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000
FXUS65 KPSR 130816
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
115 AM MST Sat Apr 13 2024

.SYNOPSIS...
Temperatures will cool closer to the seasonal normal this weekend as
a weather system passes north of the area. This system will yield
very breezy afternoon conditions, especially near foothills and
mountains of southeast California. After this disturbance passes
next week, temperatures will warm substantially during the middle of
the week as high pressure builds back into the region.

&&

.DISCUSSION...
A deep, compact negative PV anomaly was descending along the central
CA coast early this morning within a progressive flow pattern such
that this feature will steadily move inland across the four corners
over the next 72 hours. Gradual height falls and thermal cooling
will accompany this system with temperatures retreating to near and
slightly below normal levels early next week. However, impacts from
this system should be short lived as strong ridging builds back over
the region during the latter half of the week. This will result in a
50/50 chance of some lower desert communities reaching the first
100F of the season.

The first vestiges of midtropospheric height falls will enter the
forecast area today coincident with strengthening onshore flow and
tightening pressure gradient. While wind speeds within the entire
depth of the mixing layer will not be unusually strong, increased
jet flow across the coastal range atop a deepening marine layer will
promote compressional downsloping and hydraulic jumps into parts of
SE California late this afternoon and evening. Both forecast BUFR
soundings and HREF output support a classic sundowner event with 40-
50mph gusts surging through western Imperial County for a period
this evening. With the vorticity center and jet core shifting closer
to southern California Sunday, another period of strong winds
descending off higher terrain appears likely, and current wind
advisories may need to be reissued Sunday evening. On Monday as the
cold core begins to exit the region, residual breeziness may persist
across south-central Arizona higher terrain areas though the
steepest gradient and corresponding strongest winds will have
already exited into New Mexico.

Forecast confidence is excellent that pronounced midlevel height
rises will spread into the SW Conus during the middle of next week
yielding a rapid warming trend. Ensemble uncertainty hinges on the
magnitude of ridging entering the region and persistence of the
highest heights, potentially becoming dampened by low amplitude
shortwaves in the northern stream. Greater than 50% of the
NAEFS members still suggest some measure of ridge dampening later in
the week limiting the extent of the warming trend. Nevertheless, the
overwhelming ensemble mean indicates H5 heights at least briefly
reaching 585dm allowing temperatures to reach a much above normal
category. In fact, the upper end of numerical guidance spread
suggests anywhere from a 25% to 50% chance of some lower desert
communities reaching the first 100F readings of the season Thursday
and/or Friday. With ensemble members trending in this direction, the
first 100F forecast highs and moderate HeatRisk values are now
materializing in the official deterministic NBM output.

&&

.AVIATION...Updated at 0530Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Wind directions are expected to establish out of the E-SE over the
next few hours, with speeds mainly aob 8 kt overnight. Beginning
tomorrow morning, confidence is good that there will be a similar
evolution in the wind directions to what we saw today, veering out
of the SE-SSE mid-late morning, followed by a southerly cross runway
component midday, and eventually establishing out of the SSW-SW
tomorrow afternoon. Speeds will be lower, with gusts peaking in the
mid-to-upper teens to around 20 kt in the afternoon. SKC skies will
prevail through the period.


Southeast California/Southwest Arizona including KIPL and KBLH:
The primary aviation weather concern through the TAF period will be
gusty west winds, particularly at IPL tomorrow evening. Wind
directions will favor S-SW through much of the period at BLH and W
at IPL except during the day tomorrow, where a relatively light (aob
7 kt sustained) SE prevailing wind is expected. West winds will pick
up between 21-23Z at IPL, with gusts peaking upwards of 35 kts
during the evening. Accompanying the stronger gusts, temporary
reductions in visibility from lofted dust will be possible. Mostly
clear skies will prevail through the period.

&&

.FIRE WEATHER...
With dry weather prevailing, temperatures will retreat closer to the
seasonal normal through the first half of next week before rapidly
warming back into an above normal category during the second half of
the week. A weather disturbance passing to the north of the area
will result in very breezy afternoon conditions the next several
days with the strongest gusts across western districts. As minimum
afternoon humidity levels fall into a 10-25% range, a locally
elevated fire danger will exist through Monday. As temperatures
warm next week, minimum humidity levels will dry further into a 10-
20% range with single digits common across lower desert locations.
Overnight recovery will turn poor to fair in a 20-40% range.
However, lighter wind speeds will preclude a greater fire danger and
provide an excellent opportunity for prescribed burning during the
middle of next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory from 3 PM this afternoon to 11 PM PDT this
     evening for CAZ562-563-566-567.

&&

$$

DISCUSSION...18/Young
AVIATION...Whittock
FIRE WEATHER...18