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Subject: HVYRAIN: Excessive Rainfa Date: Thu Mar 28 2024 08:23 am
From: Mike Powell To: All

FOUS30 KWBC 280817
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 AM EDT Thu Mar 28 2024

Day 1
Valid 12Z Thu Mar 28 2024 - 12Z Fri Mar 29 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
EASTERN NORTH CAROLINA AND SOUTHEASTERN VIRGINIA...

...Eastern North Carolina - Southeastern Virginia...
An upper trough moving over the lower Mississippi Valley and
northern Gulf will begin to assume a negative tilt as it moves into
the Southeast today. Right-entrance region upper jet forcing will 
support a deepening low that will track north along the Southeast 
to the southern Mid-Atlantic coast later this morning. This will
support continued southwest to northeast training showers and 
thunderstorms into the afternoon, with additional heavy rainfall 
amounts expected over the region. Although instability will be 
limited, strong forcing interacting with sufficient moisture (PWs 
1.25-1.5 inches) will be enough to support rainfall rates up 1 
inch/hour and accumulations 1-3 inches. HREF neighborhood 
probabilities indicate that additional totals of 2 inches or more 
are likely within the Slight Risk area. These amounts on top of 
wet antecedent conditions can be expected to cause additional 
runoff concerns. 

...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...

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..

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

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