980
FXUS65 KPSR 180540
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1040 PM MST Fri May 17 2024

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
High pressure will strengthen over the region the next couple days
resulting in many more lower desert communities exceeding 100
degrees. A dry weather disturbance will move north of the region
early next week with temperatures retreating closer to the seasonal
normal. Occasionally breezier conditions are likely during the
afternoon and evenings early next week under mostly clear skies.

&&

.DISCUSSION...
With Rex blocking situated across the central Pacific basin early
this afternoon, downstream shortwave ridging has built into the SW
Conus with H5 heights hovering around 582dm as the separate
midlatitude and subtropical jet cores bifurcate the region. Into
early next week, a portion of the cyclonic circulation comprising
the base of the blocking pattern will eject eastward while phasing
into the amplification of positively tilted, northern stream
troughing. While the combination of forced ascent and moisture
profiles should be insufficient for precipitation generation, ample
height falls and jet energy crossing the forecast area will be
capable of supporting enhanced afternoon/evening wind gusts.
Otherwise, some form of quasi-zonal flow will persist through the
remainder of next week with H5 heights oscillating in a 572-578dm
range yielding temperatures not terribly far from climatology.

Recent objective analysis indicates midlevel heights and
temperatures increasing over the region with stronger anti-cyclonic
subsident flow building over the CWA. This pattern has resulted in
modest warming over the Southwest, and early afternoon readings were
already eclipsing the lower to middle 90s across lower desert
communities. Model guidance spread remains very narrow suggesting
excellent forecast confidence of temperatures remaining some 5F-10F
above normal through tomorrow afternoon equating to areas of
moderate HeatRisk. By the end of the weekend, the first vestiges of
cyclonic flow and erosion of high pressure will enter the area
bringing a brief, modest cooling trend along with a spell of strong,
gusty winds early next week.

While some increase in wind speeds should be realized Saturday, the
more notable winds with direct tangible impacts will arrive Sunday
and Monday. An increasing gradient Sunday will be associated with
the initial round of height falls and introduction of a
subtropical jet core punching into the region. Afternoon/early
evening gusts upwards of 20-30 mph may become common, especially
over SE California aided by terrain features and a sundowner
component. Further strengthening is anticipated Monday as the
combination of shortwave energy, jet core, and tightened pressure
gradient become maximized over the forecast area. Feel recent
developmental changes in the mandatory NBM initialization have
degraded wind forecasts at lower elevations, and have attempted to
boost speeds to match the synoptic pattern and forecast BUFR
sounding output. This would place much of the area near critical
fire weather thresholds that would be concerning for any ongoing or
new fire starts Monday afternoon. Otherwise, the remainder of the
week should be characterized by quasi-zonal flow (really just
swinging between broad troughing and flat ridging) yielding tranquil
conditions with near normal temperatures and typical springtime
afternoon gustiness.

&&

.AVIATION...Updated at 0540Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

No major weather issues will exist through Saturday night with
only FEW-SCT passing mid/high clouds at times. Wind behavior
across the Phoenix metro will be similar to the past 24 hours,
with afternoon/early evening winds gusting to around 20 kts at
times. At the SE California terminals, breezy W/SW afternoon
winds will resume again tomorrow gusting upwards of around 25-30
kts.

&&

.FIRE WEATHER...
High pressure will hover over the region through the weekend with
dry conditions and temperatures reaching much above normal. Only a
disturbance moving north of the districts early next week will allow
temperatures to cool closer to the seasonal normal. Throughout next
week, minimum afternoon humidity levels will fall into the single
digits at lower elevations and the teens across higher terrain
areas. This will follow poor to fair overnight recovery of 20-40%.
Breezy afternoon/early evening conditions with gusts around 20 mph
will be common, though somewhat stronger winds will occasionally be
possible in far western districts. The greatest weather concern will
occur Monday afternoon where frequent, widespread wind gusts closer
to 30-35 mph may be common yielding near critical thresholds when
combined with low RH and dry fine fuels.

&&

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

$$

DISCUSSION...18
AVIATION...Smith/18
FIRE WEATHER...18