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...Benedict
FIRE WEATHER...Lojero

NWS PSR Office Area Forecast Discussion