523
FXUS65 KPSR 121747
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1047 AM MST Sun May 12 2024

.UPDATE...
18Z Aviation Discussion.

&&

.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 1745Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are anticipated through the forecast period.
Winds will become established out of the W-SW at all metro
terminals this afternoon. Although speeds are expected to be
lighter than yesterday, there could still be periodic gusts up to
15-20 kts. There is higher confidence (>70%) in an easterly wind
shift returning at KIWA and KPHX by 06Z-07Z tonight. Aside from
widely scattered cu development over the higher terrain well to
the north, SKC will continue through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected through the forecast period.
Light winds will continue this afternoon at both terminals with
speeds remaining aob 8 kts. KIPL will mainly see and NW component
and KBLH will favor a N direction through this afternoon, with
periods of calms and variable possible. Winds will shift back out
of the W at KIPL after sunset. 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...Salerno
FIRE WEATHER...18