341 
FXUS65 KPSR 081031
AFDPSR

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

.UPDATE...Updated Aviation and Fire Weather Discussions...

&&

.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 
today and Thursday. Simultaneously, the 500 mb high will migrate 
to the northwest today, 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:
An increase in moisture will result in afternoon high terrain
storms with a good chance of at least isolated storms moving into
the Phoenix metro this evening. Storm outflows anywhere from north
to east should move in sometime between 01-03Z with gusty winds 
likely. Will hold off on mentioning VCTS for KPHX, but will 
include in KSDL and KIWA as confidence of storm activity over the 
foothills areas is higher.

Southeast California/Southwest Arizona including KIPL and KBLH: 

Gusty southerly to southeasterly winds this morning will
eventually diminish, but winds will remain out of the southeast 
at KIPL and south at KBLH through the period. Storm activity 
across Arizona should remain far enough to the east to only bring 
mid and high cloudiness early this morning and again tonight. 

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER... 
Thursday through Monday:
Significant moisture will affect the region at least through
Saturday and likely into early next week. This will result in day
to day thunderstorm chances 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 near 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...Kuhlman
FIRE WEATHER...Kuhlman