Flash Flood Warning 144, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
1014 AM MST Wed Sep 21 2022

.SYNOPSIS...Scattered to numerous showers and storms are forecast
today with a few strong to severe storms and flash flooding
possible. Flash Flood Watch remains in effect for southeast
Arizona through late this evening. Storms will become more
isolated Friday and Saturday before dry conditions return Sunday.

&&

.DISCUSSION...Forecast remains on tack and there is no changes to
the Flash Flood Watch.

Clearing across portions of SEAZ is leading to 1000-2000 j/kg
MUCAPE with record PWAT values (12z TUS sounding 1.89"). Deep
unidirectional southerly flow continues with an ongoing gulf
surge across the area. With the deep southerly flow, training of
strong storms with very heavy rainfall rates/amounts is likely
this afternoon. The main area of focus at this time is primarily
Santa Cruz, Pima, and Pinal Counties. Another area that may see
increased thunderstorm chances will be across SE Cochise County,
where there is clearing.

With more regards for flash flooding, there is legit concern of an
area of greater threat from Tucson west into central Pima County.
Many ingredients are coming together to enhance this threat.
Abundant moisture, adequate instability, impressive deep layer of
warm cloud rain processes, low LCLc, and potential for
training/backbuilding. We will have to watch closely how this
evolves through the day.

Storms will continue to push north through the evening with
multiple rounds likely. By midnight, the flash flood threat should
subside some, but washes will likely be flowing in many areas
that receive rain.

&&

.PREV DISCUSSION... /issued 223 AM MST Wed Sep 21 2022/...
Today through Tuesday. Scattered light to moderate rain continues
early this morning primarily over Cochise, Graham, and Greenlee
counties. Any embedded lightning has ceased at this point and
activity should continue to slowly decrease in coverage through
sunrise.

The synoptic setup that has been highlighted the last few days
will begin to transition today. The low will push onshore this
morning into northern California and continue on a northeastward
track over the Great Basin and the Dakotas through Friday. The
ridge will remain anchored over TX during this time period,
flattening as the trough passes to the north.

Today will see decent coverage of rain and storms this afternoon
and evening with NBM precip chances running between 45-80 percent
areawide. This will be the result of deep southerly flow pulling
tropical moisture northward into Arizona and the Four Corners
region. This moisture should peak today with PWAT values roughly
from 1.2" along the AZ/NM border to around 2.0" across western
Pima County. This moisture combined with around 1000 J/kg MUCAPE
values and effective shear values near 20 kts will support
isolated to scattered storm activity today. An isolated strong
storm can't be ruled out with hail and gusty winds. The flood
threat remains more paramount in impact with moisture levels
approaching daily record values at near 200 percent of normal. As
such, a Flood Watch remains in effect through 11 PM tonight for
much of the state of Arizona. The 00z HREF as well as the 12z
ECMWF EFI continue to highlight central and western Pima County
for the highest rainfall totals today. There are multiple spots in
this area with HREF neighborhood probabilities of 6 hour totals of
an inch or more at 30-40 percent with even a 10-20 percent chance
of over two inches or more in a couple of spots. Current forecast
totals through this evening are between 1.0"-1.5" with locally
higher amounts in this area. Multiple rounds of rain and/or
training activity will lead to higher flash flood concerns as well
as any heavy rain over burn scars. Some washes and rivers have
already seen some rise from the rain yesterday so any additional
high amounts will have a quicker response.

After today, westerly flow will take over and slowly dry out the
atmosphere. There will still be plenty of moisture and instability
still in place on Thursday to warrant widespread showers and
storms once again, primarily during the afternoon and evening. WPC
has kept our area in a "Marginal" for the Excessive Rainfall
Outlook as a result. Chances for precip diminish further going
into Friday and Saturday before dry conditions settle back in for
Sunday.

Temperatures will bottom out below normal today with cloud cover
and moisture in place, coming back up to near normal through the
end of the week. The ridge will shift westward across the area
late this weekend into early next week allowing temperatures to
pop back up 3-5 degrees above normal for late September.

&&

.AVIATION...Valid through 22/18z. VCSH around KOLS/KTUS continues
through around sunrise this morning. Surface winds remain near 10
kts or less, with gusty outflow winds possible with SHRA/TSRA.
SCT/NUM TSRA/SHRA expected tomorrow between 21/20z-22/03z with
very brief MVFR possible under heavier showers. Otherwise, FEW-SCT
clouds at 5k-9k feet AGL and BKN-OVC clouds at or above 10k feet
AGL. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...
Widespread showers and storms will be present today and tomorrow
before beginning a downward trend through the weekend. Isolated
strong to severe storms are possible. 20 foot winds will remain
less than 15 kts this week favoring the west to northwest each
afternoon through the weekend. Near normal temps are expected
through the end of the week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for AZZ501>515.

&&

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