000
FXUS65 KPSR 210927
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
227 AM MST Fri Jan 21 2022


.SYNOPSIS...
Dry conditions and near normal temperatures can be expected today
before a low pressure system from the north moves through the
region this weekend. The passage of this system will result in
breezy to windy conditions, especially over southeast California
and far southwest Arizona, starting late this afternoon. The
system will also bring an opportunity for light
precipitation...mainly to areas east of the lower Lower Colorado
River Valley. Best chances will be on Saturday but at lower
elevations chances remain below 30%. Somewhat cooler temperatures
can be expected as well - most noticeably over southeast
California. Dry conditions with a slow warming trend can be
expected Monday through Thursday.

&&

.DISCUSSION...
A short wave over the northwest CONUS will track southward through
the Great Basin and deepen into a closed low over northwest AZ
this afternoon. It will continue to deepen and track south tonight
becoming centered near Yuma by 12Z Saturday. The closed low will
sag southward a bit more Saturday night before tracking eastward
Sunday and weaken (low center just south of the Mexico border).

The main impacts to the sensible weather this weekend will be wind
and light rain (and higher elevation snow). The winds will be
strongest near and west of the Lower Colorado River Valley with
strong northerly winds beginning late this afternoon and
continuing through the day Saturday. In fact, the ECMWF EFI has
values exceeding 0.8 over portions of Riverside County with a
sharp drop-off in values east of there. A Wind Advisory remains in
effect. Within the Advisory, some hours will have lighter winds
than others and some places will be stronger than others. Along
with the winds, anticipate pockets of blowing dust/sand. Winds are
not anticipated to be as strong Sunday and EFI values are
substantially lower. Precip potential will primarily be east of
the strong wind area with chances starting early Saturday and
tapering off Sunday evening. PoPs over south-central AZ peak
Saturday afternoon and evening (20-30% lower elevations and 30-50%
higher terrain). Snow levels may briefly dip below 5000 ft
Saturday morning but any accumulations are anticipated to be near
and above 5500 ft and remain under an inch. As for temperatures,
the cool advection looks to be fairly modest - especially over
south-central AZ. So, temperatures don`t drop that sharply. But,
it will be noticeable - especially over southeast California and
the Lower Colorado River Valley.

Precip amounts continue to look modest despite the availability
of dynamical forcing and steep lapse rates (500 mb temps dip below
-25C). This is due to the system encountering pre-existing dry
air but more importantly the overland trajectory which limits
moist advection. Plus the system will be relatively short lived.
By way of comparison, for PHX, the upper end of EPS storm total
precip is 0.2 inch with most solutions below 0.1 inch (mean of
0.1). The GEFS is slightly more generous with the upper end at 0.4
inch and a higher percentage of members reaching the 0.1 inch
threshold. However, the mean is still just 0.1 inch. NBM
thunderstorm potential remains below 10% for any given 12 hr
period. And, models are struggling to depict CAPE reaching 100
J/kg. But with the cold core aloft and associated steep lapse
rates, very isolated lightning strikes in the Saturday afternoon
and evening time frame couldn`t be ruled out.

For the next workweek, there is good model agreement that dry
northwesterly flow aloft will be in place with most model
solutions showing a slow inland advance of the Eastern Pacific
ridge and in turn a slow warming trend.

&&

.AVIATION...Updated 0540Z.

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

Awaiting (later-than-typical) easterlies to return at PHX, which
should occur by 7Z. By and large, however, diurnal wind cycles
will prevail through the TAF period. An extended period of
light & variable / SE breezes are still projected at Sky Harbor
for a time tomorrow early afternoon before veering westerly.
Expect the arrival of mid-level cloud cover (aoa FL120) beginning
Friday late afternoon/early evening.

A mid-level low pressure system arrives Friday night. Toward the
end of the PHX TAF period (pre-dawn Saturday), winds will start to
increase just a bit and clouds should thicken above FL010. Virga
or sprinkles cannot be ruled out after 6Z Saturday; far too low of
a rain chance (570.

&&

$$


DISCUSSION...AJ
AVIATION...Heil
FIRE WEATHER...AJ

NWS PSR Office Area Forecast Discussion