Weather Service Report

FXUS65 KPSR 241149

Area Forecast Discussion
National Weather Service Phoenix AZ
449 AM MST Fri Nov 24 2017

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


Dry weather and unseasonably warm temperatures will persist 
through the weekend with near record highs each day. A strong low
pressure system will affect the region early next week, bringing a
substantial cooldown by Tuesday. Breezy to windy conditions are 
also possible area-wide on Tuesday. Temperatures will remain 
slightly above normal for the remainder of the week, with no 
precipitation expected. 


Broadly anticyclonic flow remains in place surrounding an upper
ridge centered just off the northern Baja California coast. A few
high clouds continue to stream east-southeastward, but skies are
generally clear this morning across the region. The ridge of high
pressure, already anomalously strong for this time of year, will
slowly move eastward this weekend while gradually amplifying,
resulting in modest midlevel height rises across the Southwest.
NAEFS climatological percentile data suggest both the 500-mb
heights and 850-mb temperatures will be near record-levels into
the weekend. This means a continuation of well above-normal
temperatures for our area, with even a couple degrees of warming
possible into Sunday. In fact, the current forecast of 89 degrees
for Phoenix would set a record for the date (88 in 1950 on Nov
26th), and the forecast high of 87 degrees for Yuma would tie a 
record (1950). Some guidance also suggests 90 degrees may not be 
out of the question on Sunday across some lower desert locations.

A substantial cooldown is looking more likely into next week, 
amidst what could be a longer-lived pattern change. The 
development of a sharp upper trough (perhaps accompanied by a 
closed upper low) continues to be advertised in many 
deterministic model runs, including the more bullish ECMWF. The 
track of this system across northern Arizona means southern and 
central Arizona will likely see drier air aloft across our area, 
while the strongest forcing for ascent remains displaced 
northward. However, an accompanying cold front (one of the 
strongest of the season so far) is forecast to move through our 
area on Monday night, and can't rule out some virga showers or 
even a few sprinkles. However, the more substantial effect will be
the likely increase in wind speeds that occurs Monday and Monday
night both ahead of and in the wake of the cold front. Will have 
to monitor for wind advisory potential as confidence increases. 

Much cooler temperatures are likely by Tuesday, with the forecast
high in Phoenix calling for 74 degrees (but still above normal). 
Some model forecasts even suggest upper 60s will be possible for 
highs, but given the large discrepancies will not quite buy into 
that substantial of a cooldown. The pattern will remain fairly 
progressive in the wake of the early week low pressure system, 
meaning that only a modest warmup may occur later in the week. 
Additionally, an uptick in activity in the lower-latitudes 
relative to earlier in the fall looks possible, which means 
additional low pressure systems may affect the Southwest later 
next week and beyond. Still no sign of precipitation, however, 
while high temperatures will be pleasant in the 70s, but still above


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

No aviation impacts through at least Saturday morning. Light winds
will persist and mostly follow diurnal patterns, but with several
light and variable periods. Skies will remain mostly clear aside
from periods of high cirrus. 

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday: 
High pressure aloft will allow for very warm conditions on Sunday,
but a cooling trend will take place starting Monday as a dry low
pressure system moves across the region. High temperatures will
settle into the 70s through the middle of next week. Through the
period, humidity levels stay relatively low, with minimum RH
values mostly in the teens or low 20s. Light winds on Sunday will
increase on Monday and Tuesday with gusts of 20-30mph 
commonplace. Much less wind is expected for Wednesday and 


Record highs for selected dates through the weekend:

Date      Phoenix       Yuma
----      -------       ----
Nov 24    88 in 1950    89 in 1950
Nov 25    88 in 1950    90 in 1950
Nov 26    88 in 1950    87 in 1950
Nov 27    87 in 2014    88 in 1950

Most days of 80+ during November in Phoenix: 24 in 1949.
Most days of 80+ during November in Yuma: 24 in 1954, 1950, and 1949.

Latest 90+ day in Phoenix: Nov 15 (1999)
Latest 90+ day in Yuma: Nov 25 (1950)


Spotters should follow standard reporting procedures.




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