Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 151240
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
540 AM MST Wed Aug 15 2018

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
The potential for showers and thunderstorms will remain across
much of the region through Thursday with locally heavy rainfall
and gusty winds possible. A gradual drying trend will occur
starting Friday into the weekend, though some afternoon storms
will continue over higher terrain. Temperatures will also climb
back above normal.

&&

.DISCUSSION...
As anticipated the inverted trough has moved out of northern
Mexico into far southern Arizona helping to rise moisture levels.
Storm activity that formed along the Mogollon Rim last evening
skirted across the northern Phoenix area and eventually died out
as it approached southern California. The inverted trough along
with weak difluence aloft allowed another round of storms to
develop later in the evening across southeast Arizona, eventually
moving into Pinal and southern Maricopa Counties. Current
analysis shows this activity is mostly elevated in nature, but the
ample moisture in the mid levels and MUCAPE of 500-1000J/kg
should keep it going for a few more hours as it slowly drifts
west-northwest. Earlier storms have also resulted in a couple MCVs
seen across southern Pinal and southern Maricopa which should
also aid in prolonging this overnight convection. The Phoenix area
should largely escape this rain, but the western and southern
periphery will likely see some showers through sunrise.

Forecast confidence for today is only medium at this point due to
expected extensive cloud cover and only modest instability.
Forecast soundings show instability gradually improving this
afternoon and evening, but it also shows a decent capping
inversion. This should prohibit further storm develop across the
majority of the lower deserts, but we should see at least
scattered storms develop across the high terrain and even some
isolated activity across southwest Arizona and southeast
California as the inverted trough moves through that area.
Forecast soundings show instability improving later this evening
as another moisture surge is seen moving off the Gulf of
California. This should erode the CAP and allow for more
widespread storm development, including over the lower deserts.
Models generally point toward activity increasing late this
evening and then lasting through much of tonight. Given the weak
steering flow, excessive moisture, and higher instability this
should result in areas of heavy rainfall and localized flooding.

What happens on Thursday largely will depend on how much activity
and cloud cover lingers through the mid to late morning hours.
For Thursday afternoon and evening, storms will mostly need to
form over the high terrain or along any leftover boundaries as
there appears to be a lack of any discernible mid level waves.
PoPs across the lower deserts mostly fall to around 20% as the
steering flow turns southwesterly which generally favors storms
across the high terrain of eastern Arizona.

The southwesterly flow will continue through Friday while the
upper level high center shifts westward across northern Mexico.
Eventually the high shifts well to our west turning our flow out
of the north-northeast for this weekend. Considerable drying is
shown during this time with PWATs mostly falling below 1.5". Any
storm activity Friday should mostly be across the high terrain,
but we can`t rule out an isolated storm or two across the lower
deserts. Temperatures are seen climbing to slightly above normal
readings starting Friday with a few of the warmest lower desert
spots approaching 110 degrees this weekend.

After a fairly dry day on Saturday, the flow is seen gradually
shifting out of the southeast once again providing some sort of
moisture increase starting Sunday. Chances for storms should
increase Sunday into early next week, but at this point there are
no obvious features to focus on that would create any widespread
storm activity.

&&

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

Chances for isolated, occasional showers in the vicinity will linger
across the area through early afternoon. Expect light to moderate,
variable and easterly winds during the early morning hours near 5-
10kt, and then gradually favoring the west by mid morning at
4-9kt. Tonight scattered showers are expected to move into the
vicinity from the southeast to northeast with breezy easterly
winds with gusts of 18-22kt. Skies will be partly to mostly cloudy
today with BKN decks from 7-16kft.

Southeast California/Southwest Arizona including KIPL and KBLH:

Expect light to moderate southerly to southeasterly winds for today
near 6-12kt. Otherwise skies will be mostly clear to partly
cloudy with FEW-BKN decks from 10-15kft.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Friday through Tuesday:
Elevated moisture levels will continue into Friday for all
districts resulting in enhanced chances for thunderstorms and
wetting rains. Some locally heavy rain will be possible,
especially throughout central Arizona. Slightly drier air will
slowly push into the region during the weekend and early next week,
but afternoon storms will still be possible over higher terrain
areas. Throughout the period, wind speeds will be typical for mid
summer with the usual afternoon breezes. Temperatures will start out
near average on Friday and then gradually warm near to slightly
above normal Saturday through Tuesday.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

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

$$

DISCUSSION...Kuhlman
AVIATION...Sawtelle
FIRE WEATHER...Percha/Wilson/MO


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