Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 271622

Area Forecast Discussion
National Weather Service Tucson AZ
922 AM MST Thu Jul 27 2017

.SYNOPSIS...Expect daily rounds of afternoon and evening
thunderstorms across southeast Arizona into early next week. Rain
will be heavy in some locations. As storm coverage increases,
high temperatures will cool slightly to below normal readings from
Friday through the weekend.


.DISCUSSION...Satellite imagery shows a decaying thunderstorm
complex moving west across New Mexico, just north of a 55 kt 250
mb jet max. Morning sounding showed 1.58 inches of PWAT and decent
instability except for a little warming aloft still remaining at
400 mb.

As aforementioned upper level features advance toward SE AZ,
models consistent in developing fairly widespread thunderstorm
activity over the Rim and other parts of SE AZ. While storms will
move at a modest pace, coverage of storms and rain rates will be
sufficient for some areas of heavy rain. Additionally, as storms
move into the lower deserts, DCAPE values of 1100-1300 J/kg could
result in wind gusts of 50-60 mph.

Updated the forecast for higher dew points today and adjusted rain
chances this morning slightly. Otherwise, the remainder of
ongoing forecast looks good and no other changes were made at
this time.


.AVIATION...Valid thru 28/18Z.
TSRA are expected to develop by early afternoon across much of
southeast Arizona. DUG/OLS could see development shortly after 19Z
with the onset at TUS closer to 00z. MVFR cigs and vsbys likely in
TSRA with gusty winds to 40-50 kts possible. Scattered SHRA/TSRA
will linger through the overnight hours. Aviation discussion not
updated for TAF amendments.


A return to an active monsoon pattern will begin today with daily
shower/storm chances across much of southeast Arizona into early
next week. As such, elevated humidities will remain in place
through the weekend into next week with excellent overnight
recoveries. Outside of thunderstorm winds, expect 20-foot winds to
remain at or below 15 mph and follow typical upslope/down valley
diurnal patterns. Fire weather concerns are low through at least
late next week.


.PREV DISCUSSION...We`re currently watching a decaying
thunderstorm complex heading in this direction from southern NM
under partly to mostly cloudy skies. If it gets here somewhat
intact, we`ll see a few showers and perhaps a rumble of thunder
across Cochise County by 13Z or 14Z this morning. Otherwise, dry
conditions should continue this morning. WV imagery indicates
moisture advecting northward into Arizona from Sonora, Mexico with
high pressure located over central New Mexico.

Today begins another moistening trend after a brief two-day "break"
in the monsoon pattern compared to the last couple of weeks. Expect
PWAT values to increase again due to southerly/southeasterly mid and
upper level flow as the H3 high becomes quasistationary over
northern New Mexico and the Texas panhandle into early next week.
This will lead to an upswing in showers and thunderstorms, beginning
with the sky islands and areas near the AZ/NM border today and
Friday. We`ll have to watch for embedded vorticity maxima
circulating around the southern periphery of high pressure and into
Arizona which will help to better determine the location and timing
of enhanced convection. Right now, it seems we could see one vort
max push through from the south Friday into Saturday and again early
Sunday morning. In general though, activity today should be slightly
more than what we saw on Wednesday. The official forecast then
gradually increases PoPs westward across the CWA each day through
the weekend. We`ll keep an eye out for potential flash flooding with
the stronger, more persistent cells, especially on days where the
upper level flow is weak. That said, the current GFS/NAM PWAT
forecast is for values less than 1.50 inches through Friday, but
Saturday and Sunday could see a jump to values of 1.6 to 1.8 inches
once again.

Hi-res models early this morning, including the U of A WRF`s and
HRRR, develop scattered convection mainly from Tucson/Nogales
eastward starting around 27/20z. This includes the White Mountains,
with the potential for an organized line of thunderstorms to roll
southwestward off the Mogollon Rim. If this scenario comes to
fruition, the best chance for precipitation making it into the
Tucson area and across the western deserts will be late this
afternoon into this evening. With slightly less atmospheric moisture
and near normal high temperatures this afternoon, the potential will
exist for a few strong wind gusts to occur with any storms which

With high pressure progged to gradually migrate westward into the
middle of next week, we should maintain a favorable wind pattern
with plenty of available moisture. With that, the official forecast
continues with above climo PoPs through next Wednesday. Difficult to
tell at this juncture exactly which day will be the most active,
though one or two will likely stand out as time goes on. Expect one
more day of near normal high temperatures today, with values
dropping under more cloud cover from Friday into next week.






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