Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 150322
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
822 PM MST Thu Sep 14 2017

.SYNOPSIS...Breezy to locally windy conditions again Friday with
temperatures falling to near seasonal levels. A potential moisture
increase could bring expanding thunderstorm coverage early next
week.

&&

.DISCUSSION...Shortwave trough is passing well to our north across
southern Utah at this time with southeast Arizona in southwesterly
flow aloft. Still enough moisture and weak dynamics at this latitude
to support a few showers and thunderstorms earlier this afternoon.
Latest KEMX radar shows a few of these continue this evening but
remain well northeast of Tucson and in far northern Sonora near SW
Cochise County. The showers and thunderstorms will continue to
continue to diminish in the next couple of hours with the loss of
daytime heating as drier air gradually advects in from the west as
well.

Friday is shaping up to be another breezy to locally windy day as
broad troughiness remains across the region under continued
southwesterly flow. Still enough wind for the possibility of some
blowing dust along the typical trouble spots in Pinal County but it
should be less than occurred earlier today. Meanwhile, as moisture
departs to the east and PWAT values lessen, slight chances for a
shower or thunderstorm  will be limited to near the New Mexico
border. Temperatures Friday will be a few degrees lower with highs
right near seasonal normals. Thereafter, we`ll be watching T.S.
Norma and any moisture it sends up this way later in the weekend and
early next week. For more information, see previous discussion
below.

&&

.AVIATION...Valid thru 16/06Z.
VFR with gusty southwesterly winds and isolated -TSRA/-SHRA mainly E
of KTUS through 15/06Z, then clearing overnight. SLY/SWLY SFC wind
15-20 kts with higher gusts until 15/04Z, then less than 12 kts into
Friday morning. Gusty SLY/SWLY winds again Friday afternoon.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated afternoon and evening showers and
thunderstorms are expected mainly east of Tucson through
Saturday. There will then be an increasing chance of showers and
thunderstorms areawide early in the new week. Gusty south to
southwest winds will occur today and Friday as a trough moves
north of the area. Otherwise, 20-foot winds will generally be
terrain driven at less than 15 mph.

&&

.PREV DISCUSSION...With the trough pushing in from the west and the
ridge moving east of the area, we`ve seen gusty winds and a few
degrees of cooling today. Wind speeds below advisory levels, but
enough to generate a few patches of blowing dust across I-10 between
Tucson and Casa Grande, and we continue to keep an eye out for the
area of I-10 east of Willcox to the New Mexico border. The 12Z KTWC
sounding was up to 1.26 inches precipitable water, but already
showing signs of drying around 500hPa with the increasing
southwesterly flow. GOES-16 and CIRA LPW precipitable water
estimates suggest we`ve dropped back to 1 inch or less this
afternoon. More of the same Friday, except with a little less
moisture and a few more degrees of cooling.

Invest 97E quickly turned into Norma earlier today, and at 2 PM MST
was located south of Baja around 17.7N 109.3W. Most model guidance
and the official NHC track slowly draws her northward around the
influence of the ridge that is in the process of reconsolidating
over portions of north central Mexico and southwest Texas. Possible
trouble for Cabo San Lucas Sunday or Monday. After that there is
some ensemble and operational consistency in drawing some remnant
moisture north and northeastward across portions of Sonora in the
general direction of southern New Mexico and possibly southeast
Arizona early or mid next week.

At this point, my best guess is the deepest moisture pushes
northeast toward areas east of SE AZ with the GFS being too fast to
engage the storm with higher latitude influences. It`s early, so
lots of scenarios in exactly how and when it may push this
direction, but the bottom line is we`re talking about a moisture
increase and how much it might be, not a tropical storm making it
this far north.

&&

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

&&

$$

GL
Previous Discussion...Meyer

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