576
FXUS65 KPSR 111121
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
421 AM MST Tue Jun 11 2024

.UPDATE...Updated 12z Aviation Discussion...

&&

.SYNOPSIS...
Temperatures will warm up over the next couple of days with highs
warming near or in excess of 110 degrees across the lower deserts,
especially across south-central Arizona. As a result, an Excessive
Heat Warning is in effect for much of south-central Arizona today
through Thursday. Temperatures briefly cool down Friday before
warming back up again for the weekend.

&&

.DISCUSSION...
Current WV imagery and objective analysis show the weak upper low
that had previously moved across the Southwest for the start of the
week is now situated over the Texas Panhandle while a cutoff low
resides off the coast of northern Baja. Over Arizona, heights are
rising in response to a building ridge of high pressure over the
region downstream of the cutoff low. Going through the day today,
500 mb heights will continue to rise to around 590 dm and will lead
to temperatures warming up to around 106-111 degrees this afternoon
across the lower deserts.

The cutoff low will continue to meander off the coast of northern
Baja through the middle part of the week while the upper level ridge
strengthens/amplifies over the Southwest. By Wednesday, ensemble and
deterministic guidance show 500 mb heights over south-central
Arizona peaking around 592-594 dm, which is above the 90th
climatological percentile. The greater height anomalies Wednesday
will exist further to the east, climbing in excess of the 99th
percentile near the AZ/NM border where the ridge axis and center
of the anticyclone will be situated. With heights peaking
Wednesday, temperatures will respond accordingly with Wednesday
forecast to be the hottest day through the rest of the workweek.
Lower desert highs Wednesday will rise to around 109-113 across
south-central Arizona. Temperatures will flirt with the record
high in Phoenix on Wednesday, which is 113 degrees set back in
2022. While the greatest coverage of Major HeatRisk across south-
central Arizona will occur Wednesday, temperatures today and
Thursday will also be pretty similar and near Major HeatRisk
thresholds. As a result, an Excessive Heat Warning is in effect
for much of south-central Arizona today through Thursday.

Going into the end of the workweek, ensemble clusters remain in
great agreement with the aforementioned cutoff low progressing
inland across southern California into Arizona late Thursday into
Friday. This will lead to temperatures dropping back closer to near
to slightly above normal readings Friday across south-central
Arizona. There will be an increase in moisture ahead of the upper
low Thursday into early Friday, which may lead to some
shower/thunderstorm development across mainly high terrain areas of
Arizona. NBM PoPs have trended up during this time period with
the greatest chances currently focused across the high terrain
east of Phoenix. Additionally, breezy conditions will increase
late in the week, which combined with hot and dry weather will
lead to enhanced fire weather conditions.

Following the passage of the upper low, ensembles favor flat ridging
prevailing for the upcoming weekend, leading to temperatures
increasing once again. According to the latest NBM deterministic
output, highs will once again approach or exceed 110 degrees across
the lower deserts. Anyone with outdoor weekend plans should plan
accordingly such as limiting time outdoors and maintaining adequate
cooling and hydration. Uncertainty increases heading into early next
week as a trough pushes into the Pacific Northwest with ensemble
cluster analysis showing disagreement in the depth and timing of
this trough. For now, the NBM indicates highs briefly "cooling" back
closer to near normal readings early next week.

&&

.AVIATION...Updated at 1120Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT;
No aviation weather concerns under some passing high clouds can be
expected through the TAF period. Winds will continue to exhibit
diurnal tendencies with speeds generally remaining aob 10 kts,
although some occasional afternoon gusts into the mid-teens cannot
be ruled out.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns under some passing high clouds can be
expected through the TAF period. At KIPL, winds will be out of the
southeast through this afternoon before shifting out of a westerly
direction by this evening. At KBLH, winds will generally be out of
the south to southwest. Wind speeds will remain aob 10 kts at both
sites.


&&

.FIRE WEATHER...
Hot and seasonably dry conditions will continue to support a high
fire danger across the area through the week. Temperatures will
heat up over the next couple of days with afternoon highs across
the lower deserts approaching or exceeding 110 degrees through
Thursday. Winds will continue to generally favor diurnal
tendencies with occasional afternoon breeziness of 20-25 mph
expected across most of the region. MinRHs will range between
5-10% with overnight Max RHs between 15-35% expected. Going into
the end of the work week, a weather system is expected to traverse
the region and bring increasing breeziness, which will act to
promote elevated fire weather conditions. Additionally, the
weather system will bring a low chance (less than 10%) for dry
thunder to the high terrain east of Phoenix.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM this morning to 8 PM MST
     Thursday for AZZ534-537>555-559-560-562.

CA...None.
&&

$$

DISCUSSION...Smith
AVIATION...Lojero
FIRE WEATHER...Smith/Whittock