000
FOUS30 KWBC 130031
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
831 PM EDT Fri Apr 12 2024

Day 1
Valid 01Z Sat Apr 13 2024 - 12Z Sat Apr 13 2024

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

Pereira

Day 2
Valid 12Z Sat Apr 13 2024 - 12Z Sun Apr 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE CENTRAL
CALIFORNIA COAST AND INTO THE UPSLOPE OF THE NORTHERN TO CENTRAL
SIERRA...

21Z Update: No significant changes needed for the Marginal Risk
area with relatively good model agreement and run to run
consistency for widespread precipitation beginning late
tonight/early Saturday morning. An axis of higher PWs / modest IVT
values (400-500 kg/m/s) will bring some locally heavier rain to
mainly the coastal central California areas but also extending into
the foothills of the Sierra of the central/northern Sierra.

Taylor

---previous discussion---

There is good model agreement of the southeastward movement of the
strong closed low off the Pac NW coast to a position off the
northern California coast by the end of the day 1 period and then
an eastward inland movement day 2 across central California. A
well defined area of precip expected along the slowly southeastward
moving frontal boundary. PW values along and ahead of this slow
moving front will rise to 1 to 2 standard deviations above the mean
along with 850-700 mb moisture flux anomalies of 2 to 4+ standard
deviations above the mean. The anomalous moisture flux values will
impact the central California coast range from Santa Cruz southward
to the western portions of the Transverse Range and the upslope
regions of the northern to central Sierra. Across these areas max
rainfall totals of 1 to 1.5"+ are possible. No significant changes
made to the marginal risk along the central California coast, with
a marginal risk introduced for the upslope area of the northern to
central Sierra.


Oravec

Day 3
Valid 12Z Sun Apr 14 2024 - 12Z Mon Apr 15 2024

...THERE IS A MARGINAL RISK FOR PORTIONS OF SOUTHERN CALIFORNIA...

The closed upper level low is expected to slowly move south/east
across coastal California during the period with a
secondary/embedded vort max pivoting through southern California
during the late morning and afternoon hours Sunday. With the lower
heights aloft and potential for an axis of instability to develop
across this region, some intense rain showers will be possible
across the Transverse Range. QPF signal is for an additional 1-2"
in spots and this could lead to localized/isolated instances of
flash flooding, especially for the terrain areas, so a Marginal
Risk was introduced for this area.

Taylor


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