Monday, October 02, 2023

Why The Abnormally Dry September? How Does This Year Rank?

We just finished one of the driest Septembers on record in northern Ohio. 

Comparing August to September shows how the pattern flipped to a drier one starting in late August.

It wasn't just across Ohio, much of the Ohio Valley, mid-west and dep south (exception is east coast) saw below normal rainfall in September.

The comparisons are stark when comparing the percentage of normal for the mid-west/Great Lakes versus August. Blue/green are regions above normal. Brown/tan/white colors are below normal. 

What changed in late August/September?

Upper level pattern was stalled in August. Frequent fronts and rainfall.

Pattern started changing in late August. High pressure began to build across the upper mid-west and across western Canada.
AUGUST 16-31

By September, the pattern settled into this configuration. High pressure over Canada and across the SW US.  Low pressure across the Gulf of Alaska and a weak low across the mid Atlantic (tropically driven)

You'd figure some of the moisture from the east coast/mid-Atlantic low would influence our weather across Ohio and the Great Lakes given the overall flow around the ridge over Canada.  Yet the relative humidity, degree of rising air (Lifted Index) and the zonal winds were well below average. 

Overall relative humidity:

Rising air (Lifted Index)

Zonal Winds

Jet stream across North America was especially strong from Indonesia east across the dateline into Mexico and the deep south. Northern branch was also very strong off of eastern Asia, across the Bering Sea and into the eastern Pacific.  Very weak jet across the northern half of the US/Canada. This kept the strong low pressure outside the northern US/Great Lakes.

Dry conditions contributed to above normal temps in the upper mid-west with near normal temps across Ohio.

This is not a precursor of the winter ahead.  More on a few of the drivers of winter 2023-24 in the weeks ahead.

Friday, August 25, 2023

Historic August Rainfall/Severe Weather Recap

The clean up continues after the second round of heavy rain/severe storms across northern Ohio.

17 school districts closed due to damage and power outages:

Here is the COMPLETE radar loop from August 23 at noon through early August 25 before sunrise. Warnings, watches and lightning are included for northern Ohio.

I separated the 2 day rain event into 3 separate radar loops starting at 9pm August 24 through August 25 at 3am:

August 23 - 12:30PM through August 24 - 5AM

August 24 - 5AM through August 24 9AM

August - 9PM through August 25 - 5AM

Historic rainfall over 48 hours with two separate large clusters of rain/storms:

Another vantage point shows the heaviest rain from southern Michigan through Ohio and western PA.

Since August 1, most of northern Ohio has received 200-400% of normal rainfall:

Severe storm warnings were widespread. Most of northern Ohio was under a severe thunderstorm warning at some point between August 23 and early August 25.

4 tornado warnings. 12 tornadoes. COMPLETE NWS RECAP

The EF-1 that occurred on the east side of Cleveland was the first tornado that occurred within the Cleveland city limits since July 12, 1992 per NWS Cleveland. That tornado occurred near Hopkins Airport.

Here are ALL of the tornadoes from 1950 to 2022 in Cuyahoga County

Why did this heavy rain occur?  What were the factors that lead to this?

The huge ridge of heat in the central US has been a fixture for at least a week. 

Where high pressure resides, low pressure has to follow either down or up stream. Disturbances rode up and over the ridge and down through the Great Lakes.  

Great lakes radar loop from Wednesday through Friday: The excessive heat watches/warnings are shown in red.

Couple this with the high humidity (dewpoints above 75) and you have the recipe for heavy rainfall.

Interestingly, the historic Derecho in 1969 on the 4th of July produced MORE rainfall!

Here are the final rainfall numbers between August 23-25 using the same perspective as the 1969 map above (for comparison)

Oh and almost 75,000 lightning strokes over the 48 hour period across Ohio!

Thursday, July 20, 2023

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.

Wednesday, July 05, 2023

July 3rd Warmest on Record GLOBLLY. Here is the Breakdown

According to NCEP (National Center for Environmental Prediction), July 3rd was the warmest day on record GLOBALLY.  Note this is not for one city, one state, one region or one country.  It's the entire planet. 

Global Temperatures vs Normal 18z July 3rd

The average global temperature reached 17.01 degrees Celsius (62.62 Fahrenheit), surpassing the August 2016 record of 16.92C (62.46F).   

The largest warmer anomalies are located near Antarctica.

I broke down the globe into 9 different locations. The break down is done to show how the temperature anomalies vary within each region. Each image shows the locations with above normal (warmer colors) temperatures and below normal (cooler colors) temperatures on July 3rd.  The global average takes into account ALL of these regions below.

First North America. I labeled regions that are above normal with "AN" and below normal with "BN"

Now the lower 48 states:

The Caribbean and Mexico:


South America:



Middle East: