271
FXUS65 KPSR 031055
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
355 AM MST Mon Jun 3 2024

.UPDATE...Updated Aviation Discussion...

&&

.SYNOPSIS...
Temperatures a few degrees above normal over the next couple of
days will soar towards record levels mid to late week, resulting
in Excessive Heat Watches in effect for most of the region
Wednesday-Friday. Temperatures will then trend cooler going into
and through the weekend as the strong high pressure in place late
week will weaken.

&&

.DISCUSSION...
Upper level troughing pushing into the Pacific Northwest early
this morning is sending down some scattered sky conditions across
the western districts. There will be no impacts from this system
aside from periodic scattered to broken skies over the next couple
of days. The main weather concern for this week centers around a
building ridge across western CONUS that will cause temperatures
to soar to near/at/above record levels mid to late week. Excessive
Heat Watches remain in effect Wednesday and Thursday, but have
also been extended through Friday as more widespread Major
HeatRisk is anticipated based on latest trends in ensemble
guidance.

Somewhat zonal flow will continue through Tuesday, as the latest
shortwave trough across the Pacific Northwest ejects eastward over
the next couple of days. Dry conditions, with temperatures
remaining a few degrees above normal, will continue through this
period, resulting in widespread Minor and locally Moderate
HeatRisk. An anomalously strong ridge will then build across
western CONUS going through the middle portions of the week, with
mid-level heights building to around 591-594 dam across the
region. Temperatures will then soar to well-above normal levels,
with Major HeatRisk developing Wednesday and expanding in coverage
across the region Thursday and Friday. As a result, Excessive Heat
Watches are now in effect Wednesday-Friday to account for
increasing heat levels. Record highs may also be challenged during
this period, with the current Thursday forecasted high for Phoenix
set to break the daily record high. General probabilities of 110+
(115+) will peak around 40-70% (5-15%) across the lower deserts
during this period.

The decision to extend the Excessive Heat Watch through Friday is
a result of recent ensemble model trends, where previous runs had
a more potent and quicker moving troughing feature from Baja into
the region. However, latest guidance shows a weaker and slower
moving trough, thus extending the residence time of the intense
ridge across the Desert Southwest through Friday. Looking through
the weekend, this aforementioned trough will weaken the positive
height anomalies some across the region, resulting in temperatures
cooling a few degrees. Ensemble clustering shows little variance
through Saturday, thus high confidence in impacts from the trough
being some moisture advection resulting in some enhanced PWAT
levels 125-175% of normal (~0.75") going into early next week.
Thus, there remains low (at most 10-15%) chances for higher
terrain convection (peaking Friday and Saturday), but these
chances continue to trend downward due to the weaker trough
scenario. Greater spread in the ensembles are observed Sunday
onward, where the strongest signal at this point is the ridge axis
sliding eastward of the region, with another trough potentially
developing in the eastern Pacific around 30-35N. This scenario
would result in continued above normal temperatures, but little to
no extreme heat potential through early next week.

&&

.AVIATION...Updated at 1055Z.

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

No aviation weather issues will exist through early Tuesday under
gradually increasing high cirrus decks. Across the Phoenix metro,
wind behavior and timing of typical wind shifts will follow a
near persistence forecast including occasional westerly gusts
15-20kt during late afternoon/early evening. In SE California,
winds will settle more out of a SE direction by mid morning, then
veer towards a SW component by early evening.

&&

.FIRE WEATHER...
Little to no change in the weather pattern will keep seasonably dry
and hot conditions in place through Tuesday. Expect lower desert
highs between 100 and 105 degrees, or 3-5 degrees above average each
day. MinRH values will continue to run between 5-10% across the
majority of the area each day, 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. The latter half of the week will see
even hotter temperatures with potential for highs around 110 degrees
Wednesday through Friday over portions of the lower deserts. There
will also eventually be a slight improvement in humidities by next
weekend along with a low end chance (10-15%) of some isolated
thunderstorms over the Arizona higher terrain.

&&

.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 Watch from Wednesday morning through Friday
     evening for AZZ530>556-559>562.

CA...Excessive Heat Watch from Wednesday morning through Friday
     evening for CAZ561-563-566-567-569-570.

&&

$$

DISCUSSION...Young
AVIATION...Kuhlman
FIRE WEATHER...Young/Kuhlman
CLIMATE...18