Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 272210

Area Forecast Discussion
National Weather Service Tucson AZ
310 PM MST SAT AUG 27 2016

.SYNOPSIS...Drier air associated with a weather disturbance passing
through Arizona will limit thunderstorm activity today into Monday.
With drier air in place, daytime temperatures will warm a few
degrees today through Tuesday. Thereafter, deeper moisture needed to
support daily thunderstorms will return the middle of the
week with high temperatures lowering to more seasonable readings.


.DISCUSSION...Water vapor imagery and 27/12Z upper-air plots show a
trough of low pressure currently across Utah, southern Nevada and
northwest Arizona. Plenty of dry air associated with this system
this far south. The dry mid to upper level air covers much of the
eastern Pacific waters where a large area of high pressure is well
west of the southern Baja peninsula. This dry air extends east
across southern California, much of northern Mexico and into
southern Arizona.

Visible and IR satellite imagery shows extensive cloudiness
associated with the trough mostly over southern Utah, and northern
Arizona. Some mid level clouds also extend south and cover mainly
eastern portions of my forecast area from Tucson to the New Mexico
border and areas east. All of these clouds are moving to the

The 27/12Z KTWC sounding revealed a PW of 1.10 inches, which is down
three tenths of an inch from 24 hours ago. The bulk of this moisture
was in the surface to 525MB layer. Above that, it was very dry. Some
of the sounding parameters indicated Cape ranging from just under
1000 J/KG to near 1500 J/KG, and a lifted index of minus 3 or 4
depending on the method in which the parcel was lifted. The morning
sounding is definitely no longer representative of the airmass
overhead, as significant drying has occurred since that time. Case
in point, surface dewpoints now range from the lower 30s to the
lower 50s, which is around 15 to 25 degrees cooler/drier than the
start of my shift for central areas and 8 to 12 degs cooler/drier
for eastern zones. In addition, the Univ of AZ GPS PW value for
Tucson was around 0.60 inches as of 1845Z. That is a drop of a half
inch in less than 12 hours.

The current radar mosaic from around the state shows most of the
showers and thunderstorms associated with the trough are occurring
just to the east of the New Mexico border and all of this activity
is moving east northeast.

I tailored the POP forecast for this afternoon and evening to
basically follow radar trends, but also to blend with the forecast
from the surrounding offices. That said, looking at just isolated
showers and storms right along the New Mexico border.

For Sunday we should see a repeat of today, but then rain chances
increase a bit for Monday as moisture will be right on the door step
to our east and we will have an east to southeast fetch, which will
bring increasing moisture into our region. Therefore, expect an
uptick in rain chances through the middle of the week before a
Pacific trough begins to push moisture back to the east late in the
week and into the weekend for decreasing rain chances.


Sct-bkn clouds with bases at 8-12k ft agl. Isolated -TSRA/-SHRA
through 28/02z, mainly east of KTUS to the New Mexico border. Brief
MVFR conditions possible with the stronger storms. Clearing expected
aft 28/04z. Surface wind generally less than 12 kts thru the
forecast period, except for strong and erratic outflow winds
possible with the thunderstorms. Aviation discussion not updated for
TAF amendments.


.FIRE WEATHER...Isolated to scattered afternoon and evening
thunderstorms mainly east of Tucson this weekend and during the
upcoming week, with the best chances occurring Tuesday and
Wednesday. 20-foot winds into next week will be terrain driven and
less than 15 mph in most locations. Expect the potential for strong
and gusty winds near any thunderstorms that do develop.






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