Wind Advisory 19, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
1011 PM MST Sun Mar 19 2023

.UPDATE...6Z Aviation Discussion (Below).

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.SYNOPSIS...
Weak high pressure aloft will result in dry conditions
through Monday. Thereafter, a potent storm system will affect the
region during the Tuesday-Wednesday period, delivering rain as
well as breezy conditions and much cooler temperatures. Drier
conditions are expected by the latter half of the week, although
temperatures will run well-below normal.

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.DISCUSSION...
Latest water vapor satellite imagery shows an area of low pressure
spinning over the Gulf of Alaska with a steady stream of moisture
moving in from the Pacific. Due to this stream of moisture coming
in from the Pacific, abundant mid to high level clouds have moved
in. This will maintain temperatures below normal for today,
especially over south-central Arizona.

The aforementioned Gulf of Alaska low pressure will then begin to
sag southward during the day on Monday and then move onshore into
central California during the day on Tuesday while amplifying. As
it does so, a steady plume of moisture is expected to penetrate
into the region. In terms of moisture values, model guidance
continues to be very consistent in showing IVT values in excess of
400 kg/m/s, which is above the 99th percentile. Thus, the
combination of this highly anomalous moisture plume and the
dynamical forcing from the approaching low pressure system will
result in widespread rainfall activity across central and northern
Arizona during the Tuesday- Wednesday timeframe, with the
heaviest activity expected Tuesday evening through Wednesday
morning based on the latest model trends. The rain is likely to be
significant, especially over the higher terrain north and east of
Phoenix, where the latest ECMWF EFI are up to 0.9, indicating the
potential for a highly anomalous rainfall event. At this time,
the latest official forecast calls for total rainfall amounts in
the 1.00"-2.00" range, with locally higher amounts. Given these
forecast amounts in combination with the accelerated snowmelt and
saturated soils, the potential for excessive runoff across the
different rivers, streams, and creeks is elevated and thus the
flood threat. As a result, the latest Excessive Rainfall Outlook
from WPC continues to show a slight risk (between 15-40% chance)
of the rainfall leading to flooding. As a result, a flood watch
has been issued beginning midday Tuesday and continuing through
Wednesday evening. Across the lower deserts, total rainfall
amounts will be noticeably less with the Phoenix metro averaging
around 0.5" and further west into southwest Arizona and southeast
California amounts will likely range between 0.05-0.20" due to
rain shadowing effects.

Model guidance continues to indicate the potential for a few
hundreds J/KG CAPE during the late Tuesday into early Wednesday time
frame. Thus, isolated thunderstorms cannot be ruled out with the
rainfall activity. Strong winds will also accompany the system as
well. The strong winds will begin on Monday, mainly over portions of
Imperial County in SE California where mountain rotors will likely
result in gusts in excess of 30 mph by the late afternoon/early
evening hours. The wind threat will then expand into the rest of
southeast California and into southwest and south-central Arizona on
Tuesday, with gusts potentially exceeding 40 mph at times,
especially over southeast California. With the strong wind gusts
will also come the potential for some blowing dust issues,
particularly across the dust prone areas, briefly reducing
visibilities.

The main moisture plume will have pushed east of the area by late
Wednesday morning, ending the rain threat across the majority of the
the forecast area. However, some leftover low-level moisture in
combination with upslope flow will likely yield to additional
showers, although of more limited coverage, across the higher
terrain zones through Thursday. As we head towards the end of the
week into next weekend, ensembles are indicating yet another trough
moving across the western CONUS. There are uncertainties in the
amplitude of the trough, which if it is deep enough, could deliver
another chance for more precipitation by next weekend, mainly
over the high country. Temperatures by the middle of the upcoming
week through next weekend will be well-below normal by 10-15
degrees.

&&

.AVIATION...Updated at 0510Z.

South-central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light easterly winds should persist overnight while subtly veering
more southeasterly in the morning hours. Monday afternoon, SW/WSW
breezes will pick up somewhat ahead of our next weather system -
gusts over 20 MPH are possible at that time. Considerable mid and
high cloudiness will persist with BKN CIGs well above all
thresholds through at least 9Z Tuesday. There could be some SCT
clouds down to 5-6KFT Monday afternoon. Beyond 9Z Tuesday, a few
showers could approach the metro, but confidence is too low to
include in PHX TAF this far out in time.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will be the dominant concern through the period. For IPL,
occasional stronger gusts (15-20KT) out of the west are possible
overnight - though sustained winds will average out lighter
(10-15KT). Then on Monday, winds really ramp up in the afternoon
with a few gusts 30-35KT. Then at BLH, a few rogue gusts from the
SW also on the table overnight... before a longer period of gusty
conditions arrives during the daylight hours Monday (15-25KT).
Current CIGs are the lowest they should be during the next 24HR,
with mid/high cloudiness favored.

&&

.FIRE WEATHER...
Dry weather will continue through the start of next week with
high temperatures hovering slightly below average. Minimum RH
values will generally be around 20-30% with an upward trend in
moisture starting Monday. Good overnight recovery is expected
with MaxRH values between 30-70%. Our next weather system will
arrive in the Tuesday-Wednesday timeframe, which will keep
temperatures well below average. Breezy to windy conditions will
develop Monday and last through Tuesday, with the strongest winds
in the western districts of SE CA. Probabilities for wetting
rains range from 30% in the western districts of our CWA to 90% in
the northern and eastern areas. A warming and drying trend will
return for the region in the wake of this next system, but
temperatures will continue to run below average through the rest
of next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch from Tuesday morning through Wednesday evening for
     AZZ541-545-547-549-552-555>558-560>563.

CA...None.
&&

DISCUSSION...Lojero
AVIATION...Heil
FIRE WEATHER...RW