Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 230502

Area Forecast Discussion
National Weather Service Phoenix AZ
1000 PM MST FRI JUL 22 2016

...Updated aviation...

Seasonably hot weather will continue through Saturday with
temperatures reaching excessive levels and potentially becoming
deadly. Temperatures will moderate slightly Sunday, but still remain
fairly hot through next week as thunderstorm chances increase. The
elevated storm chances will continue through much of the week.


A few scattered showers will prevail for the remainder of the evening,
but with most of the activity in the higher terrain east of Phoenix as
well as along an outflow boundary NW of the metro. Cannot rule out the
possibility of additional convection along any outflows near southern
Gila County as well.  The Phoenix 00Z sounding indicates minimal Mixed
Layer CAPE and plenty of CIN so any storms at lower elevations are
quite unlikely. Therefore, only adjusted POPs for ongoing convective


Hot hot hot. That is what we`re expecting through Saturday across the
lower deserts. Convective activity will remain muted Saturday with
broad-scale subsidence. Despite precipitable water values in excess
of 1", warming mid-level temperatures will mean little if any
instability and what does develop will be tall/skinny yielding weak

As we head into Sunday, the adjustment of the upper level (250 mb)
flow pattern still looks on track per EC/GFS ensemble solutions. It
still appears that the mid-level anti-cyclone will take-up a position
eventually over the Great Basin, which will allow deep easterly flow
to stretch up the Rio Grande Valley and across southern New
Mexico/Arizona/California. Meanwhile, convection along the Sierra
Madre Occidental will be increasing and edging northward with each
passing day. This all points to boundary layer mixing ratio values
climb back into the 9-10 g/kg range perhaps as early as Sunday but
definitely by Monday and remain there through the week. This pattern
opens the door for more instability to develop, the transversing of
easterly waves, and favorable propagation vectors to promote storm
movement off the mountains and into the lower deserts. GEFS
Reforecast PoPs show a steady upward trend next week. Starting to see
some deterministic/ensemble members depicting EPAC cyclone activity
developing and skirting the Baja Peninsula, which would result in a
further increase of moisture levels toward the end of next week.


South-Central Arizona Including KPHX, KIWA, and KSDL:
Timing wind shifts will be the primary aviation concern through
Saturday afternoon with only Few-Sct mid and high clouds. Friday
evening northerly outflow sfc winds were beginning to veer to an
easterly direction, though some period of variability is likely
before settling on a due east direction late tonight. Sfc winds
should shift to a westerly component somewhat earlier Saturday late
morning/early afternoon with little chance of any outflow boundaries
nearing terminal sites during the afternoon or evening hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
Little to no aviation impacts through Saturday evening under mostly
clear skies. Sfc winds will favor a south to southeast direction,
though some periods of variability will be likely around the sunrise
hours. A few stronger afternoon gusts will be possible, but not
likely to exceed a 20-25kt threshold.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday...
High pressure aloft will remain strong on Sunday keeping high
temperatures mostly at or above 110 degrees over the lower deserts,
however flow aloft becomes a bit more southeast allowing some
moisture to work westward and into the central deserts during the
day. As such, there will be a slight chance for afternoon and evening
thunderstorms east of the lower Colorado River valley on Sunday and
humidity levels climb into the 15 to 20 percent ballpark over most
of the lower deserts.

Increasing easterly flow Monday through Thursday will allow
increasing moisture to spread westward, reaching into southeast
California. There will be a steady increase in thunderstorm coverage
day to day with a 15 to 25 percent chance across the deserts by
Wednesday and up to 40 percent in the mountains east of Phoenix.
Humidity levels will steadily increase and most of the deserts will
range from 18 to 24 percent each day and RH values 25 to 40 percent
over the higher terrain east of Phoenix. Winds will be locally
breezy Sunday into Monday, favoring the south over the western
deserts, and the southwest to west across south central Arizona.
During the middle of the week winds will be lighter, again favoring
south to southwest directions most places.


Spotter activation is not expected.


AZ...Excessive Heat Warning until midnight MST Saturday night for

CA...Excessive Heat Warning until midnight PDT Saturday night for



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