193
FXUS65 KPSR 120810
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
110 AM MST Sun May 12 2024

.SYNOPSIS...
Temperatures will warm into an above normal category this week with
many lower desert communities nearing or exceeding 100 degrees most
days. Dry springtime conditions will also persist with the usual
late afternoon breeziness. In addition, occasional showers over the
mountains of northern and eastern Arizona may support erratic, gusty
winds descending into the lower deserts during the evening hours.

&&

.DISCUSSION...
East Pacific/western Conus omega blocking was in the process of
breaking down early this morning with a four corners closed
circulation center comprising the eastern footing of the block
ejecting into the southern/central high plains. With the entire
decaying pattern translating eastward, dampened high pressure
ridging with modest height rises was edging into the Southwest
resulting in an abbreviated warming trend. With H5 heights only
peaking near 578dm over the next few days, guidance spread remains
very narrow suggesting temperatures 4F-8F above normal. This should
equate to only the warmest lower elevation communities reaching
100F, and merely localized moderate HeatRisk through Monday.

Although the aforementioned four corners circulation was exiting the
region, residual midlevel moisture juxtaposed with steep lapse rates
and subtle subtropical jet energy may yield a few high based
afternoon showers over the Mogollon Rim and mountains of eastern
Gila County. Granted measurable rainfall would be isolated, however
NBM POPs appear too low given a large subset of HREF members suggest
a few cells leaking into the eastern CWA. Regardless, the greatest
impact from any activity would be erratic, gusty outflow winds
affecting any of the ongoing wildfires, and even potentially
surviving into lower desert communities.

During the middle of the week, ensemble members remain in good
agreement depicting the southern extension of the wave responsible
for dislodging the blocking pattern propagating into the Southwest.
This evolution will reintroduce modest height falls back across the
forecast area as H5 heights retreat closer to 572dm yielding a brief
respite in temperatures closer to the seasonal normal. While not
really importing any additional moisture, this shortwave looks to be
the next feature to support high based mountain showers, and
eventually the prevailing northerly flow on the backside of this low
center would be favorable towards more robust propagation of gusty
outflow winds into lower desert locations. Towards the end of the
week, forecast uncertainty grows as a weakness in the
midtropospheric height field may linger over the SW Conus
prohibiting stronger ridging from building into the region. Ensemble
means indicate H5 heights rebounding back near 580dm with high
temperatures returning 4F-8F above normal, however the more extreme
ensemble members hint at H5 heights closer to 585dm. Thus, the upper
25th percentile bounds of NBM output indicates some of the warmest
locations over the weekend could be flirting with the 105F threshold
and more expansive moderate HeatRisk should the stronger ridge
solution comes to fruition.

&&

.AVIATION...Updated at 0529Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
There is uncertainty in wind directions tonight, especially at KPHX.
Northerly winds now may shift back west for a few hours with some
variability. Confidence in the east shift at KPHX is low and may
occur as late as 14-15Z. The other terminals will see more typical
diurnal tendencies. Light variability is expected at all terminals
through Sunday morning followed by westerlies prevailing by noon
local time. West winds will increase up to 7-10 kts with afternoon
gusts up to 15-20 kts. SKC will prevail with the exception of a few
cumulus to the north Sunday afternoon.


Southeast California/Southwest Arizona including KIPL and KBLH:
Light winds will prevail through the night at both terminals with W
to NW component favored at KBLH, and W at KIPL. Light variability is
expected at both terminals Sunday morning. Winds shift back N at
KBLH and W at KIPL Sunday afternoon with sustained speeds up to 10
kts. Sundowner winds at KIPL Sunday evening may lead to occasional
gusts up to 20 kts. SKC will prevail.

&&

.FIRE WEATHER...
Periodically gusty winds, dry fine fuels, and low humidity levels
will yield a locally elevated fire danger this week. Temperatures
will maintain an above normal level with seasonably dry weather
persisting across the districts. Minimum afternoon humidity levels
around 10% will be common across lower desert elevations with values
in the teens over higher terrain areas. Overnight recovery will
range widely from poor to fair in a 20-50% range. Afternoon
breeziness with gusts 20-25 mph will be common over most areas with
some enhancement possible in far eastern districts due to high based
showers over mountains during the first half of the week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.

&&

$$

DISCUSSION...18
AVIATION...Benedict
FIRE WEATHER...18