570
FXUS65 KTWC 192126
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
226 PM MST Fri Jul 19 2024

.SYNOPSIS...Temperatures will remain 4 to 7 degrees 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.

&&

.DISCUSSION...The big forecast question for today is to gage how
much activity will we see across Southeast Arizona today. At 2 PM
MST this afternoon, we are seeing two distinct areas of
thunderstorm activity. The first is up along the Mogollon Rim and
the higher elevations in northern Graham and Greenlee counties.
The second is down along Santa Cruz and southern Cochise counties.

The upper pattern is defined by the 500 mb centered over central
Arizona this morning. This feature will slowly drift WNW toward
west central Arizona by this afternoon, then up toward southern
Nevada by Saturday afternoon. This will serve to setup a more
favored NE flow off the White Mountains/Mogollon Rim (rimshot
pattern) that generally results in stronger thunderstorms
impacting Southeast Arizona. Today is kind of that transition day
where all the ingredients are not setup yet like it will be for
this weekend. Expect storms to fire up in the higher terrain and
push SW into the lower elevations by late this afternoon into this
weekend. The 19/12 HREF reflects this thinking by showing a 70%
chance of outflow winds in excess of 30 kts begining across
northern Greenlee at 23Z, then expanding SW into the rest of
Graham and SE Pinal counties by 02Z. The latest GOES derived
precipitable water imagery shows a general increase in PWAT values
east and NE of Tucson (increasing from near 1 inch up to 1.25
inches) over this time yesterday morning. Dry enough to aid strong
thunderstorm downdrafts/outflows, but also enough to help
increase the potential for heavy rainfall. The 19/12Z HREF depicts
a 50% probability of 3-hour rainfall exceeding an inch with the
storms that move off the higher terrain in central Graham and
Greenlee counties. Not great, but not bad. It just means that we
will begin to transition from just wind was the primary
thunderstorm threat to a more dual threat with wind and heavy
rainfall as we transition into the weekend.

A weak mid-level disturbance moving into the far SE corner of the
state this afternoon should help initiate convection across
Cochise and Santa Cruz county during the mid-afternoon hours
today. We have moistened up a bit in these areas as well over the
past 24 hours, so the treat of a strong thunderstorm outflow is
present...but lower than yesterday. The 19/12Z HREF has this area
painted with a 50% chance of outflow winds 30+ kts starting at
22Z.

As mentioned yesterday, as we move into this weekend and next
week, the upper high positions itself near southern NV which would
suggest the stronger NE flow pattern will continue into next week
for our neck of the woods. The strongest days are still looking
like Saturday and Sunday as the mid-level flow is the strongest
for Southeast Arizona.

&&

.AVIATION...Valid through 21/00Z.

SCT-BKN clouds at 8k-12k ft AGL with SCT TSRA/SHRA through
midnight, with similar conditions expected Saturday between
20/18Z and 20/00Z. MVFR conditions in TSRA, with mountain
obscurations, vsby reductions and wind gusts to 45+ knots. Outside
of TSRA, SFC wind at most locations 12 knots or less favoring
NWLY direction during the afternoon/early evening hours and
variable in direction at other times. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Deeper moisture remains across southeast Arizona,
with typical July moisture levels expected into at least early next
week. 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 during the
afternoon hours will primarily be west to northwest through the
weekend, especially from Tucson westward and in the upper Gila River
Valley.

&&

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

&&

$$

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