803
FXUS65 KPSR 292011
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
111 PM MST Wed Jul 29 2026


.KEY MESSAGES...

- High pressure will center itself over Arizona and strengthen
  late this week resulting in record to near record temperatures
  and widespread major to extreme Heat Risk.

- Extreme Heat Warnings have been expanded to cover the entire
  forecast area starting Thursday, and continuing through the
  weekend.

- Drier air filtering into the region will limit any chances for
  showers and thunderstorms with only isolated coverage over the
  far eastern Arizona high terrain.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...
Weak troughing entering the Great Basin has displaced the monsoon
high off to our east with the center of the anti-cyclonic rotation
now over New Mexico. Deep southerly flow remains in place for much
of Arizona, keeping moisture levels relatively elevated as PWATs
continue to hover around 1.2-1.6", according to mesoanalysis,
across our lower desert areas. However, it does not appear that
the moisture profile will be conducive enough to spark much, if
any, shower and thunderstorm activity, even for the mountainous
areas of Gila County. The entire state will not be completely
deprived of rainfall today though as orographically induced
convection is expected for parts of the Flagstaff and Tucson CWAs.
Convective activity will diminish noticeably during the back half
of the week across most of Arizona, with the exception being the
White Mountains, as drier air spreads over the region and
subsidence increases as the sub-tropical high shifts to the west.

Due to the lack of monsoon activity, the main forecast concern
during the remainder of the workweek will be the building heat
and the introduction of widespread Major, to locally Extreme,
HeatRisk. Temperatures this afternoon will not be too out of the
ordinary with lower desert readings hovering around 108-113
degrees, but we add about two degrees each day through Friday as
the previously mentioned high strengthens to around 598-600dm
during this timeframe, which will be near climatological records
for this time of year. With dryer air in place as well, heating
will be more efficient, allowing for temperatures, to near, and
even exceed, 115 degrees for many locations. The highest values
the NBM shows during the short term is around 116 degrees by
Friday, but given how relatively dry it will be, and how strong
the high will become, it seems that those readings might be a bit
underdone. It would not be surprising that during the next few
subsequent forecasts the NBM values climb a few degrees, with some
areas, mainly the deserts of SE CA and far SW AZ, potentially
even seeing MaxT projections nearing 120 degrees.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Dangerous heat will impact the region over the weekend and
potentially extending into early next week. The peak strength of
the upper level ridge is forecast to occur on Friday and Saturday
before weakening Sunday into Monday. Even though guidance is
forecasting record H5 heights on Friday and Saturday, forecast
highs are barely reaching daily records. This is either due to the
modest low level moisture remaining in place holding down daytime
temperatures a bit, or the NBM is under forecasting temperatures.
We are leaning toward the NBM deterministic forecast temperatures
not being hot enough, but not enough to warrant nudging the
forecast upward. It would not be surprising to have actual highs
closer to the 75-90th percentile of guidance, or a couple degrees
higher than the current forecast. We are likely to have some areas
reaching 120 degrees across the lower deserts of southeast
California on Saturday and Sunday, while the Phoenix area could
conceivably reach 118 or even 119 degrees. Overnight lows will
also provide little relief from the extreme heat with readings
mostly in the upper 80s to the lower 90s to as high as the mid 90s
in the urban core of the Phoenix metro.

Monsoon activity is expected to remain very limited on Saturday
with little to no shot at any outflows nearing the lower deserts,
but that may change by Sunday or Monday. As the ridge begins to
weaken Sunday into Monday, guidance shows evidence of increasing
low level moisture and more monsoon activity across eastern
Arizona and northern Mexico. However, chances still remain fairly
low on Sunday and Monday with high terrain PoPs of 20-30% and
10-15% into the Phoenix area during the evening hours. As long as
the ridge continues to weaken early next week, monsoon convection
should also increase, especially by the middle of next week as
there are hints of a potential easterly wave moving into or near
Arizona. As the ridge weakens and moisture increases, temperatures
are likely to drift lower, but another day or two of Major to
Extreme HeatRisk looks possible for Monday and/or Tuesday,
especially across southeast California and southwest Arizona.

&&

.AVIATION...Updated at 1715Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns will exist through the TAF
period under periods of FEW-SCT mid and high level cloud decks.
Westerly winds will prevail through much of the period, with
occasional late afternoon gusts into the teens. An increase in
westerly winds may also occur late evening/overnight, acting to
prevent or delay the typical E/SE switch. If winds do not switch
E/SE overnight or early Thursday morning, a prolonged period of
light and VRB winds may be favored instead.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns will exist through the next 24
hours under periods of FEW high cirrus and otherwise mostly clear
skies. Winds at KBLH will continue to favor southerly directions
with speeds 8-12 kts and afternoon gusts around 20 kts. At KIPL,
winds will continue to oscillate between SE during the daytime and
SW/W during the evening into the overnight hours, with speeds
generally AOB 10 kts and a potential for a period of evening
westerly gusts into the upper teens.

&&

.FIRE WEATHER...
Strong high pressure will gradually build over the region through
the rest of the week, while drier air also moves in from the
southwest. These two factors will severely limit monsoon activity
as very little activity is expected through at least Friday.
Expect humidities to gradually lower over the next couple of days
with MinRHs settling at 10-15% by Friday. Record to near record
temperatures are also forecast for Friday and through the upcoming
weekend. Winds will mostly follow diurnal patterns, but west
southwesterly winds will be dominant much of the time with
afternoon gusts of 15-20 mph at times.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530-532-537-
     540-542>544-546-548-550-551.

     Extreme Heat Warning from 10 AM Thursday to 8 PM MST Sunday for
     AZZ531-533>536-538-539-541-545-547-549-552>563.

CA...Extreme Heat Warning until 8 PM PDT Sunday for CAZ567-569-570.

     Extreme Heat Warning from 10 AM Thursday to 8 PM PDT Sunday for
     CAZ560>566-568.

&&

$$

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

NWS Phoenix (PSR) Office