Rain increases late Sunday, brings at least some flooding threat

Low to Elevated Flash Flood Risk Again Sunday into Monday

The Finger Lakes has been on the edge of a stalled out frontal boundary for the last few days. Thankfully, so far, this front has not produced more than a few light showers in our region. That will probably change later Sunday.

A combination of factors are aligning for another potential heavy rain event. Copious amounts of moisture, strong jet stream dynamics aloft, and slow moving storms with torrential downpours will set the stage for flash flooding.

However, forecast confidence remains below normal on exactly where the greatest threat will set up. While rain and thunderstorms will be likely in most areas, isolating the greatest potential for extreme rain is difficult at best and impossible at worst.

At the current time, the greatest risk for flash flooding appears to exist across the eastern half of the Southern Tier into northeastern Pennsylvania. However, at least isolated flash flooding problems will be possible throughout the entire region.

Many areas will see over a half-inch of rain today. That should not cause too many problems. Once rain amounts start approaching or exceeding 2 inches, flash flooding will become problematic.

There are indications in the models that there is at least some potential for extreme rain amounts of 3 to 5 inches or more in a few very isolated locations. Should this be realized, it would be disastrous for the small areas in which it occurred.

Timing the Rain

A few scattered showers will continue to dot the Finger Lakes region through Sunday morning and the first part of the afternoon.

The main activity will not start to develop until the later afternoon hours, after 3 or 4 pm.

Multiple waves of rain and thunderstorms are possible through the late afternoon and into the evening hours. There is potential for the scattered showers and storms to transition into a more widespread rain event at times.

The precipitation should taper to showers and just a few isolated downpours later Sunday night and into Monday morning. There may even be a complete lull in the action during the latter half of Monday morning.

However, more thunderstorms are expected to develop on Monday afternoon. The atmosphere will not be quite as moisture laden, but flash flooding will still be a concern, especially if the rain tonight unfolds in a more extreme manner.

Showers will persist Monday night and possibly into Tuesday morning as low pressure slowly pulls out of the region. These showers will be light and should not cause additional flooding.

What About Severe Thunderstorms?

There will be a small chance for some strong to severe thunderstorms today.

The best chance will be for the western half of the Southern Tier, where the most instability in the atmosphere will be present.

Further north and west across most of the Finger Lakes, severe weather will be less likely. Still, some gusty winds will be possible. With saturated soil, trees will be less stable and more prone to uprooting, so even a borderline severe storm may be enough to cause damage.

Thunderstorms on Monday afternoon may have more to work with than they do today. This will especially be true if the precipitation does come to a complete stop early Monday and some sun can work out.

Still, the overall risk is not overly high on Monday, but it will be something to readdress Monday morning.