223
FXUS65 KTWC 161002
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
302 AM MST Mon Sep 16 2024

.SYNOPSIS...

Chances for showers and thunderstorms continue today across much
of southeastern Arizona, though with lower to no chances west of
Tucson. Heavy rainfall, strong wind gusts, and small hail will be
possible with any thunderstorm. Dry conditions then return
Tuesday through the remainder of this coming week. High
temperatures will likely fall below normal Tuesday through the
coming week as well.

&&

.DISCUSSION...

As a deep low pressure center circulated over the California coast
this morning, modestly diffluent flow was located downstream atop
a low to mid moisture level plume over southeastern Arizona. At
09Z a moisture gradient was evident on the GOES precipitable water
product over far western Pima county, which should gradually
slide east today with the eastward progression of the upper level
low, before fully moving through the area late tonight. This will
impact precipitation chances today as highest coverage will likely
be east of Tucson, with a few isolated thunderstorms possible
from Nogales-Tucson towards Sells (though continued activity this
morning may prevent redevelopment this afternoon). While overall
moisture will continue to be on the decrease tonight, some additional
convection will be possible overnight with the increasing
influence of the approaching trough.

As for thunderstorm hazards, moderate rainfall rates will be
likely again under any thunderstorm with precipitable water in the
1.15 to 1.3 inch range. The 00Z HREF rainfall probabilities
however show a bit of a lower signal for excessive rainfall today,
which is reasonable given the tick downwards in precipitable
water from yesterday as well as the expected storm motions. Dry
mid-levels will again promote the possibility of strong wind gusts
while effective shear of 20-30 knots will create an isolated hail
threat. As mentioned above, the coverage/probability of any of
these threats remains uncertain with lingering convection and
cloud cover this morning potentially impacting today`s severity.

Enough remnant moisture may remain over Graham/Greenlee counties
Tuesday morning for lingering showers/thunderstorms, but otherwise
convective activity should be done with dry air moving in.
Continued cyclonic flow this week should keep moisture away, while
high temperatures will likely be a few degrees below normal each
day before a return to normal by the end of the weekend.

&&

.AVIATION...Valid through 17/12Z.

Ceilings this morning generally FEW 4k-7k and SCT-BKN 7k-10k
feet. Very isolated MVFR ceilings possible this morning as well
before ceilings rise with sunrise. Ceilings this afternoon 6k-9k
feet. Isolated to scattered thunderstorms this morning generally north
and east of KTUS, then additional activity should develop after
16/19Z over areas of southeastern Arizona. Brief
visibility restrictions, mountain obscurations, localized heavy
rain, and gusts to 45 kts possible with any thunderstorm. Outside
of thunderstorms breezy winds out of the south to southwest
expected today with gusts to 25 kts, with lighter winds in the
KSAD area. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Chances for showers and thunderstorms continue
today and tonight, before dry air moves in late tonight. The dry
conditions Tuesday and through the remainder of the week bring
valley minimum relative humidities down into the 15 to 25 percent
range, and higher elevations 20 to 30 percent. South to southwest
winds of 15-20 mph and higher gusts will occur for much of this
week, mainly during the afternoon and early evening hours.

&&

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

$$

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