A flood watch has been issued for the entire region as a powerful storm is set to bring heavy rainfall and potentially cause the rainiest March day in 150 years of record-keeping in Philadelphia. According to the National Weather Service, the storm is expected to drench the I-95 corridor from Washington to Boston, with Philadelphia and its surrounding areas expected to receive up to 4 inches of rain.

The most significant downpour is projected to occur on Saturday morning and afternoon, prompting a flood watch from 4 a.m. Saturday until 8 a.m. Sunday. Authorities have warned that stream flooding is possible, and there may be power outages, especially along the Shore where winds could gust up to 45 mph, or 40 mph inland.

Meteorologists are closely monitoring the storm's track, which currently indicates a direct impact on the I-95 corridor. However, there remains a possibility of a corridor of very heavy rain developing, resulting in rainfall exceeding 4 inches. The weather service describes this development as a "nowcast situation," meaning the exact intensity and impact of the rainfall will only be known once it occurs.

If the forecast holds true, this would surpass the record for precipitation on any given day in March in Philadelphia, which stands at 2.79 inches set in 1912. The current record for March 23 is 1.36 inches, established in 2005.

The storm is expected to draw moisture from two sources: the already moist air across the Southeast and the warm Atlantic waters. The combination of an intensifying El Niño event and above-average sea-surface temperatures in the Atlantic has created an environment conducive to significant rainfall. As a result, the storm is forecasted to tap into "deep tropical moisture," adding to the heavy rainfall potential.

While there is a concern for overflowing streams and urban street flooding, it is fortunate that trees are not yet bearing leaves. This reduces the risk of damage caused by strong winds, as the gusts can easily pass through the bare branches. Additionally, the recent dry spell and windy conditions over the past two weeks have helped to dry out the soil, potentially minimizing the risk of widespread flooding.

The storm is anticipated to taper off by 8 p.m. on Saturday, with the return of the sun on Sunday. However, those participating in Philly's Love Run, including approximately 12,000 runners, should be prepared for a chilly half marathon or 7K, with temperatures in the low to mid-30s, north winds gusting up to 35 mph, and wind chills in the 20s.

Authorities advise residents to stay updated on weather alerts, take necessary precautions, and consider avoiding unnecessary travel during the storm.