Bylas, Arizona Weather Forecast Discussion

275
FXUS65 KTWC 182216
AFDTWC
Area Forecast Discussion
National Weather Service Tucson AZ
316 PM MST Thu Sep 18 2025
.SYNOPSIS...Moisture has moved into the region which will lead to
scattered showers and thunderstorms today and Friday with diminishing
thunderstorm chances over the weekend. Temperatures near to just
below normal into the weekend before warmer and drier weather
returns next week.
&&
.KEY MESSAGES...
-Chances (30-50%) for isolated to scattered showers and storms
forming primarily on the high terrain. Storms may linger into the
evening and overnight hours. Localized instances of flash flooding
possible.
-Chances (30-60%) for scattered showers and thunderstorms tomorrow,
mainly from Sells eastward. Localized instances of flash flooding
possible if storms form or train over the same areas. A few storms
may be strong with small hail and gusty winds.
-Limited chances (10-20%) for a few isolated showers and
thunderstorms into the weekend, but trending warmer and drier
heading into next week with Tucson likely hitting 100 degrees by
midweek.
&&
.DISCUSSION...Storms so far have been struggling to form
mainly over the higher terrain this afternoon. Later this afternoon
and evening still thinking activity could increase in coverage
though. The 18/18Z sounding at KTWC came back with 1200 J/kg of
MUCAPE compared to about 450 J/kg yesterday. The added instability
combined with the moisture already in place means it wouldn`t take
much lift to get storms going. However, the best dynamics have
remained rather tight to the circulation in western AZ/southern
CA/southern NV associated with the remnant low of Mario. While
confidence is low that we will be able to tap into the better
dynamics this afternoon, if storms are able to get going and grow
upscale in coverage the environment is favorable for localized
instances of flash flooding. Overnight, an upper jet will move into
southeast Arizona potentially aiding convective development. Right
now there is a 20-50% chance of storms continuing into the overnight
period.
Tomorrow morning we may see a ramp up in activity again after
sunrise with even more robust development possible (30-60%) heading
into the afternoon hours. This looks like a Type IV synoptic pattern
setup with the trough/remnant low from Mario over the California
coast advancing from the west and the Monsoon circulation sagging
just to our south and east in Sonora Mexico. With plenty of moisture
available to work with storms that do form could potentially grow
upscale and be sustained. We`ll need to continue to monitor how high
resolution guidance is trending, but stronger storms could support
gusty winds and small hail tomorrow in addition to localized flash
flooding from backbuilding and training storms.
Over the weekend residual moisture could fuel a few isolated pulse
thunderstorms in the afternoon, but for now chances remain low (10-
20%) as we lose favorable dynamic support for additional storm
coverage. Ridging begins to build back into southeast Arizona
resulting in a warming and drying trend. Ensembles hint at an omega
high blocking pattern setting up with a trough over southern
California and another over the central plains supporting
temperatures climbing above normal and trending much drier. This
forecast package now has Tucson hitting triple digits again by
midweek.
&&
.AVIATION...Valid through 20/00Z.
SCT-BKN clouds 6k-10k ft AGL and SCT-BKN layer AOA 18k ft AGL
thru the valid period. Isolated to scattered TSRA through this
afternoon and evening. Some overnight activity will be possible be
confidence on terminals being affected is low. Gusty and erratic
winds to around 35 kts possible near thunderstorms. Outside of
thunderstorms, SFC winds SLY to SWLY at 5-10 kts through 19/03Z
becoming variable less than 7 kts at other times. Tomorrow chances
for scattered showers and thunderstorms continue through the day
across southeast Arizona. Aviation discussion not updated for TAF
amendments.
&&
.FIRE WEATHER...Above normal moisture is in place leading to min
RH between 20-40 percent through the weekend. Expect scattered
shower and thunderstorm chances (30-60 pct chance) today and Friday,
then diminished thunderstorm chances this weekend. Heavy rainfall
will be the main threat. Dry conditions return next week. 20-foot
winds will be 8-12 mph with some afternoon/early evening gusts to
around 20 mph over the next week with normal diurnal patterns
through the weekend.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
DVS
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NWS TWC Office Area Forecast Discussion