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 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