787
FXUS65 KPSR 242021
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
120 PM MST Wed Jun 24 2026

.KEY MESSAGES...

- Temperatures around five degrees above normal will result in
localized major Heat Risk through Thursday with Extreme Heat
warnings remaining in place.

- Upper level moisture streaming into the region will continue
through Thursday resulting in expansive cloud cover, virga, and a
few isolated showers and thunderstorms.

- Drier, cooler, and breezier conditions will move into the region
late this week resulting in areas of very high fire danger.

&&

.SHORT TERM /Today through Friday/...
Early afternoon WV imagery depicts a sprawling anti-cyclone centered
over southern New Mexico with SW flow, subtle vorticity centers, and
enhanced midlevel moisture lifting through southern California and
Arizona. Steep 7-8 C/km lapse rates juxtaposed with saturated ascent
have yielded 100-200 J/kg MUCape over the region resulting in
expansive virga and isolated showers/storms. This activity should
continue to fester through this afternoon before shortwave forcing
lifts into northern Arizona this evening. Over the next 48 hours,
the subtropical high will continue to weaken while shifting south
into SW TX/northern Mexico allowing the local flow pattern to become
more westerly, gradually scouring away the midlevel moisture source
while simultaneously introducing modest height falls/cooling with a
strengthening jet core.

Objective analysis suggests the H5 anti-cyclone center near 596dm
with H7 temperatures around +15C encroaching into south-central
Arizona this afternoon. Despite these measures typically supporting
late June high temperatures easily in a 110F-115F range, the
abundant midlevel cloud cover and increased boundary layer moisture
with 8-9 g/kg mixing ratios have been detrimental to mixing depths
and full realization of the surface temperature potential. However,
the increased moisture profiles have forced low temperatures towards
the upper reaches of the guidance envelop restricting the amount of
overnight relief from the heat. Thus, the Extreme Heat warnings
continue through Thursday despite only isolated instances of major
HeatRisk centered in the Phoenix urban corridor. Otherwise, steep
midlevel lapse rates and lingering moisture could conceivably create
another round of virga/elevated showers tonight and Thursday
morning, however forecast data shows reduced ascent and more limited
saturation. Drier air will begin sweeping into the region throughout
the day, but not totally removed such that several HREF members
indicate isolated storms materializing over eastern Gila County in
the afternoon.

By Friday afternoon, large scale troughing will surge into the
western Conus with the trough base anomalously extended into
southern California resulting in seasonally unusual midlevel height
falls across the CWA. Enhanced westerly jet energy and strong
onshore flow will characterize the synoptic flow; a pattern more
common in early May vs. late June. Other than initiating a cooling
trend, this evolution will foster the inland translation of stronger
winds given deep mixing depths tapping a higher momentum airmass
aloft. Given the rarity of this pattern for late June, impacts may
be rather large and multi-faceted given the forecast winds through
the sfc-H7 layer. Initially across southeast California, a downslope
wind component and 40+kt H9-H8 winds will favor areas of blowing
dust and local advisory level wind speeds in the typical locations,
and combined with low relative humidity levels will yield the
potential for critical fire weather conditions where more dense fuel
beds exist along the lower Colorado River valley. Farther east into
Arizona, winds may not initially be quite as strong, however with
energy release components and burning index percentiles near their
maximum in this very anomalous weather setup, fire danger may become
very high. Fire Weather Watches continue for these areas with a high
liklihood of future upgrades to warnings.

&&

.LONG TERM /Saturday through Wednesday/...
Forecast concerns regarding fire danger will continue through the
weekend as wind speeds increase further and much drier conditions
persist. The large Pacific trough will only gradually shift eastward
with strong negative height anomalies diving into the Great Basin
allowing maintenance of cyclonic flow and lower heights into the SW
Conus. Thus, persistent height falls from the incoming trough will
continue Saturday while a strong pressure gradient becomes
established. Guidance shows unseasonably strong gradient winds
lasting through at least Saturday, and potentially into Sunday with
afternoon gusts of 20-30 mph across the entire area, and locally
higher gusts of 30-50 mph. Gradual drying of the boundary layer will
also lower daytime humidities to between 5-15%. The combination of
the low humidities and the strong gusty winds are likely to make for
dangerous fire weather conditions. A Fire Weather Watch remains in
effect for the Lower Colorado River Valley through Saturday evening
and extended through Sunday evening across eastern Arizona high
terrain where winds will be slower to relax while fuels remains very
receptive.

Enhanced downsloping winds with areas of blowing dust appear likely
again Saturday when the combination of height falls and onshore flow
are optimal for mountain rotors and hydraulic jumps inland. In
addition to the fire weather concerns along the lower Colorado River
valley, a myriad of other wind/dust advisory products may be
necessary given the synoptic setup. Otherwise, although H5 heights
quickly decrease to below 588dm, temperatures will be somewhat
slower to respond over the weekend, though eventually falling 4F-8F
below normal by Sunday. The latest NBM/WPC forecast highs shows
readings only in a 98F-104F range across lower elevation population
centers of the forecast area, then only warming a few degrees during
the first half of next week as H5 heights remain sequestered in a
585-588dm range.

&&

.AVIATION...Updated at 1720Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The only weather issues through the TAF period will be occasionally
gusty west winds and the potential for virga showers and very low
chances of VCSH/SHRA conditions at the terminals, primarily during
the overnight period into Thursday morning, under FEW-SCT and at
times BKN midlevel decks above 10 kft AGL. The bulk of clouds and
radar echoes have remained well west of the terminals this morning.
Isolated SHRA and a few strikes of lightning have been observed over
western Maricopa County and will continue for the next few hours,
remaining generally west of the airspace. Winds will favor westerly
directions through at least this evening, with afternoon/early
evening gusts to 15-20 kts. A typical nocturnal E/SE wind shift is
anticipated tonight.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns are expected during the next 24 hours
under SCT-BKN mid-level cloud cover. Light southeast winds at KIPL
will shift W`rly late this afternoon with gusts to 20-25 kts
developing during the evening. At KBLH, S`rly winds will persist,
tilting more to the SW during the afternoon and evening. A period of
higher gusts around 20 kts at KBLH is possible late afternoon into
the evening.

&&

.FIRE WEATHER...
Locally elevated fire weather conditions due to low humidity and
afternoon upslope/upvalley breeziness will continue through
Thursday. Temperatures will be several degrees above normal while
MinRHs values around 15% decrease into the single digits across the
western districts starting Thursday. Winds will generally remain
terrain driven with upslope/upvalley gusts during the latter half of
the afternoon into the early evening peaking around 25 mph Thursday.
Areas of critical fire weather conditions are likely Friday through
weekend as gusty southwest winds increase across the region combined
with humidity levels settling in a 10-15% range. A Fire Weather
Watch continues for the Lower Colorado River Valley Friday-Saturday,
and had been extended Friday through Sunday for the Tonto
NF/Southern Gila County districts given the rarity of this weather
scenario for late June.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Thursday for AZZ530-532-533-
     537-540-542>544-546-548-550-551.

     Fire Weather Watch from Friday morning through Saturday evening
     for AZZ131.

     Extreme Heat Warning until 8 PM MST this evening for AZZ560.

     Fire Weather Watch from Friday morning through Sunday evening
     for AZZ133.

CA...Extreme Heat Warning until 8 PM PDT Thursday for CAZ562-566-567-
     569.

     Fire Weather Watch from Friday morning through Saturday evening
     for CAZ231.

&&

$$

SHORT TERM...18
LONG TERM...Kuhlman/18
AVIATION...Whittock
FIRE WEATHER...18/Kuhlman