Friday may turn out to be another very active day across the Finger Lakes region with severe thunderstorms and flash flooding concerns from the mid afternoon well into the evening hours.
A warm front will push north into the region this morning before settling near and east of Lake Ontario. South of this front, across the Finger Lakes and surrounding areas, a hot and very humid and unstable air mass will settle into place.
With moderately strong winds aloft and good upper level support, the atmosphere seems primed for another active severe weather day. There are two events that could unfold today to watch.
Severe Event 1- Elevated Risk Mid/Late Afternoon (Orange Shading)
The first event is less certain and much more isolated, but has the potential to become an intense event. The orange shading across most of the Finger Lakes and central New York addresses this threat with an ‘Elevated’ severe risk classification- the first I have issued in 2015.
I really want to stress though- the threat in the orange area is isolated and uncertain. However, despite these limitations, the threat is real enough that I feel it is better to inform in case the threat is realized than to have people caught off guard.
So what am I concerned about in the Elevated area? One, or maybe two isolated supercell thunderstorms *could* develop in this area by mid afternoon, gradually evolving into a small line of storms. In the initial phase, when the storm is a discrete cell, damaging winds, large hail (possibly 2″ or larger) and maybe a tornado could be possible. As the cell becomes a line, destructive winds would become the main threat- though these types of lines can and do produce tornadoes at times, too.
The majority of the orange area will NOT see this type of weather. If one or two of these storms does fire though, it will be important to heed any warnings that are issued and seek shelter. Continue to monitor the forecast and radar updates this afternoon.
Severe Event 2- Low Risk Evening Hours (Yellow Shading)
The second part of today’s severe weather will be a large area of rain and thunderstorms that drops southeast out of Canada as the front begins to push back south in response to an area of low pressure that will track along the front into southern Canada.
This scenario seems more likely, and while it too may be locally intense, the storms should not have quite the same destructive potential as any afternoon supercells. Strong winds will be the main threat as the storms move from western New York in the early evening hours into the Finger Lakes during the first part of the night. The storms should weaken by 11pm or 12am as they move into central New York and northeastern Pennsylvania.
Flash Flooding Risks
All of these thunderstorms will be taking place in an environment that is extremely moist. Thunderstorms in either of the above scenarios could easily dump well over an inch of rain in an hour or less, especially if any small line segments become aligned from west to east and stall out over an area for a time.
With plenty of recent heavy rain, the amount of rain the region can handle is reduce. For most of the area, 1″ to 1.5″ of rain in an hour or less would cause flash flooding. Over a three-hour period, anything over 2″ will cause flash flooding. These numbers can certainly be met today and I would not be surprised if more than one flash flood warning is issued before the event comes to an end.
A Final Note
Severe weather and flash flood forecasting is very sensitive to a wide variety of environmental factors- some of which the meteorological community is still trying to understand and discover. Predicting exactly where and when a severe thunderstorm or flash flood will occur is simple not possible until the event has already begun to unfold. Furthermore, there is a constant decision that needs to be made balancing reporting accurate, not hyped information and addressing the potential seriousness of an event.
Finger Lakes Weather stands by its no-hype pledge, even though this forecast may seem more intensely worded than other forecasts you may see today. If, in the end, the full potential of today’s severe threat is NOT realized, I will be relieved and feel completely comfortable with having made this forecast. Thank you for your support of Finger Lakes Weather!