Flash flooding has and is occurring across many states of the Northeast, causing overflowing rivers, landslides, and damage to human infrastructure. As of Monday, July 10th, a widespread 2-4+ inches of rain have fallen with some reports of up to 9 inches of rain falling over a several hour period. This type of deluge is rare for the Northeast and is causing some impressive and dangerous flooding. 

Current Conditions: Monday Afternoon July 10th

As of Monday afternoon on July 10th, heavy rain is affecting New England through Connecticut, Maine, Massachusetts, New Hampshire, New York, and Vermont. The National Weather Service has issued several Flood Watches, Flood Warnings, and Flash Flood Warnings with rain expected to move out of the region by Tuesday afternoon. 

National Weather Service current watch, warnings, and advisories map as of Monday, 4 pm EDT,  July 10th. 

OpenSnow Radar Loop from 3 to 430 pm EDT. 

Storms will continue to move north throughout Monday with rainfall rates in excess of 1 in/hr. The current rainfall rates are not as impressive as they have been over the past 24 hours (one report up to 4.32in/hour), but are still and will continue to cause flooding in rivers, streams, and low-lying areas. A few landslides have even been reported in New York and Vermont. 

Here is a look at the current river conditions (left) and 24-hour forecasted conditions (right) from the Northeast River Forecast Center (NERFC). 

What happened on Sunday and Sunday Night (July 9th-10th)

This storm system has tapped into subtropical moisture from the southern US and interacted with a favorable atmosphere for thunderstorm development. This combination has caused storms to dump several inches of rain very quickly. Additionally, the atmosphere associated with these storm tracks has caused slow-moving storms to track over the same areas. 

Here is a look at the past 24 hours of rain (inches) from 8 am July 9th to 8 am July 10th. Several more inches of rain (especially in Vermont) have fallen on July 10th since this map was made at 8 am July 10th. 

These amounts of rain are impressive for the Northeast, especially when several of these rainfall totals fell within a few hours. The heaviest rain on Sunday, July 9th occurred in Connecticut, Maryland, Massachusetts, New Jersey, New York, and Pennsylvania.

Rivers and especially small streams have flooded and have caused a unique event for the Northeast. Based on these rainfall amounts, several impressive flood recurrences have been observed in the past 24 hours.

A flood “Recurrence Interval or Return Period” is the average number of years between floods of a certain size. This means that some of the flooding observed is once in 100 or even 200-year flood! 

Latest Forecast of Rain and Flooding

The good news is that the heaviest rain is moving out of the Northeast into Quebec and Ontario. The rain moving into these Canadian Provinces is losing its subtropical moisture, which is weakening rain showers, although some flooding is still possible in Canada. 

The bad news is that several rivers, especially in Vermont have yet to peak as the rain moves downstream from the steep terrain. The flash flood threat is still high through the rest of Monday and Tuesday as the rain finally moves out of the region on Tuesday afternoon. 

Here is a look at a graphic from the NERFC highlighting the flood concerns and a look at a few hydrographs showing major flood stages forecasts for Monday night and Tuesday morning. Tuesday evening and Wednesday, July 12th are when river levels are forecast to be normal. 

While river levels will return to normal by Wednesday, July 12th, another storm system making a similar storm track will move into the Northeast on Thursday, July 13th. This storm will bring more heavy rain through Saturday, July 15th. Some numerical model guidance has more storm systems making the same storm track through next weekend and into next week on Monday, July 17th. 

While the intensity of the forecasted storms remains uncertain, the next round of storms this week will tap into subtropical moisture and likely cause more thunderstorms with heavy rain. It is hard to say whether they will be as intense as the past and current storms, but the forecast should be eyed with some caution for more damaging floods. 

Here is a look at the forecast in Rutland, VT on Friday, July 14th with 0.7 inches of rain forecasted. The forecast from Thursday, July 13th to Sunday, July 16th has nearly 2 inches of rain for Rutland with higher totals in nearby mountains. 

Let’s also take a look at the GFS model’s prediction of precipitation type and intensity from Thursday, July 13th to Sunday, July 16th, which shows more heavy rain coming to the Northeast. 

Stay safe out there and keep a tab on the OpenSnow forecast radar and current radar for where the heaviest rain will fall. 

Zach Butler