Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 230309

Area Forecast Discussion
National Weather Service Phoenix AZ
810 PM MST Sun Oct 22 2017

The brief cool down will end today as a strong area of high
pressure begins to build over the Western U.S. This will result
in another warming trend with dry conditions and well above normal
temperatures throughout much this week. Some relief from the warm
temperatures will occur late in the week into next weekend, but
slightly above normal temperatures will likely remain in the
forecast for the foreseeable future.


Strong high pressure aloft continued to build into the desert
southwest over the past 12 hours; the main upper ridge axis was
located to the west of Arizona putting a dry northwest flow aloft
into the state and the 00z 500mb plot data showed continued 20-30m
height rises over the state. High temps today climbed back into the
90s; Phoenix was up to 92 but considering that 500mb heights over
southern Arizona were up to 594dm, it is apparent that substantial
warm air still resides above the surface and will be mixing to the
ground over the next couple of days. As such we will see highs rise
into the upper 90s over the lower deserts Monday and Tuesday with
record heat possible in Phoenix on Tuesday. IR imagery at 8 pm
showed clear skies area wide and for the rest of tonight we can
expect generally light winds, mild overnight low temperatures and
clear skies. Forecasts look to be in fine shape and no updates are
needed at this time.

Afternoon temperatures continue to rise this Sunday, warming to or
above the high temperatures from Saturday`s "cool" afternoon. Regional
air quality conditions also continue to improve, but some lofted
particulates will remain through sunset. Strong ridging continues
to build over the southwest CONUS, lifting the storm track and any
associated clouds to our north. Clear skies will continue for the
next several days as ridging dominates the forecast.

Height rises on the 500mb surface already up into the 590s on
neighboring 12z RAOBs and in spite of the cool morning start,
highs will rebound in the low 90s today. Thicknesses and
temperatures will continue to climb into the early work week,
approaching seasonal maxes on Reforecast parameters, resulting in
record/near record forecast highs for the early parts of the last
week of October. Bit of a disconnect with the 12z gridded forecast
guidance compared to climatology parameters for the early week as
forecast temperatures may peak Monday, but the anomalous 700/500mb
heights develop into the region for Tuesday. Lower level height
maxima will develop over northern California and portions of the
Great Basin, while the mid level (700/500mb) peaks develop towards
the Colorado River and south-central Arizona respectively. Record
highs for Phoenix could be topped (especially Tuesday`s), with
Yuma`s triple-digit late October records a bit out of reach.

The strong ridge will begin to break down a bit and shift
westward starting Wednesday while a fast moving shortwave trough
moves through the Four Corners area on Thursday. This will allow
for some slight cooling into the lower to middle 90s for both
days. A backdoor cold front is shown to move into the Desert
Southwest early Friday resulting in highs finally dropping back to
near 90 degrees for Friday into next weekend. A high amplitude
synoptic pattern with a ridge just to our west and deep troughing
across the central U.S. should last through next weekend keeping
our region under continued dry and warm conditions.



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

Dry northwest flow aloft will continue to result in generally clear
skies at the terminals in the greater Phoenix area through Monday
evening. Main issue will be winds; gradients are rather light so for
the most part we can expect typical diurnal tendencies with speeds
mostly 10k or lower. There will be some tightening of the NE-SW
oriented surface gradient overnight with modest low level northeast
winds developing. This pattern commonly will give KPHX light
variable or light SW winds for several hours or more after about 10z
Monday morning; by mid morning better mixing should allow winds to
pick up a bit from the northeast and continue into the afternoon
hours. The KPHX TAF will reflect this idea.

Southeast California/Southwest Arizona including KIPL and KBLH:

Dry northwest flow aloft will result in generally clear skies over
the western deserts over the next 24 hours. Light north-south
surface gradient will cause winds to favor the north at KBLH thru
Monday evening with winds picking up a bit during the afternoon and
gusting into the teens. Less wind expected at KIPL; favoring the
west overnight and then turning to the north by late Mon morning. No
aviation concerns for the TAF sites over the next 24 hours at least.


Tuesday through Saturday: The warmest temperatures of the week
will be Tuesday (close to 100 degrees lower deserts). Thereafter,
high pressure over the area slowly weakens (aided by a weather
disturbance tracking through the Rockies). In turn, temperatures
trend downward, however, highs will still be above normal. There
will be continued breeziness at times - especially Tuesday with
northerly directions favored near the Lower Colorado River Valley
with easterly directions favored elsewhere. Winds favor
southwesterly directions Thursday and Friday before trending back
to more of a north and east pattern Saturday. Minimum humidities
will be very low - below 15% for all but the highest elevations.
Overnight recovery will be modest.


Mon Oct 239886100 in 2003
Tue Oct 24998596 in 2014
Wed Oct 25      94          85          96 in 2014

YUMA     ForecastNormalRecord
Mon Oct 23      98          87          102 in 1959
Tue Oct 24      98          87          105 in 1959
Wed Oct 25      95          87          100 in 1959


Spotters should follow standard reporting procedures.




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