249
FXUS65 KPSR 121706
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1005 AM MST Wed Jun 12 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Very hot and dry conditions will continue the next couple days with
an Excessive Heat Warning in effect through Thursday across much of
south-central Arizona. A dry weather system will move across the
area later Thursday into early Friday potentially leading to some
light showers across higher terrain areas, mostly cloudy skies, and
breezy conditions. The weekend should have temperatures return
around 110 degrees across the lower deserts before readings cool
back to around normal early next week.

&&

.DISCUSSION...
The sub-tropical ridge which extends north to south from the Great
Basin into Mexico is bringing H5 heights as high as 592dm across the
eastern half of Arizona. Lower heights down to around 588dm are seen
across the western deserts through southern California as it remains
in closer proximity to a cut-off low that has been nearly stationary
west of Baja. For today and Thursday, this set-up will again bring
very hot temperatures across the majority of the area with highs
between 106-110 degrees across southeast California to 108-112
degrees across the south-central Arizona lower deserts. An Excessive
Heat Warning remains in effect through Thursday for Maricopa, Pinal,
and portions of Gila County as these temperatures represent a Major
HeatRisk for portions of the counties.

During the daytime hours Thursday, guidance shows the cut-off low
beginning to track northeastward closer to southern California
before moving through southern California into western Arizona
Thursday night. Southerly flow is forecast to increase on Thursday
into Arizona leading to some increased moisture advection in the mid
to upper levels. Model soundings show this moisture layer down to
around 13-15K feet by Thursday afternoon which should be enough to
lead to some high-based shower activity across southern and central
Arizona Thursday afternoon and evening. Given the very dry air below
the cloud bases, the most the lower deserts can expect is some
sprinkles, but some very light measurable rainfall with PoPs of 10-
20% will be possible over the Arizona higher terrain. Also can`t
completely rule out some localized gusty winds mainly across western
Arizona due to these possible virga showers.

The cut-off low will continue to weaken and move into northern
Arizona on Friday while the rebuilding sub-tropical ridge moves in
behind from the southwest. Forecast temperatures are a few degrees
cooler across Arizona on Friday due to the low, but the building
heights across the western deserts should lead to highs around 110
degrees across southeast California and far southwest Arizona. As H5
heights once again rise to between 590-592dm Friday night into
Saturday, temperatures will heat up further on Saturday as NBM
forecast highs are mostly between 109-114 degrees. These
temperatures will once again flirt with Major HeatRisk in some
areas.

Starting Sunday, ensemble guidance heavily favors a fairly strong
upper level trough digging across the Northwest U.S. with the
southern fringes of the troughing extending as far south as the
Desert Southwest. This will begin to lower heights across our
region, but the cooling will be subtle on Sunday before becoming
much more noticeable by Monday. The core of the trough is expected
to miss us to the north as it likely moves through the Great Basin
on Tuesday, but it is expected to bring some modest relief from
these very hot temperatures. NBM forecast temperatures lower back to
around normal for the first half of next week with lower desert
highs mostly between 102-107 degrees.

&&

.AVIATION...Updated at 1705Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No weather issues will exist through Thursday afternoon with clear
skies today giving way to 15-20K AGL cigs Thursday morning. An
extended period of variable wind directions (140v250) should be
common again during the transition to a westerly component early/mid
afternoon. Any gusts late afternoon/early evening should be limited
to around 15-20kt. West winds will have a greater probability of
being retained later into the overnight than usual with KPHX
possibly not flipping direction until closer to sunrise.


Southeast California/Southwest Arizona including KIPL and KBLH:
Only briefly gusty afternoon/evening winds will be an issue through
Thursday afternoon under clear skies. Winds will generally vary from
a S/SE direction during daylight hours, then veering to W/SW during
the evening/overnight. Occasional late afternoon/evening gusts 20-
25kt will be possible with periods of light and variable winds
around sunrise.

&&

.FIRE WEATHER...
Well above normal temperatures along with dry conditions will
prevail over the next couple days. Lower desert high temperatures
will top out between 107-112 degrees through Thursday. Winds will
continue to favor diurnal tendencies with occasional afternoon gusts
up to 20 mph today and to around 25 mph on Thursday when some high
based virga shower activity could bring a brief enhancement of the
winds. MinRH values will range between 5-10%, while poor overnight
recoveries can be expected with MaxRHs only reaching towards 15-35%.
Above normal temperatures will continue through the upcoming
weekend, while winds increase further with afternoon gusts of 20-30
mph likely. The combination of the increased winds and continued low
RHs will create even higher fire danger across the area this
weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ534-
     537>555-559-560-562.

CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman