Heat in Arizona, August 10, 2020

Area Forecast Discussion
National Weather Service Tucson AZ
835 AM MST Mon Aug 10 2020

.SYNOPSIS...High pressure will push our above average heat to
near record levels the second half of the week. A modest moisture
increase will bring a few storms to the area, but still well below
average for mid August.

&&

.DISCUSSION...Surface dewpoints currently in the mid 30s to mid 40s
across much of southeast Arizona, with a little higher dewpoints
along the International Border. The KTWC 200810 12Z sounding came in
with a paltry 0.83" PW and was rather stable. The models do show
moisture increasing from the south late in the day, however, much of
this will initially mix out as dry southwest flow persists across
the area at the mid/upper levels today. Isolated showers and
thunderstorms will develop well south and east of the Tucson Metro
area yet again today, mainly east of a line from Nogales to Mt.
Graham to Hannagan Meadow.

High temperatures will top out 5-10 degrees above normal across
southeast Arizona today, with mid 90s to near 100 degrees across
Santa Cruz/Cochise counties, 102-107 in the lower elevations of
Graham, eastern Pima and Pinal counties and 104-109 across
central/western Pima county.

Overall, current forecast looks on track. No updates this morning.
For more information on the latter periods of the forecast, please
refer to the PREV DISCUSSION section below.

&&

.AVIATION...Valid through 11/18Z.
SKC-FEW clouds west of KTUS with SCT clouds 10-15k ft MSL generally
east of of KTUS. Expect a slight chance of -TSRA/-SHRA this
afternoon mainly across the higher terrain of Cochise County and the
White Mountains, quickly diminishing after sunset. SFC wind less
than 12 kts and variable in direction thru the forecast period.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Still just enough moisture today for a slight chance
of showers and thunderstorms mainly across the higher terrain along
the International border from Nogales eastward and in the White
Mountains. Otherwise, hot and dry weather will be the main theme of
the week with very limited thunderstorm chances in the higher
terrain. A modest increase in moisture is possible this weekend for
a few more thunderstorms. 20-foot winds follow typical diurnal
patterns at less than 15 mph. However, this dry and hot regime will
be more conducive to producing gusty outflow winds should
thunderstorms develop nearby.

&&

.PREV DISCUSSION...The high pressure ridge across southern tier
states continues to be far enough west to bring an unfavorable flow
for importing deep moisture into the region. Our surface dew points
are in the 30s to 40s and we're actually under 1 inch precipitable
water. The good news is that there's a surge pushing up the Gulf of
California this morning, and should push into the lower deserts
later today and tonight. It doesn't look terribly deep, but it
should manage to push our dew points back to more seasonable levels.
36 hour HREF probabilities suggest 50 degree dew points through much
of the southern half of the state Tuesday morning, with 55+ degrees
near the border. NAEFS mean precipitable water percentiles nudge
closer to average with 1.25 inches pushing into the western deserts
and 1.5 inches pushing from southern back into central Sonora.

As this happens though, the western flank of the ridge will
strengthen with a new high center consolidating over southeast
Arizona and southwest New Mexico the second half of the week. Even
with the modest moisture increase, that should push heat to near
record levels around 12 to 14 degrees above average by Thursday and
Friday (heights and thicknesses actually support a couple of degrees
hotter than that without the moisture). With strong mid level
heating and subsidence, any moisture increase will be at least
partially wasted due to less favorable thermodynamic conditions for
thunderstorms.

The bottom line is hotter with the Monsoon continuing to sputter for
now.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Thursday morning through Sunday evening
for AZZ501>506-509.

&&

DISCUSSION...Zell
PREV DISCUSSION...Meyer

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