Heat in Arizona, September 9, 2016

Area Forecast Discussion
National Weather Service Phoenix AZ
917 AM MST FRI SEP 9 2016

.SYNOPSIS...
A drier airmass will move into the region with thunderstorm chances
pushing into far eastern Arizona through Saturday. However, better
moisture will head northward again across the eastern half of
Arizona late in the weekend through the middle of next week. This
will renew afternoon shower and thunderstorm chances most days over
the eastern half of the state.

&&

.DISCUSSION...
Latest satellite imagery shows clear skies across the Desert
Southwest with southwesterly flow between a closed low off the Baja
Peninsula and an anticyclone across Sonora. Despite the presence of
ample low-level moisture (surface dewpoints in the upper 50s and
lower 60s), morning sounding from Phoenix shows warm and drier air
aloft associated with the building ridge. Consequently all models
show no potential for afternoon convection. Near normal temperatures
are anticipated this afternoon. Forecast remains on track and no
significant updates are anticipated this morning.

&&

.PREVIOUS DISCUSSION...
Rather similar conditions in store for Saturday, low to zero PoPs
and seasonal temperatures.

By Sunday, moisture will return to the region from the south as an
area of low pressure sets up off the Baja Coast and high pressure
builds over Arizona and points east. This will create broad
southerly laminar flow up through the Gulf of California. Monsoonal
moisture will spread into the region as a result, maintaining
elevated humidities and the usually diurnally driven storm chances
for the mountainous areas and slight chances for some of the desert
locales at least through Tuesday. 850mb dewpoints hover around
Monsoonal levels (generally 8C) through Tuesday before drying is
forecast to transition into the area as a deeper trough builds out of
the Great Basin and increases dry advection off the Pacific. There
is a slight chance an isolated thunderstorm will develop on the
lower deserts near Phoenix and Casa Grande from convective outflows.
Otherwise the western portions of our forecast area, i.e. southeast
CA and southwest AZ should be dry. Current forecast package has PoPs
peaking Monday-Tuesday AM.

Enough moisture will linger across the eastern portions of Arizona to
continue at least slight chances for the rest of the week. Far
western AZ and southeast CA deserts will stay under mostly clear
skies and with a draw down of moisture levels, see an increase in the
diurnal curves with mild daytime temps around the century mark and
pleasant morning lows. At or below normal temperatures will reign
over forecast area by the middle of next week under southwest flow
driven by upper troughing to our northwest.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL:

Drier air filtering into the region from the west will keep skies
mostly clear at all of the PHX area terminals through the daylight
hours today. Some high cirrus clouds (coverage mainly in the FEW-
SCT range) may overspread the region from late this afternoon into
early Saturday. Winds to mainly follow typical diurnal trends, but
with afternoon westerly winds persisting later into the evening than
usual.

Southeast California/Southwest Arizona including KIPL and KBLH:

High pressure aloft and a dry airmass to keep skies mainly clear
through the TAF period. Winds to remain mainly out of a southerly
direction at KBLH. KIPL to see mainly southerly winds as well, except
for a period of westerly sundowner winds this evening.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Sunday through Thursday...

Persistent low pressure along the West Coast will turn the flow
aloft more southerly Sunday and Monday allowing a bit of monsoon
moisture to move back northward into South-Central AZ. Scattered
thunderstorms will return to the higher terrain east of Phoenix while
isolated showers/storms return to the lower deserts. A turn to more
westerly flow during the Tuesday-Thursday period will begin to push
the moisture/storms back to the east into extreme eastern AZ/NM.
Minimum humidities in the 15-35 percent range (highest extreme east)
Sunday and Monday to drop into the 10-30 percent range from Tuesday
into Thursday, with good to excellent overnight recoveries. Outside
of any thunderstorms, winds will remain mainly on the light side with
some gustiness along and west of the Colorado River.

&&

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

&&

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

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DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Nolte
AVIATION...Percha
FIRE WEATHER...Percha