Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 251049

Area Forecast Discussion
National Weather Service Phoenix AZ
349 AM MST Tue Jul 25 2017

.UPDATE...Updated aviation discussion.


Much drier air begins moving into the region today for a
significant decrease in storm chances. Expect even less storm
activity Wednesday. With less clouds and humidity, temperatures
will increase...climbing a bit above normal by Thursday. The
drying trend will begin to reverse itself on Thursday with storm
chances gradually increasing from east to west through the
weekend. Similarly, high temperatures decrease as well...most
noticeably over south-central Arizona.


Today and Wednesday...
Yesterday`s wave feature which aided the convection has now
shifted into the Great Basin. However, there appears to be a weak
trailing short wave over southwest Arizona as evident in the
models. Hard to see in satellite imagery but there looks to be a
very subtle darkening signature in water vapor. It may have also
aided storm development last evening near Gila Bend. This
perturbation may be the reason why multiple runs of the HRRR
depict redevelopment of convection later today focusing on Mohave
and Yavapai Counties (brushing La Paz County). Other hi-res models
are not as aggressive with this idea. There are some indications
that a couple of stray showers will also pass through northern
Maricopa County (including metro Phoenix) this afternoon. However,
not looking at anything remotely close to what we`ve had the past
couple days. This is due large to decreasing moisture
availability as drier air near and west of the Baja starts getting
advected into the area. With less cloudiness and shower activity
today, highs will be warmer today.

Wednesday looks to be a "low grade" Monsoon day with some
additional drying and less than ideal south-southwesterly steering
flow. Warmer temps as well but very close to normal.

Thursday through Monday...
With less troughing to the northwest, the ridge shifts northward
a little bit during the latter part of the workweek leading to
more of an easterly component to the steering flow which is
climatologically more favorable for moist advection as well as
advection of storms from higher terrain into our forecast area.
Over the weekend and early next week, GFS and ECMWF depict
amplification of the flow pattern over North America such that
steering flow becomes southeasterly (which is also
climatologically favorable) with moisture spreading into southeast
CA. A couple of other factors that may be in the mix are another
inverted trough passing through similarly to what we`ve just had.
The other item is a tropical storm depicted to track south and
west of Baja which in it`s passing could aid moist advection up
the Gulf of California. Looks a bit far south though to have a
classic Gulf surge effect. Otherwise, it looks like it will stay
far away and have no direct impact. So in a nutshell, we resume a
gradual uptrend in PoPs from east to west. Likewise, temps begin
modestly decreasing from east to west on Friday.


South-Central Arizona including KPHX, KIWA, and KSDL:

A rather quiet period appears to be in store as drier/more stable
air moves into the region. Winds will remain light and out of the
east before becoming westerly by mid-afternoon. Ceilings will be
sct-bkn mostly aoa 10kft. Storm development today will likely
remain well to the north and east of the taf sites.

Southeast California/Southwest Arizona including KIPL and KBLH:

A rather quiet period across SE CA, with sct-bkn mid/high level
cigs prevailing across this region as well. Winds to remain mainly
out of a southeasterly direction at KIPL and a southerly
direction at KBLH through the taf period.

Aviation discussion not updated for amended TAFs.


Thursday through Monday:
Humidities and storm chances begin to increase Thursday with
chances reaching southeast California by Saturday. Temperatures
will be near normal Wednesday and Thursday (a bit above normal
near and west of the Lower Colorado River Valley) before beginning
to decrease late this week. Apart from thunderstorms, winds will
follow familiar warm season patterns.


Spotters should follow standard reporting procedures.




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