Weather Blog

Find out what Seattle's chances are of feeling like 80 this weekend

Find out what Seattle's chances are of feeling like 80 this weekend
Hunter Reagan cools off in the fountains at a local water park Thursday, July 21, 2011, in Lafayette, Ind. (AP Photo/Journal & Courier, Michael Heinz)

Clint Eastwood used to ask: "Do you feel lucky?"

Those hoping to restart our summer weather with it feeling like 80 degrees will have to rely on a little luck because the odds are low in the short term.

But according to a new chart I just found -- they're not zero!

NOAA computer models say there is an 18% chance the heat index will make it feel like 80 degrees on Sunday in Seattle -- and a 1% chance it'll feel like 90!

Of course, this is just a computer model figuring out probabilities. It means there is an 82% chance it'll feel under 80.

The heat index is the summer version of winter's "wind chill" index -- it's basically what the temperature feels like when you factor in heat and humidity. A 102 degree day in Phoenix this week doesn't feel nearly as hot as a 102 day in Baltimore does.

And a high heat index is what can make a heat wave particularly dangerous, because high humidity makes it hard for your body to cool off.

So if you think heat index is a concern, this site can come in handy, which gives you a menu of chances of areas reaching a certain threshold of heat index.

Clicking on each map will bring that map up full screen, and it will shade areas in color based on probability of reaching the desired temperature. But you can click on each city on the map to get a chart showing the odds of you hitting 80, 85, 90, 95... all the way up to 115 degrees.

That's where I found that statistic about Seattle's 1% chance of 90.

For Seattle and the Northwest, this is mostly for amusement purposes. Heat index is rarely a factor here because the process that creates our heat also dries the air -- we need an east wind to keep the ocean breezes away and as that air sinks down the Cascades it dries out. It's why Seattle has the luxury of when it is hot here, it's more a desert heat where you can still cool off as opposed to a muggy East Coast heat.

For proof, I looked up the 103 degree day on July 29, 2009 in Seattle. The heat index at that time was 101 -- yes, the heat index can be lower than the actual temperature because if the air is dry enough, your body's cooling mechanisms are efficient in making it feel cooler than it is. (Of course, not like 101 will mean it's time to reach for a sweater.)

Hot days over 90 can still be dangerous around here to the vulnerable due to lack of widespread air conditioning, but at least heat indicies of over 100 are quite rare, no matter what that heat index chart thinks.

Compute the heat index on your own

If you are ever curious what the current heat index is anywhere, all you need is the temperature and dew point, or if you only have the humidity, you can use that too.

Here is a conversion table from NOAA.

Or, you can check out this handy chart that shows some of the highest heat indexes recorded from the day before across the nation. On Wednesday, some of the highest were in Iowa (123 in Council Bluffs), Illinois (115 in Taylorville) and Indiana (120 at Grissom Air Force Base). Several other cities across the midwest and east were well over 100.