359
FXUS65 KPSR 292312
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
410 PM MST Tue Sep 29 2020

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Dry conditions and clear skies will continue this week as strong
high pressure remains entrenched across the Western United States.
Temperatures will remain above normal through the period with lower
desert highs generally topping out between 100 and 105 degrees most
days through the end of the week. Slightly cooler temperatures are
possible early next week with high falling back to the low 100s.

&&

.DISCUSSION...
The strong upper level high is maintaining a very high amplitude
pattern with the very elongated ridge extending from the W coast of
Canada to SE AZ and and N-central MX. With the pronounced blocking
pattern in place, even the E-central US longwave is moving very
slow. The weak cold front that pushed west across the region last
night helped produce some locally gusty winds mostly in the teens
for the second half of the morning and early afternoon. As expected,
adiabatic downslope warming off the eastern high terrain mitigated
any substantial cooling from the modest supply of cooler air across
the region. However, at least the highs today will still manage to
top out a few degrees lower than yesterday in the upper 90s to low
100s in Phoenix and the lower deserts. Meanwhile the lingering
gradient winds are rapidly dieing off the system washes out.

There is very little change forecast in the position of the large
blocking ridge over the Western and Southwest US through late this
week. As a result a modest warming trend is likely with highs
pushing up into the mid 100s for Wednesday through Friday and a
couple of degrees warmer in far western areas. However there is
moderate to good confidence that highs will stay slightly below
records with mostly moderate heat risk being the main impact.
Although unlikely, a slight chance of isolated high heat risk can
not be completely ruled out.

For the weekend the Cluster ensembles show some slight east-west
repositioning of the ridge followed by broad reinforcement of the
ridge well north of the region with slight weakening across the
Southwest. As a result a slight cooling trend is possible beginning
late this weekend and early next week when the ridge retrogrades and
continues to slightly weaken. This may help highs to fall back to
the low 100s.

&&

.AVIATION...Updated at 2310Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Trends in winds will be the only weather challenge through Wednesday
afternoon under clear skies. While highly variable directions are
common in the Phoenix metro late this afternoon, there should be a
general tendency for some sort of light westerly component through
much of the evening. Confidence is good that east winds will settle
back into place by midnight, then experience a more definitive
switch to westerly early/mid Wednesday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
No significant weather issues through Wednesday afternoon under
clear skies. Winds will mostly favor some sort of N/NW component
through Wednesday, though prolonged periods of variability are also
likely.

&&

.FIRE WEATHER...
Friday through Tuesday:
Dry conditions and above normal temperatures will continue through
the period as strong high pressure remains in place across the
region. Highs will mostly range from 100-106 degrees under clear to
mostly clear skies. Daily minimum RHs will remain low at less than
than 10% for most days. Overnight max RH recoveries will be
generally between 20-25% in most places. Winds will remain mostly
light through the period with a bit of afternoon breeziness for the
weekend.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

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

&&

$$

DISCUSSION...Sawtelle
AVIATION...MO
FIRE WEATHER...Sawtelle/Kuhlman

NWS PSR Office Area Forecast Discussion