572
FXUS65 KTWC 081030
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
330 AM MST Wed Oct 8 2025

.SYNOPSIS...

Increasing moisture will bring partly cloudy skies and isolated
chances for light showers and thunderstorms through Friday. Then
more widespread chances for showers arrive this weekend along with
a threat of heavy rain. Temperatures transition from above normal
during the work week to below normal by the end of the weekend.

&&

.DISCUSSION...

Precipitable water continues to gradually increase over
southeastern Arizona this morning as ample moisture associated
with Hurricane Priscilla sits just to the southeast. The region
remains between a subtropical high nudging in from the east and a
Pacific Northwest trough that will dive south in the coming days.
With southeasterly mid-level flow associated with the nearby
ridge, moisture through the atmospheric column is expected to
rapidly rise over southeastern Arizona through the day today.
Precipitable water will increase to 1 to 1.5 inches by the end of
the day, then further increase to 1.25-1.8 inches on Thursday.
With this anomalous moisture in place, daily chances for showers
and thunderstorms begin today. However, lack of a stronger
triggering mechanism and meager instability will keep chances on
the lower end (10-30 percent) and overall rain rates should be
mostly light for southeastern Arizona through Friday.

This weekend, several events will bring a notable increase in
precipitation chances and rainfall rates. First, the Pacific
Northwest low will open and cross inland into the Great Basin.
Troughing and an embedded shortwave over Arizona will bring
increasing synoptic support to southeastern Arizona that didn`t
exist in the previous days. Second, Hurricane Priscilla will have
made its way north off the western coast of Baja. By Saturday (or
earlier) it`s likely Priscilla will have weakened into a remnant
low, however its moisture will likely be pulled into the
southwesterly flow generated by the aforementioned troughing
pattern. To further boost available moisture, Invest 90E sits off
the southern coast of southern Mexico and may provide a second
push by early next week.

Widespread shower and thunderstorm chances will arrive this
weekend with the combination of incoming troughing and tropical
moisture stated above. There remains a group of deterministic and
ensemble model members with eye popping QPF, though uncertainty
continues. In discussing the spread of model solutions for
rainfall totals it`s almost easier to split up potential into
three groups: drier, wetter, and something in-between. The drier
solutions for the weekend (between the 10th-25th percentiles) see
rainfall totals that range from a few hundredths to a few tenths
of an inch. Meanwhile the wetter solutions (in the 75th-90th
percentile) show QPF in the 1 inch to over 3 inch range. Those in-
between solutions sit in the 1-2 inch range. That isn`t to say
that all locations may either be on the wetter or drier side, but
that it highlights what can be expected depending on where bands
of shower/thunderstorm activity sets up. However...the 90th
percentile was listed here and that does leave room for even
greater rainfall totals. That would likely require something like
the remnants of Priscilla tracking into southeastern Arizona or
Invest 90E following up close behind...maybe a continuation of
heavy rainfall into Monday/Tuesday as the upper low sits nearly in
place. There are a lot of moving parts to make the high end
solution happen...but it is worth paying attention to. In that
scenario event total rainfalls exceeding 5-6 inches may be
possible. It`s more likely an area that sees these kind of
rainfall amounts would either be in a mountain location or closer
to the Mexico border, but there is time for that to shift.

Looking at early next week, rainfall may be lingering into Monday
or even Tuesday as mentioned above. Some guidance is quicker to
clear out moisture than others in this period, leaving 10-40
percent chances on Tuesday. Several days in a row of rainfall may
cause hydrology concerns so this period will need to be watched if
the tropical moisture feed continues over southeastern Arizona.

Finally, temperatures are expected to trend down with this active
pattern. Highs will transition from 3-7 degrees above normal today
to below normal by the end of the weekend.

&&

.AVIATION...Valid through 09/12Z.

Increasing clouds at 9k-15k feet today. Isolated -SHRA after
08/21Z continuing overnight. Surface winds southeasterly 7-12 kts
today, with 15-20 kts and gusts to 30 kts at KSAD. Aviation discussion
not updated for TAF amendments.

&&

.FIRE WEATHER...

Moisture moving in from the east brings minimum relative
humidities above 30 percent east of Tucson to Nogales today with
15 to 20 percent to the west. Minimum relative humidities above 30
percent across southeastern Arizona Thursday into early next
week. Chances for showers and thunderstorms arrive with this
moisture, though any rainfall should be light through Friday.
Greater chances for wetting rain arrives this weekend.
Southeasterly winds expected through Friday, especially in areas
exposed to southeasterly flow. The Gila River Valley will see
15-20 mph winds with gusts to 35 mph through Friday.

&&

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

$$

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Aviation...Edwards
Fire Weather....Edwards

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