Thursday, June 20, 2024

Late June Heat...For How Long?

Our first heat wave in northern Ohio since 2021 continues. The long range outlook picked up on this pattern change a few weeks prior to the start.

June started out dry but with "cooler" daytime highs in northern Ohio. June 10 was 61 degrees with low 40s for overnight lows. Then a two day "teaser period" of warmth then the first of a weeks worth of 90+ degrees starting on June 16.

You can see how the high pressure ridge (Bermuda High) expanded across the eastern seaboard to near record high levels starting Monday June 17. By the weekend, the heat ridge (dome) gradually dissipated as the ridge flattened in the deep south.

The position of the ridge east of Ohio allowed a few "weak fronts" (disturbances) to clip the southern Great Lakes with small but potent storms with heavy rainfall. Future radar from Thursday June 20 to Saturday June 22.

Rainfall totals from June 16 to June 19:

Heat Advisory was issued from Monday through Saturday across northern Ohio.

Heat Advisories and Excessive Heat Warnings extended into Michigan and New England.

Tuesday high temperatures were running well above normal eastern US with well below normal temperatures across the west.

Northern Ohio heat index forecast was showing 100+ in spots where storms didn't develop.

The last time we had a heat index 100+ was in 2022. We measure the heat index in total hours.  Here are the totals since 2012 with the warm summers of 1995 and 1988 for reference.

Dew points at/above 75 degrees only occur in small periods this far north. We reach this level June 19. We average around 2 days with humidity levels this high each summer. 2019 was the last summer with above normal of days with dew points at/above 75°.

Anytime we experience extreme weather, people will compare the current conditions to past events they remember. Stretches of heat like this elicit memories of the summer of 1988.  However, there are big differences between 2024 heat and 1988 heat.

The 2 week period where we reached 100° degrees (this was the last time) featured some cool overnight lows. In fact, we broke four low temperature records starting three days AFTER we broke the all-time high temperature record of 104°

Look at June 20, 1988 high temperatures across the US.  

Now high temperatures on June 19, 2024

Another note about the summer of 1988 in northern Ohio.  We reached 90° 35 times. Only 14 of the 35 days at/above 90° had a dew point at/above 70° (tropical) and only 5 of the 13 days at/above 95°.  So plenty of 90s with relatively lower humidity that summer.

Will this heat continue?   Expect a break as the heat shifts to the central US.

Wednesday, May 22, 2024

May Snowfall History in NE Ohio

Some have mentioned they remember "snow" in June from year's past.  After checking the observations and cross referencing with air temperatures and other conditions, the reports were probably hail and not snow. Here is the POST I wrote back in 2020 which goes into more detail.

Thursday, May 16, 2024

Rainfall: Tale of Two Different Periods

Its been more dry than normal in recent days overall. However, rainfall across northern Ohio and much of the lower Great Lakes was well above normal from mid March to mid April:

The overall pattern has shifted since April 15. Rainfall with the exception of a few locations in Holmes, Tuscarawas counties has been below normal: Dark circles indicate above normal rain areas.

Days with rain in April. Notice the high frequency of rain in the first half of April.

From April 15 to May 15, the story has been opposite:

Akron rainfall since April 15:

Wednesday, May 01, 2024

Ohio Tornado Recap Through April 30

So far this year, the Ohio tornado count has been record setting.  Preliminary numbers put the total at 43 although official tornado track analysis puts the exact number closer to 35. Either way, we haven't had a year anywhere close to this since...well, last year. 

Ohio counties that have been under a tornado warning at some point this year: 55 of the 88 counties.

Here are the totals year by year since 1950. Red bar represents total tornadoes through April 30.  The green bar are the EF2 or greater tornadoes each year.

Here is the average number of tornadoes per state through April 30:

Here is the actual number this year through April 30:

Why so many tornadoes this year?

First, we have been transitioning out of a very strong El Nino period and rapidly heading into a La Nina. These changes in the equatorial Pacific have impacted the jet stream across the central US. Throughout the winter, the storm track was absent across the US as evident by below normal snowfall across the central US.

Notice how the jet intensity was abnormally strong in mid March and April across the mid-west. Warmer colors indicate well above normal jet intensity.

The lifted index (degree of instability) was extremely favorable for rising air and storms across the Ohio Valley in mid March. Colder colors indicate rapidly rising air.

The MJO might have been a factor. Higher amplitude phase 4-6 in mid March. Moderate amplitude phase 8-1-2 in late March. However, according to this paper, the connection in March and April might be smaller. Bold print below is important:

The physical mechanism proposed in this study cannot explain the MJO–U.S. tornadogenesis relationship in the boreal early and middle spring months (March and April). Compared to MJJ, the Pacific jet is strengthened and shifted southward in March and April, but the anomalous subsidence over the northeast Pacific is very weak in March and April. Therefore, it is more likely that the relationship between MJO and U.S. tornadic environmental parameters in March and April is largely influenced by extratropical stationary Rossby waves forced by MJO-induced diabatic heating anomalies over the Maritime Continent. Thus, it is also likely that natural atmospheric variabilities originated from high latitudes such as North Atlantic Oscillation (e.g., Lin et al. 2009) and Artic Oscillation (e.g., Zhou and Miller 2005) interfere with the MJO-induced extratropical teleconnection to the United States in March and April, and thus may weaken the relationship between MJO and U.S. tornadogenesis. Additionally, in March and April, tropical Pacific sea surface temperature anomalies associated with El NiƱo–Southern Oscillation (ENSO) are of key importance in modulating the spatiotemporal variability of U.S. tornadogenesis (e.g., Weaver et al. 2012Lee et al. 20132016Barrett and Gensini 2013Allen et al. 2015Lepore et al. 2017Molina et al. 2018Chu et al. 2019).

Speaking of high latitudes, check out the height anomalies in the higher latitudes since early 2024. Heights rise, Arctic Oscillation drops. Frequent troughs track across the mid latitudes. Notice all but one of the top 7 tornado days occurred when the northern height anomalies were high. 

Here are the mid latitude 500 mB heights vs normal on those top 7 tornado days with SPC storm reports for each period:

#1 - April 26-27 (143 tornadoes)

#2 - April 1-2 (97 tornadoes)

#3 - March 14 (36 tornadoes)

#4 - April 16 (24 tornadoes)

#5 - February 27 (24 tornadoes)

Gulf of Mexico water temperatures were well above normal in March especially. Some cooling has occurred since but overall temperatures are still above normal. 

We also transitioning out of El Nino and into La Nina territory over the last 2-3 months. Notice the warmer water eroding away along the equator. This probably played a factor in the overall jet stream direction and intensity changes across the central US.