Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
1009 am MST sun Dec 21 2014
high pressure off the West Coast will result in near normal
temperatures with varying amounts of high clouds through the middle
of next week. By Thursday...a fast moving storm system will move
through The Four Corners region...bringing slightly cooler
temperatures and increased cloudiness that will last through Friday.
Dry weather is expected next weekend with below normal temperatures.
infrared satellite imagery reveals high clouds continue to spill across
most of the western Continental U.S. This morning...as the eastern Pacific
Ridge continues to amplify off the West Coast. Regional upper air
plots indicate 582-588dm 500mb heights just off the Southern
California coast...with a rather potent 140-160kt upper level jet
punching across the Pacific northwest into the northern rockies. The
jet and attendant short wave trough is prognosticated to strengthen/deepen
as it begins to slide into the central Continental U.S./Northern plains later
this evening and Monday. Surface conditions across our County Warning Area are once
again cool and dry...but the cloud cover did keep temperatures up a few
degrees overnight compared to yesterday morning. Diurnal dew point
temperature trends have dipped slightly but will still hover in the 30s-40s
across our County Warning Area today...so daytime highs will top out a bit warmer...
in the upper 60s to low 70s across the Lower Desert elevations.
The offshore ridge will continue to strengthen through midweek...but
the ridge axis will remain offshore and cloud cover will be minimal.
Temperatures are expected to warm a few degrees Monday/Tuesday...
but not to the degree if ridge axis were to move overhead. Any
warming to temperatures Tuesday will probably be offset as a weak
backdoor cold front from the expanding central Continental U.S. Trough will
finally move into our forecast area. This front will be dry and
will result in slightly cooler temperatures and increased winds
across south central Arizona...with no chance of rain. The cooler
temperatures will remain in place through Wednesday.
Looking ahead to Thursday and beyond...models are back in agreement
once again indicating the presence of a longwave trough moving
through The Four Corners...just brushing parts of Arizona in the
process. Across the lower Arizona and southeast California deserts a trough of this
nature should have a minimal impact on our weather...slightly cooler
temperatures and increased cloudiness but that's about it. From
there...broad northwesterly flow is expected to prevail into next
south-central Arizona including kphx...kiwa...and ksdl...southeast
California and southwest Arizona...including kipl and kblh...
Expect periods of high clouds into Monday with north and northwest
flow aloft. Surface winds will be light...especially over
south-central Arizona...with somewhat more noticeable northerly
winds this afternoon over portions of southwest Arizona and
Aviation discussion not updated for amended tafs.
Tuesday through Saturday...
a weather system moving through The Rockies will lead to breezy to
windy conditions from the north and northeast on Tuesday. The system
will be dry and humidities will drop dramatically Tuesday afternoon.
The system will bring some modest cooling as well. Another episode
of enhanced winds is expected Thursday night and Friday as another
system moves through. It will have limited moisture and there is
only a very slight chance of precipitation for the higher terrain of
south-central Arizona on Friday.
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