Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
935 AM MST Thu Aug 20 2020

.SYNOPSIS...Expect storm coverage and chances to increase today
into the weekend. High temperatures will moderate through the
weekend, but will still be 2-5 degrees above normal. Next week
storm chances decrease and temperatures climb back up to near
record levels.

&&

.DISCUSSION...Ongoing gulf surge, thanks to Hurricane Genevieve,
has increased moisture values across southern Arizona, especially
from Tucson west. Latest GOES PW imagery showed values from 0.90"
near the AZ/NM border to 1.2" over western Pima county, with
values up to 1.40" across Yuma county. The 12z Tucson sounding had
a PW value of 1.49" which is backed up by GPS PW at that time.
However, since release and looking at the GPS PW trace, the value
over Tucson is down to around 1.25". On the upper air charts, the
500 mb high was located over northeast Arizona with easterly mid-
level winds over the area but not as strong as previous days.

As we have been advertising all week, it will be an active day
thanks to the increased moisture. Afternoon action will be mainly
focused northeast of Tucson across Graham/Greenlee counties and
also southeast of Tucson across Santa Cruz county and the southern
half of Cochise county. East-northeast steering flow will
eventually bring storms into eastern Pima county this evening as
storms fire up along outflow boundaries. SPC has most of the area
under marginal risk of severe storms for strong gusty winds.
Localized heavy rain also a threat. Based on above thinking I
will be updating the forecast to increase PoPs northeast of
Safford and also across Santa Cruz and the southern half of
Cochise county this afternoon.

With the increasing moisture, high temperatures will be cooler and
below excessive heat criteria.

Details on the remainder of the forecast can be found in the
previous discussion section below.

&&

.AVIATION...Valid through 21/12Z.
FEW-SCT clouds 10k-15k ft MSL through much of the period. Clouds
occasionally BKN with with ISOLD-SCT TSRA/SHRA this afternoon and
evening. Sfc wind gusts 40 kts with strongest TSRA along with MVFR
CIGS/VSBYS and mountain obscurations. Otherwise, sfc winds light E
to SE this morning becoming SW to NW this afternoon 10-14 kts with a
few higher gusts. Winds become light again late in the evening.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered afternoon and evening showers
and thunderstorms into early next week. 20-foot winds will generally
remain less than 15 mph outside of any thunderstorm gusts which
could reach upwards of 40 mph. Daytime minimum relative humidity
generally 15-25 pct in the valleys today becoming 25 to 30 percent
Friday through Sunday along with good overnight recoveries

&&

.PREV DISCUSSION...Friday into the weekend storm chances continue with
the best chances Friday along the international border and the White
Mountains. Saturday storm coverage will increase to include most
of southeast Arizona and will likely be the day when the heaviest
rainfall is possible thanks to higher PWAT values and a more moist
surface profile. Saturday night models are hinting at some nighttime
storm activity for areas west of Tucson, so have included this in
the PoP forecast. Sunday expect similar coverage but with lesser
chances in the eastern portion of the CWA as drier air begins to
make its way into the area. Temperatures will be about 2-5 degrees
above normal during this time period with Saturday seeing the
"coolest" temperatures. The NBM gives about a 30 percent chance
that Tucson will see a high less than 100 on Saturday.

Next week drier air moves in but there will still be a little
residual moisture leftover for a slight chance of showers and
thunderstorms mainly in central/western Pima County and the White
Mountains each day. Temperatures will also increase again with a
return to near record levels.

&&

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

&&

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Special Weather Statement
National Weather Service Tucson AZ
116 PM MST Thu Aug 20 2020

AZZ509-510-202045-
Upper Gila River and Aravaipa Valleys including Clifton/Safford-White
Mountains of Graham and Greenlee Counties including Hannagan Meadow-
116 PM MST Thu Aug 20 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN GREENLEE COUNTY
UNTIL 145 PM MST...

At 115 PM MST, Doppler radar was tracking a strong thunderstorm 10
miles south of Blue, or 24 miles north of Mule Creek, moving
southwest at 10 mph.

Dime size hail and winds in excess of 40 mph will be possible with
this storm.

This storm will remain over mainly remote areas of northeastern
Greenlee County.

LAT...LON 3333 10936 3358 10916 3354 10904 3331 10905
      3330 10904 3329 10904 3323 10905
TIME...MOT...LOC 2015Z 035DEG 10KT 3345 10911

RH