185
FXUS65 KPSR 160927
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
227 AM MST Thu May 16 2024

.SYNOPSIS...
Above normal temperatures will continue through the weekend with
lower desert highs warming a few more degrees before peaking at
just over 100 degrees on Friday and Saturday. Isolated shower and
thunderstorm activity can be expected again today over the
eastern Arizona high country, which could cause some erratic
gusty winds reaching the lower deserts of south-central Arizona.
A slight cooling trend and continued dry conditions are forecast
for the first half of next week with temperatures likely falling
back to near normal.

&&

.DISCUSSION...
A weak upper level trough moving through the region continues to
bring slightly elevated moisture levels and scattered high based
showers. The convection is currently ongoing, but has become
solely elevated in nature and it is doubtful anything other than
sprinkles are reaching the ground across south-central Arizona.
These mainly virga showers may continue through the rest of the
morning hours as indicated by the CAMs, but they should have no
impact.

By this afternoon, the last lingering vort center is forecast to
track southward across south-central Arizona which should provide
enough lift for some additional daytime high based showers and
isolated thunderstorms focused over the high terrain northeast
and east of the Phoenix area. A north northwesterly steering flow
should keep any of this activity east of Phoenix, but the HREF
continues to show potential for gusty outflow winds attempting to
reach as far west as Phoenix. The only area that shows any
realistic rain chances is across the higher terrain of eastern
Gila Co. where PoPs range from 15-25%. Farther to the west, upper
level ridging will already begin moving into southern California
and western Arizona today. This should allow for daytime highs to
reach near 100 degrees across portions of southeast California
this afternoon.

For Friday and Saturday, the upper level ridge with H5 heights
ranging from 581-585dm will move over the Desert Southwest.
Heights of this magnitude are not unusual for mid May as they
still fall below the 90th percentile of climatology, but it will
be enough to push daytime highs between 6-8 degrees above normal.
Forecast highs across the lower deserts for Friday and Saturday
are mostly in the upper 90s to the lower 100s, while overnight
lows range from the mid 60s over rural desert areas to as warm as
the mid 70s in central Phoenix. Both Friday and Saturday show
areas of Moderate HeatRisk, mainly centered across the Lower CO
River Valley, the Imperial Valley, and across Phoenix.

By later Sunday into Monday, ensemble guidance remains in good
agreement showing another decaying upper level low approaching
northern Baja, while a larger upper level trough digs southward
through the Pacific Northwest into the Great Basin. Both dry
systems are expected to continue to weaken as they move into the
Desert Southwest later on Monday into Tuesday, but they will help
to lower temperatures back to around normal with highs as low as
the low to mid 90s on Tuesday. A progressive wave pattern then
shows multiple shortwaves impacting the Northwestern U.S. through
the latter half of next week which should keep broad troughing
over our region and any stronger ridging to our south. This
weather pattern is likely to keep temperatures at or just above
normal through the end of next week with seasonably dry conditions
persisting.

&&

.AVIATION...Updated at 0609Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Northerly winds continue to weaken following the passage of an
outflow boundary that pushed through the metro this evening.
Northerly winds are expected to further weaken, becoming light and
variable by around midnight while favoring the west at times. Winds
are eventually expected to switch to the east overnight before
switching back to the west around 18-19Z tomorrow with a few
afternoon gusts to around 15-20 kts. Could see a light shower/virga
Thursday morning which could generate some gusty erratic winds.
Uncertainty increases tomorrow afternoon as convection fires up
across the high terrain to the north. Isolated showers and
thunderstorms over the high terrain are not expected to make it into
the lower elevations tomorrow afternoon but may generate gusty
outflow winds (~30% chance of >30 kts) that make it to the
terminals. However, the timing and magnitude of outflows are
uncertain at this point and have not been reflected in the TAFs for
now. Otherwise, SCT-BKN mid/high clouds will continue throughout the
period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at KIPL will favor the west throughout the next 24 hours with
extended periods of light and variable winds. At KBLH, directions
will vary between the N and S, becoming light and variable at times.
A light shower or sprinkle will be possible at KBLH going into the
overnight period, which may lead to some erratic wind directions.
Otherwise, SCT-BKN mid/high clouds will give way to mostly clear
skies overnight.

&&

.FIRE WEATHER...
A weak weather system passing through Arizona today will again
bring high based showers and isolated thunderstorms over higher
terrain areas, mainly across eastern Arizona. The main potential
impact is expected to be gusty erratic outflow winds which could
extend as far west as the Phoenix area. Otherwise, look for
continued hot temperatures, afternoon breeziness and MinRHs around
15% over the lower deserts to 20-30% over Gila Co. Drier
conditions will filter in starting Friday ending any rain chances
and lowering MinRHs closer to 10% over the lower deserts. The
combination of dry fine fuels, continued above normal
temperatures, low RHs, and afternoon breezes could create elevated
fire danger conditions into early next week.

&&

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

$$

DISCUSSION...Kuhlman
AVIATION...Smith
FIRE WEATHER...Kuhlman