Heat in Arizona, August 20, 2024

Area Forecast Discussion
National Weather Service Tucson AZ
926 AM MST Tue Aug 20 2024

.SYNOPSIS....There will be a daily chance of mainly afternoon and
evening showers and thunderstorms through the work week across much
of southeast Arizona. The thunderstorms will be accompanied by the
typical monsoon threats of strong wind gusts, localized heavy
rainfall and flash flooding, and blowing dust. High temperatures
will be several degrees above average today before falling a
few degrees mid to late week.

&&

.UPDATE...
Today is shaping up to be another active monsoon day with a focus
of convective activity to the south and west of Tucson. PWATs are
around 1.2 to 1.4 inches over Tucson increasing gradually to 1.6
to 1.7 inches by Ajo. DCAPE values are around 1600 J/kg right now
and will be around 1600-1800 J/kg at the time of convection this
afternoon. Timing of storm development is around 1-2 PM MST along
the International Border moving generally to the northwest. There
is a chance for storms to impact the Tucson area around 4-6 PM
MST. The main concerns associated with storms today is strong
winds, there is a 10 percent chance for winds greater than 50
knots focused Tucson westward as denoted by the HREF, and locally
heavy rainfall. Flash flooding will be more of a concern for
slower moving storms and those that are west of Tucson, where
there is more moisture. High temperatures is also something to
keep in mind today. Most of southern AZ is at Moderate HeatRisk,
meaning that most individuals will be impacted by the heat,
especially those without proper cooling.

&&

.PREV DISCUSSION... /issued 131 AM MST Tue Aug 20 2024/

.DISCUSSION...Mostly clear to partly cloudy skies across SE Arizona
early this morning with just a couple of small and very light
showers from time-to-time. Most notable is a strong MCS down in
Sonora that is pushing across the Gulf of California into the Baja
peninsula. That is a favorable setup for enhancing a moisture push
up the Gulf and the high res models do indeed show a reinforcing
push of moisture into the lower deserts west of Tucson this morning.
In the mid/upper levels, the high will be centered today across NM
with an inverted trough moving west from Chihuahua into Sonora.
While our area will remain on the northern periphery of this
feature, it will enhance our mid level flow a bit today resulting in
a stronger shear profile. Moisture levels will be fairly consistent
with what we've seen the past couple of days as drier air. PWAT
values at or even less than 1 inch near the NM border, to around
1.3" near Tucson and 1.5" for western Pima County. HREF/CAMS/UofA
WRF are depicting the focus for showers and thunderstorms today to
be from the Tucson area south and westward. Given the increased
shear, a few of the storms could be on the stronger side. Expect the
typical threats today including gusty winds, locally heavy rain and
small hail.

Heading into Wednesday, the mid/upper level pattern transitions to a
more southerly flow between the high off to our east and troughiness
near the west coast. Deep low level moisture continues to be
reinforced tonight into Wednesday with PWAT values increasing on
Wednesday to around 1.2 inches eastern areas to 1.8 inches in the
western deserts. The ingredients are certainly there for a pretty
active day for convection Wednesday with more of a hybrid severe
(wet microburst) and flash flood threat.

The flow aloft gradually becomes a bit more south-southwest Thursday
into the weekend as the troughiness moves into the Great Basin and
displaces the subtropical high into the central CONUS. While
considerable moisture remains Thursday for scattered showers and
thunderstorms for much of the forecast area, a notable drying
trend is expected Friday into the weekend as the focus for mostly
isolated showers and thunderstorms shifts towards locales south and
east of Tucson. By early next week, as the flow pattern becomes more
southerly to southeasterly that will become more favorable again for
storm coverage to gradually ramp back up.

Temperatures will remain hot once again today with highs about
5 degrees above normal. Modestly cooler Wednesday through the
weekend with temperatures near to slightly above normal.

&&

.AVIATION...Valid through 21/12Z.
FEW-SCT clouds at 6k-9k ft AGL and SCT clouds AOA 15k ft AGL
this morning. Aft 20/18Z, FEW-SCT clouds (locally BKN) at 6k-9k
ft AGL and ISOLD-SCT SHRA/TSRA mainly west of KALK to KE77 line thru
21/03Z, then diminishing thru the end of the forecast period. MVFR
conditions near TSRA, with VSBY restrictions, wind gusts to 45+ kts,
heavy rain and mountain obscurations. Outside of thunderstorm wind
gusts, wind speeds will be 12 kts or less, favoring a SELY direction
this morning, then SWLY thru NWLY direction this afternoon into
evening. SFC wind variable in direction at other times. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...There will be a daily chance of mainly afternoon and
evening showers and thunderstorms across southeast Arizona through
Thursday, with a significant drying trend Friday through the
weekend. High temperatures will be 3 to 6 degrees above normal
today, lowering to 1 to 4 degrees above normal Wednesday
into the weekend. Min RH values will be in the 20-30 percent range
in most valleys locations this week (except lowering to near 15
percent in eastern Cochise and the upper Gila River valley today).
Min RH values are expected to lower by late this weekend
as the drier overspreads the area. 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.
&&

Public...Malarkey
Aviation...Aviation Forecaster
Fire Weather....Fire Weather Forecaster

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