767
FXUS65 KTWC 161629
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
929 AM MST Tue Jul 16 2024

.SYNOPSIS...Temperatures slightly above normal through the rest
of this week, with typical mid July moisture levels across the
region. This will result in the daily chances for showers and
thunderstorms. The main threats will continue to be strong gusty
outflow winds and heavy rainfall leading to localized flash
flooding.

&&

.UPDATE...It is one of those rare mornings during the Monsoon
season that we are experiencing not just your normal debris
cloud/weak showers, but showers with embedded thunderstorms
with a little more oomph across eastern Pima County (including
the Tucson Metro Area) and extending into Western Pima. The
16/12Z KTWC sounding shows decent CAPE between 600-400mb for these
storms to tap into. So, it is unstable enough for the weaker
storms this morning to move east-to-west across the area. In a
loop of the latest visible satellite imagery this morning, you
can pick out a weak MCV centered west of Sasabe...moving west
which is helping initiate thunderstorm activity farther west.
Other than the aforementioned instability, I can`t quite put a
thumb on why Tucson is as active as it is has been this morning.
In any event, these storms will weaken over the next few hours.
Expectation is that the weak MCV moving west across central and
Western Pima county will be well west of our area for it to
provide enough subsidence on the backside to delay thunderstorm
initiation across SE AZ this afternoon and this evening.


So, you might ask...what in the world is going to happen today? I
would answer...good question. The big picture is that the
500mb-300mb high is centered over central New Mexico this morning,
with the flow around this feature resulting in a diffluent area
across Southeast Arizona. In addition, as a strong trough moves
into the Pacific Northwest today, it forces the high to align
into a NW-SE orientation...which also brings some stretching
deformation into the mix to assist in the lift across SE AZ. The
third thing of note today is a weak vort max in SW Texas, which
you can see a very weak indication of this feature in a loop of
the water vapor imagery, expected to drift into the far SE corner
of the state late this afternoon into this evening.

So, our early thinking is that we will will see thunderstorm
activity begin NE of Tucson this afternoon with activity SE of
Tucson delayed a bit until the late afternoon and evening. This
matches up with the University of Arizona 16/12Z WRF-RR run that
even delays the majority of the activity well into the evening
hours and just clipping the Tucson Metro Area around 10 pm MST.

Drier air in the mid-levels of the storm residing in NM and will
push west and entrain into the thunderstorms along the Arizona/New
Mexico border. The 16/12Z HREF is suggesting a 50-70 percent
likelihood of wind gusts in excess of 30+ kts from storms east of
Tucson today. It should be noted that 16/00Z HREF run had a 10
percent chance of wind gusts in excess of 50 kts but has backed
off on this run. The 16/12Z HREF is also pinpointing the heaviest
rainfall to occur S and SE of Tucson in Cochise and Santa Cruz
counties this afternoon/evening with a 10-30 percent chance of
3-hr rainfall amounts in excess of 1 inch, and even a 10 percent
chance of rainfall in excess of 3 inches along the International
Border.

In general, the main threat from storms today will be strong and
gusty thunderstorm outflows, but heavy rainfall is also in the
mix...especially S and SE of Tucson in Cochise and Santa Cruz
county where there is a better mix of moisture, lift and instability
in the late afternoon and evening.

&&

.PREV DISCUSSION... /issued 217 AM MST Tue Jul 16 2024/

We still have ongoing convective activity early this morning
across far SW Cochise County and Santa Cruz County. This is likely
due to an MCV just south of the International Border. Latest HRRR
is struggling to pick up on this feature but do expect activity
to gradually diminish over the next couple of hours as it pushes
west. Meanwhile, for the rest of southeast Arizona, skies are
clear to partly cloudy and n o precipitation.

The broader pattern features the mid/upper level high near the Four
Corners region and this continues to result in easterly mid level
winds. Meanwhile, lower level flow will continue to slosh Gulf of
California moisture into the deserts. With that said, moisture
levels are fairly typical for this time of year with PWAT values
today around 1.25" to 1.50" from Tucson westward with some slightly
drier air hanging on for eastern areas as PWAT values are 0.75" to
1.25" east of Tucson. HREF/CAMs are pretty consistent in developing
scattered showers and thunderstorms this afternoon primarily across
Santa Cruz and Cochise Counties and another area on the White Mtns
and this will push to the west or west-southwest into the evening
hours. HREF members do tend to struggle holding convective activity
together as it pushes west of Tucson so we`ll have to see if that
holds up. With expected SBCAPE values over 1000 J/KG and DCAPE over
1500 J/KG, we`ll continue to have a hybrid severe threat for wind
and localized flash flooding threat in areas that see cell
mergers/clustering. SPC and WPC both have us in marginal risk areas
for thunderstorms and excessive rain, respectively.

The flow pattern remains similar on Wednesday. HREF members are
slightly less bullish Wednesday for convective coverage compared to
today but there isn`t a significant discernible difference in the
flow pattern or other convective parameters. Thereafter, not much
change for Thursday and Friday with continued daily rounds of shower
and thunderstorms. Expect typical variability in day-to-day trends
depending on smaller scale factors that aren`t identifiable this far
out. For this weekend into early next week, the high will shift a
bit more to the west and that will change our flow pattern to a more
northeasterly direction with increased chances of convection pushing
off the Mogollon Rim towards the lower elevations.

Temperatures through the period will remain several degrees above
normal.

&&

.AVIATION...Valid through 17/12Z.
BKN-OVC clouds 8-12k ft AGL near the International border including
KOLS will tend to diminish aft 16/12Z. Elsewhere, SKC-SCT clouds
this morning. SCT-BKN clouds redevelop again aft 16/18Z, with
diminishing cloud cover aft 17/05Z. SCT TSRA/SHRA thru 16/11Z,
mainly near KOLS. SCT TSRA/SHRA developing again for much of the
area aft 16/19Z. MVFR conditions in TSRA, with mountain
obscurations, vsby reductions and wind gusts to 40+ knots. Outside
of TSRA, SFC wind at most locations 12 knots or less favoring a SWLY
thru NWLY direction during the afternoon/early evening hours and
variable in direction at other times. The exception will be in the
upper Gila River valley near KSAD where WLY/NWLY SFC wind will be 15-
22 kts with gusts to 30 kts between 16/18Z and 17/03Z. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Deeper moisture remains across southeast Arizona,
with typical mid July moisture levels expected through at least the
upcoming weekend. This will result in the daily cycle of mainly
afternoon and evening showers and thunderstorms. The main threats
will be strong, gusty and erratic outflow winds and heavy rainfall
leading to localized flash flooding. Minimum relative humidity
values will be 20-30 percent in most lower elevation locations and
25-40 percent in mountain areas. Away from thunderstorms, 20-foot
winds will generally be 15 mph or less, with afternoon/early evening
gusts to 20-25 mph and light winds overnight. Wind direction will
primarily be southwest through northwest through most of the week.
The exception will be in the upper Gila River valley around Safford,
where afternoon/early evening winds will be west-northwest at 15-20
mph and gusts to 25-30 mph today.

&&

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

&&

$$

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