Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 170939

Area Forecast Discussion
National Weather Service Tucson AZ
239 AM MST Fri Aug 17 2018

.SYNOPSIS...We`ll see enough monsoon moisture for a chance of
showers and thunderstorms into the weekend. With high pressure
shifting into a less favorable position, some drying may limit
thunderstorm coverage to start the week, while bringing
temperatures several degrees above average. Deeper moisture
should push back into the area from the south by late Monday or


.DISCUSSION...High pressure immediately east of our area has
brought a very favorable southerly flow into southeast Arizona the
last few days, maintaining above average moisture and a busy
thunderstorm period. Precipitable water values around 1.4 to 1.5
inches and surface dewpoints in the 60s will help bring another
round of thunderstorms this afternoon and evening. That will
likely change over the next 48 hours though.

Larger scale high pressure across the desert southwest, northern
Mexico and the eastern Pacific off the California coast is in the
process of recycling with a reconsolidation of the high center
near southern California by Saturday night or Sunday morning. This
in turn will bring a drier northerly flow into our corner of the
state and limit thunderstorm coverage for at least Sunday. NAEFS
mean precipitable water values are currently in the 99th
percentile for mid August, but by Sunday afternoon drop to near
the 10th percentile. That would be from above 1.5 inches this
morning to below 1.2 inches from Tucson eastward by Sunday
evening. GEFS plumes reflect the same trends, with the mean
bottoming out at 1.1 inches Sunday evening for Tucson and around
.8 for Safford.

With a more active higher latitude pattern interrupting summer in
northern tier states, high pressure should strengthen over the
desert southwest early in the new week, with temperatures climbing
to a few degrees above climo by Sunday and Monday. If the high
shifts overhead, we may be slow to recover our moisture until
Tuesday or Wednesday.


.AVIATION...Valid through 18/12Z.
SCT-BKN cloud bases generally 8-12k ft AGL. This afternoon, isolated
to scattered -SHRA/-TSRA will be possible mainly from Tucson
eastward. Brief MVFR conditions are possible with the -TSRA. Outside
of thunderstorm wind gusts, expect SFC winds mainly less than 12
kts. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...The pattern remains favorable for scattered showers
and thunderstorms through Saturday, with lower rain chances and
drier conditions by Sunday. Slight chances for showers and storms
will occur again next week. Near average temperatures will continue
through the Saturday with slightly above normal temperatures next
week. 20-ft winds will be terrain driven at less than 15 mph, except
for in and around thunderstorms where strong outflows may occur.






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