329 
FXUS65 KPSR 081012
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
312 AM MST Wed Aug 8 2018

.SYNOPSIS...
Temperatures will cool to more seasonable, but still hot, levels 
today. With increased moisture across the region and a favorable
atmospheric pattern, precipitation chances will remain elevated 
through early next week. 

&&

.DISCUSSION...
In the latest NHC public advisory, Hurricane John was located 
230 miles south-southwest of the southern tip of Baja California 
with maximum sustained wind speeds near 100 mph. John, a feature 
that will help to increase the moisture across the desert 
southwest this week, is expected to continue moving toward the 
northwest and pass to the southwest of Baja California Sur 
Wednesday and Thursday. Simultaneously, the 500 mb high will 
migrate to the northwest tomorrow, becoming nearly stationary 
around Nevada/Utah through the end of the week. With increased 
moisture across the region and favorable mid-level easterly flow, 
precipitation chances will remain elevated through early next 
week.

Activity from last night will continue to dissipate overnight, 
with skies gradually clearing during the morning hours. The 
aforementioned 500 mb high will shift northwest today, placing our
forecast area under deep easterly mid-level flow. As a result, 
heights will be a tad bit lower today and mid-level temperatures 
will be slightly cooler. In addition, another gulf surge underway
tonight will result in even more boundary layer moisture across 
the region today. PWAT values in Phoenix are forecast to rise from
1.31 inches this afternoon to near 1.5 inches tomorrow afternoon,
in Yuma values are forecast to rise from close to 1.5 inches this
afternoon to close to 1.9 inches tomorrow afternoon, and in 
Imperial values are forecast to rise from close to 1.2 inches this
afternoon to close to 1.5 inches tomorrow afternoon. At the 250 
mb level, there is weak westerly flow which will help to keep 
anvil clouds from overspreading the region ahead of the storms 
later this afternoon. In addition, there is pretty decent 
divergence at the 250 mb level with the flow separating across 
the eastern half of the state between a trough in northern Arizona
and a ridge in in southern Arizona. This divergence aloft will 
provide extra dynamical support to enhance thunderstorm updrafts. 
With the combination of increased moisture and sufficient day time
heating, MLCAPE values are forecast to be around 1000 to 2000 
J/kg this afternoon, with the greatest instability along the 
higher terrain of south-central Arizona as well as along and west 
of the Colorado River. 

Storms will start to develop during the late morning/ early 
afternoon hours along the higher terrain in eastern Arizona. With 
very robust CAPE values in this region, steeper lapse rates, and 
very high DCAPE values, expect storms that develop to have the 
potential to produce severe winds, hail, and frequent lightning. 
The steering flow is pretty weak, so some areas could also see 
some localized flooding. Storm motion will be to the west, so the 
big question is, will these storms be able to sustain themselves 
as they move towards the lower deserts. For that to happen, there 
would need to be a strong enough outflow to overcome the 
convective inhibition that will be in place during the afternoon 
hours. With the environment out east being favorable for stronger 
storms, it's not out of the question we will get a strong enough 
outflow to move into the lower deserts and regenerate storms. The 
CAMs don't really look to optimistic though, and seem to think the
environment will be way too worked over from last nights 
activity. However, there is a little bit more dynamical support 
today than there was yesterday, so once again, storms in the lower
deserts can't be ruled out. In fact, any storm that does develop 
across the lower deserts will have the potential to be strong and 
produce gusty winds, frequent lightning, hail, and localized 
flooding. 

&&

.AVIATION... 
South-Central Arizona including KPHX, KIWA, and KSDL:
Converging thunderstorm outflows over metro Phoenix will make for
erratic surface winds and provide lift for at least isolated
thunderstorms through 07Z along with areas of visibility below 6SM
but above 3SM due to dust (localized 2-3SM). Expect isolated
weaker showers through 09Z. Anticipate southwesterly surface winds
to begin reestablishing after 07Z. Expect ceilings to remain AOA
FL100 except in showers. 

An active Monsoon pattern is expected through at least Thursday.
There are indications that Wednesday will be more active than
Today (Tuesday) has been. 

Southeast California/Southwest Arizona including KIPL and KBLH: 

South and southeasterly breeziness will continue overnight and
through the day Wednesday. Other than some mid and high clouds,
no thunderstorm activity is anticipated except perhaps for
portions of La Paz County Wednesday afternoon and evening. 

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER... 
Thursday through Monday:
Significant moisture will return to the area from the east and
bring an increase in thunderstorm activity through the period.
Storms are expected to be most prevalent over the higher terrain
north and east of Phoenix but even lower elevations will have a 
shot at precipitation each afternoon. Minimum humidities will end 
up between 20 to 30 percent over the deserts each day following 
fair to good overnight recoveries. Apart from thunderstorms, winds
will be light except for typical afternoon and evening upslope 
breeziness. Temperatures each day will remain at or just below 
seasonal normals although portions of the south-central deserts may 
drop to around 100 Thursday into Saturday as thicker clouds and 
moisture affect the region.

&&

.SPOTTER INFORMATION STATEMENT... 
Spotter reports may be needed later this week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.

&&

$$

DISCUSSION...Hernandez
AVIATION...AJ 
FIRE WEATHER...Iniguez/Hirsch/Wilson/Kuhlman/CB