Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
740 PM MST Tuesday Aug 26 2014
Synopsis...showers and thunderstorms will continue during the
overnight with a pronounced drying trend is expected over the next
several days as dry northwesterly flow overspreads Arizona.
Discussion...quick update to trim probability of precipitation back to better fit current
trends. Otherwise...forecast remains on track.
Aviation...valid through 28/06z.
Ts development will diminish over the next few hours from west to
east as the upper trough over Nevada begins to eject across the
northern half of the state. The strongest activity will be north
of the ktus-ksad line...with little to no development expected
near the international border. That being said...the deep moisture
remains over the area and the upper trough should push some added
forcing so some new development will be possible through 12z.
Still...confidence remains too low at this time to warrant mention
in the taf. Aviation discussion not updated for taf amendments.
Fire weather...showers and thunderstorms will continue to
diminish during the overnight hours. A drying trend will get
started Wednesday with much less convection expected and slightly
warmer temperatures. Thursday through the Saturday...the drying
will continue with significantly lower relative humidity levels...warmer
temperatures and no showers or thunderstorms expected. Sunday into
the middle of next week will see a bit of a moderation in relative humidity
levels but at this time it is still expected to be dry and rather
Previous discussion... /issued 209 PM MST Tuesday Aug 26 2014/
Discussion...a middle/upper level trough continues to track eastward
this afternoon. Deep moisture and instability ahead of the trough
is being enhanced...with widespread thunderstorm activity being
observed across much of the state. Strong dynamic lift is taking
place over northern Arizona and southern Utah...with some
significant deep convection taking place. The weather of Southeast
Arizona is being driven by surface based instability and lingering
deep moisture. Thunderstorms have been developing for several
hours...and are expected to continue to develop throughout the
afternoon and evening. Most storms have initially been stuck
along/over terrain areas. Heavy rainfall has been observed with
many of the storms. As the remainder of the day progresses showers
and thunderstorms are expected to fill in many lower elevation
areas as well. A Flash Flood Watch remains in effect through 8 PM
and local flooding is certainly possible.
The trough will continue its progression over Arizona tonight into
early Thursday. Initially...the trough will act to develop
convection over the area...although the threat of heaviest
precipitation will shift northward. A much drier airmass will
advect over Arizona on the backside of the trough beginning as
early as Wednesday afternoon. The dry northwest flow aloft will be
enhanced through the remainder of the week as a middle/upper ridge of
high pressure builds to our west along the West Coast. Under this
regime precipitation chances will plummet and temperatures will
Long range models show little change in this overall pattern until
perhaps the middle of next week.
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