000
FXUS65 KPSR 180600
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1100 PM MST Sun Oct 17 2021

.UPDATE...
Updated Aviation Discussion.

&&

.SYNOPSIS...
A weak cold front will move through the area resulting in somewhat
cooler temperatures Monday and Tuesday. Occasionally breezy
conditions will be common in parts of southeast California behind
this front. Otherwise, high pressure will build back into the region
during the latter half of the week allowing temperatures to rebound
back near the seasonal normal. Dry weather should persist through at
least the end of the week.

&&

.DISCUSSION...
A progressive flow pattern will continue across the Conus as
Southwest ridging shifts into the plains while moderate height falls
enter the Great Basin over the next 36-48 hours. A well defined
negative PV anomaly currently along the northern CA coast will
propagate inland while partially absorbing energy from a subtropical
jet. With the vast bulk of height falls and shortwave energy
confined north of the I-40 corridor, impacts on the local forecast
area should be quite limited. Shallow Pacific moisture will be
eradicated along the CA coast range and the local antecedent dry
airmass will result in essentially zero chance of rainfall with this
system. Most will notice the cooling trend behind a rapidly
weakening cold front Monday and Tuesday with readings some 4F-8F
below normal. While the strongest winds will be sequestered into far
northern AZ and UT, locally stronger winds will be possible across
the wind prone areas of SW imperial County Monday evening; gusts up
to 30-40 mph seem very realistic given the trajectory and conceptual
model of this weather disturbance. Elsewhere across the forecast
area, afternoon gusts 20-30 mph appear likely.

During the latter half of the week, flat ridging will become
reestablished over the SW Conus with H5 heights in a 585-588dm range
helping deflect northern stream shortwaves away from the region. NBM
and other ensemble systems exhibit rather narrow spreads providing
good confidence of daily highs flirting with the 90F mark again late
in the week. Given the generalized anti-cyclonic flow south of the
northern stream jet, dry weather is almost certain to continue
through the week. Heading through the weekend, a downstream blocking
pattern looks to have retrograded sufficiently to clog up the flow
pattern into the western Conus. The preponderance of ensemble
members stall a longwave trough feature across the East Pacific with
an incredibly strong jet core, individual shortwaves, and numerous
frontal boundaries pummeling the Oregon through central California
coast. This pattern will most likely establish a quasi-zonal or
broadly cyclonic flow configuration over the CWA mostly absent of
moisture availability or strong ascent; and it may not be until
beyond this forecast period before there is some resolution to the
blocked hemispheric pattern.

&&

.AVIATION...Updated at 0059Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
An upper level low pressure system, currently centered along the
NorCal and PacNW coast, will move through the Western CONUS over
the next couple of days. The core of the system will move through
NorCal and the Great Basin with the southern end brushing the
forecast area with a dry cool front during the late afternoon and
evening hours. Low level winds above the surface will trend from
westerly to south and southwesterly overnight and strengthen some
during the day Monday before trending southwest during the
afternoon. Surface winds tonight will be light and favor familiar
nocturnal patterns. But, conditions are not expected to meet LLWS
criteria. With mixing, surface winds will become southeasterly by
15Z/16Z then southerly by 18Z along with some gustiness (20kts).
Anticipate a slow trend toward southwesterly directions during the
afternoon with gusts of 20-25kts. Winds will weaken quickly
during the evening with westerly directions prevailing. Otherwise,
very little cloudiness.



Southeast California/Southwest Arizona including KIPL and KBLH:
An upper level low pressure system, currently centered along the
NorCal and PacNW coast, will move through the Western CONUS over
the next couple of days. The core of the system will move through
NorCal and the Great Basin with the southern end brushing the
forecast area with a dry cool front during the morning.
Southwesterly flow aloft will strengthen overnight and during the
morning. The low levels above the surface will strengthen some as
well. With the approach of the system, westerly surface winds will
be a bit stronger than usual during the overnight hours with gusts
of 25-30 kts developing during the day Monday. KBLH will have
light winds overnight but favor southerly directions instead of
typical variable/drainage patterns. The south and southwesterly
winds will strengthen during the day with gusts to 30kts. Winds
will weaken during the evening (more slowly at KIPL). Anticipate
very little cloudiness.

&&

.FIRE WEATHER...
Tuesday through Saturday:
Breezy conditions should abate on Tuesday with temperatures several
degrees below normal in the wake of a departing low pressure system.
Temperatures will be a few degrees below normal through Wednesday in
association with this system. Temperatures will climb back into the
upper 80s to near 90 Thursday through. Min afternoon RH values will
mostly fall between 15-20% across the lower deserts to 20-25% across
the high terrain. Overnight recoveries will mostly reach between 30-
50% through the period.

&&

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

&&

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

$$

DISCUSSION...18/Rogers
AVIATION...17
FIRE WEATHER...Rogers

NWS PSR Office Area Forecast Discussion