Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 251959

Area Forecast Discussion
National Weather Service Tucson AZ
1259 PM MST Tue Sep 25 2018

.SYNOPSIS...Other than a few isolated mountain showers and
thunderstorms late today and Wednesday, dry conditions are expected
through Saturday. Through Saturday, temperatures will warmer than
average and peaking 6-8 degrees warmer than normal by Friday. Showers
are possible late in the weekend into early next week.


.DISCUSSION...Thus far just a few light showers and isolated
lightning strikes over the White Mountains with just moderate
cumulus elsewhere. Still expecting a few storms over the eastern
mountains while the sun remains up later today, other than that,

For Wednesday, expecting even less convection across the CWA and
basically located over the Whites and the far eastern mountains.
Nothing significant but can`t totally rule it out either.

Thursday into Saturday, with ridging expected to build a bit over
the area, I left the forecast dry with warmer than normal

Then all eyes turn toward late in the weekend into early next week.
Its pretty certain that a tropical storm (Rosa) will develop in the
eastern Pacific off of Mexico with potential impacts for the SW. Many
model solutions point toward a deep trough developing along the west
coast and directing the remnants of this storm up across the SW
which would bring significant rains if that were to come to pass.

At this time, the GFS and Canadian ensembles have a majority of their
solutions showing this solution with a good bet for rains across
much of southeast Arizona, although generally not the focus of the
heaviest rains. The 00Z (and previous) ECMWF ensemble solutions
continue to drive the system to the west across the Pacific with
little impact to our area. However, the latest deterministic solution
does capture the TS up in the trough, just later and further west
resulting on little impact on our area.

At this point in time, have enough confidence that we have a threat
of rain late in the weekend into early next weekend in some form or
fashion, that in coordination with surrounding offices have upped the
chances for precipitation and adjusted the clouds and temps through
this period of time.

At this time, we are still not as bullish as the GEFS/Canadian
solutions but much more so than the ECMWF. The pattern across the
Pacific is very complicated at this time with multiple tropical
systems and troughs which is bringing about the rather high level of
uncertainty. This will continue to be refined over the next few days
and of note is that with these types of systems, the rain tends to
be held fairly close to the center of the remnant tropical system so
the track is critical to who gets rain and who doesn`t, so stay


.AVIATION...Valid through 27/00Z.
SCT-BKN clouds at 8k-12k ft AGL. Isolated -SHRA/-TSRA possible this
afternoon near the mountains east of KTUS. SFC winds generally
WLY/NWLY at less than 12 kts this evening before becoming light and
terrain driven overnight. Aviation discussion not updated for TAF


.FIRE WEATHER...Isolated showers and thunderstorms will be
possible mainly in the higher terrain east of Tucson, including the
White Mountains this afternoon and Wednesday. Dry conditions are
expected for Thursday and Friday before rain chances begin to
increase later this weekend into next week. 20-foot winds remain
terrain driven at less than 15 mph.





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