September Cool To Mid- September Warmth - Part II

Let's go back to the first 10 days of the month. Temperatures were below normal. We had a 5 day stretch of highs in the 60s/70s and lows in the 40s in spots. Then the pattern flipped. Starting on 9/11, the temperatures reached 80 degrees. The first of 12 straight days. 

To have 

Here is an animation of the upper level pattern starting September 6th.  Cool colors are low pressure.  Warmer colors are high pressure. Notice the cool colors over the Great Lakes at the start. See how the ridge of high pressure replaced it. It developed over western Canada, moved east and deepened between Hudson Bay and the Great Lakes. Low pressure stalled in the western US. Southern systems undercut the big ridge as indicated by the cool colors across southern states.

The overall temperatures vs normal starting September 6th:

The difference in average temperature from September 1-10 and September 11-20 was huge.  I compared each year to see where 2024's September temperature flip ranked.  Sure enough, the temperature change was the second biggest jump ever!

Here is the last 30 years for comparison. 1985 is on the left.  2024 is on the right.  2017 had the biggest jump.

The warmth (80 straight days with highs in the 80s) ended up lasting 12 days.  Here are the years that had similar stretches of September warmth.

What was unusual about this year's 80 degree stretch was the OVERALL lack of high humidity.

Here are the daily temperatures (line) in the years above during each stretch with the average dew point for each year:

You can better see the differences when you plot the daily dew points in each year. Notice that this year was lower overall.

Here is a plot of the daily dew points for each year in September since the early 1970s. Cool colors indicate comfortable dew points. Any day with a dew point UNDER 60 is shown with a blue color. Right side is the second half of the month. Notice the frequency of less humid days is much higher after September 15th (black line).

Is Late August/Early September Heat More Frequent Nowadays?

Today the temperatures reached the lower and mid 90s across not only Ohio but much of the lower Great Lakes and Ohio Valley. The question of whether or not late season heat is becoming more frequent in northern Ohio always surfaces during heat like this.  

High temperatures August 27th:

Heat Index reading on August 27th:

So how do we answer this question?  First what time period are we looking at when we say "late August/early September"?  I like to use the last week of August and first week of September. A fourteen day period that is a decent duration sample size.

August 25 to September 7

What about temperature?  First, let's take look how many instances each year the high temperatures reach 90 degrees or higher during this 14 day period? (Given the forecast we could conceivable hit 90° four times by the end of the week).

Contrary to some of our recollections, its been 6 years since we had a late August stretch of 90+ similar to this year.  This actually occurred the most frequently in the 1950s. The early 2000s are a close second with high occurrences in 2010, 2012, 2016 and 2018.  With the exception of a few years like 1973, 1983, 1991 and 1993 it rarely happened in the 1960s, 70s, 80s and 1990s.  

What was interesting about the late August/early September of 1953 period was that we were above 90 degrees eleven of the fourteen days. 

The top number is the high temperature. The bottom number is the highest heat index that day.  Notice the extreme humidity didn't accompany the heat initially. In fact, dew points were very dry the first 6 days of that stretch from August 25 through the 30th. It wasn't until later in the period -- day 7 of the 11 day stretch -- that the heat index rose above 100° for 4 straight days.

Now compare 1953 and its 10 days above 90° to the 7 day stretch in 2018.

What about the overall average high temperatures during this 14 day period.  Are there any changes locally?  Here is a look each year since 1980. 2016 and 2018 were well above normal in high temperatures as was 2010 and 2012.  

Were these warm, late season stretches just relegated to northern Ohio?

Notice that most of these late season hot periods were centered over the Great Lakes, Ohio Valley and portions of New England and eastern Canada while the western US experiences well below normal temperatures.  Below are the temperatures above normal (warm colors) and below normal (cool colors) across the US and Canada.

The bottom line is that long hot stretches don't happen every year in late August/early September like many remember. 

  

Why So Much Smoke From Canada This Summer?

The air quality across the Great Lakes, Ohio Valley and much of New England recently has been very poor due to the smoke from Canadian fires in eastern Ontario and portions of Quebec.  

June 28 Air Quality Levels

June 28 Air Quality Over Great Lakes

Earlier in the week, smoke from the fires in western Canada were the culprit. 

Current Conditions in Canada

Area Burned vs All Years Since 1980

Fire Stars Since 1980

Why has smoke from the north impacted our air quality and sky condition this summer?  Has this happened before?  Is this low air quality unprecedented? 

The smoke movement has to do with the overall weather pattern across North America. In late May and June the pattern featured an abnormally strong and stagnant ridge of high pressure over central Canada and high pressure over Texas. The flow is clockwise so the winds steered the smoke from Quebec south into the Great Lakes. Now in July the ridge over Canada has weakened. A trough has replaced the ridge. The dominant flow has been northwesterly bring in fast moving cold fronts from the west and northwest recently. The flow steered smoke from the fires in western Canada into the upper mid-west and Great Lakes. 

Watch how the high pressure ridge (warmer colors) developed in May across Canada.  Also notice how the ridge faded and emerged further east then central Canada by early June. Also notice how there was little southern high pressure. Pockets of blue indicate low pressure.  No sign of the Bermuda high to establish a southwesterly wind across the central US keeping the smoke north.

Upper Level Pattern (3 day periods) - Early May thru June 24-26

This abnormally strong Canadian ridge created record setting temperatures in May and June across western Canada

Soil moisture dropped both in western and eastern Canada.  Dry conditions began to spread across the Great Lakes.

When we look at the air pollution data since 1980 for Cleveland and surrounding locations, the time of year where pollution becomes more of a problem is summer.  Warm and often times stagnant air creates conditions that keep pollution from dissipating.  What really stands out on this graphic is the frequency of low air quality in the 1980s and 1990s between May and August. Look at the summer of 1988. 36 days with highs in the 90s with a few 100 degree days and little wind. Compare this to early summer of 2023 (bottom of graphic - red arrow). Only a few days in late May, June 28 and July 17-18 air quality was considered poor.

This was the same pattern that kept the humidity in northern Ohio at decades low levels in May and most of June although the recently higher July humidity brought up the seasonal average.

Both summer time high pressure ridges are not linked. Often times they will merge briefly. That has not happened this summer.  Below is a long range forecast for July 31, 2023.  Notice both ridges are distant.

This is also the same pattern that has kept most of the extreme heat in the deep south and away from the Ohio Valley. 

If this were a typical late spring and summer with the Bermuda High establishing itself over the southeastern US, the dominant flow would be southwesterly keeping the smoke up north. Look for this pattern to continue from time to time in August and September. The developing El Nino is probably a contributor.

Winter Snowstorm Recap MLK Day 2022 - Chapter 1 of 3 (PICTURES)

I'm breaking the snowstorm recap into three posts. The first is filled with pictures of measurements and an overall snow totals map with the final snow amount list from the NWS. Second post goes into the meteorology behind the developing storm. The third post highlights the forecast evolution.  What we got right.  What we got wrong.  What we would have done differently.

The biggest overall snowfall for northern Ohio in probably 10 years! (we had some big snowstorms in the late 2000s).  Look at these numbers:

This was the first time we've had a snowfall where more than 50% of northern Ohio had more than a FOOT OF SNOW since either 2009 or 2008.