Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 181602
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
902 AM MST THU AUG 18 2016

.SYNOPSIS...A gradual increase in moisture will result in more
showers and thunderstorms into early next week along with
slightly cooler afternoon temperatures.

&&

.DISCUSSION...Water vapor imagery and 18/12Z upper-air plots show a
trough that extends from eastern Idaho across central Nevada and
north central California. Models suggest a weak disturbance rotating
around the main trough across southeast California and western
Arizona and this seems to be evident in WV and IR imagery as cooler
cloud tops reside over north central Arizona and the latest radar
mosaic shows mostly showers, with a few thunderstorms that extend
from between Flagstaff and Winslow and southwest through parts of
the Phoenix metro and into the western deserts of my forecast area
toward Ajo. All of this activity is moving generally east, although
individual elements within this large swath of showers are moving to
the northeast.

Latest surface observations show a distinct east to west moisture
gradient across my forecast area with dewpoints in the 40s to 50s
over extreme eastern areas near the New Mexico border and in the 50s
to 60s over central areas and mostly in the 60s for the far western
deserts toward Ajo, Organ Pipe Cactus and beyond. In addition, the
CIRA LPW Total PW imagery show values around 1.6-2.1 inches over
southwestern parts of Arizona with values ranging from 0.6-1.0
inches over east and southeast locations, more specifically over
parts of Cochise, Graham and Greenlee counties. Streamlines from
various models in the low to mid levels show a southwest to westerly
flow today, which will help to spread this higher moisture eastward.
Even so, models don`t advertise a considerable increase, but do show
values ranging from around 1.25-1.5 inches for central and western
zones, especially into Friday.

The 00Z and 06Z runs of the Univ of AZ WRF/NAM & GFS both picked up
on the activity currently to our west and north, but the WRF/NAM
seems to have captured this better than the GFS. At any rate, they
both suggest that development today will be mostly from around the
Nogales area and points to the northwest and west over central and
western Pima county, with perhaps some of this activity generating
outflows that may trigger storms a bit farther east. That said, the
inherited POP forecast continues to seem reasonable through the
afternoon and into the evening hours, but will monitor satellite and
radar trends and will make adjustments as needed.

&&

.AVIATION...Valid through 19/18Z...
Generally VFR through the period. A few showers mainly west and
north of KTUS this morning, then an isolated to scattered showers
and thunderstorms developing after Noon. Normal diurnal wind
trends mainly under 10-15 kts outside of any thunderstorm
outflows. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Moisture will slowly return through the weekend
resulting in some increased chances of afternoon and evening
showers and storms. Aside from thunderstorm outflows, winds will
be light and generally terrain driven.

&&

.PREV DISCUSSION...Friday and beyond we should have sufficient
moisture throughout the area for average monsoon coverage into early
next week. Not a gang-busters pattern but there will be a good day
or two mixed in over the next several days.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...Mollere
PREVIOUS DISCUSSION...Meyer/Rasmussen

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