Flood in Arizona, December 4 to 5, 2022

Area Forecast Discussion
National Weather Service Phoenix AZ
455 AM MST Sun Dec 4 2022

.UPDATE...Updated Aviation Discussion...

&&

.SYNOPSIS...
Periodic showers activity will continue to linger across the
Phoenix metro through this morning following a record day of
rainfall on Saturday. Mostly cloudy skies will persist into early
next week as another weather system pushes in from the west
keeping the mid to upper levels moist. There is another chance
for rain on Tuesday as a front moves through the forecast area,
but the highest chances will mainly be tied to the hills east of
Phoenix. Otherwise, temperatures will trend near or slightly above
normal through Monday and then below normal through the rest of
the upcoming week.

&&

.DISCUSSION...
Current radar shows a solid line of showers stretching southwest
to northeast generally south and east of the Phoenix metro, with
more isolated showers across the Phoenix metro and southwest early
this morning. Current HREF guidance shows these isolated to
numerous showers lingering through daybreak before a downtrend in
coverage and intensity going through this afternoon across the
eastern portions of the forecast area. Conditions will slowly
improve from northwest to southeast as the axis of showers slide
off to the east today. However, expect cloudy conditions to
persist as the mid and upper level moisture lingers across
southern AZ into early next week.

The latest mid-level water vapor imagery continues to show an
impressive stream of sub-tropical moisture pushing into southern
AZ from the southwest this morning. An upper level low is also
situated off the Pacific Northwest coast with forcing from that
system bringing a stream of moisture into central CA. Forcing from
the subtropical jet will slowly slide off to the east today,
resulting in the lesser coverage of rain across the Phoenix metro
and east by tonight. Additional accumulations across the Phoenix
metro seem unlikely to reach 0.10" from 6 am onward for today as
the latest HREF guidance of the 90th percentile accumulations are
less than one tenth of an inch. Further east, higher accumulations
between 0.25"-0.50" are not out of the question as the heavier and
more numerous showers linger over the higher terrain into the mid
to late afternoon hours today.

The upper level low off of the West Coast will meander onshore
over northern CA within the next 24 to 48 hours. This troughing
feature will bring more dynamical forcing across northern AZ on
Tuesday, with a surface cold front bringing increasing chances for
rain across southcentral AZ, with the highest chances east of
Phoenix in higher terrain Tuesday into Tuesday night. Current
cluster analysis is in good agreement with the overall pattern as
the trough sets up to the west of the forecast area on Tuesday
and Wednesday, with subtle differences having little to no
differences on the rain outlook during this period. Current NBM
QPF probabilities show no accumulations (up to 0.30") expected at
the 50th (75th) percentile across southern Gila County on Tuesday,
so the potential for light rain Tuesday into Wednesday exists, but
nothing impactful is expected. As such, current NBM PoPs during
this period remains around 30-40% during this period.

As rain chances dissipate on Wednesday, the base of the trough
will lift to the north and east, but lower heights and colder,
drier air will result in cooler temperatures going through the
rest of the week. Sky conditions are expected to clear going
through Wednesday and generally persist through the rest of the
week, but high temperatures will remain below normal (generally
mid-60s) to the 90th percentile level according to NBM guidance
going through Friday. Due to drying conditions, also expect
nighttime temperatures to trend cooler into the lower 40s across
the Phoenix metro as early as Wednesday night.

&&

.AVIATION...Updated 1155Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Low ceilings will continue to be the primary aviation concern
today. Light to occasionally moderate showers will continue
across the area terminals this morning with MVFR ceilings and
brief periods of lower visibilities. Showers subside by the mid-
morning hours, but MVFR ceilings are expected to remain with a
greater than 50% probability of ceilings of 3 kft or less through
at least this evening. Light easterly winds will prevail through
the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns expected through the TAF period. Light
and variable winds will mostly predominate with SCT-BKN mid to
high-level cloudiness.

&&

.FIRE WEATHER...
Rainy conditions will continue through this morning generally east
of Phoenix with additional accumulations ranging between
0.25"-0.50" in higher terrain. RH's will remain elevated through
the early portions of next week, with minimum RH's remaining 30
percent or above through Wednesday. A chance (20-30%) of wetting
rains exist mainly in southern Gila County for Tuesday.
Otherwise, expected continued drying conditions through the rest
of next week with below normal temperatures.

&&

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

DISCUSSION...Young
AVIATION...Lojero/Kuhlman
FIRE WEATHER...Young