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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1559Z Dec 08, 2022)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1059 AM EST Thu Dec 08 2022

Day 1
Valid 16Z Thu Dec 08 2022 - 12Z Fri Dec 09 2022

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

Churchill


Day 2
Valid 12Z Fri Dec 09 2022 - 12Z Sat Dec 10 2022

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM FAR
SOUTHWEST OREGON INTO NORTHWESTERN CALIFORNIA...

There is fairly good agreement in the latest model guidance with
the amplification of the upper trof off the Pac NW coast late
Friday afternoon into the early hours of Saturday.  This will
strengthen the low level southwesterly flow into coastal sections
from northwestern California into Oregon, with 850-700 mb moisture
flux anomalies reaching 2 to 2.5+ standard deviations above the
mean from far southwest Oregon into northwestern California.  This
will support heavy precipitation during the 0000-1200 UTC Saturday
time period across the marginal risk area, with isolated hourly
rates of .50"+ possible.  The axis of anomalous onshore flow will,
however, be fairly progressive to the southeast.  This and only
slightly above average precip values over the  past week for
northwest California will keep the risk level at marginal at best.
 There were no significant changes from the previous outlook for
this period.

Oravec

Day 3
Valid 12Z Sat Dec 10 2022 - 12Z Sun Dec 11 2022

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
CENTRAL CALIFORNIA COASTAL REGION...

The amplifying mid to upper level trof off the Pac NW coast day 2
will continue to press southeastward day 3 across the coastal Pac
NW and northern California.  The axis of anomalous 850-700 mb
moisture flux on the southeast side of this amplified trof will
continue to press steadily southeastward, with values 3 to 4+
standard deviations above the mean affecting areas of central to
southern California.  This will support a period of heavy
precipitation, especially through the Sierra and along the central
California coastal range, with hourly rates topping near
.50"+/hour. Much of these regions have seen above average precip
over the past few weeks.  A marginal risk was confined to the
coastal sections from the coast range north of San Francisco,
south to approximately Santa Barbara where stream flow anomalies
from the National Water Model indicate regions of much above
normal to high flow from the above mentioned recent heavy
precipitation.  Additional heavy rains may result in isolated
runoff issues, especially across recent burn scars.   While heavy
precip is also likely in the low elevation upslope of the Sierra,
stream flows are mostly at or below average levels.  For this
reason and after collaboration with WFO STO, no risk area was
denoted here.

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