Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 140420
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST Sun Aug 13 2017

.SYNOPSIS...Scattered thunderstorms mainly south of Tucson ending
later tonight. Isolated to scattered thunderstorms mainly east to
south of Tucson Monday afternoon and evening. Dry conditions will
then prevail Tuesday through Friday. A slight chance of thunderstorms
will return next weekend. Daytime temperatures quite close to
seasonal normals except a few degrees above normal Thursday and
Friday.

&&

.DISCUSSION...Scattered showers and thunderstorms were occurring at
this time in an area from near Green Valley southward into portions
of Santa Cruz County. Another area of showers/tstms was located just
south of the international border adjacent Santa Cruz County.
Otherwise, mostly clear skies to partly cloudy skies prevailed
across southeast Arizona at this time. IR satellite imagery depicted
generally warming cloud tops during the past hour associated with
the showers/tstms north of the international border. However, cloud
tops were cooling with the cluster of showers/tstms just south of
the international border.

The high resolution models depicted different precip scenarios for
the rest of tonight. The 14/00Z Univ of AZ WRF-NAM valid 9 pm MST
was quite close to reality with the depiction of ongoing precip in
northern Sonora, but was underdone in far southeast Pima/northern
Santa Cruz County. The 14/02Z HRRR valid 9 pm MST had a better
depiction of precip south of Tucson, but was way overdone by
depicting precip from Tucson northwestward into Pinal County. Thus,
forecast confidence in the short term is somewhat low.

Slight adjustments were made to the official forecast PoP values for
the rest of tonight. The adjustments were mainly made based on
satellite/radar trends that favor the best chance of showers/tstms
for at least the next few hours to be south of Tucson. Showers/tstms
presently in east central Arizona may eventually push into our
portion of the White Mountains later tonight. Otherwise, satellite/
radar trends do not support the scenario of showers/tstms during the
next few hours in vicinity of Tucson northward.

Given the unstable environment as per the 14/00Z KTWC sounding, have
opted to maintain at least a slight chance of showers/tstms the rest
of tonight across much of this forecast area. Dry conditions should
prevail across western/central Pima County. The bulk of showers/tstms
will likely end by 6-8 am MST Monday. Isolated to scattered showers/
tstms will mainly be east-to-south of Tucson Monday afternoon.

Please refer to the additional sections for further detail.

&&

.AVIATION...Valid thru 15/06Z.
Scattered -TSRA/-SHRA mainly south-to-southeast of KTUS ending
around daybreak Monday. Isolated to scattered -TSRA/-SHRA mainly
east-to-south of KTUS Monday afternoon and evening. Brief wind gusts
near 40 kts and small hail with the stronger TSRA. Otherwise,
surface wind variable in direction less than 12 kts into Monday
morning. Surface wind Monday afternoon and evening wly/nwly
10-18 kts with gusts near 25 kts. The strongest speeds will be
northeast of KTUS and particularly in vicinity of KSAD. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered thunderstorms mostly east to
south of Tucson Monday afternoon and evening. Dry conditions will
then prevail Tuesday into Friday. Isolated to scattered
thunderstorms will likely return by next Sunday.

&&

.PREV DISCUSSION /157 PM MST...Gradual drying is beginning to take
hold Monday which should result in less convection around the area
generally limited to the Tucson area east. With the very wet soils
around the region will still have plenty of boundary layer moisture
to play with and this will help despite drying aloft.

Then west-southwest flow strengthens across the area which will
significantly dry out the air mass resulting in dry conditions
area wide Tuesday and likely into Friday. Due to reasonable heights
and thicknesses temperatures will remain near average for mid
August despite the lack of convection and clouds.

Then there is potential for the flow to become southerly enough
to start directing moisture north across the area next weekend.
Longer range models are somewhat divided on that thought at this
time so not a lot of confidence at the moment. Will have to see
how it plays out over the next couple of days.

&&

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

&&

$$

Francis
PREVIOUS DISCUSSION...Cerniglia

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