Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 210423

Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST Wed Sep 20 2017

.SYNOPSIS...A low pressure system will bring strong and gusty
winds each afternoon this week, finally decreasing on Sunday. A few
showers or thunderstorms may preceed the system, but activity should
remain very isolated. Cooler temperatures arrive Friday, with
readings holding below average through at least the middle of next


.DISCUSSION...Yet another dry sounding above 650mb this evening
as west-southwesterly flow wraps around a broad upper trough over
the western CONUS. Infrared satellite imagery shows a dissipating cu
field and mainly clear skies are expected throughout tonight. The
primary influence from the deepening trough has been a gradient
squeeze, which produced wind gusts of 20-30 mph across southeastern
Arizona this afternoon. Winds have since abated following our
typical nocturnal trend, but we`ll pick back up again tomorrow
afternoon with a bit more strength as the trough continues to
amplify to our west.

The forecast remains in good shape and no adjustments have been
made. Please see the previous discussion for further details.


.AVIATION...Valid thru 22/06Z.
SKC through tonight with variable winds less than 10 kts. SFC winds
increase Thursday afternoon SWLY 15-20 kts with gusts to 30 kts and
FEW-SCT clouds above 8k feet AGL. Aviation discussion not updated
for TAF amendments.


.FIRE WEATHER...A deepening upper trough over the western United
States will result in gusty southwest winds, especially during the
afternoon and early evening hours through Saturday. The strongest
winds are expected on Thursday and Friday, with a cooling trend
Friday through Sunday. Isolated storms will be possible over the
mountains in the eastern portion of the state before drying out this


.PREV DISCUSSION /224 PM MST/...Westerly flow continues to bring
drier air into the region which has allowed temperatures to warm to
just above normal this afternoon. Looking out of the window and at
satellite imagery, it`s clear that the cumulus clouds are not making
much progress in the growth category. With that being said, wouldn`t
expect anything other than passing clouds through the evening hours.

The overall flow will shift more from the southwest Thursday as a
trough moves through our area. The tightened pressure gradient will
cause the breezy conditions to stick around through the rest of the
work week. Gusts to 25 to 30 MPH will be possible area-wide
Thursday, with the strongest winds likely remaining from Tucson
eastward on Friday. Models are continuing to trend drier and are no
longer indicating much moisture pushing into our corner of the state
Thursday and Friday. However, a small chance for thunderstorms will
exist in the mountains east and northeast of Tucson.

A passing cold front won`t bring us any moisture, but will instead
allow temperatures to drop below normal for the first day of Fall as
we will struggle to reach 90 in most locations Friday. These
welcomed cooler temperatures will persist through at least the first
half of next week. Lows will likely dip into the 50`s for the
majority of the area, with 40`s being possible in some of the higher
elevations and eastern valleys beginning Saturday night.






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