Funnel Cloud in Arizona, September 1, 2021

Area Forecast Discussion
National Weather Service Tucson AZ
222 PM MST Wed Sep 1 2021

.SYNOPSIS...Although chances for showers and storms will generally
decrease from west-to-east this evening, a very weak disturbance
aloft will result in isolated-to-scattered storms tonight. Despite
the deep moisture in place across the area, we will see limited
thunderstorm activity the next few days. An uptick in thunderstorm
activity is expected this weekend into early next week as the upper-
level high pressure center moves into a more favorable location.

&&

.DISCUSSION...The overall upper pattern is defined by an upper low
over northwest Arizona with its trough axis extending south into
southern Arizona, and an amplified ridge of high pressure aloft over
west Texas. The northern portion of the upper trough will continue
to eject to the NE today as a more established mean trough currently
over the Pacific Northwest digs south. The sheared out southern half
of the ejecting trough will separate out, and slowly track east
across central Arizona tonight. The majority of Hi-res models have a
reflection of this feature with isolated to scattered instability
showers developing across central portions of the state tonight.
Although these storms will be capable of producing heavy rainfall,
the areal extent will be limited.

Drier air rotating along the southeast periphery of the upper trough
will continue shunt the deeper moisture east this evening. A loop of
the latest radar imagery indicated a slow moving broken line of
light-to-moderate showers along the Arizona/New Mexico border...with
most convective activity limited to Cochise and Greenlee counties
this afternoon. Given the moist atmosphere in place, we will likely
see additional showers w/ embedded thunder develop this afternoon,
generally east of Tucson. Given everything, we decided to cancel the
Flash Flood Watch in effect for Southeast Arizona during the
afternoon package because we feel that the widespread threat of
flash flooding has subsided.

Otherwise, the moist airmass will remain in place into early next
week. The upper-ridge of high pressure over west Texas broadens out
over the Southern Plains tomorrow...then expands west this weekend
with the high consolidating near CA/NV border Sunday, and moves back
through the Great Basin early next week. As the upper ridge expands
the next few days, warming in the mid-levels will make it difficult
to get anything more than low-grade thunderstorm activity across
Southeast Arizona...despite the moisture in place. Sunday into early
next week, the positioning of the upper high open us up to easterly
impulses, and a general uptick in thunderstorm activity.

&&

.AVIATION...Valid through 03/00Z.
Isolated to scattered -SHRA with embedded -TSRA decreasing from the
west-to-east this evening. Cloud bases will generally be 5k-8k ft
AGL. MVFR to IFR cigs will be possible east of Tucson this evening.
SFC wind 12 knots or less, except when influenced by thunderstorm
outflows. Aviation not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered showers with a few embedded
thunderstorms will decrease from west to east this evening. Thursday
into the weekend storm chances taper off some with isolated to
scattered activity mainly from central Pima County eastward. 20-foot
winds will generally be less than 15 mph when not influenced by
thunderstorm gusts. Minimum RH values will remain well above
critical thresholds this week.

&&

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

&&

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