Severe Weather Threat Details
Severe thunderstorms are expected in the Finger Lakes region by the midday hours.
There are four main factors that go into producing severe thunderstorms: moisture, instability, a trigger to force storm development, and support from winds above the surface. It is rare that all four factors come together strongly over our region, but the strength of one or more factors can overcome the deficiencies in other areas.
For today, all four factors are at least somewhat favorable for thunderstorms, though none of the factors are too extreme.
This is probably the least favorable of the four factors today. Dewpoints will be marginal around or just above 60 degrees. This is supportive of thunderstorms but will be a bit of a limiting factor. Higher dewpoints in the 65-75 degree range would be much more supportive of severe thunderstorms but are not expected.
This is a measure of the energy available in the atmosphere needed for a thunderstorm to grow. You may also see it called CAPE, or Convective Available Potential Energy. Sometimes, low CAPE values under 1000 can be overcome with strong enough winds in the atmosphere. That will not be necessary, with moderate CAPE values of 1000-2000 expected. Stronger CAPE values of 2000-3000+ would support more robust storms but are not expected.
This is the strongest of the factors today. A trigger is needed to initiate thunderstorm development. A powerful cold front is acting as today’s trigger. The strength of this front is evident by a drop from temperatures in the low and mid 70s ahead of the storms, to the mid and upper 50s by the late afternoon.
Increasing winds with height is necessary to support storm organization and duration. Winds that remain from roughly the same direction with height are supportive of damaging winds, but winds that also turn clockwise in direction with height are more supportive of large hail and tornadoes.
This factor will also be mid-range today. The Finger Lakes are in a favorable location relative to the jet stream, but the strongest winds aloft will stay to our south. There is some turning of the wind direction in the lower atmosphere. There have been many other cases where the winds aloft are more supportive, but there is definitely enough for the storms to work with.
Storm Evolution & Timing
Thunderstorms are already ongoing across eastern Ohio and western Pennsylvania this morning. For the next couple of hours, the storms will remain weak as they slowly track north-northeastward.
Out ahead of the storms, daytime heating will increase the fuel (instability) necessary for the storms, and an increase in coverage and intensity will take place.
A broken line of storms should move into the Finger Lakes by the late morning and midday hours, taking a couple of hours to clear the region before the mid-afternoon. The greatest threat will be between 11 am and 2 pm.
Additional thunderstorms could develop out ahead of the main line. This could cannibalize some of the fuel from the main line as a limiting factor. On the other hand, this potential could lead to multiple strong to severe storms in some locations.
The threat for damaging winds is the greatest. Due to several of the limiting factors already expressed, significant wind gusts of 75+ mph are not expected. However, wind gusts over 60 mph are likely and can cause tree damage and power outages.
Several instances of damaging winds are expected. The magnitude of the severe wind occurrences and the intensity of the wind is expected to be similar to thunderstorm events the Finger Lakes area experiences a couple of times a year.
Severe hail is defined as having a diameter of at least 1-inch. While some hail is expected, it should not be as widespread as the damaging winds. Significant hail with a diameter of at least 2 inches is unlikely to occur. The magnitude of the severe hail occurrences and the size of the hail is expected to be similar to thunderstorm events the Finger Lakes area experiences several times a year.
Several of the factors described above hint toward the possibility of an isolated tornado or two being possible. However, none of the factors are overwhelming enough to make tornadoes a significant threat.
I would not be surprised if a tornado warning or two is necessary as individual cells within the greater line show some brief periods of rotation. Whether or not a tornado actually manages to touch down is possible, but improbable. The chances of a tornado hitting your exact location remain extremely low, but any warnings should be taken seriously.
The tornado risk and the intensity of any tornadoes that do develop is expected to be similar to thunderstorm events the Finger Lakes area experiences several times a year.
The limited moisture and recent dry weather will preclude much of any flash flooding threat. Localized poor drainage areas that often see minor flooding during heavy downpours may see some water problems once again.
A severe thunderstorm watch is highly probable by the late morning hours. A watch means conditions are favorable for severe thunderstorms over a large area.
Numerous severe thunderstorm warnings are expected. Warnings are issued when severe weather is threatening a localized area within the next 45-90 minutes.
One or two tornado warnings are possible, but not an absolute certainty. No flash flood warnings are expected.
Thunderstorms are already ongoing downstream, so there is very high confidence in rain and thunder during the midday and early afternoon hours. All factors point to at least some severe threat and taken all together, numerous severe thunderstorms are likely.
While the fine details of thunderstorm events, including whether your exact location will see severe weather, are never a certainty, this event has an overall high confidence of occurring.
The Week Ahead
Most of the rest of the weather this week will be on the quiet side.
Cool air will dominate for Tuesday and Wednesday behind the cold front. Tuesday will have clouds, some sun, and a few stray afternoon showers. Blustery northwest winds will gust over 30 mph, holding temperatures to the mid and upper 50s.
Wednesday will have a good deal of sunshine and lighter winds. Temperatures will manage to rise into the mid 60s.
By Thursday, warm air will quickly move back in as highs push into the low and mid 70s. A few morning showers will be possible as the warm air moves in, followed by a few more showers in the afternoon as a disturbance passes by.
Temperatures will start to take off again on Friday. With a mix of sun and clouds, highs should push into the mid 80s.
Saturday has a good chance of being the hottest day of the year thus far with some areas approaching 90 degrees. A late-day cold front could bring showers and thunderstorms.
Sunday will be much cooler with highs returning to the low 60s. Cool air will stick around for early next week as well.
This graphic represents an average over the entire Finger Lakes region. Localized variations should be expected.