Heat in Arizona, August 28, 2024

Area Forecast Discussion
National Weather Service Tucson AZ
903 AM MST Wed Aug 28 2024

.SYNOPSIS...Isolated to scattered showers and thunderstorms through
Sunday, then a decrease in storm coverage next week especially from
Tucson westward. High temperatures will be within a couple of
degrees of normal through early next week.

&&

.UPDATE...Clear skies over western and central Pima County
this morning, with the remainder of the forecast area generally
under mostly cloudy skies. We are seeing some light shower activity
mainly from points north and east of Kitt Peak. This is all the west
side of an MCV that is currently located along the AZ/NM border near
southern Greenlee County and moving northward. The shower activity
and cloudiness will tend to be slow to diminish from Tucson north
and eastward today which may also prevent temperatures from getting
as warm as they would otherwise. HREF/CAMs do show modest
instability of around 500-1000 J/KG of MLCAPE, mostly in which areas
that do see solar insolation. Expect isolated to scattered showers
and thunderstorms to redevelop this afternoon, but not be
particularly strong today. With that said, we'll continue to have
the usual threat for locally heavy rain and some gusty winds with
the storms that are out there. HREF neighborhood probabilities for 1
hour rainfall greater than 1" are less than 20 percent so widespread
flash flooding is not expected.

&&

.DISCUSSION...In the large scale, an elongated ridge of high
pressure extends across the southern tier of states, with high
pressure centers over the lower Mississippi valley and the eastern
Pacific Ocean west of the central California coast. A low pressure
system was also moving eastward along the Canadian border in far
western Montana. Current PWAT values range from near 1.0" in far
western Pima County to 1.30" from Tucson southeastward. The
240828/00Z KTWC sounding indicates south to southeast flow in the
lower/mid levels, which will keep sufficient moisture in place
across the forecast area for isolated to scattered showers and
thunderstorms the next couple of days. By late this week and over
the weekend, the upper high currently in the eastern Pacific will
shift northeast into the northern Great Basin. This pattern will
allow drier air to begin to mix in from the west, with showers and
thunderstorms mainly east of Tucson. By early to mid next week, the
upper high shifts to our northeast over the central plains. This may
allow moisture to move back into the area from the east, but at this
time, it is to far out to tell how far westward the moisture push
will be. High temperatures will be within a couple of degrees of
normal through early next week.

For today and tonight, the CAMs keep isolated to scattered showers
and thunderstorms going through the early to mid morning hours today
and then regenerating isolated to scattered activity late this
morning through the afternoon hours, mainly east of Sells eastward
to the New Mexico border. DCAPE values support thunderstorm wind
gusts to 40-45 mph, with the main threat being isolated areas of
heavy rainfall. The WPC marginal risk for excessive rainfall
today/tonight is east of a Nogales to Tucson line. Most of the
activity is expected to diminish by the late evening hours tonight.

For Thursday through Sunday, moisture decreases across western
portions of the forecast area which will significantly decrease
storm chances in those areas. Isolated to scattered showers and
thunderstorms are expected mainly to the south and east of Tucson.

For Monday through Wednesday of next week, the current forecast has
isolated storm chances confined mainly to the International Border
southeast of Tucson and in the White Mountains.

&&

.AVIATION...Valid through 29/12Z.
SCT clouds at 8k-12k ft AGL and BKN-OVC clouds AOA 15k ft AGL along
with ISOLD -SHRA/-TSRA thru 28/15Z, then slowly decreasing clouds
thru 28/19Z. Between 28/19Z and 29/04Z, SCT-BKN clouds at 6k-9k ft
AGL and ISOLD-SCT SHRA/TSRA from Sells eastward. Slowly decreasing
clouds aft 29/04Z. Visibility restrictions, wind gusts up to 40 kts,
heavy rain, small hail and mountain obscurations possible with the
stronger TSRA. Outside of thunderstorm wind gusts SFC wind 12 kts or
less, favoring a WLY/NWLY direction during the afternoon hours and
variable in direction at other times. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...There will be isolated to scattered showers and
thunderstorms through Sunday, with a decrease in coverage late in
the weekend and next week. Min RH values will be 20-30 percent in
most valley locations, with minimum's of 15-20 percent west of
Tucson across central/western Pima County. Outside of any
thunderstorm outflow winds, 20-foot winds will generally be 15 mph
or less, with afternoon/early evening gusts to 20-25 mph and light
winds overnight.

&&

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

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