The SI Weather
10Apr/14Thu

11:00 AM | Global sea ice areal extent running above normal and experiencing a recent spike

global
[Global sea ice anomaly versus the 1979-2008 mean; recent spike pushes
sea ice areal extent to nearly 1 million square kilometers above the norm)

Discussion

Overall summary
The Great Lakes has received a lot of attention lately for its tremendous build-up of ice this winter – and it still stands at historically high levels for ice coverage (below) for this time of year - but the northern hemisphere as a whole remains at below-normal levels for sea ice areal extent by about 566,000 square kilometers (versus 1979-2008 mean). On the other hand, the southern hemisphere sea ice areal extent continues to be at or near record high levels for this time of year at around 1,342,000 square kilometers above the norm and this has boosted global sea ice to above-normal levels on the order of 1 million square kilometers. In fact, there has actually been a spike in recent weeks (above) with respect to global sea ice areal extent to these levels which have been seen only rarely in the past several years.

Great_lakes_ice_coverage_04_09
[Great Lakes ice coverage remains above 50%; well above all years back to the winter season of 1980/1981]

Northern Hemisphere Sea Ice
The northern hemisphere sea ice areal extent is still below-normal for this time of year although it has gained significantly in the past several weeks relative-to-normal and remains well above the lowest points of the past few years. The northern hemisphere sea ice areal extent has generally trended lower since the mid 1990’s to mostly below-normal levels since the turn of the century. In the past several years, however, there has been a leveling off of the trend line in terms of sea ice areal extent at those below-normal levels. In the time period before the mid 1990’s, the sea ice extent was generally above-normal dating back to 1979.

This directional change in trend that developed during the mid 1990’s correlates quite well with a northern Atlantic Ocean sea surface temperature cycle that is tracked by meteorologists through an index called the Atlantic Multidecadal Oscillation (AMO). Indeed, the Atlantic Ocean has a significant impact on northern hemisphere sea ice and the AMO index flipped in phase during the mid 1990’s from negative (cold) to positive (warm) and the trend changed at that point in time. Once the northern Atlantic Ocean sea surface temperatures flip back to cooler-than-normal values – perhaps in the next few years - the northern hemisphere sea ice areal extent should return to the normal or above-normal levels seen prior to the mid 1990’s.

Southern Hemisphere Sea Ice
The southern hemisphere sea ice areal extent continues its recent impressive run at record or near record high levels for this time of year when compared to all prior years in the satellite record-keeping era which began in 1979. This remarkable period of increasing sea ice areal extent in this part of the world has actually been occurring for the past few years with only a few brief exceptions to that overall upward trend. Back in 2011, the southern hemisphere sea ice areal extent was at below-normal levels, but it is currently running well above-normal at levels seen only a couple of times dating back to the late 1970’s (all data courtesy University of Illinois "cryosphere" web site with data originating from NOAA/NCEP Snow and Ice Data Center).

The video discussion (below) details the current ice coverage situation in the Great Lakes, the northern and southern hemispheres and across the globe.

Video

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8Apr/14Tue

12:30 PM | “Blood moon” total eclipse early next week begins a series of total lunar eclipses

moon_during_Dec_2010_total_eclipse
["Bloody red" moon during a total eclipse in December 2010]

Discussion

There will be a total eclipse of the moon early next week that will actually be the first in a series of four total lunar eclipses that will take place over the next 18 months. This first total lunar eclipse will be an early morning occurrence in the eastern U.S. with the first stages beginning around 2am early Tuesday morning (April 15th). The entire moon should be shaded by the Earth’s shadow about an hour later (3am) and this “full eclipse” stage will last until around 4:30am. The “partial” eclipse stage that follows will wind down around 5:30am.

The moon should take on a “blood red” appearance during this total eclipse which is a perfectly natural occurrence. Every time the moon passes completely into the shadow of the Earth, it turns a reddish color -- sometimes a bright copper, other times the dark reddish brown of dried blood. The “bloody” red color is caused by refraction of sunlight by the Earth’s atmosphere. It is the same effect that you see when the sun turns reddish-orange at sunset only in this case the refracted sunlight projects all the way to the moon.

It has been a long time since a total lunar eclipse has been visible from the United States - the last one took place on Dec. 11, 2011. But the good news is there are three more on the way after this one. This total lunar eclipse is the first in what is called a lunar tetrad -- four successive total lunar eclipses with no partial lunar eclipses in between, each of which is separated from the other by six full moons. The next total lunar eclipse, which also will be visible from nearly all of North America, will take place on October 8th of this year and then the following two will occur during April and September of 2015. Tetrads occur less often than a blue moon and are indeed somewhat rare. There will be only eight lunar tetrads in this century and the last one that occurred was back in 1967-1968.

This eclipse will also feature an additional astronomical anomaly as Mars will appear as a fiery red 'star' next to the moon. Mars actually makes its closest approach to the Earth since 2012 on Monday, April 14th. Together, red Mars and the red shadow on the moon's face should be a spectacular sight and an incredible photo opportunity.

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2Apr/14Wed

1:30 PM | Tornado threat increases tomorrow in the mid-Mississippi Valley, but so far the numbers this year are way down

2014_tornadoes

Discussion

Tomorrow, the mid-Mississippi Valley will have a threat for severe storms and tornadoes and it may very well be the greatest threat of tornadoes that we have seen all year; however, the overall nationwide numbers so far this year are way down and this continues a downward trend that began a few years ago. In fact, the number of nationwide tornadoes through the end of March as reported by NOAA’s Storm Prediction Center (SPC) was 70 and this is the lowest amount in the “January through March” time period of any of the past ten years. The average number of tornadoes for the first three months of the year are 243 (based on the period from 2005-2013). The yearly nationwide tornado totals for the last two years (943 in 2013, 1119 in 2012) were the lowest annual amounts of any of the past ten years according to NOAA’s SPC.

The overriding reason for the low number of tornadoes so far this year as well as for the beginning three months of last year has to do with the fact that the persistent cold and snowy weather pattern in much of the central and eastern U.S. basically squashed the threat for severe weather. A pronounced southward dip in the polar jet stream frequently pushed cold air masses into the Gulf of Mexico and this prevented deep, moisture-laden warm air from that region to flow northward into the southern U.S. – an important, and generally necessary, ingredient for the generation of tornadoes.

As far as tomorrow is concerned, a strong upper level trough will swing out of the western states into the middle of the country and combine with an influx of warm, moisture-rich air from the Gulf of Mexico to increase the chances for severe weather and tornadoes in the mid-Mississippi Valley region. Specifically, this general threat area on Thursday will likely run from northern Louisiana to Missouri with the greatest threat perhaps centered on the state of Arkansas. The threat area for severe weather will shift eastward on Friday into the Ohio Valley albeit in a slightly weakened state.

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31Mar/14Mon

11:30 AM | ***Baseball is back and so is the “Home Run Weather” app!

howard

Discussion

It has long been contemplated that weather conditions have an effect on the distance a baseball can travel. More home runs are seemingly hit on hot days or on days with the wind blowing out.

Who can forget the many games at Wrigley Field that have featured numerous home runs as the wind raced out towards Waveland Avenue? Mike Schmidt cranked four home runs on just such a day at Wrigley Field in April of 1976. That game featured nine home runs and 34 total runs and a wind blowing out strongly ahead of a cold front. Not surprisingly, most of the games with four home runs hit by an individual player have occurred with temperatures of at least 80 degrees or with a strong wind blowing out. Conversely, most people would agree that fewer home runs are hit on cold days or with the wind blowing in. The old Candlestick Park in San Francisco frequently offered such weather.

The distance that a baseball travels is indeed impacted by atmospheric conditions. In general, the less dense the air is, the farther a baseball can travel. Humidity plays a crucial role in air density. Air with higher humidity is actually less dense than drier air. This may be contrary to perception and many baseball fans have no doubt heard baseball announcers incorrectly use the phrase “heavy humid air” on a hot summer night. Dry air is mostly comprised of diatomic oxygen and nitrogen (i.e. O2 and N2) whereas water vapor (H2O) is composed of one oxygen atom and two hydrogen atoms and the moist air has a lower overall atomic mass than dry air. Thus, at a constant temperature, the more water vapor that displaces the other gases, the less dense the air will become.

Additionally, hot air is less dense than cold air and higher altitude air is less dense than air at sea level. It is for this reason that so many home runs were hit in Colorado before the humidor was put into place. The elevated humidity in the humidor that stores baseballs for the Rockies home games effectively reduces the distance that a ball will travel in multiple ways: 1) by adding slightly to its weight through absorption of water, 2) by causing the size of the ball to increase slightly which increases air drag and 3) by reducing its “bounciness” factor.

Utilizing sophisticated math and physics, meteorologists and software engineers at The SI Organization, Inc. have investigated this topic which mixes science and baseball. And the results of their efforts are available in a free, real-time baseball weather application called Home Run Weather. Developed for the iPhone and Android devices, the app relates live temperature, atmospheric pressure, humidity, field orientation, wind direction, wind speed and the drag coefficient of a baseball to the user to determine if local weather conditions, for any big league park, are favorable for home runs being hit. Twenty-four hour forecasts are available in addition to live weather.

Two approaches were combined to arrive at a “home run favorability” index, which the app displays on a scale of 0 to 10 (least-to-most favorable). The first approach was to analyze actual weather conditions and home run data over several seasons (Citizens Bank Park was chosen as the venue for this study). The second approach uses a theoretical, physics-based model that determines the distance a ball will travel based on the temperature, relative humidity and atmospheric pressure.

The Citizens Bank Park study yielded some interesting, but perhaps not too surprising, findings. First, temperatures and dew points had a clear trend line relationship with home runs, as generally more home runs were hit in hot and humid air than colder, less-humid air. It was also found that 13-percent more home runs were hit when the wind was blowing out than other wind conditions. Additionally, 6-percent more home runs were hit in the daytime as compared to nighttime games.

A full major league season of testing on the app index produced very encouraging results with respect to the average number of home runs hit per game. The low home run favorability index values (0-3) had an average of 1.38 home runs per game for the full season. The moderate index values (4-7) had an average of 1.95. And the high values (8-10) had an average of 2.47 home runs per game. In addition, the home run favorability index correlated very well with average total runs scored per game. The low home run favorability index values (0-3) had an average of 7.07 total runs per game for the season. The moderate index values (4-7) had an average of 8.08. And the high values (8-10) had an average of 9.45 total runs per game.

Whether you're a fan at the park who's interested in a home run forecast, a spirited fantasy owner or baseball analyst, Home Run Weather should provide some useful information and conversation material. For more details, visit the "Home Run Weather" page on The SI Weather website (just click on the baseball).

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