Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 241109

Area Forecast Discussion
National Weather Service Phoenix AZ
409 AM MST WED AUG 24 2016

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


A drier and more stable airmass will slowly move into the region
through Thursday. However a slight chance of afternoon and evening
thunderstorms will remain over the mountains north through east of
Phoenix. On Friday, a surge of monsoon moisture will return to
southern Arizona resulting in a threat of afternoon and evening
thunderstorms over portions of south central Arizona, while
southwest Arizona and southeast California remain dry and stable. A
strong high pressure system will subsequently build into the region
Sunday through the middle of next week for dry weather and much
warmer afternoon temperatures.


TODAY THROUGH THURSDAY...The nearly stationary and atypical trof
that was quasi-stationary over the Mohave Desert and northwest
Arizona was finally moving out of the region this morning. More
stable northwesterly flow aloft will increase over our forecast
area, southeast CA to south central AZ today and Thursday, along
with thinning monsoon moisture. However there is still a slight
chance of late afternoon and early evening mtn thunderstorms over
southern Gila County today and Thursday. Afternoon temperatures will
also warm the next few days.

Friday and Saturday...Another unusual trof is forecast to slowly
deepen into Utah and far northern AZ Friday and Saturday. This trof
has origins in western Canada. What is so unusual about this system
is its vertical structure by late Friday. For example, the 300/250
mb trof is over Salt Lake City. Its 500 circulation center is
progged to be just northwest of Las Vegas, and the 850/700
circulation center develops along the San Diego coast. Its very
unusual to have a vertical trof axis tilted toward the northeast.

Since the 850/700 mb circulation center will develop along the San
Diego coast, increasing low level south wind will import monsoon
moisture back into AZ, almost surging Friday afternoon and night. At
the moment it appears that any thunderstorm activity will be
thermodynamically driven, i.e. heat of the day storms mainly in
south central AZ. A chance of afternoon convection will develop over
the mountains with outflows possibly triggering secondary desert
convection by evening. Ditto on Saturday.

Sunday through Wednesday...A strong high pressure system is forecast
to build into the region from the southwest direction. The monsoon
moisture will be pushed to the other side of the Mexican border,
wavering across far southeast AZ at times. Much warmer afternoon
temperatures are also forecast, between 107 and 111 on the lower


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

Although moisture will continue to decrease through the TAF period,
a very small chance of thunderstorms still exists over the higher
terrain north and east of Phoenix terminals today. Thus, an outflow
pushing it`s way towards the terminals this afternoon from the north
or east is not out of the question. However, low confidence in
temporal and areal coverage PRECLUDES mention in 12Z TAF. Outside of
any thunderstorm outflows, winds will remain aob 10 kts with upslope
winds initiating around 17Z before turning downslope around 03z.
Skies will remain mostly clear with a few high clouds aoa 10kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
Skies will remain mostly clear through the TAF period, with winds
primarily out of the south-southwest with a few afternoon gusts up
to 15 kts.

Aviation Discussion not updated for amended TAFs.



Friday through Tuesday...
Southerly flow over the region will allow some monsoon moisture to
return on Friday and Saturday. This increase in monsoon moisture will
lead to an increase in convective activity over South-Central AZ,
with the best chances for wetting rains over the higher terrain east
of Phoenix. On Sunday, a drying trend will commence, with minimum
humidities expected to drop from 15-45 percent on Sunday to 10-35
percent on Tuesday. Winds each day will favor a south to southwest
direction during the day with the gustiest winds expected on Friday,
especially along the Colorado River Valley. In this area sustained
winds will be up to 15 mph with gusts up to 25 mph.


Spotters should follow standard reporting procedures.




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