Heat in Arizona, August 16, 2022

Area Forecast Discussion
National Weather Service Tucson AZ
941 AM MST Tue Aug 16 2022

.SYNOPSIS...Shower and thunderstorm chances will continue. A slight
downward trend in storm activity is expected today before ramping
back up the second half of the week into the weekend. Temperatures
will remain near seasonal averages through Wednesday, lowering to
nearly 10 degrees below normal this weekend.

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.DISCUSSION...Several weak circulations showing up on water vapor
satellite imagery this morning that recent model solutions were
having trouble resolving. One circulation was near the northern Gulf
of California and another farther south that was triggering some
thunderstorms over the Gulf's water. These features will likely play
a role in the development of thunderstorm activity across SE AZ
today. That said, the main areas of concern will be near the
International Border and central Pima county today. Thereafter, an
uptick in thunderstorms can be anticipated into the weekend as a low
pressure system centered south of the Texas Big Bend this morning
approaches from the east and becomes somewhat stalled over Sonora,
Mexico. Please refer to the previous discussion section in this
product for more details.

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.AVIATION...Valid through 17/18Z.
Expect lingering SCT-BKN high clouds through the early morning then
mostly clear skies until early afternoon. Thereafter, expect SCT-BKN
clouds 7k-12k ft AGL. ISOLD-SCT SHRA/TSRA developing around 16/20Z
and persisting thru 17/04Z mainly from Tucson south and westward.
With the stronger TSRA, expect cloud decks to lower to 4k-6k ft AGL,
wind gusts to 45+ kts, vsby reductions, and mountain obscurations.
Outside of any TSRA, SFC wind generally less than 10 kts and
favoring a NWLY direction in the afternoon/early evening hours and
variable in direction at other times. Aviation discussion not
updated for TAF amendments.

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.FIRE WEATHER...Expect a daily chance of showers and thunderstorms
through the upcoming weekend, with increasing precipitation chances
late in the week into the weekend. The main threats will be strong
gusty winds and heavy rainfall/flash flooding. There is the
potential for precipitation outside the normal afternoon/evening
cycles. Outside of thunderstorm outflows, wind trends will be light
and follow typical diurnal patterns.

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.PREV DISCUSSION.../Issued 150 AM MST Tue Aug 16/
Very little precipitation was observed across southeast Arizona
through the late evening hours and into the early overnight hours,
with just some light showers noted on the KEMX radar near Sells and
across northern Graham/Greenlee counties. A weak flow regime will
continue today, with models showing PWATs lowering to near one inch
across the eastern half of the forecast area and between 1.25-1.50
inches from Tucson westward. Mid level water vapor satellite imagery
supports this drying (especially across eastern areas), with drier
air noted over central/eastern New Mexico pushing westward ahead of
an upper level disturbance over southwestern Texas. High resolution
models all point to today having limited thunderstorm activity
across southeast Arizona, with the favored areas south to southwest
of Tucson.

Things then get very interesting in the Wednesday through Sunday
time frame. Models are in good agreement with the leading edge of
the aforementioned easterly wave/inverted trough/upper level
disturbance moving northwestward into far eastern portions of the
forecast area Wednesday afternoon/evening. Typically, the leading
edge of these features are very active convection wise. Expect
increased thunderstorm activity to persist Wednesday night and
Thursday as this features tracks westward across northern
Sonora/southern Arizona. Given the extra lift, shear profiles and
increasing moisture, organized convection/severe thunderstorms will
be a possibility, along with an increasing flash flood risk.

Friday through Sunday appear to have the highest threat for flash
flooding across southeast Arizona. ECMWF mean PWATs are over 1.5
inches and approach 2.0 inches at times. The ECMWF EFI highlights
areas right along the International Border Friday and Saturday, with
southeast Arizona highlighted on Sunday. The upper level pattern
begins to shift this weekend, with the upper high splitting into two
centers, one to the west off the California coast and one to the
southeast over central Texas. This puts Arizona into a 'squeeze
play' situation between circulation centers, potentially increasing
convection across the area as the models lift another upper level
disturbance from northern Mexico northward across Arizona. So while
all factors point to a very active monsoon pattern as we head into
the weekend, there have been times when atmospheric moisture values
approaching 2 inches have led to extensive cloud cover which has
actually limited convection due to the lack of solar heating, or
resulted in only widespread shower activity. Stay tuned. Time will
tell.

Otherwise, high temperatures today and Wednesday will be right
around normal levels, lowering to 3-6 degrees below normal Thursday
and 7-10 degrees below normal Friday through Sunday.

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

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