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Area Forecast Discussion (AFD)

Issued by NWS Phoenix (PSR)

FXUS65 KPSR 230003

Area Forecast Discussion
National Weather Service Phoenix AZ
503 PM MST Thu Aug 22 2019

.UPDATE...Updated Aviation Discussion.


Additional increases in humidity can be expected the next couple
of days along with lower high temperatures. With the increase in
humidity, storm chances return. However, storm chances will be 
slight and limited to south-central Arizona. Storm chances will be
even less Monday and Tuesday before trending up again during the
middle of next week. Anticipate high temperatures to climb a few
degrees above normal on Tuesday but not be as hot as recent days.


Today's moisture increase has lead to higher dew points and some
cumulus/towering cumulus over some portions of the forecast area
this afternoon. However, full fledged deep convection has been
limited to far southeast AZ so far. This is due to CIN associated
with cooler air in the lower levels and lingering warmth aloft.
Made an update this morning to insert a slight chance of storms
over portions of western Pinal and far southwest Maricopa County
due to localized convergence and some of the CAMS depicting some
modest activity there. This is where the main batch of
cumuliform clouds are for our area currently. For tonight, held 
on to the slight chances for portions of south-central AZ 
(including far southern/southeastern metro Phoenix) due to 
potential for outflows from southeast AZ as well as late night 
debris from decaying Sonora storms. 

On Friday, steering flow looks to be weak with a 500mb
anticyclone centered over southern AZ. There looks to be
additional moist advection but the deeper moisture is still 
confined well east of the Lower Colorado River Valley. With better
moisture, anticipate storm activity to have better coverage -
mainly over southeast AZ per CAMs. But with more outflows
available, that increases the potential for follow-on storms over
our forecast area. But, there will still be some CIN to contend
with, so PoPs are modest. On Saturday, moisture availability
improves westward. But, northwesterly flow aloft (high centered
over central/northern CA) keeps the best moisture limited to the 
southern half of AZ. With upstream areas of Yavapai and northern
Gila having limited moisture, PoPs remain conservative. On Sunday,
the high expands further into AZ reducing instability despite the
lingering moisture. Temperatures will be close to normal. 
Meanwhile, Tropical storm Ivo will be tracking northwestward well 
off the coast of Baja Mexico. Overall, it will not have a direct 
impact on our area. 

Early next week, high pressure becomes centered over Arizona and
drying takes. Thus, storm chances (what little they were) trend
down and temperatures trend up. But, they are not anticipated to
be as high as what we've had in recent days. For the middle to  
latter part of next week, an inverted trough passing through
northern Mexico is anticipated to lead to an increase in moisture
over the region along with an uptrend in storm chances. 


.AVIATION...Updated at 0000 UTC.

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

Visible satellite imagery this afternoon shows scattered mid-level
clouds beginning to push into the Phoenix metro from the south
with convection currently ongoing to the south. Not expecting any
of this activity to reach the terminals, but there is a slight
chance that a weak outflow could reach the southern portions of
the metro. However, confidence in this actually occurring remains
too low to mention in the TAFs. Otherwise, FEW-SCT mid and high
level clouds will remain through the period with a few mid-level
clouds possibly getting down to 7-8 kft overnight into tomorrow

Southeast California/Southwest Arizona including KIPL and KBLH:

No significant aviation concerns anticipated through the TAF 
period under mostly clear skies. Winds at KBLH look to remain 
elevated through the period with a few gusts to 20 kts possible 
through the remainder of this evening. Gusts then pick back up 
tomorrow afternoon at KBLH with gusts to 22 kts possible. 

Aviation Discussion not updated for amended TAFs.


Saturday through Thursday: Minimum humidities are expected to
remain above 20% through the weekend and overnight recovery will
be at least Good. Storm chances will be quite modest and limited 
to south-central AZ. Temperatures will be at, or slightly below,
normal. Humidities trend down significantly Monday and Tuesday and
temperatures trend up - though not as high as we've seen in recent
days. Humidities are anticipated to trend upward Wednesday and
Thursday. Storm chances return as well. Apart from thunderstorms,
winds will follow familiar warm season diurnal patterns. 


Spotters should follow standard reporting procedures.