September 2011 Climate Summary

Transcription

1 Ken Scheeringa and Kayla Hudson Oct 5, 2011 (765) September 2011 Climate Summary Month Summary The final blast of summer heat arrived at the start of September. It lasted just 3 days before autumn coolness settled in for much of the rest of the month. Two large cutoff low pressure systems in the upper atmosphere were players in September s cool weather: the remnants of tropical storm Lee from September 6 th through 9 th, and a second closed low system that dominated the eastern half of the country and parked itself over Indiana for nearly a week starting September 23 rd. There were many cloudy days with these systems which helped suppress the September state average temperature to 63.6, which is 2.0 below normal. Historically this ranks September 2011 as the 22 nd coolest September in Indiana since The most recent September that was cooler came in 2003, which averaged 63.4 and landed in 19 th place. The 20 th coolest September in Indiana featured a 63.5 average in The day split in September 2011 was 19 days of below normal temperature, 10 days above normal, and 1 day with normal temperature. There were 4 days this month when the daily state average temperature was at least 10 degrees colder than normal and 2 days with the daily average at least 10 degrees warmer than normal. The hottest temperature of the month was also the hottest of the year with 103 reported on September 3 rd in Terre Haute and again the next day in Shoals. The coldest temperature was 31 on September 18 th at Elwood. The late summer drought intensified the first half of the month. Significant rains returned to Indiana about September 18 th, reversing the drought cycle. Overall this month state precipitation averaged a surprising 5.39 inches, 2.3 inches above normal, which ranks as the 11 th wettest September on record. The most recent wetter September was in 2003 when 6.21 inches fell and comes in as 4 th wettest. These numbers still are far short of the 8.25 inches recorded during the wettest September on record in Regionally September 2011 precipitation ranges from one and a half times normal in northern Indiana to twice normal in southern counties. Some impressive one day rainfalls were noted in far southern Indiana. On September 25 th 5.67 inches drenched Poseyville. The next day the Patoka observer recorded 4.85 inches while 4.24 inches was observed in Jeffersonville. Soil moisture levels deteriorated the first half of the month before improving rapidly toward month s end. Nearly half the state area was classified in moderate to severe drought when the month began. As rains returned late in the month these two categories all but disappeared in the state. At the end of the month the northern half of Indiana is virtually drought free. Counties surrounding Terre Haute enter October as the driest portion of the state with a moderate drought (D1 category) classification.

2 The weather scene was rather quiet in Indiana the first half of September. Severe weather events picked up the second half of the month, including reports of 2 tornadoes. On September 26 th an EF1 tornado was confirmed in Jennings county, destroying a pole barn, damaging 2 homes, overturning a tractor, and taking down trees and power poles. Road flooding was also a problem in this area. The next day an EF0 tornado was confirmed in Elkhart county, resulting in minor roof and tree damage. There were no storm related injuries or deaths in Indiana this month. September 1 st 10 th Autumn begins this month but the hot summer of 2011 isn t over just yet. A warm frontal passage through Indiana on September 1 st allowed extreme temperatures to return for a few more days. Daily state temperatures averaged 9 to 12 above normal through September 3 rd. Maximum temperatures exceeded 100 in at least 9 locations with two cities, Shoals and Terre Haute, recording a steamy 103! A strong cold front barreled through the state on September 4 th, dropping temperatures more than 20 over the next two days. The remnants of Tropical Storm Lee entered the Indiana weather picture late in the 10 day interval, eroding away the cold to wrap up the interval at 2 below normal. For the 10 days overall temperatures finished on the cool side at 2 below normal. Typically this first week of September daily maximums are expected to range between 85 to 88 north to south across the state. Daily minimums should range from 63 in far northern Indiana to 64 in southwest counties. Most of the rain fell during these two weather systems, the cold front on September 4 th and the leftovers from Tropical Storm Lee after September 6 th. The cold front generated a quarter to a half inch of rain while the tropical storm remnants dropped up to another 0.8 inch, especially in the north. While the remnants of Lee zoomed up the Atlantic Coast a new isolated but intense low pressure center broke off from the main storm and drifted westward toward Kentucky. The wind circulation around the break away low caused the backward movement of rain showers east to west across Indiana for 3 days along with persistent cloudy skies. This low finally merged with a new low pressure system west of Indiana at the end of the 10 days carrying the dreary weather away, allowing the return of sunny skies. The combined rainfall from both weather systems totaled to near 1.2 inch in northern Indiana and 0.9 inch in central and southern areas. These totals are within 10% of normal for the 10 day interval. The heaviest 10 day totals among CoCoRaHS observers included 2.44 inches at Crown Point, 2.20 inches in Bluffton, and 2.19 inches in Winfield. The Lawrenceburg and Schererville volunteers measured 2.16 inch totals each. The cutoff low associated with the tropical storm remnants brought pesky rain showers to Indiana but surprisingly no severe weather. It was the earlier cold front that caused widespread wind damage but few reports of hail. In extreme northern Indiana hail ranging in diameter from 1.0 to 1.75 inch was reported in St Joseph and Elkhart counties with one lone report from Hancock county. On September 3 rd there were numerous reports of trees falling on power lines in north central Indiana, including in the counties of Porter, Laporte, Starke, Elkhart, and Lagrange. More reports of trees falling on power lines and roads came in from Fountain, Delaware, Madison, Marion, Hancock, Morgan, and Bartholomew counties around central Indiana. Severe weather had started on September 2 nd in Clark county of south central Indiana and continued the next day in nearby Scott county, snapping trees onto roadways.

3 Rainfall amounts are near normal so far in September but the added moisture has had little impact on the late summer Indiana drought. The National Drought Monitor edition for September 6 th reports no changes in the Indiana drought status since the week before. Except for southwest counties much of the southern half of Indiana continues in moderate drought (D1 class). Johnson and Morgan counties remain in the severe drought class (D2). Much of northeast Indiana is still considered abnormally dry (D0 class) while northwest Indiana is still drought free. September 11 th 17 th It is still summer by the calendar but late in the week it felt a lot more like autumn. A short warm up early this week was interrupted by a strong surge of cold Canadian air. A first weak cold front had crossed Indiana but then stalled along the Ohio River on September 14 th. A second much stronger front behind it quickly caught up the next day and carried the cold air south to Tennessee. The cold high pressure center then sprawled over the eastern three-fourths of the country on September 16 th before sliding eastward to end the week. Daily state average temperatures which started the week at normal had peaked at 4 above normal by September 13 th before plunging to 12 below normal two days later. A slow moderation lifted temperatures to 5 below normal to end the week. Overall for this week daily state temperatures averaged 4 below normal. Typically mid September daily maximum temperatures should range from 78 to 85 north to south across the state. Daily minimums normally vary from 57 in far northern Indiana to 61 in the southwest. A few tenths inch of rain generally fell with the passage of the cold fronts and about one tenth inch in the warmer air at the start of the week. For the week rainfall totaled about a third inch in northern and central Indiana and a half inch in the south. These amounts are about two thirds normal in southern Indiana but less than half normal elsewhere across the state. At this time of year about 0.8 inch is typical per week in Indiana. The heaviest one day CoCoRaHS amounts included 1.05 inch at Rensselaer, 0.92 inch in Williams, and 0.84 inch at Indianapolis. The greatest weekly total was 1.24 inch in Shelbyville, 1.23 inch at Evansville, and 1.15 inch in Williams. Despite the sharp temperature change the general lack of atmospheric moisture suppressed storm development. There were no reports of severe weather damage this week. But drought is still a problem in the Midwest as evidenced by the smoke from Minnesota wildfires which carried into

4 northern Indiana skies on the strong north winds of the cold front. The drought continued to intensify in Indiana as well. The National Drought Monitor increased the area coverage of severe drought (D2 class) in Indiana by 10% this week. The expanded area now includes parts of west central and southwest Indiana, that is, most of Vigo, Clay, Owen, Morgan, Parke, Putnam, Monroe, Greene, and Sullivan counties. Parts of Johnson, Vermillion, Hendricks, and Bartholomew counties are also in this classification. The portion of Indiana in moderate drought (D1 class) is generally south of a line drawn from the communities of Covington to Richmond. In addition abnormally dry conditions (D0 class) have expanded into southwest Indiana. The drought conditions have prompted a few counties to declare open burn bans. Daviess county ordered a one week open burn ban effective September 12 th. The open burn ban in effect in Sullivan county expired on September 15 th. September 18 th 24 th Weather systems picked up the pace this week as 4 fronts crossed Indiana in the space of just 4 days. But that all changed by the end of the week when an upper atmospheric storm system stalled and was left behind in the Midwest by the jet stream which shifted its track far northward into Canada. Daily average statewide temperatures started the week 4 below normal but rose steadily before peaking at 6 above normal. The first warm front passed through Indiana on September 19 th, immediately followed by its cold front the next day. The next storm system was right on the heels of the first, pulling another warm front through the state on September 21 st and followed by its paired cold front the next day. Daily state average temperatures now slid slowly on a downward trend, ending the week at 2 below normal. The slow flow and ebb of the temperature cycle averaged to normal this week. Daily normal maximum temperatures around Indiana this week generally range from about 75 in the north to 82 in the south. Typical daily minimums would vary between 53 in northern counties to 57 in far southwest Indiana. The many fronts triggered showers nearly every day with the heaviest amounts in central and southern Indiana. Regionally for the week about 0.8 inch of rain fell on average in northern Indiana, near 1.7 inch in central sections, and 1.9 inches across the south. While these totals are just 20% higher than normal in the north, rain accumulated to about two and a half times normal in

5 central and southern Indiana. In some local areas the rain which fell on September 18 th and 19 th were the most significant amounts measured since June 20 th, three months ago! Some of the heavier one day amounts recorded by CoCoRaHS observers included 2.87 inches in Melody Hill, 2.57 inches in Castleton, 2.30 inches at Woodburn, and 2.22 inches in Clay City. The highest weekly totals include 3.69 inches and 3.54 inches at two locations in Evansville, 3.51 inches in Clay City and Darmstadt, and 3.40 inches at Gosport. The first significant rains in many weeks were able to finally increase soil moisture and reverse the worsening drought situation in Indiana. The September 19 th edition of the National Drought Monitor noted a 13% reduction in the area of the state classified in moderate drought (D1 class) and a 5% area reduction in severe drought (D2 class) area. Improvement was seen in the center of the state where the severe drought area has decreased in size. Rains missed west central counties which remain in severe drought, including all of Vigo, Clay, and Owen and parts of Parke, Putnam, Greene, and Sullivan. The surrounding moderate drought area is located generally south and west of a Covington to Richmond to Corydon line, excluding areas west of a Boonville to Vincennes line. Crops in parts of west central Indiana which continue in severe drought are likely to suffer yield losses according to crop experts. A delayed spring planting season, followed by a hot and dry summer has been difficult on crops this year particularly in these continued severe drought areas. The recent rains have eliminated all open burn bans in Indiana. Officials in Daviess county have allowed the one week open fire ban there to expire on September 19 th.

6 September 25 th 30 th A huge stalled low pressure center in the upper atmosphere, cutoff from the jet stream and sprawled across the eastern half of the country, dominated our weather this week. The persistent cloudy skies and intermittent rain showers held state average temperatures 2 to 4 above normal the first half of the week. Finally the week-old cutoff low was picked up by upper level winds and transported eastward on September 29 th. A surge of cold Canadian air took its place over Indiana, lowering daily average temperatures to 7 below normal at month s end. Overall for the week daily temperatures averaged 3 below normal. Normally at the end of September daily maximum temperatures range from 72 in extreme northern Indiana to 79 in the far southwest. Daily minimums typically vary between 50 and 53 north to south across the state. Rainfall was an every day occurrence this week. The heaviest amounts fell with the passage of a first cold front on September 26 th with 1 inch readings common across northern Indiana and up to 2 inches across the south. Some locations in far southern Indiana found much heavier amounts in their rain gauges. The CoCoRaHS observer in Patoka measured 4.85 inches for that day while two Jeffersonville reporters recorded 4.24 inches and 4.20 inches. The Petersburg volunteer received 3.79 inches while 3.72 inches was noted in Poseyville. Rainfall became lighter on the following days with daily amounts just over a quarter inch in northern counties to less than a tenth inch in the south. The everyday rains really added up by the end of the week. About 2.7 inches was totaled across northern Indiana, 2.4 inches in central sections, and 3.0 inches in southern areas. These totals are more than 4 times normal in the northern and southern thirds of Indiana and just shy of 4 times normal in the central part of the state! Some of the heaviest CoCoRaHS weekly totals include 5.09 inches in Denver, 4.66 inches in Logansport, and 4.35 inches in Galveston. The intense rainfall along the Ohio River flooded roadways on the morning of September 26 th. In Clark and Floyd counties several roads were underwater and about 75 homes lost power. A little further north an EF1 tornado touched down in Jennings county, destroying a pole barn, damaging 2 homes, overturning a tractor, and taking down trees and power poles. Flooded roads were also a problem in this area. In Henry county hail up to 1.75 inch in diameter was reported. The next day an EF0 tornado was confirmed at the opposite end of the state in Elkhart county with 75 mph winds and a 0.6 mile long path. There was minor roof and tree damage. The cutoff low departed Indiana on September 29 th and the week s second cold front rushed in behind it. High 50 mph winds damaged utility lines in Tipton county and to the east in Delaware county high winds brought a tree down on top of a house. Some semi-trailers were banned for the day from the Indiana Toll Road in extreme northwest Indiana. Fortunately there were no injuries in any of the storms this week. One benefit of the heavy rain was the continued easing of the late summer drought in Indiana. According to the National Drought Monitor issued September 27 th the drought free region of Indiana has increased from 17% to 55% of the state area and consists largely of the northern half of the state. Areas classified as abnormally dry (D0 category) a week ago have decreased in coverage from 83% to 45% in area while moderate drought (D1 category) acres have fallen from 41% to 6% of total state area. There are no areas remaining in severe drought (D2 category) status. In general terms then most areas of Indiana have improved about one drought category from a week ago.

7 September 2011 Temperature Region Temperature Normal Deviation Northwest North Central Northeast West Central Central East Central Southwest South Central Southeast State Precipitation Region Precipitation Normal Deviation Percent of Normal Northwest North Central Northeast West Central Central East Central Southwest South Central Southeast State

8 Autumn 2011 (so far same as September) Temperature Region Temperature Normal Deviation Northwest North Central Northeast West Central Central East Central Southwest South Central Southeast State Precipitation Region Precipitation Normal Deviation Percent of Normal Northwest North Central Northeast West Central Central East Central Southwest South Central Southeast State

9 2011 Annual so far Temperature Region Temperature Normal Deviation Northwest North Central Northeast West Central Central East Central Southwest South Central Southeast State Precipitation Region Precipitation Normal Deviation Percent of Normal Northwest North Central Northeast West Central Central East Central Southwest South Central Southeast State

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13 Drought Summary from the U.S. Drought Monitor Below is a drought summary for the state of Indiana from the U.S. drought monitor. Areas in white are not experiencing any drought. Yellow areas are abnormally dry, but not entirely considered a drought. Drought begins when the moisture levels become more severe, with beige, orange, red, and brown indicating increasing levels of drought (moderate, severe, extreme, and exceptional, respectively). The table below indicates how much of the state is not under drought conditions, and also how much of the state is under drought conditions from its respective column upwards. For example, September 27 th has 6.1% of Indiana under at least D1-D4 drought status, 44.9% under at least D0 through D4 drought status, and 55.1% drought free. Subtracting the D1-D4 category (6.1%) from the D0-D4 category (44.9%), tells us that 38.8% of Indiana is in D0 category alone (abnormally dry). Please note, however, that these areas are not exact, and much of this drought map has been created from reports throughout the state and in estimation, so use this information as a general view rather than for specifics.

14 September 6 th Drought Summary

15 September 13 th Drought Summary

16 September 20 th Drought Summary

17 September 27 th Drought Summary