Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 272114

Area Forecast Discussion
National Weather Service Phoenix AZ
214 PM MST SAT AUG 27 2016

A unusually strong low pressure system for this time of year will
move across northern Arizona today and Sunday, where shower and
thunderstorm activity will be most widespread. For southern Arizona,
including the Phoenix area, a stray shower or storm is possible but
most likely conditions will remain dry. The low pressure system will
move eastward by late Sunday setting up a mostly dry and warm week.


Upper level low still remains northwest of our area this afternoon.
Mid-level push of dry air has cleared the AZ-NM border, leaving just
the parent low to deal with. The dry air on the southern periphery of
the low is mixing down, reflected in surface dew point values in the
30s and 40s roughly along and south of I-10. Objective analysis still
showing positive instability values around Mohave County this
afternoon. However, trends on visible satellite are not particularly
encouraging. Earlier convection west of Las Vegas did not attain much
strength, despite being near the center of the cold pool. Fairly
muted cu is noted north of I-10 where some moisture remains, and last
few frames of VIS along with MRMS radar data show some showers trying
to establish themselves in the Yavapai/Southern Mohave Counties area.
Will maintain heightened PoPs in that area for this afternoon/evening
but generally should be a quiet evening. Appears even chance for
outflow winds is not that high.

For the remainder of the week the upper level pattern will continue
to favor troughing along the West Coast. Sunday/Monday will still be
relatively quiet in the wake of today`s system, then some return flow
seems likely as a broader troughing takes hold to our west. With this
pattern, will be a bit tricky to nail down any particular day where
rain chances will be notably higher as we`ll need to watch for a push
of moisture and mid-level low come out of northern Mexico then hitch
a ride north in the southwest flow. That could be Wed/Thu based on
your flavor of model, but likely the best guess at this point
checking GEFS output.

Toward the end of the forecast period (next weekend), trough may
deepen further and really give a big eastward push to our monsoon
moisture plume. If that happens, quiet weather will really take hold.



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

Upper level low centered over the Arizona Strip at 21Z will slowly
drift eastward. Drier moving into southern AZ will keep storm
activity well north and northwest of metro Phoenix. There is an
outside possibility of outflow from very distant storms reaching the
metro area but likelihood too low to reflect in the TAFs.
Cumulus/altocumulus (bases AOA FL100) will diminish after sunset.
Expect light and variable surface winds the rest of the afternoon and
evening (favoring northerly component) before transitioning to
downvalley/drainage pattern after 03Z.

Southeast California/Southwest Arizona including KIPL and KBLH:

A stray thunderstorm or two may develop over La Paz County before
the evening is over. Too little coverage to reflect in KBLH
TAF. Surface winds will favor northeast directions the rest of the
afternoon before transitioning to light and variable winds
this evening (favoring southerly component). Cumulus/altocumulus
(bases AOA FL100) will dissipate after sunset.

Aviation Discussion not updated for amended TAFs.



Monday through Friday:

Chances for convective activity and wetting rains will remain mainly
confined to the higher terrain well north and east of Phoenix Monday
and Tuesday, with dry conditions prevailing across the lower
elevations. A modest increase in convective activity can be expected
from Wednesday through Friday across south-central AZ but still dry
for southwest Arizona and southeast California. Increasing westerly
flow aloft will then push drier air into most of the region next
weekend. Humidity trends will follow those of rain chances. No
significant winds expected at this time.


Spotters should follow standard reporting procedures.




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