Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 301649

Area Forecast Discussion
National Weather Service Tucson AZ
949 AM MST FRI SEP 30 2016

.SYNOPSIS...A drying trend from the west will reduce the chance of
storms today, all but eliminating them over the weekend. A trough
will bring cooler air and a few showers back to the area late Monday
or Tuesday. High pressure will bring dry conditions and a rapid
warming trend the second half of next week.


.DISCUSSION...We remain in between major features with the strong
trough digging down the west coast and high pressure through
Mexico and Texas. A smaller scale weakness in the flow will be
pushing across central Arizona from the west today.

Actual blue skies for most areas this morning. Considerable
drying above 550hPa over the past 12 hours. The beginning of that
drying trend allowed enough afternoon heating to help set off an
explosive thunderstorm day yesterday, but today it will start to
slow things down as it eats away at our convective potential.
Surface based CAPE around 1400 j/kg yesterday afternoon is down to
around 250 on the 12z KTWC sounding and will probably max out
around 500-600 this afternoon. Shear is down a little as well
with 30+ kts yesterday down to about 20 kts this morning, but with
an uptick back to around 25 kts possible by this afternoon. Overall
our best thermodynamics will probably be east of Tucson today, but
with plenty of solar insolation and residual moisture we will have
a few echoes dotted around other areas as well. Our current
forecast looks pretty good in that respect, so no updates expected
this morning.

Please see the previous discussion below for details beyond today.


.AVIATION...Valid through 01/18Z.
Mostly clear this morning then increasing clouds with a chance of
TSRA after 30/19Z. Clearing after 01/02Z. VFR through the period
with brief MVFR possible near storms. Normal diurnal wind trends
generally less than 12kts. Aviation discussion not updated for
TAF amendments.


.FIRE WEATHER...Isolated showers and thunderstorms today, then
generally dry conditions are expected into next week. 20-ft winds
will generally be less than 15 mph through Sunday, along with
normal diurnal wind trends. 20-ft winds will then increase on
Monday and Tuesday of next week, as a system moves across the
Great Basin and brings cooler air.


.PREV DISCUSSION...Latest models spread drier air into most of
the area by Saturday. This will limit the chances of rain to far
eastern sections by tonight. Thereafter, the drying trend will end
the rain chances for the weekend. However, this will be short-
lived as models pull moisture back into the area ahead of a low
pressure system entering the Great Basin around Monday. This will
lead to a brief period of rain chances Monday before the system
tracks northeast into the northern Plains on Tuesday. The system
will also usher in some cooler air, with high temperatures
projected to drop about 8 to 10 degrees from Sunday to Tuesday.
GFS model showed a dry westerly flow over the region Tuesday into
next weekend. High temperatures will recover to near seasonable
readings by Thursday.






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