Area Forecast Discussion
Issued by NWS Phoenix, AZ

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735
FXUS65 KPSR 201220 AAA
AFDPSR

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
520 AM MST Mon Nov 20 2017

.UPDATE...Updated aviation and fire weather discussions.

&&

.SYNOPSIS...
The streak of drier weather and above normal temperatures will
persist through the week with unseasonable warmth quickly
returning the next several days. In fact, record highs will be
likely by the middle of the week and into the long holiday
weekend.

&&

.DISCUSSION...
Another cool morning underway for many locations as much of the
forecast area is under partly to mostly clear skies and light
winds. Flow pattern through the mid and upper levels is from the
northwest, with more of a northerly pull the upper high you go
towards jet level. Some high level moisture is advecting into the
region from the north producing some thicker cirrus fields across
western AZ and the Colorado River, remnant blow off from the
atmospheric river event bringing valley rain/mountain snow for the
Pac NW and northern CA. Cloud cover will continue to filter across
southeast CA and Arizona today and Tuesday before strong ridging
lifts the storm track well to our north. Daytime temperatures will
continue their above normal stretch, as regional 500mb heights are
already at the 75th percentile of climatology from the Sunday
evening RAOBs and are forecast to stay elevated well beyond the
Thanksgiving holiday.

While the entire forecast period will be above seasonal normals
(which are in the mid 70s for both Phoenix and Yuma), Wednesday
and Thursday look to be the peak of the warming. 500mb heights
peak at climatological maxes over the Lower Colorado River Valley,
with 1000-500mb thicknesses cresting into the upper 570 dams by
mid-week. Forecast solution agreement remains high between
deterministic and ensemble suites as 594-595 500mb ridge heights
set-up in the vicinity of northern Baja by Wednesday. Ridging
peaks Wednesday but warming will continue to hold into Thursday
before ridge heights are flattened as a stronger northeast Pacific
trough skirts across the northern tier of the CONUS. This will
bring some subtle cooling to the area, but enough to take us down
out of record territory but still above normal readings for late
November.

Latest blended guidance continues to strongly suggest that
temperatures will exceed daily records by Wednesday and Thanksgiving
(see Climate section below). It`s not totally out of the question
that Phoenix could flirt with 90 degrees Wednesday/Thursday,
which would set a record for the latest 90 at KPHX (record is 90
deg on Nov 15 1999). PoPs also remain at 0 percent and it is very
likely the long dry stretch will continue into at least the end of
November, which would result in a meteorological fall (Sept-Oct-
Nov) without any measurable rainfall at Sky Harbor Airport (last
occurred in 1938).

&&

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

Dry northwest flow into the central deserts will send periods of
high clouds across the terminals next 24 hours, with bases genly aoa
20k feet. Expect BKN decks at times, often thin. Winds to be very
light and only weakly follow typical diurnal tendencies at the TAF
sites. KPHX will likely only weakly see west winds, beginning aft
22z and ending before midnight.

Southeast California/Southwest Arizona including KIPL and KBLH:

Strong high pressure centered west of Arizona will lead to periods
of high clouds across the western deserts next 24 hours. TAF sites
may see BKN decks at times aoa 20k feet but often the cirrus decks
will be rather thin. Winds to be very light with light/variable
reports common especially at KBLH. No aviation impacts expected at
the TAF sites for at least the next 24 hours and likely for the rest
of the week.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday: Unseasonably strong high pressure aloft
will bring warming conditions through the middle of the week with
temperatures reaching into the middle to upper 80s across the
deserts starting Wednesday. Rather dry air will also affect the area
through Wednesday before there is a slight boost in moisture by late
in the period. Minimum RH values will fall between 10-15% through
Wednesday and 15-20% for the rest of the week. Light winds will
dominate for the duration of the forecast.

&&

.CLIMATE...
Record highs for selected dates this week:

Date         Phoenix            Yuma
----         -------            ----
Nov 22      89 in 1950        91 in 1950
Nov 23      87 in 1950        87 in 1950
Nov 24      88 in 1950        89 in 1950

The Phoenix record high for any Thanksgiving is 87 on Nov 23 1950
and Nov 27 2014.

&&

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

&&

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

$$

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DISCUSSION...Nolte/Hirsch
AVIATION...CB
FIRE WEATHER...Kuhlman/CB
CLIMATE...MO



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