Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 282004

Area Forecast Discussion
National Weather Service Tucson AZ
104 PM MST SAT MAY 28 2016

.SYNOPSIS...A weak and slow moving upper level low will maintain
temperatures a few degrees below average into early next week. As it
passes overhead late Tuesday it will bring about a slight chance of
afternoon thunderstorms over the White mountains. Then high pressure
will build over the region the latter part of next week, resulting
in hotter temperatures with highs of 100 or more forecast across the
lower deserts Thursday into the weekend.


.DISCUSSION...An upper trough along the California coast will close
off through this evening then gradually migrate eastward. It is weak
and due to being nearly detached from the westerlies, will be a very
slow mover ending up over central Arizona Monday night and moving to
the east Wednesday. This feature will have subtle affects on our
weather, namely holding temperatures a few degrees cooler than
average and maintaining southwesterly breezes each of the next few
afternoons. As it passes over the area Tuesday, the atmosphere is
unstable enough and just moist enough for a slight chance of
thunderstorms over the White mountains during the afternoon and
evening hours Tuesday and to an even smaller extent Wednesday
afternoon. If any storms develop they will be mostly dry.

Once the low moves off to the east our area will begin to come under
the influence of a fairly strong upper level ridge that built over
the west coast and will shift east Wednesday through Friday. Until
this morning, models have been pretty consistent with this idea which
would allow temperatures to heat up quite a bit. The 12Z GFS is
throwing a wrench in the works by undercutting the ridge with an
upper low with convection developing across the region next weekend.
The ECMWF is much slower and further north with this low which is
what the earlier runs of the GFS was also showing. Looking at the
12Z GFS ensemble members, almost half of them have that low to our
SW so it is not out of the question. At this time will not jump on
this idea but something to keep in mind.

As alluded to earlier, as the ridge builds so will the temperatures.
Thursday into the weekend (assuming the ridge holds) high
temperatures are expected to rise to the warmest levels yet this
year with 100+ likely across the lower deserts. Even at that I kept
the forecast highs on the conservative side, especially when you
look at low level thicknesses which suggest even warmer Friday and
Saturday. For TIA, I kept the 99 for Thursday and went 101 Friday and
Saturday. Locally run ensembles suggest an almost 50/50 chance of
100 on Thursday at TIA, so a pretty good chance.


Expect mainly clear skies through Sunday. S to SW winds of 10 to 15
kts will have gusts of 20 to 25 kts til 29/02z. Expect normal
diurnal winds less than 10 kts overnight into Sunday morning before
SW winds increase again by 29/19z with speeds nearly 5 kts stronger
than today. Aviation discussion not updated for TAF ammendments.


.FIRE WEATHER...Expect dry conditions with moderately breezy
southwest winds during the afternoon each day through Monday.
Slightly more mid level moisture is forecast during the middle of
work week with isolated thunderstorms possible over mountains well
NE of Tucson. There could even be a few decent afternoon cloud
buildups farther south. While sustained winds will generally be
lighter midweek, erratic gusts will be possible near buildups and
thunderstorms. A significant warmup is still expected toward the end
of the work week.


.TWC Watches/Warnings/Advisories...



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