What you need to know about the heat

Heat Index Values over 105 Degrees

Friday and Saturday will be hot and very humid across the Finger Lakes with heat index values approaching dangerous levels.

Conditions will vary across the region as is usually the case due to differences in terrain and urbanization. Urban areas, the I-90 Corridor, and lower elevations of the Southern Tier will have the highest heat index values.

The heat index is a calculated value based on the temperature and humidity. It is a measure of how hot it really feels outside and how that value impacts your body. On the official heat index chart from the National Weather Service, once values begin to approach or exceed 105 degrees, there is a danger for heat-related illnesses if basic precautions are not taken.

Heat Index values Friday and especially Saturday will reach and exceed the 105 degree threshold over the areas shaded in red in the map above. Generally , the heat index Friday and Saturday will be similar, but with Saturday a couple degrees higher than Friday. The difference of a couple degrees really does not matter too much at these levels.

It is also important to realize that the map above, and other such maps, are approximations used to identify general areas of risk. There will be very small-scale variations that are much too fine to resolve on a regional map that will increase or decrease the risk.

These heat index values, and higher, have been seen before in our region. They are a bit higher than we see in a typical summer, but something we see every few years.

So, what precautions are necessary?  Basic, common sense principles.

Staying hydrated with water, avoiding strenuous outdoor activity, and taking frequent breaks will prevent most cases of heat illness at these levels. The young and elderly will be more at risk. And, of course, don’t forget to care for pets and livestock, too.

What About Thunderstorms?

The forecast gets much more complicated late Friday afternoon and evening, and again Saturday evening.

Weak impulses in the atmosphere will arrive in our region late each day. These impulses will be generated by thunderstorms over the Midwest that formed Thursday night and again Friday night.

Thunderstorm development is a complex process. Heat and humidity at the surface are very important ingredients which will be in abundance. However, cooler air in the mid-levels of the atmosphere is also important for storm development and will be lacking. Strong winds aloft to organize storms and produce severe weather will also be minimal.

Lake breezes off the Great Lakes and the varying terrain of the region may also play a role in whether storms develop and, if they do, where they form.

I am not 100% convinced that thunderstorms will develop either Friday or Saturday. It would not surprise me to see little to no activity. However, it is prudent to prepare for the possibility of scattered showers and storms after 4 PM on Friday and after 6 PM on Saturday. Not all areas will see storms, even if they develop.

Any thunderstorms that fire up will have the potential for frequent cloud to ground lightning, very heavy rain, and some strong wind gusts or small hail.

Breaking the Heat

Sunday continues to be an uncertain day as a front slowly approaches from the northwest. This front will break the heat once it moves through, but the timing of that occurring is still questionable.

The consensus in the models points to a late Sunday or early Monday frontal passage. Showers and thunderstorms will be possible both days until the front moves through.

Temperatures could approach 90 degrees again on Sunday with heat index values near 100 if the front is slow enough and if rain holds off. The heat should not be as hazardous on Sunday, however.

Behind the front, most of next week looks to have temperatures in the 70s or low 80s with few chances for rain.