South West Weather

859
FXUS65 KPSR 201057
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
357 AM MST Wed May 20 2026

.KEY MESSAGES...

- Near normal temperatures will gradually warm through the weekend
with lower desert highs reaching near 100 degrees following
comfortable morning readings.

- Dry conditions will prevail through the weekend with typical
afternoon breeziness.

- There is a slight chance for a few storms and lightning strikes
over eastern Arizona high terrain early next week, however rainfall
should be minimal, at best.

&&

.SHORT TERM /Today through Thursday/...
Latest objective analysis depicts elongated, positively tilted
troughing covering the western Conus helping depress midtropospheric
heights over the forecast area, and resulting in the recent period
of below normal temperatures. Ensemble model output over the next 60
hours strongly argues for the northern portion of the negative
height anomalies to propagate into the Upper Midwest, yet with the
trough base and marginally lower heights lingering over the forecast
area. While H5 heights will be maintained in a near persistence level
not far from 576dm, boundary layer thermal profiles will moderate in
response to the seasonally increased sfc insolation such that H8
temperatures warm from 18C to 22C through Thursday. As such,
forecast confidence is excellent that afternoon highs will rebound
very close to the daily normals with extremely narrow ensemble
numerical spread. Otherwise, widespread dry weather will continue
along the the typical afternoon May breeziness.

&&

.LONG TERM /Friday through Tuesday/...
The weak troughing will gradually migrate into the southern plains
late in the week as the Conus pattern becomes more progressive
allowing low amplitude shortwave ridging to temporarily build into
the SW Conus. While notable ensemble uncertainty exists in the
northern jet stream structure, particularly over the northeast
Pacific, only minimal model spread is evident across the forecast
area and confidence is very good that H5 heights in a 582-585dm
range will envelop the Southwest. As such, temperatures will warm
several more degrees into a slightly above normal range, but
certainly nothing particularly unusual for this time of year. As the
ridge axis shifts east into New Mexico later in the weekend, deeper
southerly flow and intense heating of higher terrain may encourage
shallow Gulf surges and import of marginally better moisture
profiles heading into next week.

Model uncertainty grows markedly next week as deep troughing enters
the NW Conus while a very strong subtropical jet punches into
northern Mexico, allowing some form of cyclonic flow and shortwave
troughing to develop over the forecast area. This type of pattern is
not uncommon for mid/late May transitioning season, but fine details
in timing, intensity, and moisture availability will determine the
extent (if any) of impacts across the region. General pattern
recognition suggests the increased jet ascent and cooling aloft will
promote deep mountain convection, tapping the marginally increased
moisture early next week with the preponderance of ensemble output
indicating Monday the most favored day for isolated storms. Given
the thermodynamic profiles and historical precedent with similar
systems, very little rainfall would be expected with this
convection, but rather numerous dry lightning strikes and gusty
outflow winds. Should this evolution come to fruition, the greatest
concern would be wildfire starts over the back country followed by
increasing winds midweek with the passage of stronger troughing
through the Great Basin.

&&

.AVIATION...Updated at 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns are anticipated through the forecast
period. East winds this morning will slowly transition back to
W-SW during the part of the afternoon with a few hours of
southerly/VRB winds expected during the shift. Expect clearing
skies this morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather issues will exist through the forecast period
under clear skies. At KIPL, westerly winds will shift to the north
mid morning lasting until the evening when winds will again turn
westerly. At KBLH, northerly winds will continue through the
afternoon before going southerly in the evening. Wind speeds will
be aob 10 kt at both terminals through the TAF period.

&&

.FIRE WEATHER...
Temperatures will gradually warm through early next week, albeit
remaining in a slightly above normal category. Dry conditions will
prevail with minimum afternoon humidity levels falling into a 5-15%
range this week, though a modest increase in moisture will result in
these levels increasing closer to 10-20% over the weekend. This
moisture increase along with an incoming weather disturbance will
lead to a slight chance for afternoon/evening storms and lightning
strikes over eastern districts high terrain. Little to no rainfall
would be expected with this activity resulting in a heightened
threat for new wildfire starts, particularly Monday afternoon. Poor
to fair overnight recovery of 20-40% will only improve slightly over
the weekend. Typical afternoon spring upslope gustiness of 15-25 mph
will be common through the period with the most pronounced gusts
over eastern district high terrain and through the lower Colorado
River valley.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

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