833
FXUS65 KPSR 212010
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
110 PM MST Sat Sep 21 2024

.SYNOPSIS...
Temperatures will steadily warm early next week reaching into an
above normal category as strong high pressure builds over the
region. Dry air will also remain entrenched over the area yielding
little to no chance for precipitation.

&&

.DISCUSSION...
An unusually strong negative height anomaly and deep cold core will
eject into the central plains over the next 36-48 hours with a
measure of weak positively tilted troughing and cyclonic flow
lingering over the SW Conus. While high amplitude ridging will be
building towards the West Coast, this pattern configuration will
temper more abrupt and intense heating with H5 heights gradually
increasing towards a 582-585dm range through Monday. With models
remaining in excellent agreement with respect to this evolution,
guidance spread is extremely narrow resulting in very good forecast
confidence of temperatures rebounding to a near normal range Sunday,
then warming a few degrees above normal Monday.

Through the middle of the week, the Conus flow pattern will be
characterized by higher amplitude features and a tendency for
downstream blocking to slow the forward progression of waves
advancing from the Pacific. As a result, stronger positive height
anomalies will become established over the Southwest with a longwave
ridge axis extending from Arizona through the northern plains.
Ensemble means suggest H5 heights peaking around 588dm and some
additional warming working into the lower troposphere. Official
temperature forecasts indicate highs about 3F-6F above normal during
the middle and latter portion of the week. However, guidance spread
does increase during this time frame with the 75th (and greater)
percentile being realized not completely inconceivable potentially
resulting in near daily record levels (see Climate section).

Ensemble spread grows more notable late in the week through early
next week stemming from uncertainty in blocking over the eastern
Conus/Atlantic basin and placement of cutoff features influencing
the advancement of the upstream pattern. A couple strong troughs
originating from the Gulf of Alaska will begin to impinge on the
Pacific Northwest, however its uncertain whether height falls will
descend far enough south to erode higher midtropospheric heights in
the SW Conus. Conversely, troughing lifting into Canada could act to
further amplify subsequent ridging in the Southwest and reinvigorate
height rises. At this time, official NBM forecasts maintain a
persistence type forecast maintaining some form of moderate strength
high pressure across the CWA though the breadth of possible outcomes
is much larger. Regardless, there is essentially no measure of
ensemble output suggesting anything other than a continuation of dry
weather through the remainder of the month.

&&

.AVIATION...Updated at 1804Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
An upper low centered near KFLG will is tracking northeastward and
will exit AZ by tonight. Due to limited moisture availability, cloud
cover over south-central AZ is limited to SCT cumulus over/near the
higher terrain east of the Valley (bases AOA FL070) with only FEW
cumulus near the TAF sites. The cumulus over the higher terrain will
diminish shortly after sunset. Westerly surface winds have started
to take hold and a westerly component will continue into the evening
hours (northwesterly being common in the late afternoon and early
evening). Anticipate occasional minor gustiness (less than 20kts)
this afternoon as well. Anticipate familiar nocturnal wind patterns
developing after 04Z.


Southeast California/Southwest Arizona including KIPL and KBLH:
Light north winds (less than 10kts) will be common this afternoon
before light and variable conditions predominate tonight.
Otherwise, clear skies.

&&

.FIRE WEATHER...
With temperatures warming above the seasonal normal next week, dry
conditions will prevail with essentially no chance of wetting
rainfall. Minimum daily humidity levels will mostly fall into the
teens with somewhat higher levels over mountainous regions, but a
few single digits across lower deserts. Overnight recovery should
deteriorate from fair to good 30-50% early in the week to a larger
spatial extent of poor 20-25% recovery later in the week. Winds will
remain fairly light through the week with only modest upslope
gustiness limiting a greater fire weather danger.

&&

.CLIMATE...

Record highs next week:

Date        Phoenix         Yuma         El Centro
----        -------         ----         ---------
Sep 25    108 in 1989    112 in 1963    110 in 2015
Sep 26    108 in 1989    111 in 2010    110 in 2010
Sep 27    107 in 2009    111 in 1963    111 in 2009
Sep 28    108 in 1992    108 in 1994    109 in 2009


&&

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

&&

$$

DISCUSSION...18/Young
AVIATION...AJ
FIRE WEATHER...18/Young
CLIMATE...18