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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0807Z Apr 13, 2024)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
407 AM EDT Sat Apr 13 2024

Day 1
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...

No changes made to the marginal risk areas along the central
California coast or into the upslope regions of the northern to
central Sierra. There continues is good model agreement on the
slow eastward inland movement of height falls from the strong
closed low off the northern California coast day 1. Simulated hi
res radars continue to depict a well defined area of precip moving
inland along the associated front in the first half of day 1
across the central to southern California coastal regions and
inland into the upslope regions of the northern to central Sierra.
Anomalous PW and 850-700 mb moisture flux values, 1 to 2+ and 1 to
3+ standard deviations above the mean respectively, expected along
the slowly southeastward moving frontal boundary. Hourly rainfall
rates with the lead area of precip expected to max out in the
.25"-50"+ range. HREF 1 hour neighborhood probabilities for .50"+
amounts show relatively small areas moving along the central CA
Coast Range and Transverse Range with the frontal precip band.
There are no HREF probabilities for hourly amounts greater than 1".
This initial precip area will then be followed by a secondary
precip area developing along the central CA coastal range from San
Francisco south to just north of Point Conception as the main
upper vort swings southward along the central California coast.
HREF neighborhood probabilities for .50"+ hourly amounts are lower
with the second precip area compared to the lead area. Most of the
hi res runs show hourly totals in the .10-.25" range along the
central CA Coast Range with the second precip area. Given the
relatively low probabilities for .50"+ hourly amounts, the risk was
kept at marginal with flash flooding remaining isolated.

Oravec


Day 2
Valid 12Z Sun Apr 14 2024 - 12Z Mon Apr 15 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
COASTAL SOUTHERN CALIFORNIA...

The secondary area of precip dropping southeast along the central
California coast late day 1 will continue to push eastward
across coastal southern California day 2. No significant changes to
the previous small marginal risk area through the Transverse Range
of southern California. Hourly rainfall rates will mostly be in
the .10-.25" range with this secondary area of precip, which is
expected to be fairly progressive. These hourly rates and the
progressive nature of the precip area should keep any runoff issues
as isolated.

Oravec

Day 3
Valid 12Z Mon Apr 15 2024 - 12Z Tue Apr 16 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE PLAINS...

The closed low that is expected to move inland from central
California into the Great Basin day 2 will be ejecting
eastward through the Central Rockies into the Central High Plains
day 3. We continue to depict a broad marginal risk area through
portions of the Plains in a region of strengthening low level
southerly flow and increasing PW values. PW values expected to
increase to 2 to 3 standard deviations above the mean along and
ahead of the strengthening north to south oriented frontal boundary
expected to push eastward into the Plains on Monday. This and and
a broad region of instability along and ahead of this front will
support increasing convection, especially late Monday afternoon
into the early hours of Tuesday. There continues to be a large
spread with qpf details among the models at the day 3 period. We
kept a fairly broad marginal risk area to cover this spread,
although we did narrow the marginal risk area to better fit the
latest spread. Two areas of concern are for a convective line
forming late Monday afternoon into the early hours of Tuesday along
and ahead of the front over the Southern to Central High Plains.
The other area of concern would be with a slow moving comma
head/deformation precip area farther to the north to the north of
the closed low track. There is somewhat better qpf agreement with
the comma head/deformation precip area compared to the convective
frontal max farther to the south. With precip totals generally
below average over the past few weeks across large portions of the
Plains, and current model qpf spread, the risk level was kept at
marginal.

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