Characteristics of Cold Front Passages Around Lake Superior

Kyle Kleckner Author

08/02/2021 Added

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In this video, characteristics of cold front passages around Lake Superior are examined through a data analysis of weather observations.

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[00:00:01.380]Hello. My name is Kyle Kleckner.
[00:00:03.990]I am an undergraduate student here at the University of Nebraska and I am
[00:00:07.260]studying meteorology. I've been assisting Dr.
[00:00:10.350]Van Den Broeke with his research this summer, and our research pertains to
[00:00:14.220]characteristics of cold front passages around Lake Superior.
[00:00:20.700]To start off, Lake Superior is a large body of water that has an extensive marine
[00:00:25.110]layer. This marine layer is characterized by relatively high dew points and
[00:00:29.730]temperatures similar to that of the Lake Superior water temperature.
[00:00:33.810]Around Lake Superior, cold fronts are a common occurrence. A cold front can
[00:00:37.620]be defined as a cold air mass replacing a warm air mass at a given location.
[00:00:43.020]The figure below explains the processes associated with a cold front.
[00:00:47.160]At the bottom of the figure,
[00:00:48.240]a cold front symbol is shown here as it would be on a weather map as it moves
[00:00:51.870]from left to right.
[00:00:53.640]The other part of the figure shows how a cold front functions in the
[00:00:56.520]atmosphere.
[00:00:58.140]The advancing cold air mass behind the cold front will force warm air ahead of
[00:01:02.550]the cold front to rise as it moves from left to right. However,
[00:01:06.900]near Lake Superior,
[00:01:08.250]it has actually been observed that warming takes place after a
[00:01:11.280]cold front passage, and this was the primary emphasis of our research.
[00:01:18.210]There were three research objectives that we wanted to answer.
[00:01:21.750]The first objective was to identify some typical temperature and moisture
[00:01:25.200]characteristics of the Lake Superior
[00:01:27.090]marine layer. The next
[00:01:29.130]objective was to identify and analyze temperature changes during and after
[00:01:32.650]cold front passages around
[00:01:34.350]Lake Superior. The last objective
[00:01:36.810]was to identify and analyze how fire weather conditions change during and after
[00:01:41.550]cold front passages. In this region,
[00:01:44.280]fire weather conditions are dependent on the temperature, relative humidity, and
[00:01:48.000]wind speed.
[00:01:49.650]Fire weather conditions are the most dangerous with higher temperatures,
[00:01:53.430]lower relative humidity values, and higher wind speeds.
[00:01:59.680]In order to answer these objectives, Dr. Van Den Broeke
[00:02:02.230]provided me with a dataset of 14 weather stations near Lake Superior that
[00:02:06.670]contained recorded weather observations.
[00:02:09.580]This data set began in January of 2010 and ended in June of 2018.
[00:02:15.280]The figure here shows the geographic area in which the data was collected from
[00:02:19.360]as well as a few of the weather stations, which are shown by the red,
[00:02:22.300]blue and gray location markers.
[00:02:25.570]There were some criteria that the cold fronts had to meet for this
[00:02:27.860]study. The cold fronts had to extend
[00:02:30.220]from the Canadian border south to at least Duluth, Minnesota,
[00:02:34.210]and the cold fronts had to be accompanied by a temperature gradient at the 925
[00:02:38.770]hectopascal atmospheric level. In other words,
[00:02:41.920]the cold fronts were not just surface features.
[00:02:47.190]The variables that I analyzed from these cold front passages include changes in
[00:02:51.120]temperature, dew point temperature, relative humidity, wind direction,
[00:02:55.740]and wind speed. For this study
[00:02:58.560]I analyzed these variables during each season at all times of the day.
[00:03:03.070]I also computed averages for each variable at each weather station.
[00:03:09.850]I then performed a paired-sample t-test on the temperature average data using
[00:03:14.020]MATLAB. For the t-test.
[00:03:16.360]I assumed the mean of the temperature data to be zero and used p-values to show
[00:03:20.980]the statistical significance of the data. In MATLAB,
[00:03:24.550]if P was less than or equal to 0.05,
[00:03:27.730]the data was deemed statistically significant,
[00:03:30.430]which in this case would be warming associated with cold front passages.
[00:03:34.390]And if P was greater than 0.05,
[00:03:37.030]the data was not considered statistically significant.
[00:03:41.260]As I mentioned,
[00:03:42.130]the purpose of performing this t-test was to determine whether or not cold
[00:03:45.550]fronts at a given location were associated with a warming effect.
[00:03:52.360]Here are some results that I found from analyzing the dataset.
[00:03:55.870]The first result is that warming events,
[00:03:57.550]due to cold front passages around Lake Superior
[00:04:00.370]occurred the most during the summer. In fact,
[00:04:02.830]9 out of the 14 weather stations had the most cold front passages
[00:04:06.910]associated with warming in this period.
[00:04:09.880]Another result is that the warming events from the cold front passages were
[00:04:13.540]maximized, or had the greatest warming, during the spring and fall.
[00:04:18.430]13 out of the 14 stations around Lake Superior had this result.
[00:04:25.330]Another result that we found from the dataset is that weather stations closer to
[00:04:29.200]Lake Superior generally observed more warming events than weather stations
[00:04:33.490]farther away from Lake Superior.
[00:04:35.740]The t-test that I used to show statistical significance found 7 of the 14
[00:04:40.300]stations were associated with warming due to cold front passages.
[00:04:44.890]We also discovered that fire weather conditions were maximized in the summer
[00:04:49.180]after cold front passages. Next,
[00:04:51.880]I will show some of the graphs pertaining to my results here in the next few
[00:04:55.120]slides.
[00:04:58.750]This example shows the temperature differences after all cold front passages
[00:05:02.590]during the spring months at the Superior, Wisconsin weather station.
[00:05:06.400]I thought the data from this station was a good representation of the overall
[00:05:09.760]results that I found.
[00:05:11.740]I would also like to mention that not all of the cold fronts had data,
[00:05:15.340]so there are some areas in these figures that don't have data measurements.
[00:05:19.240]The x-axis shows the total number of cold fronts and the y-axis shows the
[00:05:23.320]differences in temperature in degrees Celsius.
[00:05:26.740]The values greater than zero on the x-axis are indicative of warming events
[00:05:31.390]and the values less than zero are indicative of cooling events from
[00:05:36.370]cold front passages.
[00:05:38.590]The key point from this figure is to show that the most intense differences in terms
[00:05:43.300]of magnitude occurred in the spring of this location.
[00:05:49.360]This next figure shows the temperature differences after all cold front passages
[00:05:53.590]during the summer months at Superior, Wisconsin.
[00:05:56.740]The key takeaway in this graph is to show that most warming events due to cold front passages
[00:06:01.310]took place over this time period.
[00:06:06.290]The purpose of these next two figures that I will show are for fire weather
[00:06:09.350]conditions.
[00:06:11.000]This figure shows the relative humidity differences as a percentage in Superior,
[00:06:15.080]Wisconsin of all cold front passages of the dataset.
[00:06:18.830]I would like to point out that there are numerous decreases in the relative
[00:06:22.160]humidity values during the summer months,
[00:06:24.260]which are located in the middle of the graph.
[00:06:29.770]This next figure shows the wind speed differences in knots in Superior,
[00:06:33.100]Wisconsin of all cold front passages of the dataset.
[00:06:37.330]I would like to point out the numerous increases in the wind speed during the
[00:06:40.750]summer months, which are also located towards the middle of the figure.
[00:06:47.530]Here are some conclusions from this research study that pertain to our research
[00:06:50.680]questions.
[00:06:52.120]The first conclusion is that surface air temperatures are similar to that
[00:06:56.020]of the water temperature of Lake Superior
[00:06:58.690]and there is typically a plentiful amount of moisture in areas close to Lake
[00:07:02.290]Superior.
[00:07:03.880]It can also be concluded that based on the data analysis, warming associated with
[00:07:07.960]cold front passages occur the most during the summer
[00:07:10.690]and are the most intense during the spring and fall in this region.
[00:07:14.560]The final conclusion from our research is that fire weather is maximized in
[00:07:18.100]magnitude during the summer due to frequent increases in wind speed and
[00:07:21.370]temperature, as well as frequent decreases in relative humidity.
[00:07:25.750]Future research of this topic could include other variables such as the time of
[00:07:28.960]day the cold fronts passed through.
[00:07:33.910]Here are a couple of references that I used for this presentation.
[00:07:38.620]I would also like to thank Dr.
[00:07:39.880]Van Den Broeke for advising me on this research project,
[00:07:42.850]as well as UCARE for giving me the opportunity to conduct research this
[00:07:46.440]summer. Thank you!

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Characteristics of Cold Front Passages Around Lake Superior

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