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fxus65 kpsr 210515 
afdpsr

Area forecast discussion
National Weather Service Phoenix Arizona
1015 PM MST Sat Jul 20 2019

Update...
updated aviation

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Synopsis...
dry and seasonably warm conditions will persist through Sunday with
only a limited chance of an isolated shower and thunderstorm across
high terrain areas. Moisture will increase during the first half of
the week providing better chances of thunderstorms and strong
outflow winds for the first half of the week across the lower
deserts and also including western areas. Warmer temperatures and
drier conditions will return late in the week and into next
weekend.

&&

Discussion...
satellite and WV imagery confirms the mainly clear and dry
conditions and the very sunny skies being observed across the area.
The upper air analysis show dry southwesterly and westerly flow
aloft just north of a weak mid level anticyclone over north baja and
east of a weak baggy offshore trough. An elevated moisture field was
also positioned over northwest Mexico with elevated 925 and 850 TD up to
the Arizona Borderland. Today's 12z phx sounding showed westerly to
southwesterly flow through the column with a mean west of only 5.4g/kg.
Expect dry and hot conditions to continue across the area through
Sunday with afternoon highs running near to slightly above normal
and only slight chances of thunderstorms for the eastern fringes of
Arizona.

On Sunday the ridge axis amplifies northward as the subtropical high
repositions over the 4-corners area. This allows a gradual increase
in low to mid level moisture and surface dewpoints from northwest mx
beginning this weekend. The moisture transport becomes even more
pronounced from Sunday night through Tuesday night across Arizona with
mean west over 12g/kg and precipitable water above or near 2 in., Including western
locales. Significant cape from Monday into midweek will also be in
place. The result will be our first significant thunderstorm chances
on Monday evening and Monday night. On Monday evening and night
models were in agreement on inverted upper level disturbances/vort
maxes moving west along the southern periphery of the high across
Sonora and S Arizona. As a result thunderstorms are forecast to trigger
first over far southeast to east Arizona from very late Monday afternoon to early
Monday evening. Teamwork between storm outflows from the southeast
and the disturbance(s) aloft progressing westward should allow
for a fair chance of at least some convective storms to develop
and push into the lower deserts and the Phoenix valley on Monday
night. Even locations along the I-8 corridor of SW Arizona and Imperial
cty will have a chance. A fair chance of dense blowing dust with
the outflows moving into the Pinal and Maricopa counties on Monday
evening ahead of the storms also exists.

The Monday night thunderstorms will also include significant storm
activity over Sonora which should induce a possible moisture surge
from the Gulf of California which will only help to continue to condition
the airmass across large portions of Arizona. This will allow for
pronounced storm development on Tuesday evening and night first
across the Mogollon Rim. These high country storms are expected
to send outflows southwest into the region ahead of them as they
progress downhill into the lower deserts. The path of Tuesday
night's activity could also favor west-northwest Maricopa cty westward to southeast
California including Imperial cty. The main impacts from early to midweek
storms will be areas of dense blowing dust, including at night,
and and some thunderstorm downburst wind damage to trees and
structures, etc. Although not expected as a widespread threat,
some isolated nuisance and flash flooding can not be completely ruled
out.

From Wednesday night to Thursday morning the mid level high center
shifts southwest across Arizona causing thunderstorm development to be
more focused in western areas including southeast California. From Thursday through
Saturday models show the ridge taking up residence over Arizona and the
western states. Storm development across the area will thus become
mitigated with east-NE Arizona becoming the favored area for the storms.
Temperatures will also warm up late this week although lingering
moisture from earlier in the week could help to keep temperatures
closer to 110-111 degrees instead of 114-117 degrees.

&&

Aviation...updated at 0515 UTC

South-central Arizona including kphx, kiwa, ksdl, and kdvt:
no significant aviation issues through Sunday night with only
periodic thicker cirrus debris decks across the region. West winds
should hold longer tonight with kphx likely not becoming light
easterly of even just light and variable for a few hours until after
sunrise. Confidence is good that a westerly component will resume
fairly quickly late Sunday morning. Lower confidence exists
regarding timing of gusty winds which may not form until late in the
afternoon, but linger well into the late evening.

Southeast California/southwest Arizona including kipl and kblh:
little aviation concern through Sunday night under increasing cirrus
cigs. Confidence is moderate that similar trends in wind directions
and speeds should repeat again Sunday afternoon and night as has
been experienced the past several days.

Aviation discussion not updated for amended tafs.

&&

Fire weather...
Tuesday through saturday:
temperatures will remain seasonably hot with a fair chance of
thunderstorms including western areas through midweek. As a result
expect storm outflow boundaries flowing down into lower elevations
also through midweek along with a chance of wetting rains. Winds
will typically still have the usual daytime upslope gusts, and the
more prevalent thunderstorms will likely create periods with
stronger outflow boundaries and erratic wind shifts. Drier air and
hotter temperatures may move into the region beginning Thursday
reducing thunderstorm chances and coverage. Min relative humidity in the upper
teens to low 20s percent range early in the period will gradually
dry to the mid to upper teens by Thursday. Overnight recoveries
around 35-50 percent early in the period will fall to 25-40 percent
by late in the period.

&&

Spotter information statement...
spotters should follow Standard reporting procedures.

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Psr watches/warnings/advisories...
Arizona...none.
California...none.

&&

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