539
FXUS65 KTWC 050932
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
232 AM MST Wed Jun 5 2024

.SYNOPSIS...

Building high pressure will bring hotter temperatures over the
next several days. An Excessive Heat Warning is in effect for
Thursday and Friday. A weather system will bring a moisture increase
Thursday into the weekend, with chances for isolated
thunderstorms each afternoon and evening mainly south and east of
Tucson. Rainfall should be limited, with strong and erratic winds
being the main threat along with lightning.

&&

.DISCUSSION...

In the upper levels, a ridge was centered over central to southern
California, while a low pressure circulation was evident on water
vapor imagery sitting below this ridge off the southwest Baja
coast. Over the next 24 hours, the ridge axis is expected to shift
east with the anticyclonic circulation becoming centered over the
Four Corners into New Mexico. The Baja circulation should remain
mostly closed and in place until this weekend, when a northern
stream wave should approach and nudge the vorticity center
northeast into southern Arizona.

Surface temperatures will be on the rise over southern Arizona
over the next few days as upper level heights rise with the
eastward shifting ridge. With the ridge heights exceeding the 99th
percentile on NAEFS climatology guidance for this time of year,
surface temperatures in turn will approach daily records across
the lower elevations of southeastern Arizona Thursday and Friday.
An Excessive Heat Warning remains in effect for these two days.

As the ridge shifts east today, the placement of the ridge to the
north and the closed low to the south will put southern Arizona
under east to southeasterly flow in the mid-levels. This flow
should bring a modest increase in mid-level moisture with at least
slight chances for daily afternoon-evening thunderstorms as early
as Thursday. Initial coverage on Thursday should be sparse with
just minimal rain possible given the very dry lower levels and
lack of synoptic ascent. As the low approaches from the south
Friday and Saturday, probabilities for (still light) measurable
rain increases and then lingers through the weekend as the upper
low slowly crosses the region. Highest probabilities will be
closer to the southeasterly moisture source across far southern
and eastern areas of Arizona (especially the White Mountains), and
it`s still uncertain if the Tucson area will see much activity.
The overall probability of measurable precipitation for Tucson
through the weekend isn`t zero, though it`s light enough each day
where the daily forecast will be mostly dry through this period.
To the east and south probabilities rise from around 15-20 percent
on Thursday to 20-40 percent Friday and Saturday. Even with the
probabilistic rise in coverage and measurable rain, overall
rainfall total potential looks to remain low with the antecedent
dry lower levels. The main impacts will likely be strong, gusty
outflow winds and lightning.

Going into early next week the blend of overall global ensembles
lingers low but non-zero chances for precipitation with the slow
exit of the upper low, though as mean upper level flow becomes
westerly again adequate moisture should be on the way out.
Temperatures fall a few degrees with the passing of the upper low
this weekend, however remain near or just above normal.

&&

.AVIATION...Valid through 06/12Z.

Winds today remain light and generally under 10 kts, becoming west
to northwest after 19Z. A few high clouds are possible but
otherwise SKC expected. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...

Temperatures will be on the rise over the next couple days,
becoming near 10 degrees above normal by Thursday. Dangerous heat
is expected across the valleys of southeastern Arizona Thursday
and Friday. Minimum relative humidities 5-10 percent in the lower
elevations and 8 to 15 percent in the mountains through the week,
along with poor overnight recoveries between 20 to 30 percent.
Winds generally remain light through the remainder of the work
week, with some afternoon breeziness to around 12 mph. Slight chances
for dry thunderstorms begin to arrive as early as Thursday
afternoon- evening, with better chances Friday into Sunday,
especially south and east of Tucson. Gusty outflow winds will be
possible with any thunderstorm that forms.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 10 AM Thursday to 8 PM MST Friday
for AZZ501>509.

&&

$$

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