Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 241705

Area Forecast Discussion
National Weather Service Tucson AZ
1005 AM MST SAT SEP 24 2016

.SYNOPSIS...There is a slight chance of showers and thunderstorms
southeast of Tucson this afternoon and evening. The chance of
showers and thunderstorms increases early next week as a low
pressure system develops south of the area. A drying trend is
expected to occur during the latter part of the upcoming week. Below
normal daytime temperatures will prevail through midweek.


.DISCUSSION...Visible satellite imagery and surface observations
depict partly cloudy to mostly cloudy skies across Cochise/Santa
Cruz Counties east-to-southeast of Tucson at this time. Clear skies
or just a few cumuloform clouds were noted elsewhere. These clouds
were ahead of a mid/upper level trough axis that extended
southwestward from a low pressure system centered over southeast

Dewpoints at lower elevations valid 16Z ranged from the mid 40s-
lower 50s across much of southeast Arizona. However, dewpoints were
only in the lower-mid 30s across western Pima County and south-
central Pinal County. These temps were essentially unchanged across
southeast sections versus 24 hours ago, but were about 10-25 degs
lower from Tucson wwd/nwwd into western Pima/southern Pinal Counties.

Surface temps ranged from a few degs to nearly 15 degs cooler versus
this time Friday, depending upon location. 24/12Z KTWC sounding
total precip water value of 0.61 inch was about 0.30 inch lower
versus 24 hours ago. The environment was quite stable as per
virtually no CAPE and LI`s ranging from plus 3-14 depending upon the
lifting method.

Several HRRR solutions as well as the 24/12Z Univ of AZ WRF-NAM were
similar with depicting a few showers/tstms to potentially occur
across far southeastern sections this afternoon/evening. This area
is progged to have the best available moisture/instability ahead of
the southeastward moving mid/upper level trough axis. Otherwise, dry
conditions will occur across this forecast area into this evening.
High temps this afternoon will be quite similar to temps achieved
Friday, and will average about 5-10 degs below normal.

There are no updates necessary at this time. Please refer to the
additional sections for further detail.


.AVIATION...Valid through 25/18Z.
Isolated -TSRA/-SHRA southeast of KTUS and particularly in the
vicinity of KDUG this afternoon and early this evening. Forecast
confidence of this occurrence is too low to include in the TAF
however. Otherwise, clear skies west-to-northwest of KTUS into
Sunday morning. A FEW to BKN clouds around 5k-8k ft agl will prevail
elsewhere. Surface wind generally less than 10 kts thru the period
except northwest to near 15 kts near KSAD this afternoon. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...A few showers and thunderstorms may occur near the
International border near Douglas this afternoon. The coverage of
showers and thunderstorms will increase early next week due to a low
pressure system south of the area. A drying trend will then prevail
during the latter part of the upcoming week. Expect light terrain
driven winds today, then gusty east winds will develop Sunday
afternoon and continue periodically through Tuesday. Occasionally
gusty southwest to west winds will prevail during the latter part
of the upcoming week.


.PREV DISCUSSION /315 AM MST/...Clear to localized partly cloudy
conditions prevailed this morning across SE AZ. Water vapor imagery
this morning showed an upper low over SW Wyoming with an associated
main trof axis stretching across eastern Colorado and New Mexico.
Latest model runs prog a secondary trof to deepen along the Arizona/
New Mexico border today with a few showers developing across
southern Cochise county. Highs today will run about 6-8 degrees
below normal.

On Sunday the above mentioned upper trof along the AZ/NM border will
turn into a closed upper low over northern Sonora Mexico.
Precipitable water values will start to increase under easterly flow
aloft. There is a slight chance of showers or thunderstorms mainly
south and east of Tucson starting late in the afternoon into the
evening hours. PoP chances increase overnight into Monday morning
from east to west as the upper low retrogrades west across northern
Sonora Mexico. Highs on Sunday will be similar to today.

Generally cloudy day on Monday with scattered areas of light showers
and possibly a few rumbles of thunder. Cooler with highs mostly in
70s across lower elevations of Tucson with 80s elsewhere across the
area. Low level gusty easterly winds kick in Sunday evening and
continues throughout much of Monday.

Continued unsettled conditions on Tuesday with the upper low progged
to be over northern Baja. This low will then lift north northeast
across southeast California toward Nevada on Wednesday. Best chances
for storms will be across eastern half of the forecast area.
Conditions start to dry out on Thursday under westerly flow aloft.





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