Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Sun Mar 19 2023

Day 1
Valid 12Z Sun Mar 19 2023 - 12Z Mon Mar 20 2023

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Oravec


Day 2
Valid 12Z Mon Mar 20 2023 - 12Z Tue Mar 21 2023

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Oravec


Day 3
Valid 12Z Tue Mar 21 2023 - 12Z Wed Mar 22 2023

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS COASTAL
AREAS OF SOUTHERN CALIFORNIA AND CENTRAL ARIZONA...

The latest model guidance is in good agreement with a strong
closed low diving southeast day 2 across the Northeast Pacific and
inland into central California and the Great Basin on day 3. 
Strong 850 to 700 mb moisture flux expected on the south side of
this closed low, impacting areas from the central California coast
range , southeast through the Transverse and Peninsular Ranges and
into the southern Sierra during the day on Tuesday, spreading
inland into the Southwest Tuesday night into early Wednesday.  The
National Water Model streamflow anomaly map continues to show high
flows to most of the streams across the central California coast
range, southeast into coastal southern California, including the
Transverse and Peninsular Ranges, which coincides with anomalous
soil moisture values as per NASA SPoRT maps.   There is fairly
good model agreement on heavy precipitation potential across the
slight risk areas of California, with widespread 1.25 - 2.5"+
values.  Given this the previous marginal risk area across these
regions was upgraded to slight.  No changes made to the marginal
risk area over the southern to central Valley/foothills of the
Sierra with the heaviest precip here expected to fall as snow in
the Sierra, with no significant contribution to runoff from snow
melt expected. 

Inland across central Arizona, the previous marginal risk areas
was also upgraded to slight.  850-700 mb moisture flux values
expected to become very anomalous late Tuesday into early
Wednesday, 4 to 5 standard deviations above the mean,  over the
Southwest as the strong upper trof moves inland from Central
California into the Great Basin.  Snow level expected to be high
with much of the precip into the Mogollon Rim area falling as
rain.  Stream flow and soil moisture anomalies are not as great
across central AZ as points farther west across California, with
values at or slightly above normal.  However, given the strong
south southwesterly upslope flow into the Mogollon Rim region and
resultant heavy precip potential, model consensus 1 to 2"+ areal
average totals, an upgrade to slight risk was warranted.

Oravec


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt