399
FXUS65 KPSR 122159
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
259 PM MST Mon May 12 2025

.SYNOPSIS...
Gusty winds and elevated to locally critical fire weather conditions
will be the main weather concerns through Tuesday, as a low pressure
system passes over the Great Basin. Temperatures will also cool from
the upper nineties this afternoon to the eighties across much of the
lower deserts by Tuesday. Tranquil conditions return Wednesday, with
typical afternoon breezes and a gradual warming trend to near
seasonal normals during the latter half of the workweek.

&&

.DISCUSSION...
Early afternoon mid-level wv imagery shows a trough moving onshore
over the Pacific Northwest, with notable height packing evident in
500 mb RAP analysis to its southeastern periphery. Mountain wave
activity in the lee of the Sierras is quite apparent, indicative of
the strong southwesterly flow that is expected to shift over the
forecast area over the next 12-24 hours as the trough digs into the
Great Basin. While the stronger flow aloft is expected to bring
breezy to windy conditions across portions of the area as early as
this afternoon, the region still remains under the influence of high
pressure and positive H5 height anomalies today. Abundant high
clouds may limit afternoon highs from reaching the century mark
across much of the lower deserts, but temperatures will still range
from 4 to 8 degrees above normal this afternoon, mostly in the upper
90s.

As mentioned above, strong winds will be one of the primary impacts
from the incoming dry weather system through Tuesday. Wind gusts
of 25-40 mph are expected across the area, mainly during the
afternoons and evenings. The strongest winds will be focused
across southeastern CA and over the AZ high terrain. A Wind
Advisory remains in effect for much of Western Imperial County
through Tuesday night, to capture the areas most prone to mountain
rotor activity and downsloping winds. Though there will likely be
a lull in stronger gusts early Tuesday morning, most guidance
including GFS/NAM MOS for Imperial show sustained wind speeds
remaining around 25 kts, just under the Advisory threshold, so
have opted to maintain previously issued product without splitting
it up. Strong winds combined with low relative humidities between
8-15% and dry fine fuels will lead to elevated to locally
critical fire weather conditions as well. Therefore, a Red Flag
Warning remains in effect for southern Gila County and the higher
elevations of northeastern Pinal and eastern Maricopa Counties
through 7 PM MST this evening and again Tuesday from the late
morning through early evening.

The other impact of this system will be cooler temperatures. Expect
lower desert highs to fall solidly in the 80s over SE CA and SW AZ
Tuesday and close to 90F for portions of the Phoenix Metro Area,
then 80s areawide Wednesday (70s for populated higher terrain areas
like Globe/Miami, and western JTNP.) These cooler temps are around 3
to 6 degrees below normals for the time of year.

Late week, global guidance still depicts some measure of longwave
troughing/quasi-zonal flow being maintained over the Western US,
with H5 heights gradually rebounding to around 576-579 dm. Latest
NBM probabilistic guidance shows a very narrow IQR in forecast
temperatures, so confidence is quite high that temps will return to
near seasonal levels. This upcoming weekend, ensembles still show a
shortwave carving out the western side of the longwave
trough/quasi-zonal pattern over the Western CONUS. Though there
are notable discrepancies in how far south this trough will dive,
it will likely result in another cooldown to below normal and
breezy to locally windy conditions this upcoming weekend.

&&

.AVIATION...Updated at 1705Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
A period of southerly cross runway winds followed by veering
directions and increasing afternoon/early evening gusts will be the
main weather issues through Tuesday morning under periods of
mid/high cigs. Confidence is good that a few hours of 150v210 winds
will be common early this afternoon before completing the W/SW
switch. Gusts around 25kt should affect all terminals into the mid
evening before relaxing. Confidence in wind trends overnight is low
with the traditional easterly switch either failing to occur, or
only occurring for a few hours before quickly reverting back to a SW
direction.

Southeast California/Southwest Arizona including KIPL and KBLH:
Gusty winds and the potential for localized blowing dust will be the
primary weather issues under mid/high cloud decks. Gusts will
increase through the afternoon with directions generally veering
from southerly to SW. Gusts may exceed 30kt at KIPL through the
evening hours with speeds peaking 25-30kt at KBLH during the early
evening before partially relaxing overnight. These strong gusts may
result in local surface and slantwise visibility restrictions due to
blowing dust.

&&

.FIRE WEATHER...
Elevated fire danger will exist today and Tuesday as warm
temperatures, low humidity levels, and gusty winds become
juxtaposed with receptive, dry fine fuels. MinRHs of 8-15% will be
common throughout the week following poor to fair overnight
recovery of 20- 50%. Winds will gust to between 25-40 mph during
the afternoon and early evening today and Tuesday, some higher
gusts are possible in western Imperial County. Gusts will likely
be most pronounced across ridge tops and in the typical
downsloping areas. Speeds should weaken during the latter half of
the week, though still will retain the usual afternoon upslope
gustiness. Temperatures will also cool during the first half of
the week as the weather system moves into the region, however
should rebound closer to seasonal normals by the end of the week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Red Flag Warning until 7 PM MST this evening for AZZ133.

     Red Flag Warning from 10 AM to 8 PM MST Tuesday for AZZ133.

CA...Wind Advisory until 5 AM PDT Wednesday for CAZ562.

     Wind Advisory until 2 AM PDT Wednesday for CAZ563-566-567.

&&

$$

DISCUSSION...Whittock
AVIATION...18
FIRE WEATHER...Whittock/Berislavich