Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
843 PM MST sun Nov 29 2015
cool but dry weather will continue across the southwest states into
early this week. Some lower elevation desert spots will dip below
freezing during the morning hours through Tuesday...with Monday
likely the coldest. Warmer weather will arrive starting middle week and
likely lasting into next weekend. The dry weather pattern is
expected to continue through the coming week.
latest WV imagery shows drier air advecting into the Desert Southwest
around the persistent upper low across the intermountain west. Skies
have cleared rapidly this evening and with winds continuing to
subside...ideal radiational cooling conditions are anticipated
overnight. Coldest night of the season is anticipated for many
locations including the Phoenix area. Forecast low of 41 degrees in
Phoenix would be the coldest reading since January 5th. Minor
adjustments were made to the forecast...mainly for sky and hourly
temperatures. Otherwise...the forecast remains on track.
Previous discussion... short term forecast concern shifts to what
the combination of calm winds and clear skies will do with the
already cold airmass situated over The Four Corners...and where
freezing and near-freezing temperatures will result. A degree or two
of additional cold air advection airmass cooling from the entrenched Great Basin low
will support another morning with chilly temperatures. Most urbanized
areas...while seeing unseasonably chilly temperatures...appear to
stay a few degrees above the freezing mark for tomorrow morning.
However...the outlying desert locales including Casa
Grande...Quartzsite...Bouse in La Paz and some of the lowest
elevations across Yuma County have the potential to see observation an hour
or two at or just below the freezing mark. While the handful of
forecast points are not indicating an overwhelming widespread
freezing signal...given data scarcity and reports from the limited
stations out in those areas...went ahead and issued a Special Weather
Statement for the outlying/peripheral desert locales in La Paz...Yuma
and northwest Pinal counties for the near or at freezing temperatures
expected by Monday am. The upper low...responsible for funneling the
cooler air from the north into the region...will finally start to
move eastward Sunday night into Monday. A slow warming trend and atmo
thickness increase will result...but only minimally allowing for
continued cool mornings for Tuesday and still below normal daytime
A warming trend will finally pick up traction starting Wednesday as
the pattern shifts enough to allow a fairly substantial Pacific
Ridge to pass through the western United States. Highs should
rebound back to near normals on Wednesday and even climb a few
degrees above normal for late in the work week. Dry air will persist
across the region through the entire week with little sign of any
change in moisture levels. This will allow for clear to mostly clear
skies each day and still rather chilly overnight lows...but most
locations will keep lows in the 40s.
Models have been advertising some sort of a trough or upper level
low affecting the Desert Southwest Friday night into Saturday and
the past couple model runs have been backing off on the strength of
the trough and potential impacts. Timing still looks to the
same...but for now it seems little to no moisture will be advected
into the region and thus only around 10 percent probability of precipitation remain across
far eastern Gila County for Saturday morning. The trough will at
least bring some stronger winds...especially down the lower Colorado
River valley...but not looking like anything near advisory levels.
Temperatures will dip a few degrees on Saturday with the trough
passage...but likely warm back up on Sunday as another Pacific Ridge
moves into the Desert Southwest.
south-central Arizona including kphx...kiwa...and ksdl...
southeast California/southwest Arizona including kipl and kblh...
Mostly clear skies across the area overnight into Monday morning...
with few clouds at or above 12kft lingering until 02z this evening...mainly
over south-central Arizona. Expect light winds generally less than
10kt at all taf sites through at least 18z Monday.
Aviation discussion not updated for amended tafs.
Tuesday through Saturday...
high pressure will slowly build into the region through Thursday
leading to a warming trend. A low pressure system moves through the
region Friday and Saturday. Minimum humidities will be in the low-
middle teens through Thursday before increasing a bit Friday and
Saturday. Breezy conditions can be expected at times...mainly over
southeast California and southwest Arizona...favoring northerly
Spotter information statement...
spotters are encouraged to report based on Standard operating
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