Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 280952

Area Forecast Discussion
National Weather Service Tucson AZ
252 AM MST Thu May 28 2020

.SYNOPSIS...Temperatures will increase through Friday across much of
the area with the potential for much warmer than normal conditions
lingering through the weekend. A modest increase in moisture late in
the week may allow for isolated thunderstorms Friday, continuing
into the weekend and possibly early next week.


.DISCUSSION...Thanks to an omega block over the western US,
temperatures continue to climb across our area. The ridge axis moves
overhead on Friday allowing for the warmest temperatures of the
period. Some lower desert locations could approach 110 that
afternoon. The pattern gradually shifts east over the weekend
allowing for a slight reduction in temps, but the excessive heat
still holds on.

With the high over Texas and an approaching deep trough just off the
California coastline, mid-level winds adopt a southerly to
southeasterly directional component. That sounds eerily reminiscent
of a certain season that starts June 15th. A momentary sneak peak of
things to come. Mid-level moisture will start to creep into the
forecast area today, with the HRRR indicating isolated thunderstorm
activity across the White Mountains this afternoon. Areal coverage
expands tomorrow as slight chances extend from Tucson eastward.
Don`t expect to see much rainfall from these potential storms. The
sub-cloud layer remains quite dry and the primary threats will be
gusty outflow winds and lightning. NAEFS mean PWs increases to
around 0.75", which is in the 90th percentile for this time of year.

The Eastern Pacific trough attempts to inch closer early next week
and thunderstorm chances continue each afternoon/evening. There`s
quite a bit of uncertainty in how the pattern takes shape and the
widening standard deviation of the NBM temperature forecast is
indicative of that.


.AVIATION...Valid through 29/12Z.
SKC thru 28/17Z, with FEW-SCT clouds at 10k-14k ft MSL east of a FHU
to SOW line thru the remainder of the forecast period. Slight chance
of -TSRA/-SHRA in the White Mountains between 28/18Z and 29/03Z. SFC
wind generally less than 12 kts and favoring a NWLY direction the
afternoon/early evening hours and variable in direction at other
times. The exception will be in the upper Gila River valley near
SAD, where afternoon NWLY winds will be around 15 kts with gusts to
23 kts. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Hot temperatures are expected through the upcoming
weekend, with the hottest days being Friday and Saturday. Mid level
moisture will begin to move into the area from the east, resulting
in a slight chance of mainly dry thunderstorms this afternoon and
evening in the White Mountains. The dry thunderstorm threat will
expand westward on Friday to areas roughly from Tucson and Nogales
eastward, with the threat continuing across the eastern half of the
forecast area into early next week. The highest thunderstorm chances
will be over the mountains south and east of Tucson.

Minimum RH values today will be in the single digits in the lower
elevations and 10-20 percent in the mountains. Minimum RH values
will then increase into the 8-15 percent range in the lower
elevations and 20-30 percent in the mountains Friday through early
next week. Some breezy afternoon northwest winds at 15-20 mph are
expected in the upper Gila River valley near Safford today and then
gusty southeast winds at 15-20 mph will overspread the area late
tonight into Friday afternoon. Otherwise, 20-foot winds will
generally remain less than 15 mph with some afternoon gustiness due
to daytime heating.


.CLIMATE...There is a very good chance that Tucson will record its
hottest May temperature in 15 years. Current forecast calls for
107 degrees on Friday, although there is a slight chance that 108
degrees may be achieved.

1) 111F on May 29, 1910
2) 110F on May 30, 1910
3) 109F on May 22, 2005
4) 108F on May 29, 2000
5) 107F on May 21, 2005 (last of 8 occurrences)


 Excessive Heat Warning from noon Thursday to 8 PM MST Sunday for



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