Wednesday, July 16, 2014

Does a hot July mean that August will be hot?

So far, it has been a blistering July. We've seen day after day of scorching temperatures above 90°F with may locations topping 100°F. Today is the 9th day in a row that Wenatchee has seen temperatures at or above 100°F.  This sets the record for the longest consecutive streak of 100°F or higher in Wenatchee ever!  Records for Wenatchee Airport only go back to 1959, but this is still a an impressive mark.  Spokane’s streak of 90+°F days is now at 11 days and is expected to top off at 12 on Thursday before cooling down, making it the 4th longest streak in Spokane’s history. This heat has led to everyone asking one question, “What is August going to be like and will it be as hot as July?”

Well the simple answer is… we’re not sure yet. Is a hot July always followed by a hot August? Our past records have had some scorcher July's like this one and then very cool August's. For example, 1985 in Spokane saw a July much like our current one, at 5.1°F above average, only to be followed by an August that was 3.8°F below average. On the flip side of that, Wenatchee had a hot July in 2004, 3.9°F above average, only to be followed by an even warmer August that was 4.2°F above average. So there's no guarantee for August. However, based on history and our data we can make some predictions at what will happen. 

This graph shows the percentages of occurrence of a hot August, a cool August, and a normal August following a hot July. If you live in Spokane (green pyramid) and it's been a hot July, there is a 44% chance of a hot August.  But that means that there's a 56% chance of having a normal or cool August. In other words, just because it's been a hot July doesn't mean it's a sure thing that August will follow suit.

If you live in Wenatchee (blue pyramid), the numbers are a bit different.  A hot July has a 54% chance of being followed by a hot August.  However, Wenatchee also has a 27% chance for a cooler than normal August after a hot July. Those of you in the Lewiston area (red pyramid) also have about the same chance of a hot August (53%), with the next best chance being a normal August (37%). 

Even as we start off the month of July at near record high readings, it doesn't even guarantee how the rest of the month could go. July 1926 in Spokane was the hottest first half of July ever. The first 14 days were marked by temperatures in the 90s with 3 days above 100°F. However, as the month progressed the temperatures rapidly cooled off and returned to normal levels.  A few of the days failed to even warm into the 80s.  The thing to take away from this is even if the month starts off at record setting levels, there's no sure bet that it will end up the same way.  

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