The National Weather Service has issued a flood watch for most of the region as remnants of Tropical Storm Debby move closer to the Finger Lakes. Residents should prepare for significant rainfall and potential flooding, particularly east of the Genesee Valley, starting late Thursday and continuing through Friday night.
Thursday’s Transition: Mostly Cloudy with Showers
High pressure currently positioned over Quebec will shift eastward overnight, allowing winds in Western New York to veer southeast. This change will bring moisture from the Atlantic back into the region, increasing both cloud cover and surface dewpoints. This influx of moisture, combined with a developing low-level southerly wind, may lead to a few light showers, particularly in far western New York, by early Thursday morning. These showers could be enhanced near Lake Erie due to frictional convergence from the downslope flow off the Chautauqua Ridge.
Throughout Thursday, the region will see increasing cloud cover and humidity levels due to the continued southeasterly to southerly low-level flow. As the low-level wind strengthens and lifts northward, scattered showers will become more numerous, especially in the eastern Finger Lakes and North Country. Some weak instability in the afternoon may even result in a few rumbles of thunder. Meanwhile, downsloping winds may reduce shower activity across the lake plains of far western New York.
Overnight lows will range from the mid-50s east of Lake Ontario to the upper 50s and lower 60s elsewhere. Thursday’s highs will vary from the lower 70s in higher interior terrains to the lower 80s in areas with favored downslope flow, accompanied by rising dewpoints.
Heavy Rain Arrives Tonight
The remnants of Tropical Storm Debby are expected to bring significant rainfall starting late Thursday into Friday. A westward trend in the storm’s northward track suggests that the most substantial impacts will be felt east of the Genesee Valley, particularly in the eastern Lake Ontario region. As the tropical moisture advances, a band of rain showers will sweep northward, with heavy precipitation expected in some areas.
A trough digging across the Great Lakes will support a surface low moving eastward across southern Canada, dragging a cold front across the region Friday and Friday night. This setup will result in a significant rainfall event, with the eastern Lake Ontario region potentially receiving 2-4 inches of rain and western New York seeing 1-2 inches. The heaviest rainfall is expected late Friday through Friday night as the front interacts with the remnants of the tropical storm.
Given the potential for heavy rain, the Weather Prediction Center (WPC) has expanded the Moderate and Slight Risk for Excessive Rainfall into western portions of the Genesee Valley and far western New York. The forecast suggests hydrologic impacts such as flash flooding and river rises are likely. However, model inconsistencies regarding the storm’s track have kept forecast confidence low, and no Flood Watches have been issued yet.
Rain Moves Out Saturday
The plume of tropical moisture will move east into New England by Saturday, bringing mostly dry conditions to Western New York. However, a closed low entering the Great Lakes later in the weekend will generate lake-induced instability, leading to lake effect rain showers from Saturday night through Monday.
Multiple shortwave troughs will cycle through the area, bringing deeper moisture and lift. This will likely result in lake effect showers east-northeast of Lake Erie and Lake Ontario, with potential for moderate rain in some bands.
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