691
FXUS65 KTWC 151617
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
917 AM MST Thu Aug 15 2024

.SYNOPSIS...Generally dry and hot today with a slight chance of
a shower or thunderstorm along the International Border and in the
mountains of southeastern Arizona. Thunderstorm chances then
return areawide Friday and continue through at least early next
week. High temperatures will be above normal into next week.

&&

.UPDATE...The 15/12z 500 mb upper air plot showed sub-tropical
ridge over the southern tier of states with one upper high
centered over SW AZ and a second one central Texas. Dry N-NE flow
over the area with precipitable water value (PW) of 1.21" on the
12z Tucson sounding which is down about 0.25" from Wednesday
morning. Overall across SE AZ, PW values ranged from 0.90" near
AZ/NM border to 1.25" west of Tucson. Surface dewpoints ranged
from the mid 50s to the mid 60s at 9 am while satellite imagery
showed a clear sky. For today, any storm activity this
afternoon/early evening will be near the mountains along the Intl
border. Highs today will run up to 5 degrees above normal. See
previous discussion below for further details on scattered storms
returning to the area tomorrow into the weekend.

&&

.PREV DISCUSSION... /issued 243 AM MST Thu Aug 15 2024/
Upper level objective analysis depicts a high pressure center from
southern California through southern Arizona. This center will be
ushered east over the coming 36 hours as a Pacific Northwest
trough deepens and nudges the ridge axis into New Mexico.

Today, high temperatures are expected to be 3 to 6 degrees above
average for this time of year thanks to the warming ridge pattern
aloft and clearer skies. Shallow instability will allow for some
afternoon cloud build ups with potentially an isolated
thunderstorm over the southern mountains, but otherwise a stout
mid- level cap keeps the forecast mostly dry.

Friday the ridge centers over New Mexico, cooling temperatures in
the mid levels a few degrees and returning moisture with
southeasterly flow. Both will contribute in bringing thunderstorm
chances back to southern Arizona, though areas in Pinal, Graham,
and Greenlee counties (outside of the White Mountains) may
struggle to see much with the upper high still in the vicinity.
Friday may be worth watching for a potential severe wind gust day,
depending on details with the pattern transition. Dry mid-levels
would allow for evaporative cooling enhancements of downbursts
and the forecast presence of 20 knot winds at 500mb may aid in
producing longer lived thunderstorm cells. The lingering presence
of the mid-level cap from the nearby ridge will impact
thunderstorm coverage and potentially intensity, so there remains
some uncertainty in the severe hazard ceiling.

Through the weekend the upper high remains generally in place to
the east, keeping southeastern Arizona under favorable
southeasterly flow for moisture transport and thunderstorm
impacts. Though there is some wobbling in amplitude and location,
ensemble solutions generally keep this pattern going through next
week. This produces daily chances for thunderstorms with likely
day to day variance in coverage with the shifting of the upper
level high.

&&

.AVIATION...Scattered clouds at 7k to 10k feet AGL from 15/18Z
to 16/03Z, especially across KOLS- KDUG terminals. Slight chance
of -SHRA or -TSRA across the south during this period as well.
Clearing skies after 16/03Z. Erratic wind to 40 kts with -TSRA.
Otherwise wind 12 kts or less favoring west to northwest direction
during the day, then light and variable late.Aviation discussion
not updated for TAF amendments.

&&

.FIRE WEATHER...A slight chance of a thunderstorm in the
mountains mainly south and southeast of Tucson today, with dry
conditions expected elsewhere. Moisture then returns Friday into
next week, with a daily chance of showers and thunderstorms across
much of southeastern Arizona. High temperatures will be 3 to 6
degrees above normal through at least early next week. Min RH
values will be in the 20-30 percent range in most valleys
locations (lowering to near 15 percent in eastern Cochise and the
upper Gila River valley) through early next week. 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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Aviation...Aviation Forecaster
Fire Weather....Fire Weather Forecaster

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