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000
FXUS65 KPSR 131804
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1104 AM MST Sat Apr 13 2024

.UPDATE...Updated 18Z Aviation Discussion.

&&

.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 1800Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
SE winds will become more southerly over the next couple of hours.
The southerly winds will likely have variability between SW-SE
before a more predominant W-SW develops late this afternoon/early
this evening. Winds will then go back easterly late tonight. Wind
speeds will start to pick up this afternoon with gusts up to 20
kt lasting through just after sunset. Skies will remain clear
through the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:
Wind speeds will pick up this afternoon at both terminals with
southerly to southwesterly gusts up to 25-30 kt at KBLH and
westerly gusts up to 35-40 kt at KIPL through this evening. Winds
will subside after 08Z at KBLH. While at KIPL, winds with gusts of
20-25 kt will persist through the overnight. The strongest winds,
at KIPL, this evening will be capable of kicking up some dust and
creating hazy skies, which could briefly lower visibility. Skies
will remain clear through the TAF 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...Berislavich
FIRE WEATHER...18