649
FXUS65 KTWC 081724
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
1024 AM MST Mon Jul 8 2024

.SYNOPSIS...Excessive heat continues through mid-week with high
temperatures expected to approach record levels in some locations.
Substantially drier air moving in from the north has reduced
thunderstorm chances today, but returning moisture should begin to
increase chances again starting Tuesday.

&&

.UPDATE...Excessive heat. Nobody is a fan of it becasue it is
potentially deadly. Its almost a broken record at this point, but
it remains significantly impactful for Southeast Arizona not only
today but well into this week. The 08/13Z NBM probabilities for
Tucson exceeding 110 degrees this week are 80% today/55%
Tuesday/55% Wednesday/55% Thursday and 25% Friday. We are running
approximately 0 to 4 degrees warmer than this time 24 hours ago
across the CWA, with KTUS already at 99 degrees at 10 am MST.
Current forecast high temp for Tucson is 111 degrees and this
seems on track.

With regards to thunderstorm activity, today will be another quiet
day across the entire forecast area. The SE extent of the upper
ridge centered over central California will be just too much warm
air for us to overcome this afternoon. Even surface dewpoints are
meek this morning, with values in the upper 40s to mid 50s in the
valleys which will continue to mix out thru the afternoon. So, no
storms today with maybe some cumulus developing over the higher
terrain.

This will begin to change as we move through the week though. A
N/S oriented jet streak seen on the eastern periphery of the upper
ridge this morning will assist in the re-orientation of this
feature from a negative tilt this morning to a more neutral tilt
Tuesday. As this occurs, areas east of Tucson will start to see
an area of weak diffluence and stretching deformation aloft,
which will in turn assist in the overall lift. In addition, CAMS
are suggesting an outflow from storms in NM today will import
some lower level moisture into the eastern locales overnight. The
combination of these two things will bring back thunderstorm
activity east of Tucson tomorrow. With the excessive heat in place
and pockets of dry air in the middle levels, the threat tomorrow
will be from strong thunderstorm outflows. At this stage, I dont
believe the extent of any outflows impacting locations as far west
as Tucson will occur tomorrow, but we will see thunderstorm
coverage expand west across the rest of the CWA beginning Wednesday
as the flow aloft becomes NE (more favorable for a rim-shot).

In any event, down today but thunderstorm activity will ramp up
this week.

&&

.PREV DISCUSSION... /issued 253 AM MST Mon Jul 8 2024/

.DISCUSSION...

The heat spell across southeastern Arizona continues with
forecast highs approaching or exceeding at times daily record
highs over the next several days. Forecast highs today and
tomorrow in Tucson (111 and 110 degrees) would tie records for
each day. The strong ridge over the western CONUS responsible for
these hot temperatures will remain generally stationary through
Tuesday, then will begin to shift east before becoming centered
over Utah/Colorado this weekend. With this pattern shift will come
a turning of the mean winds from northerly to easterly, and in
turn better flow for moisture return into the region. The ongoing
Excessive Heat Warning was expanded into the Santa Cruz county
area zone and extended into Wednesday. It`s possible excessive
heat may continue into Thursday, however the influx of moisture at
that point adds uncertainty to the mix.

Mid-level warming and a dry atmospheric column remains in place
today, which leaves little opportunity for convection to develop.
A very slight chance of a thunderstorm is forecast near the
southern and eastern edges of Cochise county. On Tuesday, 500mb
temperatures will cool a couple degrees and allow for modestly
better instability to develop. While precipitable water should
remain unimpressive still, a few thunderstorms will be possible
Tuesday afternoon and evening, generally near and east of Tucson-
Nogales with best chances closer to the New Mexico border. With a
deeply mixed boundary layer in place, strong outflow winds will
be possible under any thunderstorm.

Similar setups are likely Wednesday and Thursday before flow
becomes more easterly by Friday, ushering in richer moisture for
the weekend. Daily precipitation chances increase notably through
this period across southeastern Arizona as precipitable water
values should range from near 1 inch to 1.5 inches and the upper
low will become favorably positioned to usher in a stream of
easterly shortwaves.

&&

.AVIATION...

SKC across southeastern Arizona outside of areas near KDUG and the
New Mexico border where FEW-SCT ceilings around 12k feet are
possible after 08/18Z, with a slight chance of a thunderstorm
through the evening. Winds today become west to northwesterly and
increase to 10 to 15 kts with gusts to 20 to 25 kts after 08/17Z,
decreasing after 09/02Z.

&&

.FIRE WEATHER...

Today should see the lowest minimum relative humidities of the
week as moisture is expected to gradually push back into
southeastern Arizona in the coming days. Relative humidity values
should fall into the single digits in lower elevations today,
while west to northwest winds of 12 to 16 mph, with wind gusts up
to 25 mph, are expected. Tuesday through Thursday minimum
relative humidities should remain in the 10 to 16 percent range in
lower elevations and 15 to 30 percent in mountain areas. 20-foot
winds will generally be 15 mph or less each afternoon with
occasional gusts to 20 mph. Daily chances for thunderstorms begin
to arrive Tuesday, with the possibility of strong outflow winds
under any thunderstorm.

&&

.CLIMATE...
Near record to record high temperatures today, Tuesday, and
Wednesday.

DATE                         Jul 08           Jul 09           Jul 10
                          FCST RCD/YR      FCST RCD/YR      FCST RCD/YR
Tucson Intl Airport       111 111/1994     110 110/1979     110 109/2021
Picacho Peak              114 114/2017     113 113/1994     112 111/1995
Safford Ag Station        112 107/2002     108 108/1956     108 110/2003
Sierra Vista FD           102 102/2023     100 103/2003     100 102/2003

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM MST Wednesday for AZZ501>506-
509.

&&

$$

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