Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 090934

Area Forecast Discussion
National Weather Service Phoenix AZ
234 AM MST Fri Dec 9 2016

.UPDATE...Updated Aviation and Fire Weather Discussion.


Dry weather with seasonably comfortable temperatures will persist
through the weekend and into at least the middle of next week. Only
periods of passing high clouds will interrupt an otherwise beautiful
stretch of early winter weather while no precipitation will affect
communities into next week.


At 2 am this morning, flat upper ridging was building into the
desert southwest, with dry and subsident northwest flow in place
over Arizona and SE California per the latest plot and raob data. IR
imagery showed generally clear skies over eastern Arizona, with
another batch of high clouds headed our way from the west. Despite
the increase in high clouds today we should see temperatures
continue to warm as heights/thicknesses rise and the warmer lower
deserts will top out in the low 70s.

From this weekend into the latter portion of next week, we are not
looking at any significant changes to the weather pattern.
Operational model guidance such as the GFS and ECMWF as well as GEFS
ensemble members continue to depict a very zonal regime keeping dry
westerly flow aloft in place across the area. Progs keep the upper
jet axis pretty much north of Arizona through the period, with
anticyclonic shear and subsidence or at best weak UVV in place over
the deserts each day. With the storm track so far to our north, any
possible precip-producing short waves will remain to our north and
do little other than to temporarily thicken the mid and high clouds
that will be present during much of the forecast period. With the
fast zonal flow, it will be easy for high clouds to sweep in from
off the Pacific and overspread the deserts - they race in then race
back out, leaving partly cloudy skies during much of the period. One
possible period where mid/high clouds may be excessively thick will
be Saturday night into Sunday, as the upper jet drops south and just
north of the AZ border, and a fast moving wave cuts through the four
corners area bringing in quite a bit of mid to high level cloud
cover. We may see some virga at times Sunday but chances for
measurable rain are slim and POPs will stay in the single digits.
For the most part, temperatures will not change much day to day and
should remain near or several degrees above seasonal normals,
although depending on how thick the high clouds are, the
temperatures may be suppressed such as on Sunday. Look for desert
highs in the low to mid 70s on most days.

There does appear to be a change coming in the weather pattern but
it will likely arrive after the end of the current 7 day forecast
which will be next Friday into the following weekend. Although
spaghetti ensemble members are very jumbled, preponderance of
guidance suggests a deep trof will set up over the western CONUS by
next Friday, leading to a chance of showers, much cooler high
temperatures and the potential for some very strong winds especially
over the western deserts. We will be keeping a close eye on this
developing shift in the weather pattern in the days ahead.


South-Central Arizona including KPHX, KIWA, and KSDL:
There are no weather concerns for aviation. The winds will favor
typical diurnal patterns while remaining light through the TAF

Southeast California/Southwest Arizona including KIPL and KBLH:
There is little weather concerns for aviation as winds will remain
light while favoring diurnal patterns. There may be some directional
variability due to the light winds.

Aviation discussion not updated for amended TAFs.


Sunday through Thursday:
There are no significant fire weather concerns for the period.
Slightly above normal temperatures and mostly dry conditions are
will persist with high clouds moving across the area at times. Winds
each day will mostly stay on the light side with typical afternoon
breeziness favoring the southwest or west. Humidities will be
elevated through the five day period with minimum RH values mostly
between 20 and 30 percent each day with great recoveries.


Spotters activation will not be needed this week.




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