Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 251154

Area Forecast Discussion
National Weather Service Phoenix AZ
454 AM MST Sun Jun 25 2017


High pressure will keep temperatures hot today and Monday. A chance
of afternoon thunderstorms will also return to the mountains of
eastern Arizona. A series of Pacific weather disturbances are
forecast to move into the western states north of Arizona Tuesday
through Saturday. Developing dry westerly winds will weaken the high
pressure system for cooler temperatures, and push most of the
moisture east and out of Arizona.



Today and Monday...

Significant boundary layer moisture from New Mexico continued to
push deeper into southeast AZ at 2 am this morning. Last evenings
weather Balloon soundings El Paso, Midland, and Chihuahua Mexico all
detected 850 mb southeast winds in the 15 to 25 knots range. In fact
low level moisture convergence along this moisture front fueled the
large Meso Scale Convective storm in far southern New Mexico last
evening. Perhaps outflow winds from this system in combination with
the synoptic scale back door low level easterly winds will send
appreciable humidity all the way to Phoenix this morning.

Models continue to forecast a weak upper level disturbance, at and
above the 300 mb level, to move into east and southeast AZ by
evening. This should lead to a larger area of convective threats,
including portions of our mountainous southern Gila County Zone east
of Phoenix. However enhanced 850/700 mb westerly flow, typical for
the month of June and is climatological, should help push most of
the boundary layer moisture on the south central deserts into the
mountains east and southeast of Phoenix. Therefore the only
convective threats in our forecast area, southeast CA to south
central AZ, will be in southern Gila County. One caveat though. If
large early evening convection develops closer to Tucson, there is a
possibility of gusty northward moving outflows and blowing dust on
the deserts between Phoenix and Casa Grande.

Following the Sunday evening upper level disturbance in southern AZ
a more anti-cyclonic flow regime at and above 300 mb will likely
stabilize the atmosphere over most of our forecast area Monday.
However weak upper level deformation is still forecast by the models
along the eastern AZ border where convective threats can be
expected. Otherwise partly cloudy skies, and dry and hot weather
will cover our forecast area Monday. The exception is a slight chance
of thunderstorms over the higher terrain of southern Gila County
bordering the White Mountains.

Very hot weather will continue Monday and with slightly hotter
temperature forecasts, The Excessive Heat Warning has been updated
to now cover all the lower deserts of southeast CA, and southwest and
south central AZ.

Tuesday through Saturday...

A series of weak Pacific disturbances are still forecast to move
into the western states mainly north of AZ this period. Resulting
dry westerly flow AZ will weaken the regionally strong high
pressure, and push most of the boundary layer moisture out of AZ
into New Mexico Tuesday, then into west Texas Wednesday through
Saturday.  As a result, cooler afternoon temperatures are forecast
along with mostly clear skies.


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

Persistence forecast with typical diurnal wind shifts and
afternoon breeziness today across the Phoenix area. Any
thunderstorm activity that develops during the late afternoon is
expected to remain confined to the higher terrain of Gila County.
However, there is a slight chance that an outflow boundary
propagating from the east or southeast could produce brief wind
gusts mid to late evening.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather impacts expected. Winds will retain a
southerly component at KIPL/KBLH with winds generally less than 10
to 15 kt.

Aviation discussion not updated for amended TAFs.


Tuesday through Saturday:

A high pressure system will remain over the southwest allowing
temperatures to continue to soar well above normal. Temperatures
will begin to decrease through the week as the high pressure weakens
and some moisture moves into the region. The moisture is primarily
moving into southeastern California/ southwestern Arizona and
eastern Arizona. The best chances for any thunderstorms will be
confined to the mountainous regions including the Rim and southern
Gila County. However, dry lightning will be a concern as the amount
of precipitation with any storm may be limited. Otherwise, minimum
relative humidity will be in the 8-12 percent range for desert
locations, a little higher over the higher terrain, and both with
meager overnight recoveries. Finally, winds look to be the strongest
Tuesday evening and into Wednesday with gusts up to 30 mph possible
though much of the area.



Record highs this week:

Date           Phoenix            Yuma
----           -------            ----
6/25         120 in 1990        119 in 1994
6/26         122 in 1990        122 in 1990


Spotters may be needed in southern Gila County on Sunday


AZ...Excessive Heat Warning until 8 PM MST /8 PM PDT/ Monday for

     Heat Advisory until 8 PM MST Monday for AZZ557-558.

CA...Excessive Heat Warning until 8 PM PDT Monday for CAZ560>570.



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