What is A Drought? How Does Summer 2024 Compare to Others?

Rainfall over the last 24 hours as of this writing (August 3) has been the most widespread in quite some time across Ohio and surrounding states. We needed it!

Yet each summer, it seems as if we go through the same process:  Rain at the beginning in May and early June with a gradual drying out with limited rain across northern Ohio by late June/July and into August. The grass gets brown. We mow every two weeks or longer versus every other day in early May. Most of us will mix in the word "drought" in  everyday conversation describing the conditions as we exclaim "this happens every summer."  At least that's how we perceive it. But is this really the case?  What does the data show?

First what is the definition of a "drought"?

Drought is generally defined as "a deficiency of precipitation over an extended period of time" resulting in a water shortage. This is per the National Integrated Drought Information System on drought.gov (a great resource). However drought can mean different things to different regions. If you are a farmer, a drought means below normal rainfall resulting in damage to crops. So not enough water means low crop yield for the season. 

Scientifically, drought can be measured through comparing precipitation departures over a period of time along with soil moisture, evaporation, temperatures among others.  A great way to compare year to year is to use the US Drought Monitor.  This is a blend of around a dozen different variables including the ones listed above. This is combined along with potential drought impacts and other expert insight. 

The US Drought Monitor index is on a scale of zero to four. One being low on the drought scale up to four meaning highly extreme drought conditions as defined above.

Just looking at precipitation changes since April you can see how the conditions in parts of Ohio/southern Ohio, the Ohio Valley and into the Carolinas/SE US have dried out significantly.

Interestingly, the corn belt and most of the Great Lakes, conditions have not been dry at all. In fact, soil moisture has been well above normal.

Back to the original question. What about the comment that we are always in a drought every summer here in northern Ohio.  Is this true?

Look at the Drought Monitor history for Ohio as a whole. Here are the years since 2000 (data only goes back that far) with portions of the state in at least a D2 drought with areal percentages.  The last time ANY part of Ohio was under a D2 drought was 2016.

Can we go back further?  Absolutely, but we need to use a different set of data.  It's called the Palmer Drought Severity Index. This data goes back more than 100 years. The PDSI is good at determining long term drought using temperature and precipitation data to estimate dryness.  So a +4 shows extremely wet conditions. A -4 is extremely dry. 

Here are the PDSI conditions across the US as of late July:

Notice that the conditions across Ohio are not as severe when looking at the LONG TERM drought conditions.

Let's go back in time just looking at the summer months of June, July and August combined. To do this, we can examine specific climate divisions versus state wide conditions. Here in northern Ohio, we have four climate divisions that encompasses our viewing area. Two, three, six and seven.

I highlighted some of the memorable drought summers for Division two. The dust bowl years of the 1930s, the early 1950s and 1960s were long periods with summer drought. Of course 1988, 1991 and the early 2000s also featured very dry summers.

Here is climate division 3:

Climate division 6:

Climate division 7:

As you can see, there are much drier periods over the last 100 years across northern Ohio.  There are also (green bars on these charts) with above normal summer wet conditions.  In fact in the last 30 years, the summers with above normal wet conditions have outnumbered the abnormally dry ones. 

Number of Abnormally Dry summers (JJA) Since 1995

Climate Division 2:  9 of 30 summers

Climate Division 3:  12 of 30 summers

Climate Division 6:  9 of 30 summers

Climate Division 7:  9 of 30 summers

While our lawns dry out each summer to some degree, is it true that every summer or even most summers in northern Ohio we end up with drought conditions?  Not even close

Below Zero Wind Chill History: What Years Experienced More?

It's been two years since I updated this chart.  It shows total hours at each below zero level from last winter (2021-2022) back to the winter of 1976-1977.

Here are some take home points: 

*  No -20 wind chill since early 2019

*  Coldest winter (wind chill) in recent memory was 2013-14.  Also the last time we had a long duration period with wind chills under -30

* Winter of 1992-1993 was the only one without a wind chill below zero. 1997-98 was close.

* Some notable winters (total hours below zero):  

2018-19:  669

2017-18:  842

2008-09:  772

1996-97:  1022

1993-94:  1605

1989-90:  1089

1983-84:  1958

1976-77:  2125

Is Late Summer Heat Becoming More Common?

Many people have said that it seems late summer heat is becoming more common in northern OH. After all, kids are heading back to school weeks earlier nowadays. Current temperatures this year are running warmer than normal with high humidity. So what does temperature history tell us?  

The graph below shows average high temperatures compared to the 20 year average for each period from August 15 to September 15 since 1980 for Cleveland, Ohio.

While we've had some warmer than normal late summers in the early 1990s the overall average high temperature is almost 2 degrees WARMER over the last 2 decades when comparing 2000-2020 to 1980-2000.  So yes, the temperatures over the past 5 years have been well above normal in late August/early September.

The warmest day late summer day in 2019 was 94 degrees on September 11th. How widespread was the heat that day?   Much of the eastern 2/3 of the US was also WELL above normal--lots of 90s.

How about the hottest late summer day(s) in 2018?

How about 1978's late summer heat?

...and 1959?

What about extreme heat...90 degree days in Cleveland?

We've had our fair share of 90s in late summer over the past decade. 2020 had only one, 5 in 2019 and 7 in 2018.  I labeled each year with more than 4 between mid August and mid September. The 1940s had more late summer 90s compared to any decade.

Many people will draw climate change conclusions based on this data. I would refrain on doing so.  It's not that climate change's influence is not present. You shouldn't draw conclusions based on one location's data--in this case Cleveland (with a few years' temperature contour maps for spatial perspective).  You need many other locations' data across a larger area over a longer time frame along with analyses of other variables to derive any climate conclusions. That's way above my paygrade.

How Does This Winter's Consistent COLD Compared To Recent Years?

Lake Erie from 30,000 feet (February 5, 2021)

One of the biggest canned responses I get when I mention winter cold is "Winter is supposed to be cold. What's so special about the cold?".  My qualifying reply usually mentions the fact that it's not the average cold we address in the forecast, it's the extreme cold that is the biggest concern for people. This winter since January 1 has been unusual in that we haven't had much extreme cold (until now, February 7).

I checked the high temperature for each of the last 5 winters from January 1 to February 7. This graphic below first shows the last 4 winters (minus 2021). Notice the ups and downs. Blue and red dots denotes the days above 50. Red dots are highs below 20. Blue curved line are the 2021 high temperatures. Notice how much flatter the curve is this year.  No extremes either way. Just consistent cold...until now.

Interestingly, the last time we had a high temperatures above 50 degrees was early Christmas Eve (before the holiday snow). 

Here is the list of longest stretches WITHOUT reaching 50. Some of these started in November and December. The blue asterisk denotes years (8 total) that didn't reach their first 50 under AFTER February 15th. Only 4 made it into March without a 50 degree day: 1963 (March 11), 1978 (March 19), 1940 (March 17) and 2003 (March 7). It's looking more likely we won't see a 50 until at the earliest, the last week of February.

History of Snow Between Thanksgiving and Christmas: Are Our Chances Higher This Year?

In late October, we issued our WINTER WEATHER OUTLOOK for 2020-2021.  The general idea is for a backloaded winter with shorter "teaser" periods of cold and snow in December.  So far (as of this writing before Thanksgiving, we've had under an inch of snow). 

Sledding with my kids when they were much younger!

How much snow do we typically get between Thanksgiving and New Years' Eve? We average around 10" over the last 10 years although the trend for early season snow has dropped over the last 15 years.

How about actual snowfalls?  We average around 4 one-inch snowfalls during the holidays.

Snowfall is one thing. But snow on the ground during the holidays is entirely different. More days with snow on the ground, the better chance we will remember it as a "snowy" holiday. We average around 8 days with snow on the ground over the last 10-15 years. 

As of this writing we are watching for changes in the pattern that strongly show more cold.

* Ridge developing across central Asia

* Jet stream across the North Pacific changing

* More frequent lows across Northern Pacific

All of this is resulting in the high pressure across the western US/North America with low pressure across eastern US. We call this a +PNA pattern (Pacific North American)

The super-long range model output into Christmas week is also strongly hinting at this eastern TROUGH/COLD lasting beyond December 20th. While I think this is probable, my confidence is high ONLY through the first two weeks of the month.

Animation from Thanksgiving to December 21st

Historically we average 15 days with temperatures in the 30s or COLDER over the last 10-15 years. Last winter we had 14 days in the 30s or COLDER before December 31st

Either way, cold and BELOW NORMAL temperatures are coming the first week of December with good chances of accumulating snow along with lake effect multiple times! Winter is coming everyone...

Updated Rainfall vs Normal

Rainfall vs normal last 60 days across Ohio Valley and Midwest

Rainfall vs normal last 14 days

Ohio Valley rainfall last 72 hours (June 15 morning thru June 18 morning)

Updated rainfall numbers at NWS Cleveland (Hopkins Airport)

Which Counties See the Most Spring Tornadoes in Northern Ohio?

Add caption

 The tracks of each tornado in each month

A Brief History of Drought in Northeastern Ohio

Since June 1st, we continue to accumulate a rainfall deficit across northern Ohio and many parts of New England. The overall pattern has featured storm clusters to travel northwest to southeast through the corn belt.  Yet much of northern Ohio, parts of Michigan and New England has missed out on frequent rainfall this summer.

As with many meteorological events, people on social media are comparing this dry period to other droughts of the past. For me, the big droughts of 1988, 1991 and 2002 come to mind. 1988 always appears on the top of my list because of the intense heat that summer. I didn't mow a lawn for 3 months!

Is there a way of comparing past periods of drought accurately? The Palmer Drought Severity Index is a great tool in comparing historical periods of above or below normal dryness or wetness of an area.

Per NOAA: "Palmer Drought Severity Index: attempts to measure the duration and intensity of the long-term drought...long-term drought is cumulative, so the intensity of drought during the current month is dependent on the current weather patterns plus the cumulative patterns of previous months".

Ohio has 10 climate divisions. I downloaded the historical PDSI monthly numbers for the northeastern Ohio climate division #3 and plotted them in roughly 30 year time periods. Green indicates wetter than normal, yellow shows drier than normal. THE SCALE ON THE LEFT CHANGES ON EACH GRAPH SO BE CAREFUL IN YOUR COMPARISONS

A few things to note based on these observations:

*  July 2016 PDSI is probably closer to -3.5. Montly numbers are not available as of this writing.

*  The 1991-92 drought was longer and more severe than any drought since the mid 1960s even beating the hot summer of 1998!

*  Frequency of wet periods were much higher than dry periods since 2000

*  The drought of 1962 to 1966 is comparable in duration to the drought of the early 1930s. These           drought events mark the only two instances where the PDSI dropped below -6

*  Many periods of drought from the 1910s to the 1930s with very little long term recovery

*  Three major droughts between 1895 and 1910

These graphs are great but they are annual monthly plots.  How about summer droughts? I singled out the summers (May through September) where PDSI levels stayed below -1. (NOTE: I CHANGED THE SIGN OF THE PDSI NUMBERS TO POSITIVE TO BETTER REFLECT THEIR SIGNIFICANCE GRAPHICALLY)

Some years to note:

* The summer droughts of 1991 and 1999 started off earlier and lasted into September. 1988 was tame in comparison.

*  During the summers between 1930 to 1934, fifteen of the twenty-five months had drought levels below -3.  During the 1960s' summer droughts, only six of those twenty months saw levels that dry.

* Yes, our soil moisture is significantly dry. But we have a long way to go before this drought becomes historic