Quantitative Precipitation Forecast
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
000
FOUS30 KWBC 290008
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
808 PM EDT Thu Mar 28 2024

Day 1
Valid 01Z Fri Mar 29 2024 - 12Z Fri Mar 29 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHEAST U.S....

...New England...
A Slight Risk of excessive rainfall remains over portions of New
England into early Friday morning. The expectation is that neither
rainfall rates nor rainfall amounts will be blockbuster in
magnitude and that rain in most places would be handled under most
circumstances (as suggested by HREF neighborhood probabilities
showing very low chances of reaching 1-/3-/6-hour Flash Flood
Guidance), or even 0.5" in an hour.  However, the amount of water
added by melting and compaction of the snowpack may be enough for
more than isolated problems with runoff in areas of poor drainage.
The risk areas remain in place with no changes, which helps to
support messaging related to New England`s flood watches.

Roth/Bann


08Z Excessive Rainfall Discussion...

...New England...
As the previously noted low develops and approaches from the south,
a slow-moving front will provide the focus for deepening moisture
and soaking rains across much of coastal New England. Overall,
models have remained consistent in showing a long stripe of 1-3
inch amounts extending from eastern Connecticut to DownEast Maine.
Rainfall rates will be limited by a lack instability, likely
topping out near 0.25 inch/hour. However, given the recent rainfall
and saturated soils, there remain some runoff concerns, promoting
the continuation of a Marginal Risk.

Pereira


Day 2
Valid 12Z Fri Mar 29 2024 - 12Z Sat Mar 30 2024

....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN CALIFORNIA...

20Z Excessive Rainfall Discussion...
Few changes were needed with models continuing to bring a closed
low southward along the northern California coast on Friday
night/Saturday morning. Higher rainfall rates look to approach the
central and southern coast of California late Friday night or very
early Saturday morning. The previous outlook had that covered and
only minor adjustments were made based on the 12Z suite of model
guidance and WPC QPF. Likewise...made minor adjustments to the
northern extent of the Marginal Risk area in Maine given the latest
spaghetti plots of higher QPF. In addition...there should be a
change in precipitation type from rain to snow as cold advection
sweeps across Maine which will help mitigate excessive rainfall
concerns.

Bann


08Z Excessive Rainfall Discussion...

A well-defined shortwave diving west of a closed low centered west
of Vancouver Island is expected to support the development of a
closed low further south that will drop south along the northern
California coast Friday into Saturday. Models continue to advertise
an anomalously deep system for this time of year, with 500 mb
heights dropping 1-3 standard deviations below normal across much
of California this period. Deep southwesterly flow ahead of the low
will support increasing IVTs, with the highest values dropping
south along the coast from Monterey Bay into the Transverse Ranges.
A Slight Risk was maintained over Santa Barbara and Ventura
counties, where the models continue to show a decent signal for
locally heavy amounts in the favored terrain. The consensus of the
deterministic guidance shows amounts of 1-3 inches in the region,
with locally heavier amounts possible by 12Z Saturday. There is
also some signal for locally heavy amounts further to the north
along the immediate coast, indicating the Slight Risk area may need
to be drawn further to north into central California. But for now,
maintained a broad Marginal Risk that covers much of central
California from the coast into the Sierra foothills.

....DownEast Maine...
Rain developing across the region on Day 1 is expected to carry
over into early Friday with an additional 1-2 inches of rain
expected before precipitation changes over snow and diminishes
behind of the departing low. As on Day 1, a lack of instability
will limit rainfall rates and the potential for flash flooding.
However, areal flooding will remain a concern given the saturated
soils.


Pereira

Day 3
Valid 12Z Sat Mar 30 2024 - 12Z Sun Mar 31 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN CALIFORNIA..

20Z Excessive Rainfall Discussion...
Consistent model and ensemble QPF across southern California and
with WPC QPF meant little need for more than minor adjustments to
the previously issued Slight Risk across portions of southern
California and the eastward extension of the Marginal risk into
portions of southern Nevada and western Arizona.

Bann


08Z Excessive Rainfall Discussion...

As an anomalously deep low continues to drop south, excessive
rainfall concerns developing on Day 2 are expected to continue and
expand further south across portions of southern California this
period. Increasing IVTs associated with a well-defined frontal
boundary will push across southern California on Saturday, with PWs
reaching 0.75-1 inch (2-3 standard deviations above normal). A
Slight Risk remains in place from the Transverse into the
Peninsular Ranges, where areal average amounts of 1-3 inches are
expected.

Moisture spreading east of the mountains will support widespread
precipitation, with locally heavy amounts possible into the lower
Colorado Basin, where a Marginal Risk was maintained for portions
of southern Nevada and western Arizona.

Pereira


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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.