Climate Summary for October 2010
"A Strong Dose of High Pressure and One Massive Storm"
William Hurley, EIU WeatherCenter Analyst
November 11, 2010
This summary is a requirment for Mr. Hurley's Independent Study with Cameron Craig.
Usually a month of stormy and uneven transition weather, October is often remembered for some of the incredible storms and windy conditions it can bring, with this year being no exception. Occasionally, October even witnesses the first snowflakes of a season, though that was not the case this year for Charleston. However, this October did see one of the most powerful storm pass over the country in recent history, which will surely be noted for years to come. During the month of October, temperatures become noticeably cooler as the sun retreats to the south, with northern latitudes seeing a net loss of solar radiation. As a result, the month often opens warm and ends cool as was seen this year, though the warmth did not go down easily.
The first day of October in Charleston saw nice, fair weather as a cell of high pressure sat across the Midwest, bringing clear skies and light northwest winds of 4-7 mph to Charleston (Map 1). These nice conditions brought the day’s high to a comfortable 75̊ F, giving the day an almost quintessential feel to it. However, sitting far to the north over the central Canadian provinces was an even stronger high pressure system, measuring 1032mb at its core, compared to the 1020mb that the high pressure over the Midwest measured (Map 1). The reason for this high pressure being stronger was likely due to its proximity underneath an area of convergence at the 500mb level over south-central Canada, which acted to push air downward towards the surface, thus creating an area of high pressure (Map 2). As it strengthened, this high pressure cell began riding underneath the jet southward into the United States with enough force and a strong enough temperature gradient that it generated a cold front on its own accord, without the help of an organized area of low pressure, something not commonly seen (Map 3). Though the day experienced a high temperature of 71̊ F, this reading was at some point in the earlier hours of the day, with temperatures falling throughout the afternoon as the high pressure pushed into the area. Strong north winds were also experienced on the 2nd, with speeds in excess of 20 mph, helping to make for quite the cold and miserable day. The passage of this cold front also generated .24 inches of rainfall, as extremely cold temperatures aloft mixed with dew points of up to 50̊ F and forced the water vapor to condense and then precipitate. As the rain fell, the dew point began to drop, and continued to do so for the next 36 hours, helping to underscore the intense strength and aridity of the cold continental air mass that was arriving over the U.S.
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Map 1. Surface Chart of October 1, 2010. NOAA |
Map 2. 500mb Chart of October 1, 2010. NOAA. |
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Map 3. Surface Chart of October 2, 2010. NOAA |
Map 4. Surface Chart of October 3, 2010. NOAA. |
Despite a rough and intense arrival, this air mass did mark the beginning of several days of extremely calm conditions once the skies had cleared behind the cold front. Sunday October 3rd saw mostly clear skies, with scattered clouds throughout the afternoon and winds still out of the north around 12 mph. The high for the 3rd reached a cooler 62̊ F, a noticeable departure from the 75̊ F experienced just two days prior, as the massive high pressure parked itself over the Upper Midwest (Map 4). Dew points continued to fall throughout the day, reaching 40̊ F on the morning of the 3rd, and then dropping down to the mid 30s by the afternoon and evening. Air pressure continued to rise too, reaching up to 1027mb that morning before briefly backing off for the usual retreat of air pressure associated with a warming surface under the rays of the sun.
This high pressure remained firmly in place for the next several days, with temperatures gradually climbing as clear skies from the cell allowed generous amounts of sunshine to reach the earth and gradually begin warming it in the wake of a violent temperature shift. Monday the 4th experienced only a few occasional clouds in the morning, with a high temperature going up to 64̊ F from a low of 33̊ F that morning. That morning also recorded the end of the 36 hour downward march of dew points, with the value bottoming out at 32̊ F, before heading up to 35̊ F that afternoon as some moisture moved into the area. These calm conditions were then repeated on the 5th of October, with clear skies being observed throughout the entire day, with a high temperature of 69̊ F from another morning low of 33̊ F. Of scholarly note here, the observations for the 4th and 5th as well as the following couple of days provide an example of how in the absence of clouds or significant changes in weather, the temperature of a given area will gradually increase over time. This would be due to clear skies being repeatedly recorded, which allowed the maximum amount of sunlight to reach the earth, heat the surface and be absorbed, producing a heat surplus that is added to each day, helping to raise the temperature over time. By the 6th of October and with high pressure and clear skies still in place and southwest winds of 9-14 mph, this surplus allowed the high temperature to shoot to 77̊ F, with low temperatures being affected too after 42̊ F being recorded that morning.
By the 7th of October, an area of high pressure still remained over the area with clear skies being observed, but the weather story finally changed just slightly. An extremely weak cold front passed over the area that morning as a trailing extension of a low pressure system that moved across southeastern portions of Canada and the northeastern United States (Map 5). But regardless of its efforts, even this slight hiccup in the weather story was not enough for the casual observer to notice. Skies remained clear and the high temperature peaked at 79̊ F, another day of unseasonable warmth. The only indicators that something had changed about the weather set up was first the changing wind direction, which now turned over to the northwest at 7-10 mph from southwest winds observed on the afternoon of the 6th. The second indicator was that the high temperature only reached 79̊ F, a mere two degrees more than the previous day. While this may still be an unseasonably warm temperature, it is a marked difference from the previous few days, which had been seeing gains of five to eight degrees over the previous day due to the surplus in the heat budget.
High pressure still held the claim to king of the hill over the Midwest though, with the 8th of October seeing still clear skies and a high temperature of 83̊ F (Map 6). Dew points held in the low 40s for the day, giving an extremely dry feel to the air as relative humidity values dropped to around 25%. Another thing to note that contributed to the stubbornness of this high pressure system was that a ridge of high pressure also existed in the upper atmosphere over the Midwest, as seen in Map 7. This meant that high pressure was stacked all the way upwards through the column of air over Charleston, leading to highly stable conditions that would not budge without the influence of a major weather system.
There were signs of hope for this on the 8th of October though, as a trough and area of low pressure developed on the eastern side of the Rocky Mountains (Map 8), but quickly occluded (Map 9), and then stalled out and dissipated over the Midwest by October 10th before reaching Charleston (Map 10). Though one thing this system did do for Charleston was that it allowed high temperatures to tie the records for both the 9th and 10th of October. Despite some cloudiness over the area, southerly winds from the low pressure to the northwest and high pressure to the southeast combined to push temperatures to 87̊ F on the 9th and 88̊ F on the 10th, tying the records for both of those days.
By October 11th, temperatures cooled off slightly due to some clouds moving in during the afternoon hours and limiting afternoon heating to a high of 86̊ F. Southwesterly winds of 5-10 mph were experienced that day as a weakened cell of high pressure sat over the southeastern United States (Map 11), which logically should help to boost temperatures. But because of a colder air mass situated over Canada, these warm and fairly moist winds that brought dew points up to 56̊ F encountered a boundary of cold air, which condensed the moisture in the air to form partly cloudy conditions, which then limited surface heating as the afternoon progressed. These clouds also helped to keep things slightly warmer overnight, with 54̊ F being the low that night into the morning of the 12th. Cloud cover increased to mostly cloudy conditions throughout the day on the 12th as an organized cold front approached from the west, again being the trailing elements of a low pressure system centered far to the north in Canada (Map 12). The day began with southeasterly winds feeding some heat energy into (Map 12) the system, but then winds turned over to the northeast as another high-pressure driven cold front sagged south into the area that afternoon. This combination of clouds and northeast winds helped to keep the high temperature a bit cooler, at only 79̊ F as opposed to the 80s of the previous few days. Then alas, the cold front to the west finally passed over Charleston during the early AM hours of October 13th, turning winds to the northwest at 12-17 mph, where they remained for the entire day. In addition, a wide and fairly strong high pressure to the west over the Rocky Mountains began spilling into the area, tightening the pressure gradient and helping to strengthen the northwest winds too (Map 13). That day saw the high temperature reach to only 72̊ F as cloudy conditions continued during the morning hours and only began to clear later in the afternoon and early evening, too late for the temperatures to climb any higher.
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Map 11. Surface Chart of October 11, 2010. NOAA |
Map 12. Surface Chart of October 12, 2010. NOAA. |
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Map 13. Surface Chart of October 13, 2010. NOAA |
The clearing conditions allowed the low temperature to drop down a low of 41̊ F as radiation was released into the infinite blackness of a clear night in the early morning of October 14. Northwest winds continued overnight at 8-12 mph as high pressure moved into the area, but started to shift more to the west on the afternoon of the 14th as high pressure moved over the Plains under the influence of a tight 500mb level and ridge of high pressure in the upper atmosphere (Maps 14 and 15). Clear skies with only a few occasional clouds passed overhead on the afternoon of the 14th, but nonetheless, the effects of the cold front and a tight jet stream bringing cold air southward in the trough kept the daily high to only 70̊ F.
The weather set up changed very quickly from the 14th to the 15th though. While clear skies continued on the 15th, the low pressure over the East Coast seen on Map 14 quickly strengthened as it hit a fairly large area of divergence that day, as shown on Map 15. Warm air was also pushed northward into it from the Bermuda High, as shown by the sudden turn to the northeast of the warm front extending from this system (Map 14). This sudden infusion of energy allowed the system to re-strengthen and reach up to the 500mb level, which tightened the pressure gradient on its backside at that level and produced a surface high pressure over the western Great Lakes and northern Midwest regions (Maps 16 and 17). What this did for Charleston was turn winds back to the northwest at 10-15 mph for the 15th of October and bring cooler air southward, with a high of 66̊ F being recorded that afternoon.
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Map 14. Surface Chart of October 14, 2010. NOAA |
Map 15. 500mb Chart of October 14, 2010. NOAA. |
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Map 16. Surface Chart of October 15, 2010. NOAA |
Map 17. 500mb Chart of October 15, 2010. NOAA. |
From there, the high pressure that developed in the wake of that low pressure system moved southward over the Mississippi and Ohio River valleys, which kept skies clear again on the 16th. Light southeast winds of 4 mph were recorded that morning as the high pressure settled into the area, but by the afternoon they had moved over to the southwest and increased to 13 mph as the pressure gradient tightened in advance of a cold front and associated trough draped across the Upper Midwest (Map 18). The high for the 16th reached up to 74̊ F as still somewhat cooler temperatures where mixed with heating from still abundant sunshine overhead.
As this cold front approached the area, it became fairly disorganized as the low pressure that was steering it became occluded and began to dissipate far to the north over Canada’s Hudson Bay, with the cold waters of the bay quickly killing off an already dying system (Map 19). This cold front did manage to turn winds over to the north-northwest at 5-10 mph, but it was not enough to produce any clouds, with clear conditions still continuing all day on the 17th. Nor did this cold front pack much, if any,amount of a punch either, because the high temperature for the 17th climbed up to 77̊ F, a full four degrees higher than the previous day in spite of the passage of the cold front.
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Map 18. Surface Chart of October 16, 2010. NOAA |
Map 19. Surface Chart of October 17, 2010. NOAA. |
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Map 20. Surface Chart of October 18, 2010. NOAA |
Map 21. Surface Chart of October 19, 2010. NOAA. |
Sky conditions finally changed on the 18th day of October as the weak and dissipating cold front lapsed into an east-west orientation over the Ohio River (Map 20). High pressure to its south over the southeastern U.S. and another high pressure to the north over the upper Midwest and Plains states made this cold front into more of a stationary than a cold front, as displayed on the map. As a result, northward moving warmth and moisture from the Gulf of Mexico and southward moving cold, dry air from the Plains collided along this stationary front, producing mostly cloudy conditions overhead, with a meager .02 inches of precipitation being squeezed out of the sky. Charleston wound up falling under the influence of the high pressure to the north though, with northeast winds of 5-10 mph prevailing all day, and a high temperature reaching 71̊ F. These northeast winds then shifted more to the northwest at 3-6 mph on the 19th as the influential high pressure over the Plains shifted its weight eastward over the Midwest, bringing cooler temperatures with it (Map 21), as the high only reached up to 66̊ F. Skies also cleared on the morning of the 19th as dryer and more stable conditions aloft resumed with this high pressure system. These clear and dry conditions helped to drop temperatures down quite a bit that night though, bottoming out at a chilly 37̊ F on the morning of the 20th. Clear skies once again continued throughout the day on the 20th, but winds turned to the southwest and increased to fairly decent speeds of 16-22 mph as the low pressure over the Great Lakes began to strengthen in the wave phase of cyclogenesis and draw air in towards it (Map 21). These breezy southwest winds and clear skies together helped to buoy the high temperature up to 73̊ F for the day, albeit the strength of the winds somewhat mitigated the feeling of warmth. By the 21st of October, the low pressure system that had been gaining strength over the Great Lakes moved eastward, with yet another high pressure building on its backside, which brought northwest winds of 10-20 mph to the Charleston area (Map 22). As has been the case as well, clear skies were once again the favored overhead condition. As the day wore on, the air pressure rose as is typically seen with the dominance of a high pressure system, however this would not remain the case for very long. To the west, a very small trough was starting to develop over western portions of Oklahoma and Kansas (Map 22), which in a couple of days would grow to be one of the strongest storms to pass over the country in recent history. But at this point, it was just a small and developing trough, with a weakened high pressure over the lower Mississippi River feeding small spoonfuls of warm air and moisture into it.
Continuing along the scale of time, the 22nd of October saw that cell of high pressure sitting fairly square over the east-central parts of the country (Map 23), which acted to push temperatures down to a low of 34̊ F that morning, with patches of frost scattered across the area where temperatures dropped below freezing. The quick movement and development of this high pressure helped to turn winds over to the south and southeast for the whole day at speeds of 5-10 mph, as the cell became positioned to the east of Charleston. This aided the daily high in its climb up to 71̊ F for that afternoon, with partly cloudy skies starting to develop as moisture was pulled northward into a realm dominated by cooler air. Out to the west, the weak trough that had developed the previous day was still slowly gaining strength. A very weak and hardly distinct warm front trailed southeastward across Kansas from it from modest southerly wind flow, and the trough had also elongated, stretching south through Texas (Map 23). The air pressure in Charleston on the 22nd topped out at 1022mb and then started to slowly fall as the day progressed, which in conjunction with increasing clouds signaled that something might be changing about the weather.
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Map 22. Surface Chart of October 20, 2010. NOAA |
Map 23. Surface Chart of October 21, 2010. NOAA. |
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Map 24. Surface Chart of October 22, 2010. NOAA |
Map 25. Surface Chart of October 23, 2010. NOAA. |
Cloud cover continued to increase throughout the night of the 22-23rd, which helped to insulate the Charleston area and keep the low temperature at a rather warm 58̊ F for the night. Cloudy skies continued all day on the 23rd, with the air pressure falling to 1012mb by that evening. Southwest winds blew through Charleston for the entire day as well at speeds up to 20 mph, which helped to bring the high temperature up to 79̊ F in spite of overcast skies. This came about due to the high pressure that had been sitting over the eastern parts of the Midwest being pushed to the east as the area of low pressure over western Kansas became more distinct and tightened the gradient between the two pressure cells (Map 24), helping to send warm air northward. At this point in time, that low pressure system started the transition from the wave to the open stage in cyclogenesis as a more distinct warm front became associated with it, with a dryline being sent blowing across Texas as warm, dry air was swept eastward out of New Mexico by the system. It also had created a trough across the Upper Midwest that stretched from the Great Lakes southwestward to the center of low pressure, meaning that warm air was starting to rise across this entire area (Map 24).
As the 24th of October rolled around, south winds continued at speeds between 12-20 mph with the air pressure still falling in Charleston, signaling the potential for a major change in the weather. Looking at the surface and 500mb maps of the 24th (Maps 25 and 26), the low pressure that had been slowly building over Kansas started moving northeastward in the open stage of a cyclone’s life. This movement helped to bring still southwest winds, which again helped the high temperature to repeat the 79̊ F of the prior day, despite still mostly cloudy conditions. Also at this time, a massive area of divergence existed across the entire central portion of the country and extended north into Canada before turning westward as part of a trough associated with an upper-level low off the coast of British Columbia (Maps 25 and 26). What this did was create a huge area where warm air could rise high into the atmosphere and aid in the development of surface low pressure systems. Additionally, a surface trough was developing between this growing surface low pressure and the one off of the western Canadian coast, indicating that something else was likely to happen if the low over the Midwest did not quickly depart and move to the east.
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Map 26. Surface Chart of October 24, 2010. NOAA |
Map 27. 500mb Chart of October 24, 2010. NOAA. |
By the morning of Monday October 25th, the air pressure in Charleston had fallen to 1002mb and showed no signs of stopping anytime soon. Cloudy conditions stumbled slightly as breaks in the stratus clouds allowed partly cloudy conditions to be observed that afternoon. Strong south winds continued all day, reaching up to 22 mph with gusts closing in on 30 mph. For a third day in a row, these southerly winds helped to keep the high temperatures at unseasonable levels, this time reaching up to 78̊ F for the daily high. As this was occurring, the jet stream and the area of divergence over the country’s heart was being pulled to northward, helping to turn the direction of wind flow in the atmosphere more towards the northeast. What this wound up doing, is that it pulled the low pressure that had been passing over the Midwest backwards in a westward direction, something rarealy seen at these latitudes. Such a strong trough had developed over the North Dakota/Montana area that the low pressure essentially “slid” down the pressure gradient into this area of little air pressure resistance, which allowed it to strengthen at an incredible rate (Maps 28 and 29). The system also met little resistance at the 500mb level, with an upper-level low positioned over southwestern Canada, meaning that there was more than ample space for this system to grow and expand into. As it moved backward into this huge trough, the system brought with it warmth and moisture that stretched all the way south to the Gulf of Mexico due to the the broad range of the pressure gradient pulling air in towards the system. This provided the energy needed once these warm temperatures encountered the bitter cold air that was being brought south from a small low pressure system that was starting to develop over Saskatechewan, Canada, underneath the upper level-low that the Midwest surface low slid into. The result was the explosive growth of a storm of epic proportions. In the open phase during the 25th, the system started moving eastward, with the central pressure continuing to fall as massive amounts of warm air was pulled northward and forced to rise in the system.
This process continued all day on the 26th of October, with the cold front moving rapidly across the Midwest overnight and impacting Charleston during the morning hours (Map 30). Heavy rain and severe thunderstorms were witnessed in Charleston that morning, dumping .42 inches of rain on the town. To the east, tornados were spawned across the western and central counties in Indiana as the instense cold front pushed through, bringing wind shear throughout the atmosphere with the severe thunderstorms. The high temperature for the 26th was 73̊ F and occurred in the early morning hours ahead of the cold front, with temperatures dropping all day on the back side of it. As this system churned eastward, it continued to strengthen, despite it becoming occluded during the morning of the 26th. The central air pressure dropped to a low of 955.2mb or 28.21in/Hg at Bigfork, Minnesota (Grumm, 2010). While this did not set a record, it was certainly one of the strongest storms to cross the area in recent history and will be remembered for years to come. As it pushed out of the Charleston area, skies began clearing by the afternoon hours, with strong southwest winds continuing on the backside of the low.
Overnight, skies were clear but winds continued at speeds of 12-17 mph with the air pressure finally rising again. As the sun began passing overhead, southwest winds continued to strengthen again, up to 25 mph with partly cloudy conditions as wrap-around moisture from the system clouded the skies. As before the storm, these winds helped support another slightly warmer day than expected, with 71̊ F being observed, masking the realities of the harsh cold front that had passed through. Indeed, temperatures quickly began to fall that afternoon, dropping down to 39̊ F for a low with only continued overcast skies preventing it from dropping any lower. These cloudy skies continued all day on the 28th of October, again the product of left over moisture from the low pressure system, which by this time was decaying over East-Central Canada (Map 31). These clouds helped to keep the high temperature cooler though, with only 65̊ F being recorded for the high. Winds also shifted over to the west-northwest as a strong high pressure built up over the interior of the country in the wake of the huge low pressure system at speeds of 15-22 mph.
By that night, skies had finally cleared of any water vapor left over from the system, which in conjunction with the high pressure, dropped temperatures to a frigid-feeling 29̊ F in Charleston and prompting hard frost advisories across the Midwest. Daytime conditions remained clear, with winds dying down to 3-8 mph out of the northwest as high pressure settled over the area once again, though the high temperature only reached 56̊ F as cold air firmly took a hold in the Midwest.
Then on Saturday the 30th of October, windy conditions resumed over Charleston, at speeds of 20-30 mph from the southwest as a small low pressure system skirted to the north across the Great Lakes, aided by the high pressure system affecting Charleston, which had moved eastward by this time (Map 32). Once again, these southwest winds helped to lift the high temperature higher than it would otherwise be, reaching up to 70̊ F for the day as warmer temperatures were pulled to the north from the southwesterly winds. A couple of scattered cirrus clouds made their way overhead too, but played no noticeable role in the surface weather.
The final day of October dawned with a cool temperature of 40̊ F being observed in Charleston. As had been the case for most of the month, high pressure dominated the Charleston area, with winds out of the northeast at 11-17 mph as a high pressure system moved in from Canada, forcing that small low pressure system quickly out to the east. Clear skies were again recorded, with the high temperature going up to 63̊ F to finish out the month (Map 33).
To round-out the weather for October, 2010, the month saw fits and starts throughout its course, ranging from record highs in the upper 80s, all the way down to sub freezing temperatures with frost advisories. One common occurrence throughout the month though, was a regime of high pressure sitting either over or to the southeast of Charleston. More often than not, this high pressure cell acted to keep temperatures above average and conditions dry as clear skies and south to southeast winds prevailed underneath it. Best described as the high pressure resulting from the convergence of the Hadley and Ferrell cells in the upper atmosphere, this weather phenomenon was the dominant force throughout the month. Truly, the only notable event to deviate from this warm, dry pattern was the storm of October 25-27, which was of near record proportion. This was truly a notable month; both for its warmth and one massive storm.
References and Further Information
Grumm, R. U.S. Department of Commerce, National Weather Service. (2010). The Historic Storm of 24-26 October 2010. Retrieved from http://nws.met.psu.edu/severe/2010/25Oct2010.pdf.
National Oceanic and Atmospheric Administration
Charleston, Illinois Climate Data (EIUWC)
Cameron Craig, cdcraig@eiu.edu
