Morristown, Arizona Weather Forecast Discussion

764
FXUS65 KPSR 242023
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
123 PM MST Wed Sep 24 2025
.KEY MESSAGES...
- Warmer-than-nomral temperatures will be common across the
  region through Thursday with lower desert highs near 105
  degrees.
- Shower and thunderstorm chances begin to increase Thursday,
  with potential activity focused over areas to the east of
  Phoenix.
- Rainfall activity becomes more widespread across south-central
  and eastern Arizona Friday. Strong to severe storms will be
  possible along with locally heavy rainfall that could lead to
  flooding.
&&
.SHORT TERM /TODAY THROUGH THURSDAY/...
WV imagery reveals high pressure across much of the Intermountain
West in between a closed low spinning just off the California Coast
and another trough stretching into the Central Plains. With ridging
overhead, conditions across the Desert Southwest this afternoon will
remain quiet while day-to-day temperatures see a bit of an increase
compared to what was observed yesterday. Readings this afternoon
across the lower deserts will hover around 105 degree, a good 5-8
degrees above normal for late September. As a result, widespread
moderate, to locally major, HeatRisk will make a return. These
HeatRisk levels, especially areas in the major category, are
primarily driven by the spread between forecasted values and the
normal highs during this point in the year which are now in the
upper 90s. Previous extreme heat episodes this year have been
headlined by temps that have been around 10 degrees warmer compared
to what can be expected both today and tomorrow. Even though
forecasted highs will be relatively abnormal for this time of year,
they are not uncommon compared to what we have seen over the past 3-
4 months, so no Extreme Heat products will be issued. Nonetheless,
heat precautions should continued to be taken into account if you
plan on being outdoors during the hottest portion of the day.
The aforementioned Pacific Low will eventually meander onshore by
Thursday morning and will set a pattern change in motion for the
remainder of the week and into the weekend. Before we get to bigger
changes, ridging will still be overhead but the axis will have
shifted further east. As mentioned above, warmer-than-normal
temperatures will continue with areas of moderate to major
HeatRisk once again. The once exception will be out in southeast
California where readings will be slightly cooler due to the
proximity to the westward disturbance. The other forecast
parameter for Thursday will be increasing moisture that will lead
to rising shower and thunderstorm chances, mainly for south-
central Arizona. Favorable upper-jet dynamics, combined with that
increase in moisture flux, will promote convective activity
Thursday afternoon and evening, with the majority of it focused
over areas to the east of Phoenix. Main concerns will be gusty
outflow winds and isolated heavy rainfall. Confidence for rainfall
coverage around the Phoenix metro and lower desert areas of
Maricopa and Pinal Counties is not as high, but some isolated
activity cannot be completely ruled out. If shower and storms over
these areas were to be realized, they will be heavily reliant on
outflow boundaries from distant activity. Due to higher-than-usual
moisture and dynamic support, convection will continue to be
possible overnight for areas from Phoenix eastward.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
Friday still holds fairly high potential for thunderstorm impacts
across south-central and eastern Arizona. Models are in very good
agreement showing the low moving southeastward into southeast
California during the daytime Friday. Even though this low is not
expected to be as strong as other transition type systems that
have brought severe weather outbreaks for our region, it still
could end up being quite the impactful weather system. As the low
enters our region on Friday, south southeasterly low and mid
level flow will increase further. We are likely to see a narrow
corridor of high instability building across our area by Friday
morning with MUCAPEs of 1500-2000 J/kg. The ingredients are likely
to be there for a line or a cluster of strong to severe storms to
develop somewhere across Maricopa, Pinal, and Gila Counties during
the first part of the afternoon as upper level forcing becomes
maximized. Forecast 0-6km bulk shear looks to be the strongest
during the morning hours Friday before gradually weakening during
the afternoon. It`s not impossible for some strong to severe
storms to develop during the morning hours, but it is more likely
to occur during the afternoon hours Friday. Strong to severe wind
gusts, moderately large hail, and heavy rainfall will all be
possible on Friday.
Moisture levels on Friday are not expected to be excessively high
with PWATs as high as 1.1-1.3" in a narrow corridor, but low
level mixing ratios will be quite good at 10-11 g/kg. The heavy
rainfall and flood threat will mostly come from persistent showers
and thunderstorms training over the same area over a period of
several hours. Average forecast rainfall amounts from late
Thursday through Friday are currently between 0.25-0.75" over the
Phoenix area to 1-2" across the high terrain east of Phoenix. At
this point in time, it seems quite plausible a few locations will
see localized higher rainfall amounts of 2-3". However, any
drastic change in the cut-off low`s strength and eventual track
may cut back on our forecast rainfall amounts.
Higher uncertainty is seen for Friday night and Saturday as the
cut-off low will likely begin to weaken and the position of the
low center is a bit uncertain. We are likely to still see decent
(30-40%) rain chances across a good portion of the area during
this time, potentially extending through southwest Arizona into
southeast California as the flow should temporarily shift out of
the east advecting better moisture westward. We are likely to lose
a good amount of our upper level jet forcing by Friday night, but
some residual forcing may still be in place across eastern
Arizona. Overall, any additional rainfall amounts beginning Friday
night should be on the lighter side with the flood threat likely
ending. We may even see rain chances extend into Sunday depending
on how long it takes for the low to eventually exit the region to
the north.
Temperatures will take a dive starting Friday with daytime highs
at most in the low to mid 90s. Some lower desert locations across
south-central Arizona may even fail to reach 90 degrees on Friday
depending on how early the convection starts. The lower heights
from the cut-off low will persist through the weekend with highs
likely only topping out in the upper 80s to around 90 degrees on
Saturday and Sunday, or 5-8 degrees below normal. Beyond Sunday,
forecast uncertainty remains somewhat high as a large Pacific
trough is likely to gradually shift southward along the northern
part of the West Coast. This should help to initially raise
heights over our region early next week, but it may eventually get
close enough to lower heights again. For now the NBM temperature
forecast shows highs remaining below normal through at least
Monday before inching back to near normal during the middle part
of next week.
&&
.AVIATION...Updated at 1758Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected through much of
the TAF period under mostly clear skies. Breezy E/NE winds this
morning, with a few gusts upwards of 15-20 kts, will continue
through the remainder of this morning before becoming light and
variable by this afternoon. Winds are expected to switch to a
W/WNW component by late afternoon around 22Z-00Z before switching
back to the E by 05Z-06Z. Speeds this afternoon through the
overnight hours will remain light, mostly aob 7 kts. Southerly
winds will prevail mid/late morning tomorrow before breezy SW
winds develop by the afternoon. A few vicinity showers/storms may
develop tomorrow afternoon, however, confidence is too low at this
time to include in the TAFs.
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are anticipated through the next 24
hours under clear skies. Light winds (AOB 6 kts) will prevail at
both terminals through most of the period with prolonged periods
of VRB winds. W/NW winds will increase this evening at KIPL with
sustained winds around 10 kts and a few gusts up to 15-20 kts.
&&
.FIRE WEATHER...
Hot and dry conditions will continue today with moisture and rain
chances beginning to increase on Thursday. Expect isolated to
scattered thunderstorms over the eastern districts by Thursday
evening with chances increasing into Friday. MinRH values will
hover around 20% today before increasing Thursday into Friday with
values upwards of 50% over the eastern districts on Friday. Winds
will follow familiar diurnal trends today and most of Thursday
with some breeziness likely on Thursday. The slow-moving low
pressure system impacting the region late this week should lead to
widespread wetting rains across the eastern districts on Friday
and possibly Saturday. Below normal temperatures and elevated
humidities are expected for Friday and through the weekend.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch from Friday morning through Friday evening for
     AZZ545-547-549-552-553-555>558-560>563.
CA...None.
&&
$$
SHORT TERM...RW
LONG TERM...Kuhlman
AVIATION...Smith/Whittock
FIRE WEATHER...Kuhlman

NWS PSR Office Area Forecast Discussion