355
FXUS65 KPSR 142030
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
130 PM MST Fri Jun 14 2024

.SYNOPSIS...
Dry conditions with above normal temperatures will persist through
the weekend with local Excessive Heat Warnings remaining in effect.
The hottest day will be Saturday with highs at least 5 degrees above
normal and breaching 110 degrees for many lower desert communities.
Readings will retreat several degrees back closer to normal levels
early next week as a series of weather disturbances stream north of
the area. A return to warmer than normal conditions is likely during
the latter half of next week.

&&

.DISCUSSION...
While a compact low pressure system ejects through the four corners
early this afternoon, dry anti-cyclonic flow was building into the
SW Conus with modest height rises. In fact, HREF members suggest H5
heights rising into a 590-593dm range tonight and Saturday with
notable midtropospheric warming behind the departing cold core. This
evolution will result in temperatures once again reaching 4F-8F
above normal Saturday with local excessive heat warnings remaining
in place, though readings should hover several degrees below daily
records. Although HeatRisk will only briefly touch a major category
over very localized areas this weekend, warnings in the Phoenix
metro are mandated through Sunday despite temperatures already
quickly retreating closer to the seasonal normal.

Forecast confidence is excellent that broad longwave troughing
currently over the NE Pacific will progress into the western Conus
with individual shortwaves carving out a deeper trough axis
resulting in notable midlevel height falls into the forecast area
during the first half of next week. Ensemble means suggest H5
heights retreating into a 580-582dm range with minimal temperature
guidance spread equating to readings falling near or even a couple
degrees below the daily normal. The approach of this larger trough
and passing shortwaves will also induce periods of stronger
afternoon wind gusts (particularly Monday). While not terribly
anomalous for the early summer season, combined with warm
temperatures and low humidity levels, a dangerous fire weather
scenario may materialize (see Fire Weather section).

The near normal temperatures will be rather short lived as strong
subtropical ridging impacting the eastern Conus early next week will
retrograde towards the SW Conus later in the week as longwave
troughing becomes repositioned over the northern plains and Great
Lakes. The haste of this transition and eventual position/magnitude
of the high pressure center remains rather uncertain with subtle,
but very important differences among ensemble members. There is
general ensemble agreement that the H5 ridge core in a 590-592dm
range will drift along the southern Arizona border towards the end
of next week resulting in another period of locally excessive heat.
However, a minority of ensemble output suggests more dampened
ridging with renewed troughing and lower heights affecting the
region. On the opposite end of the spectrum another minority of
models indicates ridging building poleward allowing better quality
moisture to seep into southern Arizona setting the stage for deeper
mountain convection. At this time, feel the preponderance of
evidence supports an NBM mean solution of H5 heights in a 590-592dm
range advancing directly over the CWA yielding temperatures 5F-10F
above normal during the latter part of next week.

&&

.AVIATION...Updated at 1734Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns are anticipated through the TAF period
under clear skies. Winds will return to their more typical light and
diurnal tendencies tonight. This morning, extended periods of calm
or variability and some earlier than usual westerly directions have
been observed at the terminals. Very light speeds (aob 5 kt) and
variability can be expected into the afternoon before SW directions
are definitively established and speeds increase to aob 8 kt
sustained. Confidence is high that the typical E`rly switch will
occur tonight between 07-09Z at KPHX. Otherwise, expect some high-
based cumulus development over high terrain to the north today and
(with less coverage) tomorrow.


Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation impacts are expected through the next 24 hours under
clear skies. Winds at KIPL will favor a westerly component aob 10 kt
sustained until early tomorrow morning before they establish out of
the SE. Some westerly breeziness (gusts up to 20 kt) is possible
this evening at KIPL. At KBLH, light and variable winds will become
SW`rly this evening before returning to light and variable early
tomorrow morning.

&&

.FIRE WEATHER...
Hot and dry conditions with low humidity levels will continue to
yield a slightly elevated fire danger this weekend with the typical
daytime upslope gustiness. A weather disturbance moving through the
Great Basin early next week will allow temperatures to cool closer
to normal, however strengthening afternoon winds will create an
environment of heightened fire weather concern during the first part
of next week. In fact, there is at least a 30% chance of critical
conditions materializing over eastern districts Monday with
widespread, frequent gusts 25-30mph possible. Minimum afternoon
humidity levels will generally fall into a 5-10% through the weekend
with only modest improvement closer into a 10-15% range early next
week. This will follow primarily poor overnight recovery of 15-30%.
Strong high pressure should build back over the districts during the
latter half of next week resulting in warming temperatures, but also
weakening winds. There are a few models suggesting somewhat better
moisture sneaking into eastern Arizona beyond next weekend yielding
a few thunderstorms over mountain areas, yet confidence is very low
given any early season activity typically results in little actual
wetting rainfall.

&&

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

CA...Excessive Heat Warning until 8 PM PDT Saturday for CAZ562-563-
     566-567-570.

&&

$$

DISCUSSION...18/Kuhlman
AVIATION...Whittock
FIRE WEATHER...18