Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 192156
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
256 PM MST Sat Aug 19 2017

.SYNOPSIS...Expect scattered thunderstorms during much of the
upcoming week. The greatest coverage of thunderstorms should occur
east to south of Tucson, but the lower deserts won`t be completely
left out. Daytime temperatures will be close to seasonal
averages.

&&

.DISCUSSION...Pretty much going as expected so far this afternoon
with lots of debris cloud blocking the sun, so limited surface
heating. Our 18Z KTWC sounding showed our precipitable water up to
1 inch, and satellite estimates still showed a sharp gradient
pushing up to 1.6 inches in northern Sonora. The shallow surface
moisture increase is mixing out with dew points with only border
locations holding on to the middle and upper 50s this afternoon.
Our best coverage will be rolling in from other locations, i.e.
western New Mexico and northern Sonora. Moisture will continue to
increase overnight, with outflows from those locations probably
keeping showers and isolated thunderstorms going overnight in
mainly eastern and southern locations (Greenlee, Graham, Cochise,
Santa Cruz and maybe eastern Pima counties).

We should shake off the debris cloud a little better tomorrow,
and with deeper moisture and a degree or two of cooling in mid
levels should see better thunderstorm initiation in the mountains.
We still may not have a strong enough flow for a lot of valley
storms but some will stray off.

Beyond that, typical moisture for late August most of the coming
week with some up days and down days. An average chance of storms
to start the week with a general southerly flow open to whatever
cares to wrap around the high. Medium range model resolutions are
advertising one such mid level impulse from central Mexico through
Sonora and then us Wednesday and/or Thursday.

Another pattern change around the end of next week with a high
center reconsolidating west of our area. That would tend to tamp
down thunderstorm activity and start to once again limit moisture
across our area next weekend.


&&

.AVIATION...Valid thru 21/00Z.
Isolated to scattered -TSRA/-SHRA mainly east to south of KTUS
this afternoon into tonight, with better chances Sunday.
Otherwise, VFR conditions with surface wind variable in direction
mainly less than 12 kts. Aviation discussion not updated for TAF
amendments.


&&

.FIRE WEATHER...As moisture increases once again from the south,
our chance of showers and thunderstorms will also increase.
Expect scattered mainly afternoon and evening thunderstorms most
of the coming week. A gradual reduction of thunderstorm coverage
may again occur by next weekend. Normal diurnal wind trends
outside of any gusty and erratic thunderstorm outflows.

&&

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

&&

$$

Meyer

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