000
FXUS65 KPSR 281143
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
443 AM MST Mon Nov 28 2022

.UPDATE...Updated 12z Aviation Discussion.

&&

.SYNOPSIS...
A fast moving weather disturbance will move north of the area
Tuesday pulling a decaying cold front. This will result in a brief
period of isolated breezy conditions and somewhat cooler
temperatures. However, readings should quickly moderate back towards
normal levels during the latter half of the week ahead of the next
weather disturbance arriving over the weekend and early next week.

&&

.DISCUSSION...
Early morning WV imagery shows broad troughing with several
vorticity centers digging towards the northern Rockies and Great
Basin downstream of high amplitude ridging through the north Pacific.
Meanwhile, a separate, weaker southern stream shortwave associated
with a subtropical jet was advancing towards the southern California
coast spreading thick cirrus cover inland while also ensuring a
strengthening downstream jet core. This progressive orientation will
limit the amplification of wave breaking, quickly translating the NW
Conus troughing into the central/northern plains and returning the
SW Conus into quasi-zonal flow during the middle of the week.

Very little change in forecast thinking over the next several days
as shortwave energy remains well north of the forecast area, and
height falls along the trailing trough axis stay modest at best.
Westerly winds should be enhanced this evening near N-S oriented
terrain features along a decaying cold front where a downslope
component will be favored. While nowhere near an optimal setup, H8
winds may briefly reach 40kt in SE California along the theta-e
gradient where the marine layer pushes inland forcing some measure
of mountain wave activity. HREF output suggests advisory criteria
winds in the most favored areas of far SW imperial County while
forecast BUFR sounding data suggests gusts ~30mph more removed from
terrain features.

For the majority of the area, the only notable impact from this
system will be a brief cooling spell (~5F) and the chance for
freezing morning temperatures in outlying sheltered valleys. Recent
NBM forecasts have deteriorated chances of reaching 32F Wednesday
morning closer to 10-30% in both SW AZ and southern Gila Co. Given
most of these locations have already touched 32F this season and
these types of readings are very typical for late Nov/early Dec,
impacts would be minimal. Ensemble confidence is very good that
heights will quickly rebound Wednesday and Thursday allowing
temperatures to moderate back towards normal levels under quasi-
zonal or shortwave ridging type flow.

Somewhat better ensemble agreement exists towards the end of the
week and early next week as multiple shortwaves break over a
stationary central Pacific high amplitude ridge. A preponderance of
evidence suggests subtropical Gulf of Mexico ridging retrograding
into northeast Mexico effectively deflecting and shearing the
initial incoming wave energy to the north of the forecast area.
However, the elongated extent of east Pacific troughing and phasing
of north and subtropical jet cores may tap a stream of subtropical
moisture within broadly cyclonic flow impinging into the SW Conus.
NAEFS IVT forecasts are somewhat anomalous (90th percentile),
however overall IWV magnitude and lack of stronger forcing
mechanisms may preclude a more robust response. Modeling does
suggest some regional theta-e advection and isentropic ascent,
however wide variations in timing and positioning exists. As a
result, official NBM POPs in a 10-20% range are spread through much
of the weekend period in what can be termed a lower confidence
forecast.

&&

.AVIATION...Updated 1142Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Diurnally favored winds of easterly this morning and then becoming
weak westerly early this afternoon is expected across all
terminals. However, more variable winds ranging from southwesterly
to southeasterly will develop between 01-03z at all terminals
before eventually turning back to easterly overnight. A thick
cirrus deck will persist into this afternoon before scattering out
this evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
Light and variable winds across the area will strengthen out of
the WSW early this afternoon with gusts ranging between 20-25 kts.
These windy conditions will persist into this evening before
weakening in the 04-06z timeframe. A thick cirrus deck will
persist into this afternoon before scattering out this evening.

&&

.FIRE WEATHER...
A cold front and slightly cooler temperatures will spread into the
districts the next couple days, though rapidly moderating back
towards normal by the end of the week. A modest increase in winds
near terrain features is likely today and Tuesday, especially over
western districts, however the strongest wind should remain isolated
and not pose a widespread problem. Minimum afternoon humidity levels
will mostly fall in a 20-30% range except slightly higher behind the
cold front Tuesday, then more moist late in the week. Overnight
recovery will continue to be good to excellent in a 50-90% range.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory from noon today to 7 AM PST Tuesday for CAZ562-566.

&&

$$

DISCUSSION...18
AVIATION...Young
FIRE WEATHER...18

NWS PSR Office Area Forecast Discussion