436
FXUS65 KPSR 212324
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
424 PM MST Sun Jun 21 2026

.UPDATE...Updated 00z Aviation Discussion...

&&

.KEY MESSAGES...

- Temperatures will slowly rise to above normal levels over the
  next few days creating widespread Moderate Heat Risk by Tuesday.

- Strong high pressure will peak across the region midweek with
  daytime highs likely reaching their peak on Wednesday or
  Thursday between 110 to 114 degrees across the lower deserts.

- Localized Major Heat Risk will be possible on Wednesday and
  Thursday before a cooling period begins starting Friday.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...
The subtropical high, which current 500 mb RAP analysis centers
over northern Sonora, remains flattened under broad troughing to
our north. Guidance remains in excellent agreement that this
troughing in the northern stream will progress from the
Intermountain West into the Northern and Central Plains early in
the upcoming work week. As this troughing departs, heights aloft
will begin to rebound Monday, resulting in a warming trend through
the first half of the work week. Ensemble means advertise current
H5 heights rising from 590 dam to around 593-596 dam late Monday,
with the subtropical high building to our southeast over far
Northern Mexico near the AZ/NM and international borders. These H5
heights late Monday represent values around the 96th-98th
percentile of climatology. Following one more morning with
widespread lows in the 70s, lower desert highs are forecast to
rise to between 105-109 degrees on Monday putting the bulk of the
area into the Moderate HeatRisk category. The placement of the
subtropical high will also switch flow aloft out of the south,
supporting an increase of moisture especially for the western CWA
beginning Monday. The increasing humidities will have a bigger
impact on overnight temperatures starting Monday night with lows
staying above 80 degrees in the Phoenix area to only down in the
mid 70s for rural desert locations.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
The main forecast concern for the rest of the coming week is the
potential for Major HeatRisk to develop across portions of the
area as early as Wednesday and remaining a possibility through
Friday. Guidance is in good agreement showing the subtropical
high strengthening into Wednesday, likely reaching peak H5 heights
of 595-597dm late Tuesday and Wednesday. Additional Gulf moisture
surges are also expected Monday night and Tuesday night
increasing low level moisture enough to potentially bring some
isolated showers and thunderstorms starting Tuesday across
southwest Arizona and southeast California. The highest PoPs are
between 10-15% across the higher terrain areas of southwest
Arizona, while chances should remain well below 10% across south-
central Arizona due to the stronger subsidence closer to the high
center.

Models are somewhat trending away from even higher heights that
looked possible a couple of days ago, but they are still right
near the threshold of potentially needing Extreme Heat headlines.
The latest NBM still shows some very localized Major HeatRisk
developing by Wednesday before reaching its peak coverage of
roughly 20-30% of the lower deserts on Thursday. Forecast highs
are also 1-2 degrees lower than previously advertised with peak
readings of 111-114 degrees on Thursday. Due to the remaining
uncertainty in the strength of the ridge, we will hold off for now
on any Extreme Heat Watches. Models are also now trending toward
a quicker decline in heights later this week, starting as early as
Wednesday night. Heights are favored to slowly decrease on
Thursday and likely continuing through next weekend as another
trough is forecast to pass by to our north. Daytime highs should
fall below 110 degrees by Saturday and potentially go back into
the normal range by next Sunday. Moisture levels are also expected
to begin to drop off starting Thursday with any isolated
convective potential disappearing by Friday.

&&

.AVIATION...Updated at 2320Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns under some passing high cirrus cloud
decks can be expected throughout the TAF period. The overall wind
pattern will favor the typical diurnal tendencies with overall
speeds aob 10 kts. Some occasional afternoon/early evening gusts
in the mid to upper teens will be possible.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns under some passing high cirrus
cloud decks can be expected throughout the TAF period. At KIPL,
winds out of the west will prevail into the overnight period
before shifting out of the southeast Monday morning. At KBLH,
winds will generally fluctuate out of the south-southeast to
southwest. Overall wind speeds will remain aob 12 kts along with
some minor afternoon/early evening gustiness.

&&

.FIRE WEATHER...
Near normal temperatures and very dry conditions will continue
through Monday with fairly light winds. MinRHs will be in the
single digits each day, while overnight recoveries will be poor,
ranging between 15-35%. Some afternoon and early evening upslope
breeziness will be common, but gusts will mostly stay below 20
mph. Even with the light breezes, the very low RHs should still
lead to elevated fire weather conditions during the latter half of
the afternoon/early evening hours. Going into the middle part of
the week, moisture will improve raising MinRHs to between 10-15%
by Wednesday, but temperatures will also warm to above normal.
Daytime breeziness should also increase with more gusts reaching
the 20-25 mph range.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Watch from Tuesday morning through Wednesday
     evening for AZZ560.

CA...None.
&&

$$

SHORT TERM...Whittock
LONG TERM...Kuhlman
AVIATION...Lojero
FIRE WEATHER...Kuhlman

NWS Phoenix (PSR) Office