Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
105 PM MST Sat Jul 8 2017

.SYNOPSIS...The weather pattern will remain favorable for moisture
to increase across the region. This increase in moisture will
translate to a gradual upswing in thunderstorm activity and
subsequently cooler daytime temperatures.

&&

.DISCUSSION...
Active weather already in place across portions of central Arizona
as of 20Z with convection blossoming along the Mogollom Rim.
Mountain cu have developed across much of southeast Arizona, yet
skies remain precip free as of early afternoon. Also worth noting is
the fact that dewpoints have mixed out into the mid 40s and this has
allowed temps to rise a few degrees higher than anticipated. May end
up topping out just shy of the 110 degree mark, but still not at the
point where we need to have any heat products in effect.

Still a challenging forecast today as a decent gulf surge across
southwest Arizona/southeast California imported deep moisture into
those areas earlier this morning, but only shallow moisture made it
into southeast Arizona. Hence the dewpoints in the 40s on this side
of the state while readings are in the mid 70s near El Centro and
Imperial. Regardless, nearly all the deterministic guidance
advertises impressive amounts of MLCAPE west of Tucson as well as in
the White Mountains, with a sizable void in between. In terms of
winds aloft, modest mid level flow around 20-25kts will remain in
place through the rest of the afternoon, meaning any storms that
form stand a decent chance of getting organized.  Unfortunately,
what looked like impressive mid level lapse rates on this morning's
KTUS sounding are slowly eroding as slightly warmer H5 temps are
moving into the area from New Mexico. Nearly all convective allowing
models, including past few runs of the HRRR, indicate convection
along the Rim as well as along the US/Mex border this afternoon and
evening , but with much less coverage in between (including Tucson).
So far this is verifying well per regional radar imagery. I made
some slight upward adjustments to PoPs for this afternoon into
tonight to the west of Tucson and in the White's where I believe
storms will be focused but I'm hesitant to go too high to the east
where even drier air is being advected into the area. Also including
a mention of blowing dust in the forecast north and west of Tucson
later today/tonight.

Storm chances look more impressive area-wide on Sunday as whatever
convection develops in Sonora tonight will result in a sharp
increase in moisture across southeast Arizona. Once again nearly all
available hi-res models and ensembles that reach into Sunday
indicate more areal coverage tomorrow vs. today and there is a much
higher probability of storms actually making it into Tucson before
exiting to the west. Larger scale models are hinting at the presence
of a weak mid level inverted trough over Sonora that could be the
catalyst for storm development. While mid level winds will be less
than what's been observed today, deeper moisture and MLCAPES around
800-1200 J/kg should be more than sufficient for storm development.

The forecast for next week has been left relatively unchanged as we
finally look to settle into a favorable pattern of easterly flow,
decent BL moisture, cooler mid level temperatures, and above average
afternoon instability. Daily PoPs will remain at or above climo
through the end of the week. Consequently, afternoon highs will
retreat back to where they should be for early July.

&&

.AVIATION...Valid thru 10/00Z.
Isolated to scattered -TSRA this afternoon and especially this
evening with SCT clouds 8-12k ft AGL. MVFR VSBYS and gusts to near
50 kts in strongest TSRA. Otherwise, VFR conditions and SFC wind
mainly SELY 10-15 kts with gusts to 20 kts this afternoon. Winds
diminishing to less than 12 kts overnight into Sunday. SFC wind NWLY
at 8-12 kts Sunday afternoon with another round of scattered -TSRA.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Thunderstorm coverage will continue to increase into
the upcoming week, along with the prospect of more significant
rainfall. While strong wind gusts remain more likely than heavy rain
this weekend, increasing moisture will help humidity values
somewhat. Daytime temperatures will moderate closer to seasonal
normals Sunday into next week. Outside of gusty thunderstorm
outflows, 20-foot winds should generally remain under 15 mph.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

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weather.gov/Tucson

Special Weather Statement
National Weather Service Tucson AZ
403 PM MST SAT JUL 8 2017

AZZ502-082345-
Tohono O'odham Nation including Sells-
403 PM MST SAT JUL 8 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTH CENTRAL PIMA COUNTY UNTIL
445 PM MST...

At 403 PM MST, Doppler radar was tracking a strong thunderstorm 15
miles southwest of Sells, moving west at 15 mph.

Wind gusts of 50 mph and blowing dust will be possible with this
storm.

Locations impacted include...
Papago Farms and Cowlic.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

Areas of blowing dust may briefly reduce visibilities to near or
below 1 mile. If you encounter localized dense blowing dust, do not
drive into it if at all possible.

&&

LAT...LON 3174 11237 3186 11238 3184 11196 3161 11194
TIME...MOT...LOC 2303Z 086DEG 15KT 3175 11204

Cerniglia

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