Level 3 – Elevated Flash Flood risk Wednesday afternoon and evening

finger lakes weather forecast wednesday july 17 2019 elevated flash flood risk
Multiple rounds of thunderstorms with torrential downpours will impact the Finger Lakes and Southern Tier today, possibly leading to flash floods.

Flash Flood Potential Set Up

Copious amounts of moisture in the atmosphere associated with the remains of Hurricane Barry will bring the potential for flash flooding today across the Finger Lakes and, in particular, the Southern Tier.

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A series of disturbances in the atmosphere will pass through today, tapping into the very high moisture content of the atmosphere. Thunderstorms will develop and be capable of torrential downpours. Rainfall rates well over one-inch per hour are likely.

Modeled flash flood guidance indicates that most areas can take at least 1.5 inches of rain in an hour before flash flooding begins. That should limit some of the flooding potential. Urban areas, gorges, and areas that saw heavy rain yesterday will be able to take on less water, however.

Pinpointing the areas most at risk for these heavy downpours is nearly impossible in advance. This is especially true today with multiple rounds of rain possible. How one batch of rain unfolds will impact the next.

One batch of rain scooted mainly north of the Finger Lakes early this morning. Already, the second area is working into western New York. This should cross the Finger Lakes in the late morning and midday hours.

Some thunderstorm development will be possible with this rain as it moves into the Finger Lakes. If that happens, it will be the first shot at flash flooding, especially for Cayuga, Onondaga, Cortland, Tompkins, and Chemung Counties, where heavy rain fell yesterday.

finger lakes weather wednesday july 17 2017 midday weather update
The midday radar over the Finger Lakes shows light rain as another batch of precipitation moves through. Thunderstorms are developing to the east of the region. The late afternoon remains the primary concern. Click to enlarge.
12:40 PM Update-
 
The midday wave of rain is working through the Finger Lakes. Thunderstorms are developing on the leading edge of this, but to the east of the Finger Lakes.
Some heavier pockets may still develop within the lighter rain overhead.

That area should move east by the early afternoon with a lull in the activity until about 4 PM. This lull will give the atmosphere a chance to recover and become favorable for additional storm development.

The main question with the late afternoon is how far north will storms develop. Currently, storms look most favorable south of a Dansville-Penn Yan-Cortland line. These storms may be slower moving and could move repeatedly over the same areas. The storms should weaken after sunset.

finger lakes weather tuesday july 16 2019 radar estimated rainfall
This map shows radar estimated rainfall from Tuesday, July 16, 2019. These are estimates and may not fully represent how much rain fell. Areas in yellow saw over an inch of rain Tuesday. Click to enlarge.

What are the risks?

The greatest risk for flash flooding is highlighted in orange on the map at the top of this blog post. I have issued a Level 3- Elevated risk for this area. A level 3 means areas of moderate flooding will be possible. However, there is the potential for significant (level 4) flooding. There is too much uncertainty in how the day will evolve to pinpoint where within the orange area that could be, though.

The flooding I am concerned about is the type that can put lives in danger and cause significant property damage. Our region has a long history of these types of flash floods, especially in cases where the atmosphere is similar to how it is today.

Flash flooding will be less likely to the north, but the eastern half of the region is at a higher risk than the western half. There are two reasons for this. First, areas east of Cayuga Lake saw more rain yesterday that areas to the west. Second, there is a higher chance for heavy downpours early this afternoon over eastern areas.

For these reasons, I have shaded eastern areas in yellow, representing a Level 2- Low risk for flash flooding. I extended this all the way into the Auburn area, which saw some of the highest rain totals yesterday, and into Syracuse, where the vast urban sprawl will increase the chances for flooding if a heavy storm moves into the city.

Areas in green are at a Level 1- Minimal risk for flooding. While not completely out of the question, the ingredients for flooding do not line up nearly as well in these areas.

I may start a live blog to track the flooding risk for this afternoon and evening. Be sure you sign up for email alerts to be notified of any new posts and updates. See the end of this post for a sign-up.

Looking Ahead- Heat on the Way

Impactful weather will continue in the Finger Lakes through the weekend, but the risk will change from flooding to heat.

Thursday will be a relatively quiet day, however. Expect a fair amount of clouds and a couple stray showers. Temperatures will reach the low 80s with moderate humidity levels.

Friday will have more sun and a southwest wind to pump heat and humidity northward. Look for highs to push 90 degrees in many areas with excessive dewpoints all the way into the low and mid 70s. Heat index values will approach 100 degrees during the afternoon.

Saturday will be a couple degrees warmer with widespread low 90s. Dewpoints will remain very high, sending the heat index over 100 degrees, especially in urban areas. Sunday will be equally as hot and humid.

Overnight temperatures will only drop to the mid 70s Friday and Saturday nights, providing no relief. Heat Advisories and High Heat Warnings will likely be issued later this week.

A few scattered showers or storms may be possible each afternoon before a better chance for rain late Sunday into Monday.

Don’t Miss an Important Update

Keep updated with the latest on the flash flood potential today, this weekend’s heat, and all of the weather in the Finger Lakes. Signing up for email alerts will ensure you always get the latest information — Facebook and other social media channels pick and choose what you see and are thus not reliable for getting the most updated information!

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Meteorologist Drew Montreuil
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Meteorologist Drew Montreuil has been forecasting the weather in the Finger Lakes region since 2006 and has degrees in meteorology from SUNY Oswego (B.S. with Honors) and Cornell (M.S.). Drew and his wife have three young boys and also run a goat milk soap business, Ye Olde Goat Cart. When not working or playing with the boys, he is probably out for a run through the countryside.