The North American Heat Wave of July 2011-Draft By Richard H. Grumm And Jason Krekeler 328 Innovation Blvd Suite 330 National Weather Service Office State College, PA 16803 The meteorological conditions associated with the persistent heat event of July 2011 Abstract: A persistent upper-level ridge brought a prolonged period of above normal temperatures to much of the United States and southern Canada. A broad mid-tropospheric ridge dominated the pattern the Great Basin to the East Coast. Cool air was limited to the Pacific Coast with a mean trough anchored over the northwestern United States and southwestern Canada. The heat wave peaked in mid-july over the plains. From 16-22 July 2011 a close 5940 m contour and +2 temperature anomalies dominated most of the central United States leading to record high temperatures and many new record high low temperatures. The ridge and associated warm air moved eastward. During the 3-day period of 21-23 July 2011 850 hpa and 700 hpa temperatures were +2 to +3 above normal. Record high temperatures were set or broken over much of the eastern United States during this time period. This paper will document the pattern and the anomalies in the pattern during the month of July 2011. The value of anomalies in diagnosing heat waves is employed here focusing on the period of peak heat from 16-23 July 2011.
1. INTRODUCTION A strong and persistent blocking ridge over southern North America during the month of July 2011 (Fig.1) brought above normal warmth to much of the eastern United States and southern Canada. The heat peaked in intensity between 17-24 July over the central United States and southern Canada. Over 100 daily high temperature records were tied or broken between 20-24 July (Table 1). During this span of time 136 high temperatures records were tied or broken in the State of Pennsylvania (Table 2). The upper-level ridge weakened as it moved eastward, but the anomalous mid-tropospheric temperatures contributed to 2-3 days of record heat in the eastern United States. Previous research has shown the importance of subtropical ridges and heat waves (Brugge 1995), Chang and Wallace 1987; Galarneau et al. 2008; Kunkel et al. 1996; Lipton et al. 2005; Lyon and Dole 1995). Namias (1982) and Robinson (2001) showed the patterns associated with protracted heat waves over North America. Schar and Jendritzky (2004) examined the meteorological conditions associated with the European heatwave of 2003. This event primarily impacted central and western Europe. Brugge 1991 showed the importance of a blocking anticyclone during the record heat of August 1990 in the British Isles. Thwaytes (1995) completed a study of Northern Hemispheric heat waves. Strong ridges are a common theme in most of these cited works. Heat waves often have significant impacts on human activities. Goklany (2008) and Changnon et al. (1996) showed that heat waves are a leading cause of weather related deaths. The elderly often suffer the most during heat waves. Palecki et al. (2001) examined mortality rates in Chicago and St. Louis during the 1999 and 1995 Midwestern United States heat waves. Despite the fact that the 1999 event was meteorologically more intense than the 1995 event, the lower mortality rates
during the latter event suggests that cities can learn from these events and mitigate their impacts. Prolonged heat waves are often associated with droughts (Chang and Wallace 1987; Lyon and Dole 1995). Grumm (2011) documented the large scale conditions and standardized anomalies of key fields associated with the record heat wave over central Europe during the summer of 2010. Russia experienced a prolonged period of record heat for most of the month of July into mid-august. During the peak periods of heat over Moscow, a closed 5940 m contour was present along with 3 above normal temperatures at 850 hpa. The value of standardized anomalies in showing the persistence of heat waves was first examined by Wolfson and Atlas (1986). Their study shows the value of using standardized anomalies to diagnose the persistence of the heat wave of the summer of 1980. This paper will document the large scale conditions associated with the North American heat wave of July 2011. The focus is on an analysis of anomalies associated with key features. This is based on the work of Lipton et al. (2005) and Grumm (2011) which showed the value of anomalies in identifying heat waves and warm episodes. 2. METHODS The 500-hPa heights, 700-hPa temperatures, and other standard level fields were derived from the National Centers for Environmental Prediction Global Forecast System (NCEP GFS) 00-hour forecasts. The means and standard deviations used to compute the standardized anomalies were derived from the NCEP/NCAR Reanalysis data as described by Hart and Grumm (2001). Anomalies were displayed in standard deviations from normal, as standardized anomalies. All
data were displayed using GrADS (Doty and Kinter 1995). The composites used in the analysis were produced from NCEP GFS data. For each 6-hour time period, the NCEP GFS analysis was used to compute the mean field and anomalies of the respective field. Composites were limited to 500-hPa heights, 850-hPa temperatures, 250-hPa winds, and precipitable water. These variables selected based on the work of Lipton et al. (2005) and Namias (1982) and are believed to be important in describing and identifying both a subtropical ridge and a heat wave. The standardized anomalies are computed as: SD (F M) (1) where F is the value from the reanalysis data at each grid point, M is the 21-day running mean for the specified date and time at each grid point and σ is the value of 1 standard deviation at each grid point. Daily images were also produced using GFS data, which represent a single time. The times displayed were based on news accounts of heat records over the United States, east of the Rocky Mountains. The heat maximized over the southern plains (Fig. 2). Any city in the southern Plains would exhibit a similar trend but Oklahoma City was chosen as it was near the region of maximum heat and the data was readily available. The NCDC maximum temperature records data for the month of July was retrieved to determine the records set or tied by station, State, and geographic domain. These data were used to produce the listings in Tables 1 & 2.
It should be noted that the GFS with horizontal resolution at T574 (27km) is of finer resolution than the 2.5 x 2.5 degree climate data used here. The actual GFS data used here were on 1 x 1 degree grid which was of finer resolution than the 30-year climatological data use to compute the standardized anomalies. The GFS was remapped to the climate data. The impact is minimal for variables above the planetary boundary layer. However, variables such as precipitable water will generally be higher than those in the re-analysis data and thus will likely produce higher anomalies than the re-analysis data might show. The JRA25 and the NCEP-NCAR re-analysis data are used here to re-construct the pattern associated with previously hot periods from 1948 to present. Whenever practicable the higher resolution data is used. 3. RESULTS a. Composite pattern for July 2011 The composite pattern for July 2011 (Fig. 1) showed a broad ridge over the eastern United States. The expansive 5880 m contour extended from southern California to the Dakotas and over the southeastern United States (Fig. 1a). The 500 hpa heights averaged 0.5 to 1.0 above normal over the central United States during this period of time. The 700 hpa and 850 hpa temperatures indicated that most of the central United States was 0.5 to 2.0 above normal during the month of July. At 850 hpa the largest anomaly was over the southern Plains (Fig. 1c) while the deep warm air at 700 hpa peaked over the Midwestern United States.
As with previously documented heat waves and strong ridges, there was a surge of high precipitable water (PW) air along the western periphery of the ridge. PW anomalies were above normal along the Gulf Coast and into the central Plains. PW values remained at or near normal for the month over the northeastern United States. b northern Plains heat surge The period of 16-22 July 2011 was extremely warm over the northern plains of the United States and the southern plains of Canada. Record high temperatures were set in many locations from 16 to 22 July 2011. Minneapolis, MN set a record dew point of 28C (82F). The warm moist air lead to several days of record high and record high-low temperatures over much of the northern plains and Great Lakes region. The large scale pattern during this period (Fig. 3) showed a close 5940 m anticyclone at 500 hpa and a broad area of +1 to 2 height anomalies (Fig. 3a). Both 700 and 850 hpa temperatures were in the +1 to +2s above normal range over most of the eastern United States and southern Canada during this period (Figs. 3b-c). The PW anomalies during the 6-day period averaged +1 to +2 from northern Missouri into southern Canada. The above normal PW values likely contributed to the deep moisture, which limited diurnal cooling and relates back to the record high dew point set in Minneapolis. By 22 July the record high had shift to the south and east of the northern Plains and western Great Lakes. c. Eastern US Heat episode
The heat began to affect the eastern United States on 19 July with record high temperatures set in eastern cities from 19-26 July. The most intense days with the most record high temperature records broken were the 21 nd and 22 rd of July. The data for Pennsylvania (Table 1) shows record highs and daily highs over 100F at 3 of the 4 ASOS sites on 21-22 July. The State College COOP site broke 100F for the first time since 1988 with a reading of 101F on 23 July 2011, 1 degree below the all-time record high of 102 set on 17 July 1988 and 9 July 1936. The large scale pattern associated with the period of extreme heat in the eastern United States (Fig. 4) showed the height anomaly with the 500 hpa ridge over the region during this time period. The 5940 m contour which dominated earlier in the event was no longer present, however, the 10C contour at 700 hpa, at +2 to +3 thermal anomaly was present over most the northeastern United States and Mid-Atlantic region (Fig. 4b). Additionally, the 850 hpa temperatures were over 20C and were associated with +2 to +3 temperature anomalies. The thermal anomalies peaked in the eastern United States at 0000 UTC 22 and 23 July 2011. On both days a close 24C contour was present in the eastern United States and 850 hpa temperature anomalies were over 3 above normal. At 0000 UTC 23 July (Fig. 5) a small 5940 m contour was present off the East Coast most of the region from Maryland to southern New England was encompassed by the 24C contour. A large area from central Pennsylvania to the western Atlantic experienced 3 to 4 850 hpa temperature anomalies. The PW values were abnormally low under much of this hot air from central Pennsylvania to New England.
The PW anomalies were slightly above normal in the eastern United States, though the larger PW anomalies were focused on the western periphery of the ridge (Fig. 4d) from Kansas, across Iowa and into Ohio and western Pennsylvania. This moisture plume produced a heavy rainfall event in northern Illinois on 23 July. Chicago received 6.86 inches of rainfall setting a new alltime record rainfall for the city. d. Previous heat waves Three comparative events from the past were selected based on records related to high temperatures in Pennsylvania. The NCEP/NCAR re-analysis for the month of July of 1955 (Fig. 6), and the JRA25 data for the July 1980 (Fig. 7) and July 1998 (Fig. 8) are used here. The pattern during the maximum heat in the eastern United States from 22-23 July 2011 was similar to the pattern associated with record heat event of July 2010 (Grumm 2010). The pattern for July 1955 (Fig. 6) showed the persistent ridge over central United States and southern Canada and the warm air at 850 hpa over the same general region. The overall pattern at both 500 and 850 hpa was similar to the July 2011 pattern. The pattern for July 1980 (Fig. 7) had the ridge displaced to the south and west with a similar displacement of the temperature anomalies at both 700 and 850 hpa. The pattern for the summer of 1988 showed stronger westerlies (Fig. 8) over the eastern United States with some minor 0.5 850 hpa temperature anomalies over the region. The multi-day pattern of 03-08 July 2010 showed the sharp ridge and warmth in the eastern United States while the monthly pattern (not shown) suggested that the ridge was suppressed to the south and west.
e. Temperatures over eastern United States The high temperatures from 19-24 July 2011 (Fig. 10) show locations where a high temperature record was tied or exceeded. These data show the eastward progression of the record heat and the focus of the heat over the eastern United States from 21-23 July 2011. The heat in the Mid-Atlantic region peaked on 22 nd & 23 rd which matches well with the data in Tables 1 & 2 showing that during the peak heat the Pennsylvania and New York set many records. Pennsylvania tie or exceed 47 and 39 maximum temperature records on the 22 nd and 23 rd respectively. The heat began to retrograde back to the west on the 24 th (Fig. 10f) and the 25 th. f. Forecasts The generalized pattern of the heat wave was well predicted by the NCEP GEFS and GFS. Showing all forecasts would be prohibitive and two forecast examples related to forecasting record temperature (Fig. 11) and forecasting a persistent pattern (Fig. 12) are presented. Figure 11 shows the ensemble mean pattern at 1800 UTC 22 July 2011. These data show the potential for above normal 500 hpa heights and 850 hpa temperatures over the region at this time. Additionally, they show the high probability of extremely warm 2m temperatures. This was one of the two warmest days of the event over the eastern United States and the focused heat lines up well with Figure 10. The persistence of the pattern was determined using a 72-hour period to acquire the mean field for the period and the mean anomaly for the period. These data focused the heat for the 21-23 rd of July over the Mid-Atlantic region. It is impressive to see +2 to +3s temperature anomalies at 700 hpa for such a prolonged period of time. The 850 hpa temperature anomaly was focused over Pennsylvania and Virginia. These data, along with Tables 1 & 2 show that the GEFS was predicting a multi-day event which verified close to the indicated location.
4. CONCLUSIONS A large ridge dominated the pattern over most of the eastern United States from the Rocky Mountains to the East Coast during the month of July 2011. This produced a prolonged period of above normally warm temperatures over most of the central United States. The most persistent and hottest air was focused over the southern Plains (Figs. 1 & 2). The ridge amplified and moved northward into the northern Plains on 16 July and then moved eastward. This lead to a period of record heat in the northern Plains and Midwest from 17-22 July and a period of record heat in the eastern United States from 20-24 July 2011. Over Pennsylvania 22 and 23 July were the two hottest days, the temperature in State College topped 100F on 22 and 23 July for the first time since 1988. The pattern associated with the heat of July 2011 (Fig. 1) showed a persistent ridge over the United States with an expansive area of above normal 700 and 850 hpa temperatures. A plume of high PW was present on the western periphery of this ridge. This is a classic heat wave pattern which clearly persisted, in the mean, for the month of June. A similarly persistent pattern developed over central Europe in July 2010 producing the Russian heat wave of 2010 (Grumm 2011). These data clearly showed the persistent pattern associated with this event. The ability to predict when persistent patterns may develop may aid in better prepare for future episodes in the future. An interesting aspect of the flow of July 2011 was the high PW in the southern plains and southwestern United States, as diagnosed by the GFS 00-hour forecasts. Despite the high PW over southern plains and southwest, the region was unseasonably dry during this period.
During the middle of July, the ridge in the central United States strengthened and moved northward. This caused the warm air to surge into the northern Plains and into southern Canada. A close 5940 m contour developed at 500 hpa (Fig. 3), a feature often associated with summertime heat waves. Though rare, 6000 m contours can appear but during heat waves (July 2003) but this event never quite produced heights over 6000 m. During the surge of warm air from 16 to 22 July, an expansive area of 1 to 2s above normal 850 and 700 hpa temperatures affected the central United States. The warm air moved eastward and produced several days with record high temperatures in the eastern United States. The number of locations in the eastern United States setting or tying record high temperatures peaked on 22 & 23 July 2011. Most of the major cities from Washington to Boston saw daytime highs peak at or over 100F. During the peak of the heat in the East, 850 hpa temperatures peaked at over +3 above normal with an expansive region covered by the 24C contour (Fig. 4 & 5). The persistence of the pattern for several days with such anomalous conditions (Fig. 4) likely contributed to the number of records set. Though not shown, many locations set all-time record high low-temperatures. The pattern and the anomalies at 0000 UTC 23 July 2011 show how extensive the warm air mass was and how at 850 hpa the air mass was significantly above normal..the data in Figures 6-9 suggests that no two summers are a like. Cleary, July 1955 and 2011 had a distinct pattern with a northward shifted ridge and positive 500 hpa height anomalies. Despite the extreme warmth and records set in 1988, the monthly data show the ridge was well south and west of the ridge position in July of 1955 and 2011. Table 1 (Grumm 2010) showed how
episodic heat waves can be in the eastern United States, the episodic nature of heat waves over the eastern United States makes it difficult to compare monthly composites and see a coherent pattern. The two forecasts shown here indicated that the GEFS did well in predicting the overall pattern and the area where the heat would maximize for the period of 21-23 July 2011 (Fig. 12). The use of multi-period products may be of value in predicting areas of heavy rainfall, persistent heat or cold and persistent drought. The variables chosen here depict the large scale ridge often associated with heat waves, the need for deep warm air, and the flow of warm moist air on the western periphery of most significant ridges. More products of this type need to be developed to address specific forecast issues and problems. The NCDC database could be used to determine heat events across the United States and tie these data back to the patterns associated with heat waves. 5. ACKNOWLEGEMENTS The Climate Prediction Center (CPC) is acknowledged for access to images of 30, 60 and 90-day plots of select cities in the United States. The National Climatic Data Center (NCDC) site was used to gain access to maximum temperatures set or tied for the month of July 2011. 6. RERERENCES
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Figure 1. Mean pattern over the United States and southern Canada from the NCEP GFS 00-hour forecasts for the period of 0000 UTC 1 July through 1800 UTC 31 July 2011. Data shown include a) 500 hpa heights (m) and standardized anomalies, b) 700 hpa temperatures ( C) and standardized anomalies, c) 850 hpa temperatures and standardized anomalies, and d) precipitable water (mm) and standardized anomalies. Standardized anomalies are shown in standard deviations from normal, 500 hpa heights are very 60m, 700 hpa temperatures every 5C, 850 hpa temperatures every 4C, and precipitable water is every 4 mm. Return to text.
Figure 2. Temperatures from May-July 2011 at Oklahoma City, Oklahoma. Upper panel shows the departure of the daily temperatures from the mean temperatures (black line), middle panel shows the daily departure and the lower panels show the daily high and low temperatures. Return to text. http://www.cpc.ncep.noaa.gov/products/global_monitoring/temperature/tn72353_90. gif
Figure 3. As in Figure 1 except for the period of 0000 UTC 16 through 1200 22 July 2011. Return to text.
Figure 4. As in Figure 1 except for the period of 0000 UTC 21 to 1800 UTC 23 July 2011. Return to text.
Figure 5. As in Figure 1 except for 0000 UTC 23 July 2011. Return to text.
Figure 6. NCEP/NCAR re-analysis data showing the mean a) 500 hpa heights and height anomalies and b) the 850 hpa temperatures and temperature anomalies for 0000 UTC 01 July though 1800 UTC 31 July 1955.
Figure 7. As in Figure 1 except for 0000 UTC 01 July 1980 through 1800 UTC 31 July 1980. Return to text.
Figure 8. As in Figure 1 except for 0000 UTC 1 July through 1800 UTC 31 July 1988. Return to text.
Figure 9. As in Figure 1 except for the mean pattern from 0000 UTC 03 July through 0000 UTC 8 July 2010. Return to text.
State Records Set PA 136 TX 129 KS 85 NY 78 MI 73 NC 59 WI 56 IN 52 VA 38 IL 36 OH 35 IA 34 NJ 32 WV 31 FL 24 Table 1. List of the number records set or tied by State from 17-24 July 2011. Data based on NCDC data set. Only States that set or tied 24 or more records during the period are listed. Return to text.
Date Number of records PA records 14-Jul 41 0 15-Jul 36 0 16-Jul 48 0 17-Jul 46 2 18-Jul 65 2 19-Jul 69 7 20-Jul 140 6 21-Jul 205 20 22-Jul 261 47 23-Jul 246 39 24-Jul 148 13 25-Jul 98 6 26-Jul 57 0 Table 2. Number of records exceed or tied by date and for the State of Pennsylvania. Return to text.
Figure 10. Temperatures (F) when temperature was a record or tied a record high. Red values are 100 or greater orange values are less than 100F. Data for the period of a) 19 to f) 24 July 2011. Return to text.
Figure 11. NCEP GEFS forecasts initialized at 0000 UTC 18 July 2011 showing conditions valid at 1800 UTC 22 July 2011 including a) the ensemble mean 500 hpa heights and the probability of +1.5SD height anomalies, b) ensemble mean 850 hpa temperatures and probability of 850 hpa temperatures exceeding 2.5SD above normal, c) ensemble mean precipitable water and the probability of precipitable water exceeding 2.0SDs above normal, and d) ensemble mean 2m temperatures and the probability 2m temperatures would be 2.5SDs above normal. Return to text.
Figure 12. As in Figure 11 except showing ensemble mean pattern and mean anomalies for the 72 hour period from 0000 UTC 21 to 0000 UTC 24 July 2011. Data include a) 72-hour mean 500 hpa heights and anomalies, b) 72-hour 700 hpa temperatures and anomalies, c) 72-hour mean 850 hpa temperatures and anomalies and d) 72-hour mean precipitable water and anomalies. Return to text.