FXUS65 KPSR 170831

Area Forecast Discussion
National Weather Service Phoenix AZ
130 AM MST Sat Nov 17 2018

High pressure will remain stationed over the area through early next
week resulting in temperatures near or just below the seasonal
average. Dry conditions and light winds will also prevail through
Monday, before a mostly dry storm system moves through the region
during the middle part of next week.


Early this morning, dry west/northwest flow aloft was in place
across Arizona as seen by latest plot and raob data. IR imagery
depicted variable amounts of high cloud moving through the flow but
overall skies were mostly clear over the deserts. Surface dewpoints
remained rather low, ranging from the teens to low 30s over the
lower deserts. For the next few days there will be very little
change in the forecast, as flat upper ridging and dry west to
northwest flow aloft will persist. Don't expect much in terms of
temperature changes day to day with readings remaining near seasonal
normals as desert highs stay largely in the mid 70s.

The first shot at any weather across the area will be next Tuesday;
operational GFS and ECMWF as well as GEFS ensembles consistently
paint the picture of an upper low off the California coast that will
rapidly open up and move inland across southern California and
Arizona on Tuesday. This is advertised as a very dry system; most of
the moisture will remain aloft and above the 700mb level. We will
see increasing mid and high clouds but precip chances - even over
the higher terrain - will stay negligible despite a modest amount of
QG forcing as the low moves across. The low will do little to cool
us down; highs will stay in the mid 70s over much of the desert
despite the increasing cloud cover.

For the latter half of next week, conditions become slightly more
unsettled but overall we should continue to see a rather dry pattern
as fast moving, progressive zonal flow affects the western CONUS.
Model guidance - especially the GEFS ensemble members - have trouble
resolving the various short waves moving inland and through the area
in this fast flow. Best bet at the moment is for a weak short wave
to pass through the state on Thursday, bringing a slight chance of a
shower to the higher terrain mainly east of Phoenix. Otherwise we
will mostly see variable mid/high clouds during the period and
temperatures trending slightly downward with time. By next Friday
many of the lower deserts will see highs in the upper 60s to lower
70s with Phoenix expected to reach 71 degrees. For now uncertainty
is the word with the latter portion of the extended forecast.


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

Very weak weather disturbances embedded in light westerly to
northwesterly flow aloft to continue to push SCT-BKN high cirrus
cloud decks over the entire region through the TAF period. Strong
high pressure at the sfc to keep winds quite light through the TAF
period, with directions mainly following typical diurnal trends.
Extended periods of light/variable winds are likely to occur at all
of the TAF sites as well.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday: For the most part, dry westerly flow aloft
will dominate the desert southwest over the next 5 days keeping
conditions dry. There will be a couple of fast moving weather
systems pass through the districts but they will bring little if any
chance for precipitation; the system on Thursday may be a bit wetter
and could result in a few showers over the higher terrain east of
Phoenix but little else. High temperatures will fluctuate slightly
day to day but generally remain near seasonal normals with desert
highs staying in the low to mid 70s for the most part. Look for
minimum RH values in the deserts mostly 15 to 25 percent through
Tuesday, then climbing into the 20 to 35 percent ballpark later in
the period, as the stronger weather system moves through the area.
Winds will be on the light side each day only weakly following
typical diurnal tendencies.


Spotters should follow standard reporting procedures.





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