Mid-West Heavy rains 18 April 2013

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1 Abstract: Mid-West Heavy rains 18 April 2013 By Richard H. Grumm and Charles Ross National Weather Service State College, PA The relatively wet conditions during the first 16 days of April 2013 set the stage for potential flooding over the Midwest. A strong frontal system and a strong ridge to the east pushed a plume of deep moisture and high values of precipitable water into the Mid-Mississippi Valley and Great Lakes region. This plume of moisture produced heavy rains, several areas received 50 to 100 mm in 12 hours and 75 to 175 mm in about 36 hours. The heavy rains produced flooding and disrupted transportation in towns and cities. The intense rainfall disrupted autos, rail, and air transportation in Chicago. As the water flowed into rivers and streams, it produced flooding along many rivers. The Grand River in western Michigan and the Illinois river in Illinois both had major flood and near record flooding. From a prediction perspective, both the pattern and the probability of heavy rainfall were relatively well predicted by the NCEP guidance systems. The GFS produced over 100m of QPF and the SREF showed a broad region to receive in excess of 100 mm of QPF.

2 1. Overview A surge of deep moisture ahead of a strong frontal system brought heavy rains to the Midwest. A large region from Columbia, MO northeastward to Chicago had heavy rainfall (Fig. 1). The heavy rains produced flooding in Chicago (Chicago Magazine 2013) and surrounding regions of Illinois. The heavy rains in Chicago flooded roads, closed interstates, and opened a massive sinkhole which consumed several cars (Chicago Magazine 2013, Huffington Post 2013). An examination of hourly rainfall data implied that showers and thunderstorm moved over northeastern Illinois after 1500 UTC on 17 April. The boundary the convection was along extended back into southern Iowa. A second surge of steady rainfall affected northeastern Illinois from around 0400 through 1200 UTC 18 April. The 3-hourly rainfall totals showed periods of rain in excess 1 inch per hour rainfall rates for in excess of 3 hours from northeast Missouri into northeastern Illinois. This resulted in the swath of heavy rainfall over the region as shown in Figure 1. Most of the rain in the Chicago area fell between 0600 and 1200 UTC on 18 April The event of 18 April produced over 4 inches of rain over broad regions (Fig. 1). These locally heavy rains combined with previous rainfall over northern Illinois likely provided good ideal antecedent conditions to produce flooding. Thus, after the flash flooding issues, the water found its way into rivers and streams resulting in river flooding. The Illinois River experienced record flooding which caused barges to break free damaging a dam near Marseilles, IL (ABC News Chicago 2013). The Illinois River peaked at 29.35ft at Peoria, topping a 70 year record (AP 2013). The AP stories reported about flooding coming to the Mississippi and flooding along rivers in western Michigan. The heavy rains produced flooding in Michigan. The Grand and Maple rivers exceeded flood stage and produced damage in portions of Michigan (The Republic Newspaper 2013). Major flooding due to the rains affected Iowa, Wisconsin, Illinois and Michigan (USA Today 2013). The wet spring combined with heavy rains likely produced ideal antecedent conditions for flooding. The conditions associated with the heavy rainfall were similar to those often associated with heavy rainfall in most regions of the northern hemisphere. The pattern included a strong downstream ridge with a deep upstream trough (Fig. 2a). At low-levels strong low-level southerly flow (Fig. 2b) and a plume of deep moisture (Fig. 2c) impinged upon the region. A surface trough was present (Fig. 2d) separating to strong and contrasting air masses. The heavy rainfall in the Midwest (Fig. 1) fell in the return flow of deep moisture about the downstream blocking ridge (Figs. 2c & 2a).

3 Forecasts of the frontal system and the rain event play a critical role in the ability to anticipate and thus appropriately act during an event. The NCEP models and ensemble forecasts systems provide forecasts of both the pattern and quantitative precipitation (QPF). An examination of QPFs is provided to see how well the heavy rainfall was forecast. This paper will examine the heavy rainfall of 18 April The focus is on the pattern and conditions in which the event developed and the resulting heavy rainfall over the Midwest. The focus is on the value of standardized anomalies to characterize the pattern and the value of QPF guidance from ensembles and high resolution models to better anticipate this and similar events in the future. 2. Data and Methods The large scale pattern was reconstructed using the 00-hour forecast of the NCEP Global Forecast System as first guess at the verifying pattern. The standardized anomalies were computed in Hart and Grumm (2001). All data were displayed using GrADS (Doty and Kinter 1995). The precipitation data was obtained from the NMQ-Q2 site and from the NCEP Stage-IV data flow. NMQ Q2 data were examined in 1, 3,6,12 and 24 hour period to define the period of heavy rainfall. The Stage-IV data was examined using 6-hourly data. NCEP models and ensembles were used to compute the QPF and probabilities of QPF exceeding critical thresholds. Radar data from the local AWIPS archive were used to make images of the radar evolutions. 3. Pattern over the region The regional PW pattern shows the surge of high PW air into the Mid-Mississippi Valley (MMV) and toward the Great Lakes on April 2013 (Fig. 3). The surge of high PW air (Fig. 3) came on strong low-level southerly flow (Fig. 4). The 850 hpa winds were 2-3σ above normal in the MMV ahead of the frontal system (Fig. 3). The strong low-level winds and high PW air produced a surge of high moisture flux (MFLUX) and moisture flux anomalies in the MMV and Great Lakes region. The MFLUX anomalies peaked over +6σ above normal (Fig. 5), a condition often associated with heavy to near record rainfall amounts. These data suggest a strong frontal system and deep moisture were present to produce a potentially high end rainfall event. If the guidance could predict the pattern there was some hope that the guidance could predicted the heavy rainfall. 4. Forecasts

4 The focus here is on the SREF forecasts. Most systems examined, including the SREF, GEFS,GFS and NAM all forecast a similar large scale pattern and thus each predicted the potential for heavy rainfall. The focus here is on the SREF with a few examples from other systems to reinforce these data. The SREF PW and 850 hpa winds and v-winds anomalies (Figs. 6-7) show that the SREF correctly predicted the surge of deep moisture into the MMV and the strong low-level southerly winds. Thus the SREF was able to predict the larger scale pattern relatively well and due to a convergence of solutions, both the PW and v-wind anomalies were relatively large. Similar anomalies and patterns were predicted by the NAM, GFS, and GEFS but are not shown. The resulting probability of 50mm of QPF and mean QPF for the 36 hour period ending at 1200 UTC 19 April 2013 show that the SREF predicted large area which could receive in excess of 50 mm (2 inches) of QPF (Fig. 8). The run-to-run inconsistencies reflected some uncertainty with the location and intensity of the frontal system over the MMV and Great Lakes. Thus, the axis of heavy rainfall and probabilities of over 50 mm showed some variability moving 50 to 200km between runs. The corresponding mean QPF (Fig. 9) and each members 50mm contour showed the extent of the precipitation shield and the potential area to be affected by heavy rainfall in in SREF atmospheres. The axis of heavy rainfall extended from Missouri into Michigan but did vary from run-to-run. The 24-hour probability of 50mm of QPF (Fig. 10) showed heavy rainfall was predicted to fall over the 24 hour period of 18/0000 to 19/0000 UTC. Most of the rainfall was predicted generally west of Chicago. The heavy rainfall focus from 18/1200 to 19/1200 UTC (Fig. 11) was forecast to shift to the east of Chicago, focusing on Michigan southward into Illinois and Indiana. These latter forecasts drop off the 15 April SREF showing the 18 April SREFs prior to 1200 UTC showing how the forecasts continued to incrementally improve as forecast length decreased. The NCEP GFS showed the potential for heavy rainfall (Fig. 12) in the warm sector of the strong frontal system. The start time was staggered to allow the 18/0000 UTC to be employed. These data show forecasts by 19/1200 UTC of 50 to 100 mm in every GFS cycle presented. Several forecasts show over 100mm of QPF in the 30 hour period. Similar to the SREF, the axis of heavy QPF shifted from run-to-run showing the uncertainty in the forecasts. 5. Rainfall Figure 1 showed the total rainfall over the region for the 3-day period. These data showed the heaviest rainfall extended in two distinct bands. The larger band extended from northern Missouri across Illinois into western Michigan. A large portion of this region was covered by the 100 mm contour with some embedded regions of 125 to 175mm of precipitation. A smaller band was present over northeastern Kansas into Iowa.

5 The 24-hour rainfall values (Fig. 13) ending at 1200 UTC locally each day show that the big rainfall periods included 1200UTC April and 1200 UTC April The 12-hour data further refined the period of heavy rainfall in (Fig. 14) showing heavy rainfall over Iowa from 1200 UTC 17 to 0000 UTC 18 April 2013 and heavy rainfall over northeastern Missouri into northern Illinois and western Michigan from 0000 UTC to 1200 UTC 18 April Additional rain fell over Michigan in the following two 12-hour period with about 25mm of additionally rainfall by 1200 UTC 19 April (Fig. 14d). The key point is most of the rainfall came in a short period. 6. Summary A strong frontal system and strong flow of deep moisture about a ridge over the western Atlantic produced heavy rainfall from April 2013 over the Midwest. The heaviest rain fell over Iowa and Missouri northeastward across Illinois and Michigan. The heavy rains produced flooding in Chicago and many towns and urbanized regions disrupting transportation. As the water drained into streams and rivers, it led to flooding and areas along the Illinois and Grand rivers it lead to record flooding. All of the SREF QPFS (Figs. 8-11) show that these forecasts implied the SREF improved the amount and region to be affected by heavy rainfall as the forecast length decreased. The shorter range SREF on 18 April showed higher heavy rainfall threat once the rain moved East of Chicago for portions of Michigan and Indiana (Fig. 11). Overall, the NCEP guidance did well predicting the potential for heavy rainfall. This combined with previous rainfall set the stage for the flooding and record river flooding in Illinois and Michigan Figure 14 shows that most of the rainfall came in a short period. Most locations received upward to 80% of the event total rainfall in about 12 hours. This likely contributed to the flooding issues in urban regions like Chicago where roads and underpasses flooded. This also likely played a role in sink hole issues and disruptions to both air and land based transportation. The overall pattern of the rainfall (Figs 1 & 12), covering the entire Illinois River basin, likely contributed to the river flooding issues over the days after the rain ended. The total rainfall from 1-16 April over the region was in the 75 to 100 mm range (not shown) implying that most of the region from Missouri to Wisconsin, Illinois, Indian, and Michigan was relatively wet. This may have led to higher base flows on rivers and a reduced capacity for runoff. Thus, the swath of 75 to 100 mm of rainfall (Fig. 1) in addition to rainfall earlier in the month indicated wet conditions (Fig. 15) with a broad region of from northeastern Kansas to Michigan receiving over 100 mm of rainfall during the first 20 days of April. Within this broad area of 100 mm there were embedded area of 175 mm of rainfall and a few locations were the 20 day totals exceeded 250 mm of rainfall. The areas covered by both the Grand and Illinois rivers each had over 175 to 200 mm of rainfall (Fig. 15) during the first 20 days of April. The event of

6 18 April accounted for over 50% of the total rainfall but the overall data suggests that antecedent conditions implied a high threat for flooding. 7. Acknowledgements 8. References Associated Press 2013: Midwest awaits retreat of floods, bloated rivers. 24 April And related stories. Doty, B.E. and J.L. Kinter III, 1995: Geophysical Data Analysis and Visualization using GrADS. Visualization Techniques in Space and Atmospheric Sciences, eds. E.P. Szuszczewicz and J.H. Bredekamp, NASA, Washington, D.C., The Republic Newspaper, 2013: Grand River in West Michigan receding after record-setting flooding leves; cleanup taking place. The Republic, Columbus, Indiana. USA Today, 2013: Worst Flooding many not be over and related stories. 23 April 2013.

7 Weaver, S. C., and S. Nigam, 2008: Variability of the Great Plains low level jet: Large scale circulation context and hydroclimate impacts. J. Climate,21, Figure 1. Estimated rainfall (in) for the event from 1200 UTC 17 to 1200 UTC 20 April 2013 from 6-hour stage-iv data. Return to text.

8 Figure 2. GFS 00-hour forecasts valid at 0600 UTC 18 April 2013 showing a) 500 hpa heights and height anomalies, b) 850 hpa winds and v-wind anomalies, c) precipitable water (mm) and precipitable water anomalies, and d) mean sea level pressure and pressure anomalies. The black dot in panel a is the location of Chicago. Return to text.

9 Figure 3. NCEP GFS 00-hour forecasts in 6-hour increments showing the precipitable water (mm) and the precipitable water anomalies for a) 1200 UTC 17 April, b) 1800 UTC 17 April, c) 0000 UTC 18 April, d) 0600 UTC 18 April, e) 1200 UTC 18 April and f) 1800 UTC 18 April Contours every 5mm and anomalies as in the color bar. Return to text.

10 Figure 4. As in Figure 3 except for 850 hpa wind and v-wind anomalies. Return to text.

11 Figure 5. As in Figure 4 except for 850 hpa moisture flux. Return to text. NWS State College Case Examples

12 Figure 6. As in Figure 3 except for NCEP SREF ensemble mean precipitable water and anomalies valid at 0000 UTC 19 April 2013 from SREF initialized at a) 0900 UTC 15 April, b) 2100 UTC 15 April, c) 0900 UTC 16 April, d) 2100 UTC 16 April, e) 0900 UTC 17 April and f) 2100 UTC 17 April Return to text.

13 Figure 7. As in Figure 6 except for SREF 850 hpa winds and v-wind anomalies. Return to text.

14 Figure 8. As in Figure 6 except for SREF probabilities of 50mm or more QPF in the 36 hour period ending at 1200 UTC 19 April The mean 50mm contour is thick black and probabilities are as in the color bar. Return to text.

15 Figure 9. As in Figure 8 except for the ensemble mean QPF (shaded) and each member s 50 mm contour (colored) and the thick black contour sis the ensemble mean 50 mm contour. Return to text.

16 Figure 10. As in Figure 8 except for 24 hour probabilities valid at 0000 UTC 19 April Return to text.

17 Figure 11. As in Figure 10 except from SREF initialized at a) 0900 and b) 2100 UTC 16 April; c) April and d) 2100 UTC 17 April, and e) 0300 UTC 18 April a f) 0900 UTC 18 April Return to text.

18 Figure 12. NCEP GFS accumulated QPF (mm) showing the QPF in the period of 0600 UTC 18 April through 1200 UTC 19 April GFS forecsats from a) 0000 UTC 16 April, b) 1200 UTC 16 April, c) 0000 UTC 17 April, d) 1200 UTC 17 April, e) 1800 UTC 17 April, and f) 0000 UTC 18 April Data are staggered to 0600 UTC to show the input provided by a recent forecast for the period of heavy rainfall. Return to text.

19 Figure 13. As in Figure 1 except rainfall estimates in 24 hour periods ending at 1200 UTC a) 16 April, b) 17 April, c) 19 April, and d) 20 April Values in mm as indicated by the color scale. Contours 25,50,100,150 and 200mm. Return to text.

20 Figure 14. As in Figure 13 except for 12 hour rainfall amounts for the 12 hour periods ending at a) 0000 UTC 18 April, b) 1200 UTC 18 April, b) 0000 UTC 19 April and d) 1200 UTC 19 April Return to text.

21 Figure 15. Total rainfall 1-20 April 2013 ending 0000 UTC 20 April Values in mm (color key) and contours 25,50,100,150,200,250,300 mm. Return to text.