986
FXUS65 KPSR 181116
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
416 AM MST Wed Jun 18 2025

.UPDATE...Updated 12Z Aviation Discussion.

&&

.KEY MESSAGES...

- Hot and dry weather will continue through at least Friday with
  the hottest day falling on Thursday.

- Extreme Heat Warnings are in effect across south-central Arizona
  for today through Friday with high temperatures ranging from
  108 to 116 degrees across the lower deserts.

- A cooling trend will be seen over the weekend with temperatures
  falling to slightly below normal starting Sunday and lasting
  through early next week.

&&

.DISCUSSION...
The weak shortwave trough that passed across northern portions of
the region yesterday has left dry northwesterly flow in place
with little change in air mass temperatures. Highs yesterday did
drop 3-4 degrees from Monday`s readings due to the trough, but
much of the western lower deserts still managed to breach 110
degrees. The center of the sub-tropical ridge has been displaced
to our southwest due to the passing through, but it is already
starting to move back into our region. H5 heights will creep
upward some today into Thursday as the center of the ridge moves
back to the northeast, briefly stalling out over New Mexico on
Thursday. The hot and dry conditions will continue to prevail as
this shift occurs with temperatures reaching 109-113 degrees today
before peaking on Thursday between 112-116 degrees. Widespread
Moderate HeatRisk will persist across the area with areas of Major
HeatRisk mainly focused on Thursday across south-central Arizona.

By Friday, a large Pacific low is forecast to shift southeastward
into the Northwestern U.S., gradually displacing the sub-tropical
ridge farther to the east of our region. The residual hot air mass
for Friday will still be enough to keep our daytime highs at
around 110 degrees, but H5 heights will quickly drop to below
590dm. The gradient will also increase over our region starting
Friday resulting in breezier conditions. Guidance has been
consistent in showing this low eventually moving fully over the
Great Basin and the Desert Southwest by Sunday, dropping H5
heights over our region to as low as 582dm. This trough is
expected to be deep enough to bring height anomalies into the
10th percentile of climatology across the Great Basin for this
weekend. Models are still uncertain on how far south the center
of the low will reach early next week, but overall they agree the
large scale trough will stall out over the Western U.S. through
early next week, keeping heights below normal for this time of
year.

Temperatures will respond quickly to the incoming trough this
weekend with H8 temperatures falling from 31-33C on Thursday to
24-26C by Sunday. This will translate to at least a 12F drop in
surface temperatures during that time as forecast highs drop to
around normal on Saturday and to a few degrees below normal on
Sunday. NBM guidance shows highs dropping to between 99-103
degrees for Sunday and Monday before gradually beginning to warm
again into the middle of next week as the trough weakens and
begins to lift to the northeast. After this happens, we are likely
to see the ridge move back into our region during the latter half
of next week, likely pushing temperatures back to above normal by
next Thursday or Friday.

Dry conditions will continue to prevail across our entire area
through at least Friday, but starting this weekend guidance
indicates some moisture attempting to advect into southeast
Arizona, and maybe even portions of south-central Arizona by next
Monday or Tuesday. The trough situated just to our northwest is
likely to keep southwesterly winds and dry air working into at
least western portions of Arizona, but at the same time deep
moisture over northern Mexico may be able somewhat seep into
eastern Arizona. At the moment, the most likely scenario calls for
some marginal monsoon moisture to make its way into southeast
Arizona providing for isolated to scattered convection as early
as Monday, but more likely into Tuesday. There may also be some
low end chances for showers and storms as far north as the White
Mtns and into Gila County by Tuesday. It will definitely be
something to watch over the coming days.

&&

.AVIATION...Updated at 1115Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
No major aviation concerns through the TAF period under clear
skies. The overall wind pattern will continue to follow the
typical diurnal tendency with speeds aob 10 kts, with some
occasional afternoon and early evening breeziness into the mid to
upper teens. Extended periods of light and variable to calm winds
are also expected, especially during diurnal transitions.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns will exist through the TAF period under
clear skies. Both terminal will continue to see light and variable
winds through the early afternoon. At KBLH, early this afternoon
winds will become southerly. At KIPL, early this afternoon winds
will go southeasterly and then southwesterly late this evening.

&&

.FIRE WEATHER...
Hot and dry conditions will continue today with overall light
diurnal winds. Starting Thursday, winds will increase modestly
with afternoon gusts up to around 20 mph, and then up to around 25
mph on Friday. Humidities will stay low with MinRHs between
5-10% and overnight MaxRHs only between 15-30%. Afternoon gusts
combined with the dry conditions may lead to some elevated fire
weather conditions for Thursday and Friday, especially across the
higher terrain east of Phoenix. Temperatures will remain above
normal with highs near or above 110 degrees across the lower
deserts through Friday. By the weekend, a dry weather system will
eventually move into the region from the west, dropping
temperatures to around or just below normal while also increasing
MinRHs into the teens. Winds Saturday are also expected to be
quite breezy with elevated fire weather conditions still possible.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Friday for AZZ537-540>544-
     546-548>551.

     Extreme Heat Warning from 10 AM this morning to 8 PM MST Friday
     for AZZ534-538-539-547-552>556-559>562.

CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...Berislavich/Lojero
FIRE WEATHER...Kuhlman