Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
300 PM MST Monday Nov 30 2015
Synopsis...below normal temperatures will continue tonight...with
some Lower Desert areas dipping below freezing. A warming trend is
expected Wednesday and Thursday as a ridge of high pressure builds
over the region. Somewhat cooler conditions are anticipated next
weekend but still near normal. Breezy conditions can be expected
from time to time as well.
Tonight through Thursday...
A large high pressure system is forecast to build into the region
from the west this period. Nearly cloudless skies and very dry air
will result in another unseasonably cold Tuesday morning...then
temperatures start to warm the remainder of the week under high
pressure. The large regional high pressure system will be
transitory this week...ahead of another Pacific trough forecast to
move into the western states Friday and Saturday. Therefore no
weather problems are expected through Thursday.
Friday and Saturday...
As mentioned above...another Pacific low pressure system...but a
fast mover...will approach Arizona on Friday...then move into the state
Saturday morning. Models forecast this system to be dry and
breezy...however there may be more low level moisture into southern
Arizona than models forecast. For example...by Wednesday evening as the cold
front approaches within 600 miles of the central California coast...a long
700 mile fetch of gale force winds develop ahead and behind the cold
front. An extensive area of rough and white capped seas should
mechanically lift some appreciable boundary layer moisture into the
frontal zone which has the potential to sweep into southern Arizona late
Friday night...with perhaps a slight chance of showers south and
east of Phoenix on Saturday. Again...current models are very dry for
Also...the European model is a little deeper with this trough over Arizona
by Saturday morning as opposed to the GFS. The earlier GFS model was
identical to the European. We believe the European model may be more
correct due to wavelength considerations across the Pacific...and a
minor blocking system over the eastern U.S. These conditions should
track the approaching system a little farther south into Arizona per the
The warmest day in southeast California and the Colorado River will be
Thursday ahead of the front...before the frontal passage late in the
day. The warmest day in south central Arizona including Phoenix will be
Friday. A regional Post frontal cool day is expected Saturday.
Sunday and Monday...
Another high pressure system is forecast to build into the region
this period for mostly clear skies and slightly warmer days.
south-central Arizona including kphx...kiwa...and ksdl...
southeast California/southwest Arizona including kipl and kblh...
Clear/mostly clear skies and light diurnally driven winds are
forecast at all sites through at least Tuesday morning.
Aviation discussion not updated for amended tafs.
Wednesday through Sunday...
temperatures will gradually warm from Wednesday into the end of the
week but humidities will remain low. A fast moving trough will move
through northern Arizona Saturday although the only impact appears to
be a slight increase in cloud cover and slightly increased
winds...but no precipitation. Following this trough...temperatures
will retreat back to near normal for early December.
Spotter information statement...
spotters are encouraged to report based on Standard operating
Visit US on facebook...twitter...and at weather.Gov/Phoenix