Forecast-Discussion

499
FXUS65 KPSR 192055
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
155 PM MST Sun Nov 19 2017

.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...
A fast moving, low amplitude shortwave was progressing into southern
New Mexico this afternoon helping reinforce dry advection and
subsident flow in its wake. After the coolest morning since the very
beginning of April, temperatures have responded quickly this
afternoon breaking a shallow, steep inversion. With ambient
temperatures, dewpoints, and the synoptic setup nearly identical to
yesterday, an overnight forecast of near persistence looks very
applicable. This will yield another crisp, refreshing morning with
widespread 40s and 50s.

Models remain in excellent agreement through the weekend,
depicting gradual height/thickness rises associated with a building
ridge across the Intermountain West. The ECMWF ensembles, in
particular, are exhibiting remarkably low variability (NAEFS members
also display a similar low variance). This will equate to a
pronounced warming trend through late in the week with NAEFS 500mb
heights in excess of 590dm likely setting records Tuesday-Thursday,
particularly in the Yuma vicinity (H5 records near 588dm per KTWC
historical sounding data). Similarly, midtropospheric H7
temperatures will probably touch record levels as well (+11C vs
records +8-10C). Some subtle cooling will spread into the region
during the weekend though temperatures will remain well above normal
as the ridge slides eastward into the Plains.

Latest blended guidance continues to strongly suggest that
temperatures will exceed daily records by Wednesday and Thanksgiving
(see Climate section below). Given the exceptionally low standard
deviations evident in the ECMWF temperature guidance, the official
forecast was adjusted above the median of all available guidance
resulting in a forecast high of 89 degrees for Phoenix Thanksgiving
Day. 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:
Easterly winds will continue into the early afternoon and will
struggle to go westerly for KPHX this evening. However, should see
at least a few hours of NW to NNW winds before eventually
switching back to a light easterly flow late tonight and into
Monday morning. FEW to SCT high clouds expected over the next 24
hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns through Monday morning as winds favor the
north and west directions at both KIPL and KBLH. FEW to SCT high
clouds expected with no other aviation concerns.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Tuesday through Saturday:
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. Unusually dry air will also affect the area through the
middle of the week 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 late in 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...MO/Hirsch
AVIATION...Wilson
FIRE WEATHER...Kuhlman
CLIMATE...MO

NWS PSR Office Area Forecast Discussion