FXUS65 KTWC 242142
Area Forecast Discussion
National Weather Service Tucson AZ
242 PM MST Sat Aug 24 2019
.SYNOPSIS...Isolated to scattered showers and thunderstorms will
continue today, mainly from Tucson southward with daytime high
temperatures near normal. A drying trend resumes Sunday with
isolated storms limited to near the International border as high
pressure starts to build overhead. Dry conditions generally prevail
Monday and Tuesday with above normal temperatures returning.
Thereafter, moisture returns by Wednesday, resulting in a chance of
showers and thunderstorms the latter half of next week.
.DISCUSSION...With a trough digging into the central Plains, high
pressure is building into our region from the northwest. This is
weakening our flow, and the morning sounding showed 3.5 degrees of
warming at 500mb. There's still plenty of moisture in play with
1.2 to 1.3 inches of precipitable water in eastern areas, and up
to 1.7 inches in the lower deserts. With the mid level warming and
weaker shear, overall we should see less valley thunderstorm
coverage today compared to recent days. Best dynamics will be
east through southwest of Tucson.
T.S. Ivo has been a little too far west to do much for our
weather, and is slowly drifting toward cooler waters west of the
Baja spur. Conditions remain favorable for tropical development
off the west coast of Mexico. A weak wave pushing offshore
near the southern Gulf of California is given a 30 percent chance
of cyclone formation by the NHC over the next 5 days. Something
to keep an eye on. Otherwise, with the flow reversing once again
we will see some drying in SE AZ over the next 72 hours. GEFS and
NAEFS ensembles push or precipitable water back down to around 1
to 1.2 inches by Monday. However, a weak and shallow low level
seep from the south should continue to bolster our dew points, so
we won't dry out completely. That will probably only make itself
known with patchy afternoon cumulus fields by Monday.
With the high center reconsolidating over the desert southwest,
temperatures will jump back up to around 6 to 8 degrees above
average Tuesday afternoon. Flirting with low end Excessive Heat
levels, but 3 or 4 degrees short of the recent 109/110 in Tucson.
The heat combined with the easterly wave pushing across the
southern Gulf (whether or not it develops into a depression) will
likely initiate a strong and deep surge by next Wednesday or so.
That should help put thunderstorms back into our forecast, but as
for the rest of the state it's not clear with the possibility of
the high wobbling back westward over western Arizona and southern
California later next week.
.AVIATION...Valid through 26/00Z.
Isolated to scattered -TSRA/-SHRA developing and persisting thru
25/06Z mainly south of KTUS and in the White Mtns northeast of KSAD.
Brief wind gusts to 45 kts and MVFR cigs/vsbys with the stronger
TSRA. Otherwise, cloud decks mainly 10k-15k ft MSL. Surface wind
wly/nwly at 8-18 kts with gusts to near 25 kts thru 25/04Z and then
again aft 25/19Z. The strongest speeds apart from tstm gusts will be
near KSAD. Surface wind variable in direction and less than 12 kts
at other times and aside from tstm gusts. Isolated -TSRA/-SHRA
developing again aft 25/19Z, mainly along the International Border
from west of KOLS to KDUG. Aviation discussion not updated for TAF
.FIRE WEATHER...Isolated to scattered showers and thunderstorms
are expected through the evening hours tonight favoring areas south
of Tucson and across the White Mountains. Isolated showers and
thunderstorms will occur Sunday afternoon mainly along the
International Border from west of Nogales to Douglas (southern
Cochise/Santa Cruz Counties), with mostly dry conditions elsewhere.
Dry conditions will then prevail across much of the area Monday and
Tuesday. A favorable flow regime returns Wednesday and continues
through Saturday for scattered mainly afternoon and evening
thunderstorms. Aside from thunderstorm wind gusts, 20-foot winds
will be terrain driven mainly under 15 mph.
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