Long-Range Thoughts (Summer)April 24th, 2012 at 11:10 am by Bill Steffen under Bill's Blog, Weather
One of the highlights of summer – the Coast Guard Festival Fireworks in Grand Haven the first Saturday of August. If you’re just looking for the numbers forecast, scroll down to the bottom. The weather geeks here like a little background:
Well, we’ve just come through a winter with a La Nina that behaved like an El Nino. For the most part, the cold, Arctic air never really made it down into the Lower 48 states. We had above normal precipitation in all three winter months, but it was warmer than average, so more of the precipitation fell as rain instead of snow. We had the warmest March ever in the Great Lakes and in some cities (inc. Grand Rapids and Chicago) April is going to turn out cooler than March. The sea-surface temperature anomaly map shows that La Nina is fading. The water along the Equator is still cool in the central Pacific, but it’s warmed to a little warmer than average west of South America. So, let’s assume that La Nina is fading to either neutral (sometimes called La Nada) or a weak El Nino. You can also see the cold PDO (Pacific Decadal Oscillation) (note how the PDO tracks with global temperature…warm from 1910-1950, cooler in the 50s to 70s, then warmer) which is colder than average water from Alaska down the west coast of the U.S. and Mexico. This should lead to cooler than average temperatures this summer along the immediate Pacific Coast (and a fairly brisk ocean breeze) and fewer and weaker hurricanes off the West Coast of Mexico. You can also see warmer than average water in the Gulf of Mexico (this could lead to early hurricane/tropical storm formation in the Gulf of Mexico – though fading La Ninas usually don’t have high numbers of tropical storms (not to see you can’t have one or several major impact storms). I think the mean (warm) ridge will in the mean be over the eastern Rockies and western High Plains, where temperatures will be warm. Drought will continue to be a problem from West Texas up into western Kansas and in parts of the Southeast U.S. (though rainfall there should be a little closer to average in the East than it has been so far this year).
Here’s the list of La Nina/El Nino years. I tried to find similar years to see what followed. Note that we’ve had a La Nina for nearly two years going to a level of -1.5. I looked at 1951 (we had a cool summer and then the snowiest winter EVER in W. Michigan in 1951-52 after a La Nina), 1956-57 (the Standale tornado was 1956 – though both the Standale and Palm Sunday tornadoes were preceded by cold weather in March, unlike this year), 1972 moved to a strong El Nino and I think this one coming will be weaker – 1972 featured a cold March and a cool fall, the long La Nina of 1973-76 – more on this later, 1986 (also moving toward a more significant El Nino – we had just five days that hit 90 in the summer of 1986), 1989 (that was a cool summer with only one 90-degree day and a brutal start to winter with cold and 19.4″ of snow in Nov. then Dec. 1989 was the coldest December EVER in G.R., more than 10 degrees colder than average, then January was 10 degrees warmer than average – quite a flip – we did get 90″ of snow that winter). 1999-2001 was a long and strong La Nina. In 2000, we only had 9 days all year that reached 85 degrees. In 2001, it didn’t snow much until just before Christmas…then it hardly stopped snowing and we had 4 feet of snowfall in a week (it was fluffy stuff that settled down and I don’t think we had above 18″ on the ground. In 2001, we had 8 days that hit 90 degrees. The winter of 2008-2009 was pretty average. In 2008 and in 2009 we only had 3 days that hit 90 all summer. The pattern is that you don’t see a lot of really hot days when you pull out of La Nina. The trek coming out of La Nina often features a cold winter. Will that be this coming winter, or the next one? March of 1910 was very similar to this year. That year was very warm in March, but it got cool after that. It was the winter of 1911-12 that was the very cold one. The winter of 1976-77 was brutally cold – following La Nina. In general, years when La Nina fades to neutral or weak El Nino have average to below average temperatures.
One thing that I found interesting about the years pulling out of the 1973-76 La Nina was that the following several years all had very warm periods in spring. In 1976, we were 4.8° warmer than average and had four days in the 70s. April had 72% sunshine and a five-day stretch in mid-April when the average high temp. was 82°. The summer than followed was 0.6° warmer than average. In 1977, March was 6.9° warmer than average and April had a stretch from the 10th to the 21st that was 17.5° warmer than average, and May 19-26 was the warmest week of the year with an average high for that week of 90.1°. The summer than followed was 0.8° cooler than average. In 1978, the warmest week of the year was warmest week of the year with an average high of 89° and no rain. Following that, all 3 summer months were cooler than average. Note that all 3 years had periods of unusual warm weather in spring, followed by an average to cool summer…and…the winters were cold and snowy!! The winter of 1976-77 tied 1903-04 as the coldest ever in G.R. The winter of 1977-78 featured the Blizzard of ’78, followed by the coldest February and the 5th coldest March ever in G.R. And the winter of 1978-79 saw the Great Lakes freeze over! So winters coming out of La Ninas can be cold and snowy. I thought it was also interesting to note that the number of 90-degree days in G.R. decreased during this period. We had 21 days of 90-degree heat in 1976, 11 in 1977, 8 in 1978 and 5 in 1979. We didn’t get to double-digits again until 1983. From 1974 to 1986, we didn’t have a single day above 95 degrees.
So, my forecast for the summer calls for near normal temperatures (+0.5° above average), 65% of possible sunshine (slightly above average), a summer maximum temperature of 94° and 9 days reaching 90-degrees at the Ford Airport, the maximum water temperature at the mid-Lake Michigan buoy of 75° (five degrees cooler than last year). Precipitation (which can vary greatly over short distances with summer convection) I’ll peg at 11.2″ or slightly above average, though I wouldn’t be surprised to see a dry stretch (around 2 weeks) in late summer. Our greatest severe threat will be damaging wind from fast moving storms coming from the west or northwest. Fast-moving storms can come on you quickly, so stay up with the forecasts on thunderstorm days if you’re boating, at the beach or camping. With the La Nina fading, the overall tornado count will go from above average back to near normal (La Ninas have more tornadoes, more long-track tornadoes, more strong tornadoes and more single-day outbreaks of +30 tornadoes).
I’ve looked through years when we have had similar weather conditions. It’s interesting to note that if you take the three warmest March months in the last 100 years in G.R., all three had above normal snowfall the following winter. While it’s not saying much, the ocean currents and analog years certainly favor a cooler fall and earlier snow this year. A very cold and/or very snowy winter is certainly within reason either this coming winter or the next. This year mirrors 1910 very closely and the cold winter was the second in 1911-12. Note the cold and snowy winters that followed the 1973-76 La Nina. 2001-02 was also a snowy winter here in W. Michigan. I discounted 1992 because of the influence of the Mt. Pinatubo volcano, which cooled the Earth by 1/2-degree.
Some other forecasts: Environment Canada is forecasting a warm summer for most of Canada. You can assume they’d have Michigan on the warm side. The Climate Prediction Center’s forecast overall looks pretty good to me (though I don’t think it’s not going to be a warm summer on Catalina Island). I’d have the heat ridge at least one state to the east of where they have it and I’d include above normal precipitation areas, mainly to our south. The warm Gulf of Mexico will continue to feed some quality moisture northward. Here’s the CFSv2 forecast – which has temperatures here close to average.
To sum it up…the pattern will be cooler than last year and cooler relative to average for the Great Lakes to Northeast for the summer and fall.