Areal Flood Warning 27, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
901 AM MST Tue Aug 17 2021

.SYNOPSIS...Some strong thunderstorms around on Wednesday before
most locations show a drying trend into the weekend. Temperatures
will climb back to near seasonal averages by Saturday with storm
chances increasing again early next week.

&&

.DISCUSSION...After being worked over the past 12 hours, the
weather shortened 12Z KTWC sounding was a classic onion with
limited convective potential to start the day. Plenty of
insolation in eastern areas where things are clearing out first.
Less activity over the past 18 hours south and east of Tucson,
including Santa Cruz, Cochise, and Greenlee counties. That should
be our focus for the afternoon with some outflow possibly reaching
the Tucson area in the early evening with some storms overnight.

The main change is going to be a flow reversal as the remnant of
the easterly wave that pushed through us late last week shears
into the base of the low developing north of our area and tracks
back through Wednesday afternoon. Short term hires models are
hinting at a modest flow reversal before midnight, with steering
flow solidly out of the southwest Wednesday. The dry air intrusion
associated with this could make for some interesting strong storm
development Wednesday. Our current forecast handles this pretty
well. No updates.

&&

.AVIATION...Valid through 18/12Z.
SCT -SHRA/TSRA dvlpg after 17/19z mainly S and E of KTUS. Gusty
winds up to 45+ kts are psbl with these storms today, otrw expect
sfc winds 10 kts or less. Clouds will be SCT-BKN 6k- 11k ft MSL
thru the pd with ocnl MVFR conds in SHRA/TSRA. Aviation discussion
not updated for TAF amendments.

&&

.FIRE WEATHER...The active monsoon continues through Wednesday as
a series of weather disturbances transition across the area and
plenty of moisture remains in place. By Thursday into the weekend
most locales should remain dry with isolated thunderstorms mainly
limited to the higher terrain of Graham and Greenlee County
Thursday. Below normal temperatures are expected through mid-week
before a gradual warm up begins late in the week. Min RH values
remain well above critical levels. 20-foot winds will generally be
less than 15 mph when not influenced by thunderstorms.

&&

.PREV DISCUSSION... /issued 348 AM MST Tue Aug 17 2021/
The convective complex from last night into early this morning
will be moving into northern Mexico in the next several hours. An
MCV can be seen on the Tucson radar near Kitt Peak and this will
also move across the Intl border by 5 am. We've have some
impressive rainfall totals north and west of Tucson with the main
concern being Brawley Wash. See hydrology section below. As of 330
am, radar was showing an extensive area of light to moderate rain
across central and eastern Pima county with thunderstorms near
the Intl border moving into Mexico. Showers will continue past
sunrise before ending. For today, areas that were worked over from
the overnight activity, from Tucson west and north will see
little chance of thunderstorms. Best chances will be east and
south of Tucson. With a moist atmosphere still in place, heavy
rain will be a concern. Can't rule out a couple severe
thunderstorms across Graham and Cochise counties.

Wednesday: An upper level low, what once was our inverted trof
that passed through the area late last week, will approach the
area from the southwest. I expect a more active day versus today,
especially east of Tucson.

Wednesday night into Saturday: The above mentioned low, now an
open wave trof Wednesday night will usher in much drier air under
westerly flow aloft. This will set the stage for a downturn in
thunderstorm activity that will continue into Saturday.

Sunday and Monday: A return of monsoonal moisture under southerly
flow aloft will bring a chance of afternoon and evening
thunderstorms back to the area.

Below normal temperatures will continue this week, warming up to
seasonable levels this weekend into early next week.

&&

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

Meyer/G/Z

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