Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
955 am MST Wednesday Jul 23 2014
Synopsis...enough moisture is back in place for a chance of showers
and thunderstorms. Hotter temperatures are possible again today and
Thursday. Thunderstorms are expected to increase this weekend...
especially Saturday afternoon and Saturday night.
Update...aviation discussion updated below.
Discussion...a little more confident in storm development today
than we have experience recently. Southeast low level winds based on
the 12z sounding helped improve our moisture content. Precipitation water
value hit 1... matches the satellite derived precipitation water
fields with the 1.50 inch values across much of S.E. Arizona. Sounding
also showed more instability in place than recent days...and with
abundant sunshine so far today and expected high temperatures a few degrees
above climatology...we are in good shape to realize that potential. There
were also a few mesoscale convective system events overnight across northern Mexico which
likely contributed to our moisture increase today.
Hi resolution models...hrrr and WRF variants...have a few
consistencies for today. The consistencies would point to the best
shot for storms developing in the 18 to 20z range over the eastern
zones...then spread west into Pima County due to the better ll
easterly mean flow starting around 22 or 23z. Certainly some
potential for a strong wind gust or two. In fact...our local WRF run
and the uofa WRF both hint at strong outflow impacting Pinal County
today. That makes ME a little nervous for blowing dust...but given
that the hrrr is not showing the outflow at all...I plan to play the
wait and see game today and hold off on issuing any dust advisories.
Fingers will be on the trigger though if radar trends support the
WRF runs. Either way...be aware of the blowing dust potential across
Pinal County today.
Aviation...valid through 24/18z.
Fair amount of clearing has occurred this morning which has allow
for some good mixing. The good thing is there isn't much wind in the
low/middle levels to tap into. This should keep most of the gust well
below 20kts. The one caveat to that will be given the inverted v
profile seen in point soundings from across the area all terminals
will have the potential for gusty outflow winds with the convection.
Enough instability exist over the area for convection though there
isn/T much in the hail growth zone which will limit lightning
activity. That being said...once storms develop and modify the
environment this will likely change quickly. However...given the low
confidence in where storms will develop at this time will keep ts
out of all terminals and will handle with amend once development
occurs. Aviation discussion not updated for taf amendments.
Fire weather...moisture has returned to Southeast Arizona today
with scattered mainly afternoon and evening showers and
thunderstorms across most of Southeast Arizona today. There will be
a brief downturn in storm coverage Thursday before a more typical
monsoon pattern moves in by this weekend. Expect strong...gusty and
erratic winds with the stronger thunderstorms. Potentially hotter
temperatures Wednesday and Thursday with strong high pressure
nearby...but with this will be mitigated somewhat by the moisture
back in the picture.
Previous discussion...moisture had finally returned to Southeast
Arizona as dewpoint temperatures were running around 60 degrees
early this morning. Recent infrared satellite imagery was showing some
extensive cloud cover across the area...with radar showing a few
light showers around especially across central Pima County. That
said...still expecting hotter afternoon temperatures today even
though the rain chances have increased and a cloudy sky was present.
This moisture increase will be brief as drier air pushes in from the
east and the upper high shifts southward tomorrow. This break will
also be short lived as models track an upper level disturbance
through Mexico which will likely bring a noticeable upswing in
thunderstorms activity over the weekend. High temperatures will be
above normal throughout the forecast period...but the warmest days
will occur today through Friday...when readings will be 8 to 12 degrees
above normal. Otherwise...expect highs to be 3 to 6 degrees above
normal. Lows generally 4 to 6 degrees above normal each day...but the
warmest mornings should occur Wednesday through Friday.
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