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172
FXUS65 KPSR 100954
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
254 AM MST Mon Jun 10 2024

.SYNOPSIS...
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Near to slightly above normal temperatures will continue today
before temperatures begin increasing starting Tuesday. Excessive
heat conditions are expected to develop across south-central
Arizona Tuesday through Thursday as afternoon temperatures
approach or exceed 110 degrees. Dry conditions are favored to
continue through the forecast period.

.DISCUSSION...
Early morning WV imagery showed the weak cutoff low that had been
positioned off the coast of the Baja Peninsula last week is now
situated over the AZ/NM border. Outside of bringing an increase in
high clouds to the region, this weak system brought temperatures
back down to near to slightly above normal readings over the
weekend. Temperatures this afternoon will be similar to yesterday
as highs are forecast to top out around 102-107 degrees for most
places across the lower deserts. However, these near to slightly
above normal temperatures won`t last for long as the weak low
continues to exit the region and hotter temperatures return after
today.

Going forward, an upper low currently positioned off the coast of
southern California and northern Baja will cutoff while downstream
ridging amplifies across the Southwest early to midweek. As the
ridge strengthens/amplifies, ensemble guidance indicate mean 500 mb
heights rising to around 590 dm Tuesday before further rising to
around 592-594 dm Wednesday and Thursday, primarily over the
eastern half of our CWA. This will translate to temperatures
warming up once again near or in excess of 110 degrees across the
lower deserts during the Tuesday-Thursday time period primarily
across south-central Arizona. While the greatest coverage of
Major HeatRisk is expected mainly Wednesday for south-central
Arizona, temperatures Tuesday and Thursday will be similar and
near Major HeatRisk thresholds. Thus, the Excessive Heat Watch has
now been upgraded to a warning for Tuesday through Thursday.
Temperatures may flirt with records during this time with the
latest NBM showing about a 30-40% chance of tying/breaking the
record high in Phoenix on Wednesday. Out west, temperatures won`t
be quite as hot given the closer proximity to the cutoff low.
Afternoon highs across southeast California and southwest Arizona
are forecast to be around 105-110 degrees for the middle part of
the week.

Heading into the end of the workweek, ensemble cluster analysis
shows great agreement that the aforementioned cutoff low will begin
to move inland across the Desert Southwest. Ensemble and
deterministic guidance show this occurring late Thursday into
Friday, which is expected to push temperatures back down to near
normal readings Friday. Guidance show mid-level moisture
increasing into the region ahead of the low Thursday, which may be
enough for some weak shower development across the AZ high
terrain, but for now PoPs remain around 10% or less for most
places. Additionally, breezy conditions will increase for the
latter half of the week in response to the upper low. The increase
in winds combined with hot, dry conditions will lead to enhanced
fire weather conditions.

For the weekend following the passage of the upper low, uncertainty
increases in regards to how a trough expected to pass through the
Pacific Northwest will evolve. For now, flat ridging is expected to
prevail across the Southwest for the upcoming weekend into early
next week, keeping highs around 105-110 degrees across the lower
deserts according to the NBM.
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&&

.AVIATION...Updated at 2335Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT;
No aviation weather concerns are anticipated through the TAF
period under SCT-BKN clouds mainly aoa 15 kft. Wind speeds will
mostly remain aob 10 kt sustained, but some gusts up to 15-20 kt
out of the westerly direction could persist over the next couple
of hours before subsided. The typical E`rly switch will occur
sometime between 07-09Z, preceded by a period of very light speeds
and variability. Winds will again follow typical diurnal patterns
for tomorrow, with the westerly shift anticipated between 20-22z.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are expected through the next 24
hours under FEW-SCT clouds mainly aoa 20 kft. Westerly winds at
IPL are anticipated to weaken over the next several hours before
turning out of the southeast direction during the overnight
hours. At KBLH, winds will maintain a southerly component
throughout the period.

&&

.FIRE WEATHER...
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Hot and seasonably dry conditions will continue to support a high
fire danger across the area through the week. Near to slightly
above normal temperatures will continue today before heating up
once again heading into the middle part of the week. Winds will
continue to generally favor diurnal tendencies with occasional
afternoon breeziness of 20-25 mph expected across most of the
region. MinRHs ranging between 5-15% with poor to fair overnight
recoveries of between 20-45% are expected.
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&&

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

CA...None.
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&&

$$

DISCUSSION...Smith
AVIATION...Young/Whittock
FIRE WEATHER...Smith/95