Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 300927

Area Forecast Discussion
National Weather Service Tucson AZ
227 AM MST MON MAY 30 2016

.SYNOPSIS...A weak and slow moving upper level low will maintain
temperatures near to slightly below average to start the week. As it
passes overhead Tuesday into Wednesday...a modest moisture increase
from the south will bring a slight chance of afternoon showers and
thunderstorms to the area. Strong high pressure will then build over
the region the latter part of the week and into the weekend,
resulting in hotter daytime temperatures with highs in the triple
digits from Tucson across the lower deserts.


.DISCUSSION...Water vapor imagery shows the weak upper low that will
move slowly across the Desert Southwest during the next couple of
days is currently over extreme southeast California and western
Arizona. IR satellite imagery shows mostly clear skies across the
region, although there has been recent mid level cloud development,
mainly east of Tucson into New Mexico.

As mentioned by the evening shift in their discussion yesterday,
satellite derived Precipitable water imagery, such as the CIRA Layer
PW Total and the Blended Total PW indicate that moisture has
increased significantly to our south in the past 24 hours or so with
higher values being transported farther north. Latest imagery shows
PW`s over central Sonora, Mexico near Hermosillo approaching the 1
inch mark, with higher values farther south. With IR imagery already
showing some cloud development over northeast Sonora and into
extreme southeast Arizona, we could see a slight chance of
showers/thunderstorms over parts of Cochise county this afternoon.
That said, the evening shift introduced slight chances in that area.
In addition, the latest run of the HRRR shows isolated convection
developing this afternoon over parts of Graham, Greenlee and Cochise
counties. Also, MOS POP numbers today for Douglas show values of 2%
from the NAM, 13% from the GFS and 43% from the ECMWF. Although, I
don`t necessarily buy into the extremes, the middle ground of 10-20%
seems reasonable based on recent moisture increases to our south.

As the upper low moves nearly overhead Tuesday into Wednesday we
will see isolated shower and thunderstorm development, mostly over
the White mountains of northern Graham and Greenlee counties, but
depending on how much development we see today, could have
implications for Tuesday and Wednesday. At this point, the MOS
numbers show single digit POPs for Tuesday afternoon at DUG, then in
the slight chance range for Wednesday. This is already reflected in
the inherited POP forecast, but the day shift can make further
adjustments based on the arrival of the 30/12Z run of model data.

Once this slow upper low exits the region, high pressure will build
in behind it late in the week and the weekend. This will result in a
significant warming of temperatures. We could see our first 100
degree day on the year in Tucson this Thursday. If not then, it will
easily exceed that value for Friday into the weekend, when highs
will hover within a degree or so of 105 for Tucson, with values
ranging from 105 to 108 for the deserts west of Tucson toward Ajo
and Organ Pipe.

For Tucson, highs temperatures will generally be around 2 to 4 degs
below normal today through Wednesday, then 3 to 6 degs above normal
Thursday and Friday, followed by 7 to 9 degs above normal for the
weekend. Low temps will be around 2 to 4 degs below normal Tuesday
morning, then near normal Wednesday and 2 to 4 degs above normal by
Thursday. Thereafter, lows will range from 6 to 8 degs above normal
Friday through the weekend.


Mostly clear skies except for sct-bkn cumulus clouds around 10k ft
AGL east of KTUS through this evening with isold -tsra east of
Benson 30/16z thru 31/02z. Light surface wind will become sly/swly
at 12-18 kts with gusts to 25 kts late this morning into this
afternoon then become light and variable aft 31/03z. Aviation
discussion not updated for TAF ammendments.


.FIRE WEATHER...A shallow moisture surge up from Sonora Mexico may
bring some isolated thunderstorms to zone 152 today with dry
conditions expected elsewhere.  Then as a weak upper low continues
to approach from the west, there is a small threat of isolated
thunderstorms again Tuesday and Wednesday mainly east of Tucson and
over the mountains.  Any storms that develop will be mostly dry and
capable of strong gusty winds.  Strong winds are also possible near
any large buildups regardless of thunder.  Also, Haines 6 conditions
are likely each afternoon through Wednesday across zone 153 and much
of zone 152.

Thursday onward a large upper ridge will build over the region
resulting in very hot temperatures, low relative humidities and
generally light winds at least through the coming weekend. As a
result of the hot and dry air mass, unstable Haines 6 conditions
will develop across much of southern Arizona from Friday onward
through Monday.  Cerniglia


.TWC Watches/Warnings/Advisories...None.




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