975
FXUS65 KTWC 161517
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
817 AM MST Thu May 16 2024

.SYNOPSIS...Locally breezy today, with showers and thunderstorms
likely in the White Mountains and a slight chance of showers and
thunderstorms to the east of Tucson. A slight chance of showers and
thunderstorms persist in the White Mountains on Friday with dry
conditions elsewhere. Dry conditions return areawide Saturday into
next week. High temperatures will be right around normal today, with
highs warming to several degrees above normal Friday into early next
week.

&&

.UPDATE...As a disturbance rounds the backside of the mid/upper low
this afternoon, the lift from this combined with modest instability
of 250-500 J/KG due to some mid level moisture, a few more
showers/thunderstorms may occur than previously expected. CAMs/HREF
are showing a few mainly dry thunderstorms as far west as Sells this
afternoon. We went and did a quick update to the forecast to nudge
PoPs higher and added slight chance of mainly dry thunderstorms to
may locales from central Pima County eastward. These thunderstorms
will produce little measurable rainfall but may produce gusty winds
in excess of 40 mph due to DCAPE up to around 1500 J/KG.

&&

.DISCUSSION...Partly to mostly cloudy skies were observed across
most of the state early this morning. While some weak convection
still persists across southeast Arizona at 0145, the trends over the
last hour are downward and little if any precipitation is reaching
the ground (maybe a few sprinkles). Dewpoints remain low across the
forecast area, in the mid 20s to mid 30s, although mid level
moisture has increased versus 24 hours ago. Satellite based total
precipitable water values are generally between 0.50-0.65", with
lower values around 0.35" along the International Border.

A weak upper low lifting northeast across the forecast area today
will interact with this moisture, resulting in precipitation chances
across mainly the eastern half of the forecast area. The highest
probabilities for measurable rainfall will be in the White
Mountains, with likely pops this afternoon/early evening. Overall,
there will be a slight chance of showers/thunderstorms east of an
Oracle to Sierra Vista line. However, the thunderstorms further
south will be mainly dry, with gusty/erratic winds and lightning
potentially causing new fire starts, but little to no rainfall.
Observed and model soundings across the south/southeast portion of
the forecast area have the classic inverted V look with mid level
moisture residing between 600-650 mb (and DCAPE values around
1500J/kg), which all translates into the potential for some stronger
thunderstorm outflows. Outside of any thunderstorm outflows, this
system will result in elevated wind speeds and near critical fire
weather conditions to the east of Tucson today, with west-northwest
winds of 15-20 mph and gusts to around 30 mph (although min RH
values may be just above the critical thresholds of 15 percent).

Shortwave ridging begins to build in across the desert southwest on
Friday. This will lead to warmer temperatures and drier conditions,
with just a slight chance of showers/thunderstorms persisting in the
White Mountains. High temperatures will top out 3-5 degrees above
normal on Friday. Dry conditions then return areawide Saturday and
Sunday with even warmer temperatures. Highs will be 6-9 degrees
above normal, with readings in the upper 90s in the lower deserts
from Tucson westward. Tucson hitting the century mark either
Saturday or Sunday is not out of the question.

The ensembles/deterministic models show another weak system moving
across the area at the start of next week. This will result in
breezy to locally windy conditions on Monday and high temperatures
lowering back to near or slightly above normal readings by Tuesday.

&&

.AVIATION...Valid through 17/12Z.
SCT-BKN clouds at 8k-11k ft AGL thru the forecast period. Numerous
-SHRA/-TSRA to the northeast of KSAD in the White Mountains between
16/17Z and 17/05Z, with a slight chance of -SHRA/-TSRA east of a
KE77 to KALK line between 16/19Z and 17/03Z. SFC wind less than 12
kts and variable in direction thru 16/17Z and again aft 17/04Z. SFC
wind between 16/17Z and 17/04Z, WLY/NWLY at 12-20 kts and gusts to
22-30 kts, with the strongest SFC wind east of KTUS in the vicinity
of KALK, KDUG and KSAD. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...High temperatures will be right around normal
today. Highs then warm to 3-5 degrees above normal Friday and 6-9
degrees above normal Saturday and Sunday, before lowering back to
within a couple of degrees of normal next Tuesday. Min RH values in
the valleys will be in the 10-20 percent range today and then in the
single digits to lower teens Saturday into the middle of next week,
with values in the mountains between 20-35 percent today and 10-20
percent Saturday through the middle of next week. 20-foot winds will
generally follow typical diurnal wind trends through early next
week, with afternoon and early evening gustiness due to strong
surface heating. The strongest 20-foot winds will be today and next
Monday, especially to the east of Tucson, with wind speeds of 15-20
mph and gusts to around 30 mph. West-northwest winds are expected
today, with southwest-west winds on Monday. Mid level moisture in
place, combined with a weak upper low will result in showers and
thunderstorms likely in the White Mountains today and a slight
chance of showers and thunderstorms to the east of an Oracle to
Sierra Vista line. While some wetting rainfall may occur in the
White Mountains today, the majority of the thunderstorms will be
dry, with gusty/erratic winds and lightning, but little to no
measurable rainfall.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

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