Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 190402

Area Forecast Discussion
National Weather Service Tucson AZ
0902 PM MST Wed Oct 18 2017

.SYNOPSIS...Continued above normal temperatures. A fast moving
disturbance will bring isolated showers and thunderstorms Wednesday
night into Thursday, mainly near eastern mountains. Expect some
modest cooling Friday and Saturday, then near record high
temperatures are expected early next week as high pressure aloft
builds over the area.


.DISCUSSION...It was another hot day across southeast Arizona with
high temperatures well above normal. Cumulus, scattered altocumulus,
and cirrus dominated the skies leading to a picturesque sunset. Just
east of our area a line of thunderstorms formed from southwest New
Mexico into northern Chihuahua, but over the past hour most of those
storms have dissipated.

Current water vapor imagery shows a shortwave trough located over
southern Nevada extending into California. This shortwave will be
the main driver of our weather the next day or so. It will track to
the east moving through northern Arizona tonight through Thursday
then eventually get absorbed into the larger scale flow. This system
will advect just enough moisture into our area to initiate isolated
to scattered showers and thunderstorms starting tonight through
Thursday afternoon. Any precipitation will likely be light to
moderate since PWAT values over the region are around 0.7-0.8 inches
and the 19/00Z TUS sounding showed a fairly dry lower atmosphere.
Most storms will be to the north and east of Tucson with the best
chances in the mountains east of Tucson. Please see the previous
discussion and climate section below for additional details.


.AVIATION...Valid thru 20/06Z.
FEW-SCT clouds at 8-12k ft AGL and SCT-BKN clouds above 20k ft AGL
through a majority of the forecast period. Isolated -SHRA/-TSRA will
be possible over Pinal County tonight and then over areas east of
TUS starting Thursday morning into the afternoon. Best chances for
storms will be over the mountains Thursday morning into the
afternoon. SFC wind variable less than 8 kts overnight into Thursday
morning. Thursday afternoon sfc winds southwesterly between 8-12 kts
with some gusts up to 18 kts possible. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...As a weak disturbance moves through the region,
isolated showers and thunderstorms will develop along the eastern
portion of the state through Thursday. Dry conditions then
overspread the area lasting into next week. Normal diurnal wind
trends will continue through Thursday, becoming breezy from the
southwest on Friday. An easterly wind regime then sets up for Sunday
into early next week.


.CLIMATE...Today marks the 178th day of 90 degree temperatures
this year. That ties the record (1989 and 1910), with tomorrow
likely breaking the record. It`s also 132nd day of 95 degree
temperatures, which ties 1988 as 5th most.

After a break over the weekend, record or near record high
temperatures are likely early next week as an unseasonably strong
ridge of high pressure aloft builds over the area. Current forecast
high of 97 for Tucson Intl next Tuesday, if correct, would be the
2nd latest occurrence of 97 in the calendar on record. The record
latest date is Oct 27 2016. There is a small chance next Tuesday
that the high at Tucson Intl could hit 98, which, if that happens,
would be the latest occurrence of 98 in the calendar on record,
besting the current latest date of Oct 19 in 1921 & 1991.

         Tucson International Airport
             Forecast  Record
Mon Oct 23      95       94
Tue Oct 24      97       96
Wed Oct 25      95       95


.PREV DISCUSSION...Our ridge is buckling and dirtying up as the flow
becomes a little more zonal. A bit of moisture around for a few
showers well east of Tucson earlier this afternoon.

An impulse coming in off the Pacific will bring a little more
moisture over the next 24 hours with a few more showers or
thunderstorms Thursday. Orographics will help with best chances near
eastern mountains.

Some respite from the temperatures, as a trough pushes through the
region Friday into Saturday. Breezy southwest to west winds by
Friday afternoon, with cooler air filtering in as a dry
northwesterly flow sets up behind the trough Saturday. Daytime
temperatures will actually approach seasonal normals Saturday
afternoon. Saturday night and Sunday night will by on the chilly
side compared to recent weeks. Some isolated locations in coldest
Cochise County valley locations could touch freezing.

Strong high pressure will build in from the eastern Pacific through
Arizona and California early in the new week. Forecast height and
thickness values support temperatures more like the end of August or
beginning of September, with record values around 12 to 14 degrees
above average the first half of next week. Please see the Climate
section below for additional details.






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