118 
FXUS65 KPSR 122310
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
410 PM MST Thu Dec 12 2019

.UPDATE...Updated aviation discussion.

&&

.SYNOPSIS...
High pressure will result in a slight warming trend through
Saturday. Skies will be mostly clear with just a few periods of
clouds. A mostly dry weather system will arrive Sunday bringing
cooler temperatures across the area with chilly morning low
temperatures Monday and Tuesday. Temperatures will rebound slowly
through the first half of next week. 

&&

.DISCUSSION...
500 mb heights will continue to increase through this evening as 
high pressure builds into the region from the southwest. 
Thereafter, the high will start to get pushed southward as a 
relatively dry Pacific weather system moves towards the desert 
southwest. Until then, high temperatures will be on the increase, 
with highs topping out in the upper 60s/low 70s this afternoon and
in the low 70s by Saturday. High clouds observed today will 
decrease from west to east, mainly after midnight with mostly 
clear skies expected on Friday.

A mostly dry system will pass through the area late Saturday/Sunday
causing temperatures to cool by 5 to 10 degrees with Monday being
the coolest day in the forecast period. Overnight low temperatures
will be chilly with most desert locations reaching the low 40s or
upper 30s. For Sunday, tightening of the pressure gradient and
strong 850 mb winds will translate into breezy conditions, first 
across southeast California and then south-central Arizona, with 
the strongest gusts reaching 30-35 mph. Overall moisture content 
will be limited with insignificant PoPs on Sunday across the 
forecast area except for the higher terrain north and east of 
Phoenix such as the Mazatzals and other mountains in Gila County. 
The overwhelming majority of GEFS and EPS members show no rain for
KPHX although a stray shower in the general Phoenix area still 
cannot be completely ruled out.

Ridging will again rebuild in the wake of that trough with 
temperatures warming a few degrees through Wednesday. Another 
weather system late next week will at least repress the ridge 
keeping temperatures from returning to the 70s. This system may 
dip far enough south over the Pacific enabling enough moisture to
enter the region and provide a better environment for showers as 
compared to the upcoming system this Sunday.

&&

.AVIATION...Updated at 2310Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT;
Southeast California/Southwest Arizona including KIPL and KBLH: 

Weak high pressure aloft will allow for variable amounts of high 
clouds to spread across the terminals with SCT-BKN cirrus decks 
during the TAF period. Winds will be very light and only weakly 
follow typical diurnal tendencies, with periods of variability.

&&

.FIRE WEATHER...
Saturday through Wednesday: Dry conditions under increasing high 
pressure aloft will prevail through Saturday before a weak low 
pressure system affects the region Sunday into Monday. Moisture 
levels with the late weekend system should be rather dry, hindering 
precipitation chances although there is a chance of rain or high 
elevation snow on Sunday and Sunday evening over high terrain east 
of Phoenix. Above normal high temperatures Saturday give way to 
somewhat cooler conditions Sunday into early next week as highs fall 
a bit below normal by Monday. A few degrees of warming return 
Tuesday into Wednesday. Minimum humidity levels initially should 
stick around 25-35% much of the period, potentially lowering 
slightly into early next week. Winds will stay light through 
Saturday before some breezy conditions move in for Sunday and 
Monday, mainly over deserts west of Phoenix. Light winds return 
again by Tuesday as weak high pressure aloft returns to the area.

&&

.SPOTTER INFORMATION STATEMENT... 
Spotters should follow standard reporting procedures.

&&

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

$$

DISCUSSION...Hernandez/Deems
AVIATION...Rogers/Benedict/CB 
FIRE WEATHER...Kuhlman/CB