876 
FXUS65 KPSR 241153
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
453 AM MST Fri Feb 24 2017

.UPDATE...Updated Aviation and Fire Weather Discussions...

&&

.SYNOPSIS...
Cooler than average temperatures will persist through early next 
week with two fast moving weather disturbances moving into the 
region Sunday and again Monday night. The weather system Monday 
night will have better potential for spreading rain across the area. 
Dry conditions and much warmer temperatures will return by the 
middle of next week. 

&&

.DISCUSSION...
A dry, stable pattern has become established over the SW Conus this 
morning with strong quasi-zonal flow trapping moisture and lift well 
north into the central/northern Rockies. Persistent 564dm H5 heights 
will keep temperatures in a slightly below normal category though 2C-
5C of warming in the boundary layer will allow for a nice moderation 
Saturday as compared to today. Otherwise, upstream WV imagery shows 
good potential for thicker cirrus to begin overspreading the region 
tomorrow. Almost all guidance captures this evolution in advance of 
a blocked Pacific flow pattern opening up and forcing at least 2 
waves through the SW US early next week.

The first such shortwave will deamplify over cntrl/srn California 
becoming sheared into a downstream jet entrance region Sunday 
afternoon. Attendant moisture associated with this wave will be 
extremely limited and focused primarily in the mid and upper levels 
of the atmosphere (above H7). Not surprisingly, model QPF reflection 
is meager at best and almost exclusive to higher elevations of 
northern and eastern AZ. This scenario had already been accounted 
for necessitating only minor forecast adjustments where virga and 
sprinkles would be the most likely outcome for the vast majority of 
people. 

On Monday and Tuesday, the trailing 'kicker' shortwave will descend 
southward towards the developing longwave trough base, absorbing a 
piece of subtropical Pacific energy and moisture slug along the way. 
Unfortunately, forecast confidence has deteriorated in the past 
several model runs with frequent run to run changes in shortwave 
depth, speed, and moisture transport. The 00Z operational GFS 
remains much more dampened and faster with the shortwave passage 
while also narrowing and displacing the subtropical moisture flux 
south of the CWA. This solution has only limited support from the 
ensemble majority and other operational global members. The 00Z 
ECMWF is much slower with the wave passage, though has also backed 
off the idea of a more organized subtropical plume surging into 
central AZ. With the true outcome likely somewhere in between, have 
utilized an ensemble mean which resulted in a modest reduction in 
POPs on Monday and spread more into Tuesday morning. 

The flow pattern will become more predominated by longwave features 
during the second half of next week with mean troughing over the 
eastern Conus and ridging through the NW. There is excellent model 
agreement that a nearly cutoff wave will spin and meander over 
northern Mexico albeit completely devoid of appreciable moisture. 
While H5 heights in a 570-576dm range are fairly typical for early 
March, increased sun angle and insolation should push temperatures 
back into a near to above normal range. Kept forecast highs fairly 
conservative in the mid/upper 70s for the most part, however would 
not be shocked to see reading eclipse the lower 80s by the end of 
next week. 

&&

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

Dry northwest flow will keep skies mostly clear. Variable light
winds this morning in the Phoenix area will become more dominant 
out of the west through this evening. North to northwest winds 
will persist for KIPL and KBLH at 6-9kts.

Aviation Discussion not updated for amended TAFs. 

&&

.FIRE WEATHER...
Sunday through Thursday...
Dry conditions should prevail for most areas on Sunday ahead of an
approaching Pacific low pressure system. This weather system will
bring chances of wetting rains mainly later Monday through Tuesday
morning focused especially across the high terrain of Arizona. 
Below normal temperatures are expected through next Wednesday with
a significant warming trend likely late next week. Breezy 
conditions on Monday are expected in most areas with breezy 
conditions persisting down the Lower Colorado River each afternoon
through Thursday. Increased humidities with minimum readings
between 25 to 35% through Tuesday will dry out starting Wednesday
with afternoon readings closer to 15% over the deserts for 
Wednesday and Thursday.


&&   

.SPOTTER INFORMATION STATEMENT... 
Spotter reports will not be needed through the weekend. 

&&

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

$$

Visit us on Facebook, Twitter, and at weather.gov/phoenix

DISCUSSION...MO
AVIATION...Kuhlman
FIRE WEATHER...Kuhlman