Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 222045
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
145 PM MST Fri Mar 22 2024

.SYNOPSIS...
Temperatures will begin a cooling trend this weekend, quickly
reaching below normal levels early next week in response to a potent
weather system moving into the region. This system will result in
widespread windy conditions Saturday with periodic rainfall chances
increasing across south-central AZ Sunday through Tuesday. A return
to calmer conditions will arrive during the middle of next week as
temperatures moderate back to near normal levels.

&&

.DISCUSSION...
Afternoon WV imagery depicts an expansive negative height anomaly
hovering just offshore with numerous vorticity centers circulating
within the entire trough structure. The lead shortwave has acted to
dislodge high pressure ridging over the western Conus sweeping a
steep cold front onshore in northern California and the Pacific NW.
Subsequent shortwaves and a 150+ kt jet streak pivoting to the
eastern side of the trough will aid in further translating height
falls inland across the Southwest this weekend. While the overall
pattern will remain progressive, the expanse of the trough along
with additional energy carving out the western periphery of the
cyclonic flow will keep unsettled weather affecting much of the
forecast area though Tuesday.

Strong west flow in the H9-H7 layer will develop as early as
tomorrow morning in response to a tightening pressure gradient ahead
of the incoming frontal boundary. Robust height falls and mechanical
mixing during daytime heating will result in windy conditions
coincident with fropa across a large portion of SE California. This
pattern is common during the spring and quite favorable for
downsloping winds and mountain rotors during the late afternoon and
evening hours. NBM probabilities of 40+ mph gusts are very high
immediately downstream of terrain features, however taper off
relatively quickly closer to the Colorado River. Recent wind events
have identified a few dust source regions east of Borrego Springs as
well as around the northern Imperial Valley near the Salton Sea, and
as a result, localized areas of blowing dust will be likely with
regional lofted dust/haze. Between shortwaves Sunday morning, winds
will likely relax over much of the area, however additional height
falls ahead of the next vorticity center Sunday afternoon may
reinvigorate wind speeds, although not to the extent or expanse as
Saturday and the current advisory may be able to be pared back.

While winds will be the greatest impact with this system, rain
chances continue for much of south-central Arizona with models now
suggesting occasionally better chances over a more prolonged period.
Latest ensemble guidance is far more optimistic with respect to
initial moisture intrusion now advertising mixing ratios closer to 6
g/kg and PWATs around 0.75". Additionally, model consensus also
indicates more robust frontogentical forcing and isentropic ascent
further west into the Phoenix metro Sunday morning, and
corresponding NBM POPs have increased notably during this time
frame. Another shortwave will dig into the trough base Sunday night
providing the next chance of showers, however the trajectory of this
vorticty center should take the best forcing into far southern
Arizona after moisture levels have already decreased. The final
shortwave looks to descend in NW flow Tuesday digging through the
western side of the trough acting on residual moisture left behind.
This pattern is notorious for allowing mountain showers and storms
to descend into lower elevations given the flow trajectories and
colder temperatures aloft. As a result, made some modest increases
to NBM POP`s Tuesday afternoon. When all is said and done, rainfall
amounts should range from little to nothing across the western half
of the forecast area, to 0.05-0.33" around the Phoenix metro, and
0.25-0.75" over higher terrain of the eastern CWA.

Once the main trough slides east of the region Wednesday, heights
will begin increasing, however notable differences remain amongst
ensembles on how amplified and persistent the pattern becomes
through the remainder of the week. The preponderance of ensemble
members shows the next Pacific trough rapidly punching into the
western Conus in a progressive flow regime, albeit with the
strongest height falls and forcing remaining well north of the CWA.
Nevertheless, this evolution would temper warming during the latter
half of the week while also producing another round of breezy spring
conditions along a dry, decaying frontal boundary.

&&

.AVIATION...Updated at 1740Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns are anticipated through this TAF period
under increasing high clouds. Winds will follow typical diurnal
tendencies with a westerly shift anticipated at KPHX at 20Z followed
by a return to easterly at 05Z at KIWA and 07Z at KPHX. There will
likely be increased breeziness tomorrow afternoon at all metro
terminals and will likely introduce mention by the next forecast
timeframe.


Southeast California/Southwest Arizona including KIPL and KBLH:
The main aviation concern will be gusty winds at IPL late in the
forecast period. Winds will remain light through this evening,
generally 11 kts or less at both terminals before increasing out of
the west at IPL late tonight. Winds will ramp up across SE
California through the morning and early afternoon tomorrow as a
weather system approaches the region.

&&

.FIRE WEATHER...
Dry and tranquil conditions expected through today. Above normal
temperatures today will cool to well below normal by late weekend.
Windy conditions will develop tomorrow and last through Sunday, with
areas across the western districts gusting in excess of 40 mph (up
to 55 mph in higher terrain areas). MinRH values through tomorrow
will generally hover around 15-20% for the lower deserts and 25-35%
for the higher terrain of south-central Arizona before moistening
above 25% for the lower deserts ahead of the next rain chances
Sunday into Monday. Wetting rain chances are highest in the higher
terrain areas of southcentral AZ Sunday into Monday around 30-50%,
while lower desert chances area marginal around 10-25%. Generally
drier and warming conditions expected going through early next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory from 8 AM Saturday to 6 AM PDT Monday for CAZ560-
     562>567.

&&

$$

DISCUSSION...18/Young
AVIATION...Salerno
FIRE WEATHER...Young


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