Wind Advisory 27, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
1056 AM MST Tue May 2 2023

.UPDATE...Updated 18z Aviation Discussion...

&&

.SYNOPSIS...
Temperatures will gradually cool through the week reaching a below
normal category by Thursday in response to low pressure slowly
ejecting inland from the California coast. This system will also
result in occasionally breezy conditions during the afternoon and
evening hours. Despite this low pressure system moving into the
region, a continuation of dry weather should be expected.
Temperatures should moderate back closer to the seasonal normal over
the weekend.

&&

.DISCUSSION...
Early morning WV imagery shows a classic omega block pattern
materializing across the Conus with a seasonally deep PV anomaly
cutting off over central California. The leading vorticity max was
pivoting through southern NV and midtropospheric front responsible
for the enhanced low level pressure gradient sweeping east into SW
Arizona. An expansive circulation center will essentially stall
along the California coast over the next 72 hours with individual
vorticity pockets rotating within the larger vortex. Towards the end
of the week, the blocking pattern will begin to release allowing the
trough to move inland albeit while weakening substantially. However,
the synoptic pattern will retain some measure of cyclonic flow
across the western Conus through the first half of next week.

With height falls slowly seeping east into the forecast area,
temperatures will gradually decline the next couple days with fairly
narrow guidance spread depicting below normal readings in SE
California and a near normal outcome in south-central AZ. The low
level pressure gradient will relax somewhat today keeping the
stronger wind gusts relegated to the typical downslope areas in the
far western CWA. However, deep mixing depths will still tap some
higher momentum across the entire region yielding common spring
breeziness. On Wednesday afternoon, a more defined vorticty center
pivoting towards southern California will result in enhanced
baroclinicity, jet dynamics, and pressure gradient focused into the
forecast area. NAEFS output suggests H8-H7 winds just tipping over
the 90th percentile of climatology, though ECMWF EFI data is
completely unimpressive, Nevertheless, the pattern should support
downsloping stronger gusts through SE California where advisories
may be necessary and blowing dust becomes a concern again.

By Thursday, the blocking pattern will begin to realign forcing the
west coast vorticty center to propagate from southern California
into far NW Arizona. Ensemble membership still indicates little
chance of rainfall as moisture get trapped on the windward side of
the coastal range and total column mixing ratios never exceeding 4
g/kg inland. Cannot completely rule out an isolated shower around
the Joshua Tree area (~10% chance), however any notable showers
should be relegated to northern AZ/southern NV closer to the cold
core. Some enhanced winds may be possible over higher terrain
locations east of Phoenix, though once again forecast standard
deviations and EFI output on Thursday is quite muted. Regardless,
confidence is very good that temperatures Thursday will languish 10F-
15F below normal with lower elevation communities failing to even
reach 80F.

Although the bulk of shortwave energy will have lifted into the
Rockies during the end of the week, excellent ensemble agreement
exists that broad cyclonic flow and sheared vorticity will persist
over the SW Conus. The greatest uncertainty is tied to the speed at
which heights rebound, and recent model trends indicate H5 heights
holding under 570dm through the weekend delaying a more rapid
moderation in temperatures. Nevertheless, the preponderance of
ensemble output shows at least some temporary height rises early
next week forcing temperatures back into a near normal range.

&&

.AVIATION...Updated at 1800Z.

South-Central Arizona including KPHX, KIWA, KSDL, KDVT:
No aviation concerns are expected during the TAF period. S/SSW
flow will prevail during the afternoon with speeds around 10 kts.
Winds will continue to veer over the next several hours before
eventually emanating out of the W/SW by this evening. Some
afternoon breeziness is expected with gusts primarily 15-20 kts.
FEW-SCT high clouds will be present over the region during the
period.

Southeast California/Southwest Arizona including KIPL and KBLH:
At IPL, light SW winds this afternoon will give way to W/WNW
breezes by early this evening. Gusts are likely to range 20-25
kts, with some higher gusts possible. At BLH, winds will generally
be out of the S/SW during the period with some afternoon gusts
upwards of 20 kts. Speeds there will diminish by late this
evening. FEW- SCT high clouds are expected to prevail over the
forecast period.

&&

.FIRE WEATHER...
Dry conditions will persist through at least early next week with a
gradual cooling trend the next several days. Below normal readings
will be common across all districts during the latter half of the
week with some moderation early next week. Breezy conditions will be
common during the afternoon and evening hours with the most
pronounced gusts in western districts Wednesday and across higher
terrain of eastern districts Thursday. With cooling temperatures,
humidity levels should also improve modestly as minimum afternoon
levels only fall into a 15-25% range and overnight recovery falls in
a 40-70% range. While these humidity levels will preclude critical
conditions, the frequent afternoon breeziness will commonly yield a
slightly enhanced fire danger where fine fuels have become
receptive.

&&

.HYDROLOGY...Updated 1000 PM MST 5/1/2023

Salt: Releases from Granite Reef Dam continue decrease with releases
currently around 125 cfs. Thus, the Flood Warning between Granite
Reef Dam and Tempe Town Lake has been canceled.

Gila: Flow in the Gila River continues to travel downstream through
Yuma County as water releases from Painted Rock Dam continue.
Releases from Painted Rock Dam remain above 3000 cfs. Continued
releases from the dam will lead to inundation of downstream
unbridged river crossings through Yuma County. Several unbridged
roads in Yuma County have already reportedly been closed due to
flooding. Flood warnings remain in effect downstream of Painted Rock
Dam to the Colorado River. The latest USGS gauge observation along
the Gila River near Dateland recorded a depth around 8.9 feet, which
is above action stage (8 feet) and just shy of minor flood stage (9
feet). The latest forecast from the CBRFC indicates that flow in the
river will remain above action stage through at least the next week.
The USGS gauge closer to the town of Yuma, near Dome, shows flow
continuing to increase with a current flow height near 19 feet
(Action stage is at 20 feet). Thus, Flood Warnings along the Gila
River remain in effect through at least May 7th.

&&

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

DISCUSSION...18
AVIATION...RW
FIRE WEATHER...18
HYDROLOGY...Smith/Benedict