Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 180416

Area Forecast Discussion
National Weather Service Phoenix AZ
916 PM MST Thu Aug 17 2017

.UPDATE...Updated aviation discussion.


Relatively dry conditions will persist through Friday before a
gradual increase in moisture and storm chances begins over the
weekend. At this time, best chances of storms looks to be during
the first half of the next workweek. Anticipate temperatures to be
near normal.


Weak upper trough over the southwest CONUS extending off the
California Coast for southwesterly flow aloft. Deep moisture
remains south of us but not too far away (over northwest Mexico).
In fact, an MCS is still dissipating over the southern Gulf of
California (and adjacent land areas). The models initialized an
MCV associated with that feature. More distinct cyclonic
circulations include a weak upper low centered west of southern
Baja and another larger one centered near the far south Texas
coast. Meanwhile, a subtropical high is centered over the Gulf
Coast. Models continue to show the upper trough becoming a closed
low and the subtropical high migrating eastward leading to more
southerly flow and some moist advection over us. The moist
advection becomes more noticeable over the weekend. The MCV may
migrate into Arizona during this time as well. Both GFS and ECMWF
show peak moisture values on Tuesday before starting to trend
down from west to east on Wednesday then drop off more distinctly
on Thursday. Accordingly, there is a gradual uptrend in PoPs with
storm chances starting on the lower deserts of Arizona on Sunday
then expanding westward. However, at this time, conditions for our
forecast area overall are not looking overly impressive in terms
of storm activity. May not see more than one active night for any
given location in our forecast area through next Thursday.

Temperatures warm only slightly into Saturday before starting to
decline with more humidity and cloudiness around.


South-Central Arizona including KPHX, KIWA, and KSDL:
Winds have shifted out of the east/northeast at KPHX a bit earlier
than previously anticipated, and are expected to persist overnight
and into early Friday afternoon. Speeds should be light, less
then 7 kt, at area terminals. Clear skies will continue with
minimal aviation concerns.

Southeast California/Southwest Arizona including KIPL and KBLH:
Westerly winds overnight at KIPL will persist, before becoming
more variable in direction across all of southeast California.
Skies will remain clear.

Aviation discussion not updated for amended TAFs.


Sunday through Thursday:
Seasonably hot temperatures combined with moderate Monsoon
moisture will dominate the region resulting in a slight to
moderate chance of afternoon and evening T-storms, with the best
chances in the higher elevations of Gila county. However, modest
storm chances will work into the lower deserts of Arizona by early
in the week. A few of the stronger storms may produce only a
slight chance of wetting rain. Breezy southerly and southwesterly
winds near 10-15 mph with gusts to 20 mph can be expected from SE
CA to SW AZ by late afternoon and early evening each day through
Wednesday. With the increase in moisture, min RH values in the
12-18 percent range over the lower deserts on Sun will gradually
increase to the 17-24 percent range by Thu. Expect overnight
recoveries to be good to occasionally excellent.


Spotters should follow standard reporting procedures.




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