096
FXUS65 KPSR 042014
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
114 PM MST Tue Jun 4 2024

.SYNOPSIS...
One more day of near to slightly above normal temperatures will
precede a warming trend that will bring the hottest temperatures
of the year through the rest of the week, with some spots at risk
of breaking daily high temperature records and warm low records.
Cooler, but still hot, temperatures are expected going through
this weekend, with moisture levels rising.

&&

.DISCUSSION...
The hottest temperatures of the year so far are expected during
the second half of this week, including potential record high and
record warm low temperatures, as strong high pressure builds over
the region. Lower desert highs will reach and exceed 110F
widespread Thursday and Friday, as well as potentially on
Wednesday and Saturday in some localized areas like Downtown
Phoenix. Morning lows will be quite warm for this time of year,
reaching the upper 70s to middle 80s. These hot temperatures will
lead to widespread Major HeatRisk Thursday and Friday and high-end
Moderate to isolated Major risk on Wednesday. An Excessive Heat
Warning remains in effect for most lower desert and valley areas
of AZ and CA. There is potential for the warning to be extended
through Saturday as forecast temperatures are not too dissimilar
to Wednesday. However, there is still uncertainty at this time as
there may be increased cloud cover over the area late this week
into this weekend as mid and upper level moisture increase over
the area down stream of a weak Pacific low.

.PREVIOUS DISCUSSION...
Mid-level heights will build in excess of 591 dam Wednesday
through Friday, resulting in temperatures warming significantly
during this period. HeatRisk will reach the Major category for
large portions of the region, with the hottest temperatures
anticipated for Thursday and Friday. As a result, Excessive Heat
Warnings remain in effect for most of the forecast area during
this period. Probabilistically, chances for peak highs of 115+ are
highest Thursday and Friday around 10-30% across the lower
deserts.

Heading into the weekend, ensembles continue to trend the weak
troughing feature hanging off the Baja Peninsula weaker and slower
moving, thus the cooling trend is becoming more muted for
Saturday. However, the temperatures likely (>75% chance) will
cool enough to not warrant an extension of the Excessive Heat
Warnings through Saturday at this point, as increasing clouds will
moderate temperatures a few degrees. Moisture advection with this
troughing feature continues to trend drier for Friday due to the
slower progression, with the highest PWAT levels now for Saturday
at around 0.75-0.90". Subsequently, the higher PoP potential now
resides for Saturday, with higher terrain areas generally around
10-20%. However, the very dry low levels will mute most of the
potential for accumulating rains for any showers or storms that
develop. Dry lightning could be a risk with this regime due to
the rarity of thunderstorms for this time of year and very dry
conditions, so will have to keep an eye on how storm chances
trend going through the week (chances currently no higher than
5-10% for the higher terrain).

As the weak troughing feature progresses across the region going
into early next week, temperatures are expected to remain slightly
above normal due to sub-590 dam heights and persistent mid to
upper level cloud coverage. Ensembles show very subtle differences
in the mid-levels through this weekend, which could result in some
shifting towards higher or lower shower/storm potential. However,
most solutions lean towards the lesser chances at this point.
Going into early next week, ensembles are more uncertain on how
amplified the pattern will become, specifically another troughing
feature in the eastern Pacific well offshore of the Baja
Peninsula. Should a strong trough develop, upstream ridging would
likewise be stronger, precluding another warming trend going into
the middle of next week. Ensemble clusters are split pretty evenly
between a stronger or weaker trough forming during this period,
thus uncertainty remains decently high, at least for how hot
temperatures may trend through the middle of next week.

&&

.AVIATION...Updated at 1705Z.

South-Central Arizona including KPHX, KIWA, KSDL, KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns are expected across the region during the TAF
period. Winds will follow diurnal trends with occasional afternoon
gusts in the mid-teens to around 20 kts. Considerable high cloud
cover will eventually start to move out this afternoon and evening
before mostly clear skies prevail through the nighttime hours.

&&

.FIRE WEATHER...
Seasonably warm temperatures will continue through today, ahead of
a strong warming trend through the rest of the week, where
temperatures will soar between 110-115F for highs through Friday.
MinRH values will continue to run between 5-10% across the
majority of the area through the rest of the week, while overnight
recoveries will continue to range from poor to fair at around
25-40% over the eastern districts to 35-50% over the western
districts. Winds will remain fairly light following diurnal
tendencies with periodic afternoon gusts of 15-20 mph. While
humidities will improve by a few percentage points by this
weekend due to a weak disturbance advecting moisture into the
region, a low end chance (5-10%) of some isolated thunderstorms
over the Arizona higher terrain may result in a non-zero dry
lightning threat Friday and/or Saturday.

&&

.CLIMATE...

Record high temperatures:

Date        Phoenix         Yuma         El Centro
----        -------         ----         ---------
June 5    113 in 2016    115 in 1957    114 in 2016
June 6    111 in 2016    114 in 1928    113 in 2002
June 7    115 in 1985    116 in 1985    113 in 1985

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM Wednesday to 8 PM MST Friday
     for AZZ530>556-559>562.

CA...Excessive Heat Warning from 10 AM Wednesday to 8 PM PDT Friday
     for CAZ561-563-566-567-569-570.

&&

$$

DISCUSSION...Benedict
PREVIOUS DISCUSSION...Young
AVIATION...Kuhlman
FIRE WEATHER...Young
CLIMATE...18