941
FXUS65 KPSR 162020
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
120 PM MST Fri May 16 2025

...Key Message...

1) Gusty winds over the weekend resulting targeted advisories and
locally elevated fire danger

2) Substantial warming trend latter half of next week resulting in
widespread moderate HeatRisk

.DISCUSSION...

Weather Pattern Overview:
Broadly cyclonic flow continues over the SW Conus with a subtle, but
otherwise innocuous shortwave ejecting over northern Mexico early
this afternoon. However, WV imagery shows a robust upstream jet core
with a strong vorticity center nearing the Pacific NW poised to
buckle the flow pattern and create deep negative height anomalies
over the Great Basin this weekend. Height falls will begin to impact
the CWA Saturday with the leading jet max cresting the coastal range
during an extremely favorable afternoon time frame for downsloping
winds and mountain rotors. In fact, GFS BUFR soundings continue to
suggest 40-50kt compressed in the sfc-H9 layer surging down the
leeward side of the San Diego mountains Saturday evening where
advisories currently exist. However, with the initial shortwave
already ejecting towards the central high plains by Sunday morning
and secession of height falls, the strongest advisory level winds
should be rather short lived.

Behind the first wave, a secondary robust negative PV anomaly will
dig into the trough axis late Sunday and Monday acting to reinforce
cooler tropospheric temperatures and a higher momentum airmass
aloft. However, recent model trends are keeping bulk of energy
confined to far northern Arizona; and without notable height falls,
a reduced pressure/thermal gradient and proximity south of the jet
core will keep wind speeds and gusts more muted than previous
forecasts. Any modest moisture intrusion ahead of this system also
appears reduced with only 4-5 g/kg mixing ratio nowhere near
sufficient to achieve saturation under warmer midlevel thermal
profiles located on the anti-cyclonic side of the jet core. Given
the trend in evolution, temperature forecasts are not nearly as cool
as previous iterations, yet still around 5F below normal during the
first part of next week.

With the downstream flow pattern briefly progressive and re-
orienting into a renewed blocking configuration, the entire trough
structure will dislodge into the plains by the middle of the week
resulting in pronounced height rises and longwave ridging becoming
established over the SW Conus. Ensemble mean forecasts suggest H5
heights reaching at least 586dm during the latter half of the week
with some of the more aggressive members still around 590dm peak
heights. Nevertheless, massive downstream blocking over the eastern
Conus and Atlantic basin will ensure a stagnant pattern and some
manner of ridging stuck over the forecast area. There are some
ensemble members attempting to realign the blocking pattern and
erode the ridge axis with Pacific flow by the end of next week,
however these type of blocking patterns typically take longer than
models indicate to break down. Regardless, rather widespread
moderate HeatRisk should take hold of the area towards the end of
next week with temperatures nearly 10F above normal.

Forecast Confidence & Deviations:
Confidence in temperature forecasts remains very good through the
weekend with somewhat lower confidence early next week, albeit
improving given the consolidating trend among modeling suites
keeping shortwave energy further to the north. Should this system
end up digging farther south, temperatures would be a few degrees
cooler than current forecasts while winds early next week could be
somewhat stronger. With a very favorable pattern, have continued to
increase wind speeds Saturday afternoon and evening over the
automated NBM. Forecast confidence for hotter temperatures during
the latter half of the forecast period remains good, but some
adjustments to these readings (maybe a 1F-3F higher) may eventually
occur, especially over the Memorial Day weekend depending on the
pattern evolution.

&&

.AVIATION...Updated at 1722Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
No aviation weather concerns are anticipated through the forecast
period. Typical diurnal trends will be common at all terminals, with
the exception of a more NW`rly component this evening.  Speeds will
remain at or below 8 kts through this afternoon, but intermittent
gusts into the teens will be possible at the Phoenix this afternoon
into the evening. Mostly clear skies will prevail over the region.


Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are anticipated through the forecast
period. KIPL will be E`rly through this afternoon, going W`rly by
tonight. KBLH will be predominantly S`rly. Winds at both terminals
will generally be aob 10kts, but look to increase near the end of
the TAF period, especially at KBLH with speeds increasing into the
teens. Mostly clear skies will prevail over the region.

&&

.FIRE WEATHER...
Wind speeds will increase markedly Saturday with gusts 20-30 mph
becoming common in the afternoon resulting in an elevated fire
danger. MinRHs will fall into a 10-15% range Saturday across the
eastern districts with readings across the western districts
improving to 20-25%. Humidity levels will increase modestly Sunday
precluding critical conditions despite heightened wind speeds.
Overnight recovery will be fair to poor with readings between 20-30%
over the eastern districts and 30-50% over the western districts
with some improvement early next week. Very warm and dry weather
will return during the middle of next week with minRH in the single
digits following poor overnight recovery, however wind speeds will
be much weaker as high pressure starts building into the region.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory from 2 PM Saturday to 7 AM PDT Sunday for CAZ562.

     Wind Advisory from 4 PM Saturday to 2 AM PDT Sunday for CAZ563-
     566-567.

&&

$$

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