FOUS30 KWBC 120106
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
806 PM EST Wed Dec 11 2024

Day 1
Valid 01Z Thu Dec 12 2024 - 12Z Thu Dec 12 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN LONG=20
ISLAND UP THROUGH NORTHERN MAINE...

Primary adjustment for the 01Z update was to shift the western
extent of the previous outlook areas further east across the
Northeast and remove the Mid-Atlantic, which is now post-frontal.
Deep moisture (PWs 1.25-1.5 inches) and strong ascent ahead of an=20
approaching, negatively-tilted shortwave will contine to support=20
periods of the moderate to heavy rain across portions of Long=20
Island and New England this evening into the overnight. This rain=20
is expected to move east along with the advancing cold front=20
overnight. However, some areas, especially from eastern Long Island
northward through eastern New England into northern Maine, may see
an additional 1-2 inches before the rain ends. Limited instability
is expected to keep rates in check, however given the wet soil=20
conditions throughout the region and snow melt across portions of=20
northern New England, these amounts may cause localized runoff=20
concerns.

Pereira

Day 2
Valid 12Z Thu Dec 12 2024 - 12Z Fri Dec 13 2024

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

Chenard


Day 3
Valid 12Z Fri Dec 13 2024 - 12Z Sat Dec 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHWEST CALIFORNIA AND SOUTHWESTERN OREGON...

20z Update: Forecast still looks on track. The latest model
guidance expands the higher QPF a bit further south across coastal
northern CA, and thus the Marginal risk was expanded in this
direction. Generally expecting 1-3" of rain over the Marginal risk
area through 12z Sat, with localized amounts of 3-4" within the
most orographically favored terrain within the south to
southwesterly low level flow.

Chenard

...Previous Discussion below...

Fairly robust disturbance over the Pacific will translate
southeastward towards the North-Central CA coast by the end of the
week with a persistent IVT pulse oriented southwest to northeast
into the coastal plain over the course of the forecast period
leading to waves of moderate precipitation to impact areas north of
the Bay area. Current progs indicate precip totals on the order of
2-4" with locally higher embedded within the coastal ranges
spanning north of Santa Rosa. Current rates anticipated to be
modest with upwards of 0.5-0.75"/hr at peak intensity lending to a
lower end threat for flash flooding, however totals are significant
enough to warrant a low-end threshold MRGL, mainly for the coastal
urban areas of Northwest CA up through Southwestern OR where
totals will be on the order of 2-4", especially into the windward areas
of the Klamath Range. MRGL was generally maintained from previous
forecast with only some minor modifications to align with the
latest guidance.

Kleebauer

Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!_f1dHYJrtJ9b0h3z5nh_GPcEkWGAqK4YTFU4_sJ0cfFR=
CfRs3A2CVNvGsXdlmrYdhh6vQ0ooblY1Mfx1sP0lwZM9e9o$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!_f1dHYJrtJ9b0h3z5nh_GPcEkWGAqK4YTFU4_sJ0cfFR=
CfRs3A2CVNvGsXdlmrYdhh6vQ0ooblY1Mfx1sP0lX1FiwSQ$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!_f1dHYJrtJ9b0h3z5nh_GPcEkWGAqK4YTFU4_sJ0cfFR=
CfRs3A2CVNvGsXdlmrYdhh6vQ0ooblY1Mfx1sP0lIuTYtY4$=20

=3D =3D =3D
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