Heat in Arizona, June 26, 2018

Area Forecast Discussion
National Weather Service Tucson AZ
840 AM MST Tue Jun 26 2018

.SYNOPSIS...Dry conditions with above normal temperatures
through Wednesday. A few thunderstorms may develop Thursday
afternoon across far southeast sections. Enough moisture will then
prevail Friday into early next week for a chance of mainly afternoon
and evening thunderstorms, especially east to south of Tucson.

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.DISCUSSION...Upper air plots this morning placed the upper high
center just north of Tucson with weak easterly flow over the area.
Atmosphere has dried out in the past 24 hours with the
precipitable water value on the 12z Tucson sounding coming in
around a half inch which is down two-tenths of an inch since
Monday morning. This is really reflected in the surface dewpoints
which are down 10-30 degrees across the region since Monday morning.

The upper high will strengthen a bit today as the center moves
into west-central New Mexico this afternoon. This will result in
warmer daytime temperatures with highs running 2-4 degrees warmer
than Monday. Similar temperatures on Wednesday with the high
center remaining over west-central New Mexico.

Infrared satellite imagery this morning showed a few remnant
debris clouds south of Tucson that were associated with last
nights thunderstorm complex that was over west-central Chihuahua
Mexico. Water vapor imagery showed weak inverted trof off Baja
California with a strong inverted trof south of the Texas Big Bend
over the Mexican state of Coahuila. Looking at precipitable water
imagery across Sonora Mexico this morning values ranged from 0.50
near the Intl border to 1.4" near Hermosillo to 1.9" across the
southern part of that state.

Thunderstorm activity will continue to increase across eastern
Sonora/western Chihuahua over the next several days as the above
mentioned inverted trof south of the Big Bend continues to move to
the west. Thunderstorm outflows will send shallow moisture seeps
toward southeast Arizona over the next several night. May have
enough moisture near the International border Thursday afternoon
and evening for a very slight chance of high based thunderstorms.

An approaching upper level trof late Thursday into Friday will
bring a more southerly flow over the area resulting in the higher
moisture values across Sonora Mexico to be advected north across
southeast Arizona. Differences still remain between the wetter GFS
and drier ECMWF for Friday. Current forecast leans more toward
the wetter GFS. Thus see no reason to back away from the isolated
to scattered showers and thunderstorms Friday afternoon and
evening with lingering storms continuing into the overnight hours.
Could see a few severe storms Friday with inverted-V profiles with
areas of blowing dust possible.

Moisture then hanging around for the weekend for a slight chance
of showers and thunderstorms. Models suggesting the upper high
will be position near the four corners region next week putting
the area under a favorable easterly flow pattern.

&&

.AVIATION...Valid through 27/15Z.
FEW clouds AOA 20k ft AGL south of KTUS this morning. Expect FEW
clouds at 10k-14k ft AGL to develop mainly east and south of KTUS
this afternoon. SFC winds will remain light and terrain driven
through the morning before becoming WLY/NWLY at 10-18 kts with
gusts to 25 kts possible. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Dry conditions will prevail through Wednesday before
thunderstorm chances increase along the International Border
southeast of Tucson Thursday afternoon. Chances will expand Friday
and into early next week to allow for isolated to scattered
thunderstorms each afternoon in the Tucson vicinity and areas east
and south. 20-foot winds will generally remain below 15 mph, except
for in and around thunderstorms where gusty outflow winds may occur.

&&

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

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