Areal Flood Warning 13, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
328 AM MST THU AUG 11 2016

.Update...Aviation and Fire Weather Discussions.

&&

.SYNOPSIS...
The weather pattern will allow for a transition to drier and more
quiet conditions for the end of the week as moisture levels trend
down. With this drying trend, temperatures will also increase
through the weekend and into early next week with readings at or
above normal levels.

&&

.DISCUSSION...
The current synoptic picture shows an upper level trough moving
through the Great Basin with the main shortwave well north of our
area. An unseasonably strong upper level jet currently stretches
from northern Baja northeastward into the central Rockies. This set
up is providing some support for ongoing storms over central and
northern Arizona, but largely more neutral to weakly subsident flow
is seen over southwest and south-central Arizona. Moisture levels
remain quite high over southern Arizona with PWATS of 1.50 - 1.75
inches and ML CAPE values of up to 1000 j/kg. This instability
should be enough to overcome the weak subsidence and should result in
a few isolated showers or thunderstorms this morning.

Daytime heating today will be the main forcing mechanism for any
storms this afternoon and evening. The threat for localized flooding
has mostly ended, but can't rule some minor flooding out a storm or
two this afternoon. Though high-res models have a poor track record
over the last couple days, the vast majority show storm activity
mostly confined to high terrain areas with little activity over the
deserts. The expected little or no activity over the deserts later
today should be because of the drier air aloft mixing down and a
modest southwest steering flow keeping high terrain storms from
propagating into the deserts. May be able to get a few storms over
the deserts this afternoon, but would mostly have to come from
intersecting outflows from high terrain storms.

From Friday into early next week, moisture levels decrease
substantially with 1000-700mb mixing ratios dropping below 8g/kg in
most areas as a high pressure center shifts off the Pacific into the
Great Basin. This northerly flow aloft around the high will bring
even drier air into the Desert Southwest as daytime surface dew
points drop into the 40s to low 50s. Any thunderstorm chances during
this time period will reside mostly over far eastern Arizona which
includes eastern Gila County. As the atmosphere dries, temperatures
will subsequently rise to above normal levels. Highs should even top
110 over southeast California and southwest Arizona and will come
close to Excessive Heat levels in the Imperial Valley by Sunday.
These above normal temperatures will likely persist through Monday
before gradually decreasing, especially over south-central Arizona
where a modest moisture return is forecast for the middle of next
week. Both the GFS and European generally show some monsoon moisture
working back into portions of Arizona starting next Wednesday
bringing a return to storm chances.

&&

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

Tropical moisture still covers the region. A few disturbances in the
unusually strong southwesterly jetstream winds will develop a few
showers and thunderstorms at times today and early tonight. Through
17z Thu...sct clds near 8 thsd agl with bkn clouds 10 to 14 thsd
agl. Isolated showers and or thunderstorms. Light and variable wind
under 8 knots.  From 17z Thu to 03z Fri...sct clds based 8-10 thsd
ft agl. Tstms developing over the distant mtns n-se of PHX with a
chance of shwrs/tstms in the Phoenix valley during the late
afternoon and evening hours. West wind 6 to 10 knots.

Southeast California/Southwest Arizona including KIPL and KBLH:

Through 03z Fri...sct clds 8-10 thsd agl. South wind 8 to 12 knots.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday...

A drier and warmer airmass will cover the region Saturday and
Sunday. No mountain thunderstorms. Minimum relative humidity will
range from 10 percent in southeast California to 20 percent in
southern Gila County. Afternoon west winds 8 to 15 mph. Excellent
overnight recovery.

From Monday through Wednesday, monsoon moisture will return to the
region providing a slight chance of afternoon and evening mountain
thunderstorms in southern Gila County. Minimum relative humidity
will increase into the 10 to 15 percent range in southeast
California to near 35 percent in southern Gila County. Afternoon
southwest wind 5 to 15 mph. Good overnight recovery.

&&

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

&&

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

Visit us on Facebook...Twitter...and at weather.gov/phoenix

DISCUSSION...Kuhlman
AVIATION...Vasquez
Fire Weather...Vasquez

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