Wednesday, July 07, 2021

What Summer Was The Most Humid?

First a brief tutorial on why we use dew point versus relative humidity:

It's more of an absolute measure which isn't relative to temperature. For example a relative humidity of 50% when the temperature is 95 degrees would feel incredibly tropical.  An RH of 50% when the temperature is 55 degrees wouldn't feel nearly as humid.  A dew point of 70 is super-tropical all the time.  A dew point of 45 is comfortable regarding of temperature or time of year.   This graphic illustrates this idea very well. 

So far through July 7 we've had about half of the total number of 70 degree dewpoint hours compared to last summer. 

What's the most humid summer since 1950 in northern Ohio (Cleveland)?  1995

2018, 2010, 1987 and 1973 round out the top 5

I did some research on the years with the highest heat indices measured in hours in northern Ohio. You can read about it HERE (written in 2019)

There is an upward trend for more humid summers over the last few decades in northern Ohio.

Monday, July 05, 2021

Summer Weather Pattern Thus Far. Will It Continue Into July?

The pattern across the US has featured THREE dominant features. Ridge of high pressure western areas, persistent trough/low pressure in the central US and the Bermuda High starting to inch west along the east coast. It took us more than 300 days in northern Ohio to reach 90 degrees. The longest stretch without a 90 in over 10 years!

Temperatures since mid May have fluctuated across the central/eastern US. Storm systems have been frequent.  Below shows upper level pressure pattern on the left.  Temperatures on the right.  You can see how the domes of COOL and WARM air developed over time.  Each image is a 6 day period from mid May through mid June.

May 15-20: upper level heights & temperatures vs normal

May 21-26: upper level heights & temperatures vs normal

May 27-June 1:  upper level heights & temperatures vs normal

June 2-7: upper level heights & temperatures vs normal

June 8-13:  upper level heights & temperatures vs normal

June 14-19:  upper level heights & temperatures vs normal

Evolution of storm systems was mainly in the central US since early June. Below are the pressure anomalies since mid June across the corn belt. BLUE areas are consistent low pressure areas.
Widespread rainfall across the Ohio Valley over the last month. Below normal indicated with tan colors.

Rainfall over the last two weeks (June 20-July 4)

Hard to believe but a large portion of Ohio NEEDS RAIN when looking at the rainfall numbers since June 15th.

How about rainfall vs normal since June 1st?

Green areas are above normal
Warmer colors are below normal

Yet the daily rainfall occurrence is more frequent.

Temperatures are running above normal since June 1st.

Interesting to note that the EPO (East Pacific Oscillation) has turned negative since mid June. This has partial supported the Pacific Northwest ridge of heat (along with other factors) which in turn has kept the central US trough locked in.

Long range outlook shows the same general pattern through mid July: Central US trough with semi-frequent frontal passages through the first three weeks of July.  The Bermuda high is stronger which should support more heat in new England, mid Atlantic and portions of the Ohio Valley. More heat out west.

OVERALL rainfall will be above normal across Ohio and a large portion of the Midwest.