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000
FOUS30 KWBC 120751
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 AM EDT Fri Apr 12 2024

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


...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHERN NEW ENGLAND...

Strong southerly low level flow in an axis of much above average
PW values...3+ standard deviations above the mean...expected along
and ahead of the lead frontal boundary pushing across eastern New
England early Friday. A period of heavy rains likely to push fairly
quickly eastward Friday morning across New Hampshire, eastern
Massachusetts and Maine. There is pretty good agreement on a stripe
of heavy precip in the area of strong upslope flow from northern
New Hampshire into central Maine. Not a lot of changes made to the
previous slight risk area, which continues to correspond well where
the HREF neighborhood probabilities are high for 1 and 2"+ amounts
and where the HREF EAS for 1"+ amounts are also high. This heavy
rain, along with snow melt will continue the risk of flash
flooding, especially during the morning hours of Friday.

A second line of convection may form along the secondary frontal
boundary pushing eastward into far eastern Pennsylvania, northern
New Jersey and eastern New York. The previous marginal risk area
across northern NY State was extended southward to cover locally
heavy rains with this second band of convection moving across this
area Friday morning into early afternoon. The marginal risk fits in
well where the HREF neighborhood probabilities are high for 1"+
amounts.

Oravec

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...

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

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

Oravec


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