Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 281626

Area Forecast Discussion
National Weather Service Phoenix AZ
925 AM MST SUN AUG 28 2016

A drier and cooler airmass will spread across the region into Monday
with temperatures near to slightly below normal. Moisture will begin
to return through southeast Arizona during the middle and end of the
week with higher humidity values building across the area. Along
with warmer temperatures, afternoon thunderstorm activity initially
confined to the eastern Arizona mountains may begin to descend
towards lower elevation communities.


A well defined circulation center and vorticity maximum were
spinning across NE AZ this morning and will slowly eject into New
Mexico with its attendant cold core this afternoon. Midlevel
instability and forced ascent were evident in satellite imagery
ahead of this feature in far eastern AZ with dry subsident flow
predominating through the bulk of the forecast area. 12Z regional
sounding data depicted the result of this contradictory monsoon flow
pattern with sfc-H7 mixing ratios plummeting to only 5 g/kg while
total column PWATs of 0.67in have fallen below the historical 10th
percentile for the day.

Therefore, other than a stray shower clipping far eastern Gila
County later this afternoon (as occasionally hinted at by several
HRRR iterations), essentially no chance of rain (much less
appreciable cloud cover) exists for the remainder of the day. This
pattern will continue to hold through Monday, albeit with slightly
higher heights aloft resulting in warmer temperatures. Given current
observational trends of temperatures not terribly different than
Saturday morning, trimmed a degree or two from the forecast highs
despite also cutting cloud cover forecasts yielding full daytime
insolation. All in all, quite a pleasant late August day considering
the alternatives for this time of year.


/453 AM MST SUN AUG 28 2016/
Tuesday through Saturday...
Models continue the trend moving a
significant amount of monsoon moisture back into the southeast
quarter of Arizona from old and New Mexico. This will return a
general threat of afternoon thunderstorm activity to the mountains
northeast through southeast of Phoenix.

There might be a mid week day where a threat of thunderstorms could
encroach on the lower deserts in the vicinity Phoenix and Casa
Grande, or on south central deserts either Wed or Thu. However its
hard to tell because recent medium range model forecasts of the
upper level kinematic flow has been way off. Therefore the forecast
period Tuesday through Saturday will focus most of the convective
threats in mountains east of Phoenix.


South-Central Arizona Including KPHX, KIWA, and KSDL:
No aviation weather impacts expected at the Phoenix terminals through
Monday. Shower and thunderstorm activity this afternoon will likely
remain confined to eastern Arizona. At the terminals, winds will
follow diurnal tendencies with speeds lighter than normal.

Southeast California/Southwest Arizona including KIPL and KBLH:
Mainly clear skies and lighter than normal winds will prevail at

Aviation Discussion not updated for amended TAFs.


Tuesday through Saturday:
Chances for convective activity and wetting rains will remain mainly
confined to the higher terrain well north and east of Phoenix Monday
and Tuesday, with dry conditions prevailing across the lower
elevations. A modest increase in convective activity can be expected
from Wednesday through Friday across south-central AZ but still dry
for southwest Arizona and southeast California. Increasing westerly
flow aloft will then push drier air into most of the region next
weekend. Humidity trends will follow those of rain chances. No
significant winds expected at this time.


Spotter reports will not be needed through Monday.





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