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1 New England Record Maker Rain Event of March 2010 By Richard H. Grumm National Weather Service Contributions by Frank Nocera National Weather Service Office Taunton, MA 1. INTRODUCTION The second of two significant nor easters affect the northeastern United States struck on March The combined effects of these two storms, the first occurring on March 2010 led to many locations in southern New England setting new monthly rainfall records. The second storm produced record flooding in Rhode Island and Massachusetts. The total rainfall from the unified precipitation data for the event is shown in Figure 1. These data show around 128 mm (~5 inches) of rainfall in the gridded data from eastern Long Island into eastern Massachusetts. A small region of Rhode Island, near Providence, had mm contour over it. This heavy rainfall led to record flooding in Rhode Island which closed portions of I-95 and cause Amtrak 2 to cancel trains. Records for the event included 1.96 and 2.93 inches at Logan Airport on 29 and 30 March respectively. The monthly total at Logan was inches making March 2010 the wettest March on record and the second month on record, behind the set in the famous 3 tropical August of Blue Hill set a record of inches eclipsing the August set in At Providence 5.32 inches of rainfall was observed on 30 March which was the 5 th largest daily rainfall record for the site. The two day total (30-31 March) was 8.79 inches breaking the previous all-time record of 1 Due to UTC time the went passed 0000 UTC 31 March. Local time used in text to define dates. 2 Wall Street Journal article on the storm. 3 From KBOX Record Event report of 31 March inches set on October Providence set a new all-time monthly record of inches breaking the previous record of inches set October Worcester had its second wettest March on record with inches compared to set in March Worcester had 1.67 and 2.43 inches on the 29 th and 30 th respectively. Figure 2 shows the 24- hour rainfall for the days that encompassed the event. This devastating heavy rainfall event had all the signals indicative a significant heavy rainfall event. Based on the work of Stuart and Grumm (2009) and Maddox et. al. (1979) this event possessed to classic characteristics of a heavy rainfall event. Early in the event the sharp northsouth frontal and moisture zone had a synoptic event type pattern. The atmospheric River (Neiman et al 2008) along the coast brought heavy rains to the region. The PW surge had above normal PW anomalies and above normal v-wind anomalies. It will be shown that as the surface cyclone rolled up the frontal boundary, the event transitioned into a frontal system (Maddox et al 1979) and the strong easterly winds focused the heavy rainfall in the region of this strong and anomalous easterly jet (Stuart and Grumm 2009). This event had persistent and anomalous moisture and anomalous southerly and then easterly flow, all the ingredients for a significant heavy rainfall event (Doswell et. al 1996). From a prediction perspective, it will be shown that the NCEP models and ensemble prediction systems correctly predicted the pattern and anomalies. The value of ensembles and anomalies of key ingredients associated with heavy rainfall were demonstrated by Junker et al (2009). Other studies have shown the value of

2 Figure 1 Total observed liquid precipitation (mm) from 1200 UTC 29 March through 1200 UTC 31 March From the unified precipitation data set. Return to analysis section. anomalies in identifying and predicting heavy rainfall events (Hart and Grumm 2001; Grumm and Hart 2001; Graham and Grumm 2010; Stuart and Grumm 2006;Junker et al 2008). This case is a classic case on the value of anomalies in identifying a potentially significant heavy rainfall event. The NCEP short range ensemble forecast system (SREF) is used to show the probability of heavy rainfall associated with this event. Though the 32km SREF would likely under predict the local maximum rainfall, it did well in predicting the pattern, distribution and probability of heavy rainfall. This paper will document the historic rainfall and fooding event of March The focus is on the pattern and anomalies associated with this meteorologically and climatologically significant event. Some forecasts from the NCEP models and ensemble forecast systems (EFS) are presented to show the value of ensembles in the forecast process. 2. METHODS AND DATA The 500 hpa heights, 850 hpa temperatures and winds, other standard level fields were derived from the NCEP GFS, GEFS, and the NCEP/NCAR (Kalnay et al. 1996) reanalysis

3 Figure 2. As in Figure 1 except showing the 24-hour precipitation ending at a) 1200 UTC 28 March, b) 1200 UTC 29 March 2010, c) 1200 UTC 30 March and d) 1200 UTC 31 March data. The means and standard deviations used to compute the standardized anomalies were from the NCEP/NCAR 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 standardized anomalies computed as: SD = (F M)/σ ( ) Where F is the value from the reanalysis data at each grid point, M is the mean for the specified date and time at each grid point and σ is the value of 1 standard deviation at each grid point.

4 Figure 3.GFS 00-hour forecasts of 500 hpa heights (m) and 500 hpa height anomalies (standard deviations) valid at a) 0000 UTC 29 March, b) 0600 UTC 30 March, c) 1200 UTC 30 March, d)1800 UTC 29 March, e) 0000 UTC 30 March, f) 0600 UTC 30 March, g) 1200 UTC 30 March, h) 1800 UTC 30 March and i) 0000 UTC 31 March Model and ensemble data shown here were primarily limited to the GFS and GEFS. The 1.25x1.25 degree JMA data may be used when it becomes available. The NAM and SREF data were also available for use in this study. Displays will focus on the observed pattern and some forecast issues associated with the pattern. For brevity, times will be displayed in day and hour format such at 31/0000 UTC signifies 31 March 2010 at 0000 UTC. 3. RESULTS i. Synoptic scale pattern

5 The larger scale pattern is shown in Figures 3-5. These data show the short-wave length and high amplitude 500 hpa trough moving over the region (Fig. 3) with -1 to -2SD height anomalies. To the east of this upper-level system, a plume of high PW air (Fig. 4) was pulled into the region. The PW plume showed a strong subtropical connection and contained PW values over 32 mm as far north as New Jersey with 2 to 4SD above normal PW values in this plume or atmospheric river (AR: Neiman et. al 2008 & 2002; Ralph et al. 2006) of high PW air. The 500 hpa trough cut-off over the northeastern United States around 30/0600 UTC and then lifted slowly to the north and east though 31/0000 UTC (Figs. 3f-i). The initial jet along the coast was elongated from south to north (Fig. 5) but weakened over the northeastern United States as the system cut-off. The impressive feature at 250 hpa was clearly the strong Pacific jet to the west which flooded the United States with relatively warm Pacific air and would usher in an early season warm episode later in the week over much of the eastern United States. ii. Regional pattern and anomalies The regional depiction is presented by the NAM 00-hour analysis. The NAM surface pressure field for the period of 29/0000 UTC through 31/0000 UTC is shown in Figure 6. The accompanying 850 hpa winds and u-wind anomalies are shown in Figure 7. These data show a weak cyclone in the Ohio Valley with a trailing front at 29/0000 UTC. Though not shown, a surge of cold air pushed below normal 850 hpa temps into the Gulf States which was associated with the cyclogenesis to the south (Fig. 6a-d) which produced the cyclone which rolled up the coast on the 30 th (Figs 6e-h). The initial heavy rainfall on the 29 th was associated with the approaching cyclone and the enhanced southerly flow. The 850 hpa wind and v-wind anomalies showed 3 to 4 and at times 4-5 SD v-wind anomalies from Maryland into southern New England (Fig. 7a-d). The first phase of the rainfall was dominated by this surge of strong southerly flow and the high PW air iii. along this zone (Fig. 4). Lacking a strong frontal zone in a thermal context, the system had a strong moisture zone oriented from south to north. This strong low-level jet was embedded in this moisture zone. The development of the strong 850 hpa easterly jet north of the advancing cyclone (Fig. 8f-8i) focused the heavy rainfall on the 30 th over New Jersey, Long Island and southern New England (Fig. 2d). Interestingly the period of heavy rainfall on the 30 th was associated with the strong southeasterly jet and -3 to -5 SD u-wind anomaly into southern and eastern New England. Figure 9 shows the NAM PW and PW anomalies for the event. These data show the AR moving up the coast with the surge of strong southerly winds. The PW anomalies are 2-3SDs above normal as the v-winds peak over New England (Figs 9b-9e). As the cyclone develops and the easterly winds increase, the PW field pivots over New England and Long Island (Figs. 9e-h) and then lifts to the north as the cyclone and u-wind anomalies slowly lift to the northeast. The PW field clearly shows the double whammy over Long Island and southern New England. Forecasts-GEFS The ensemble mean here is clearly an under use of ensemble data. It is used here to illustrate the forecast of the pattern, not the correct or most effective use of EFS data. But it illustrates the point about how relatively predictable and well predicted this event was. The large scale PW plume from 9 GEFS forecasts is shown in Figure 10. These data show the AR as forecast by GEFS valid at 29/1200 UTC. The key point is that the GEFS correctly predicted the AR to surge up the coast. Subsequent forecasts show the inflection of the AR with time. Relative to the NAM PW analyses, these data suggest that the GEFS correctly predicted the large scale pattern. Though not shown, the GEFS also forecast the strong southerly winds within the moisture plume.

6 Figure 4. As in Figure 3 except for precipitable water (mm) and precipitable water anomalies. The GEFS 850 hpa winds are shown at 30/1200 UTC (Fig. 11) as the event was transitioning from a north-south to more east-west oriented event. Due to uncertainty issues (large spread), the longer range forecasts (Fig. 11a-c) did not depicted the strong wind anomalies. As the forecasts converged and the spread decreased, the GEFS showed larger total wind anomalies and a significant south-south east jet into New England (Figs. 11e-i). Probabilities would likely improve upon evaluating this situation. The ensemble mean QPF for the event valid at 31/1200 UTC is shown in Figure 12. These data show the impact of the first surge of rain with the Maddox Synoptic event with an elongated North- South axis of heavy rainfall. Clearly, these coarse data underestimated the potential maximum rainfall and they produced too much rainfall too far to the west. They correctly showed the potential for a heavy rainfall and correctly outlined the general threat region quite well.

7 Figure 13 is a better and more effective use of the EFS data as its show the probability of 4 inches or more QPF and each member s 4 inch contour. The shorter range forecast converged on the potential for a wider area of 4 or more inches of QPF. Note prior that forecasts from both 26 and 27 March (not shown) indicated some potential for over 4 inches of QPF in the same general time window. Due to uncertainty issues it was a low probability outcome event. iv. SREF forecasts The SREF predicted the event with comparable skill to that of the GEFS. However with higher resolution it predicted locally higher QPF amounts. The SREF QPF probabilities valid for the period ending at 31/0000 UTC are shown in Figure 14. These data show that the heavy rainfall (Fig.14a) was focused over New Hampshire and Maine and that during the past 24, 30, and 36 hours, heavy rainfall was supposed to affect southern New England and Long Island. The ensemble mean 4 inch contour is shown in Figure 14d. The area encompassed by the 4 inch contour was quite extensive. Other SREF cycles showed comparable skill with the QPF threat area. This due to the SREF s ability to correctly predict the pattern, illustrated in Figure15. These data show the probability of the 850 hpa u-winds to be -2.5SDs below normal (Fig. 15a) the probability of the 850 hpa total winds to be +2.5SDs above normal (Fig. 15b), the probability of the PW to be 2SDs above normal along with the 6.25 and 25mm mean contours (Fig. 15c) and the probability of the mean sealevel pressure being -1.5 SDs below normal. These data show a classic high probability of key features associated with heavy rainfall over southern New England.. 4. CONCLUSIONS A record breaking rain event affected Long Island, New Jersey and southern New England on March The storm brought over 4 inches of rainfall to a large swath of the region and locally produced in excess of 8 inches of rainfall over Long Island, Rhode Island and Massachusetts. The rain led to widespread flooding in southeastern New England. Rhode Island experienced what was reported as the worst flooding in over 200 years. The pattern and the QPF were relatively well predicted by the NCEP ensemble forecasts systems and provided good clues to the potential for this record event. The heavy rain ending at 29/1200 and 30/1200 UTC (Fig. 2) was primarily associated with the strong southerly flow (Fig. 7) and surge of high PW air in this moisture zone (Fig. 9). This produced locally mm of rainfall over eastern Long Island and Rhode Island (Figs. 2b-2c). This was in an impressive event in and of itself. The event had a classic Maddox Synoptic signature. The transition from a Maddox Synoptic to Maddox frontal type system produced the second round of heavy rainfall on 30 March (Fig. 2d). The developing strong easterly jet and strong u-wind anomalies and implied strong moisture flux indicated the potential for heavy rainfall. Figure 9 clearly shows that evolution of the moisture field with an inflection in the high PW plume or AR as the easterly jet pulled the moisture westward, pivoting it over eastern Long Island and southeastern New England. This led to the record rainfall on the 30 th (ending in Figure 2 on 31 March) and the devastating 2 day rainfall totals. This double whammy led to the historic flooding in Rhode Island.. It should be noted that in the cold season the normal or more common transition is from easterly flow too southerly flow produces heavy rainfall in the eastern United States. The April 2007 event was classic example of this type of evolution (Stuart and Grumm 2009). The event of March 2010 fit the archetype of the 2 primary rainfall events observed over the eastern United States. The unique aspect of this event was the transition from a north-south oriented event to a more east west oriented event. This latter evolution is more common in the warm season and can produced extremely heavy rainfall such as that observed in the June 2006 heavy rain and flood event in the eastern United States (Stuart and Grumm 2009). The forecast guidance shown here suggested that the NCEP GEFS and SREF both did relatively well

8 predicted a pattern conducive to heavy rainfall. They both predicted strong southerly flow with an AR moving into the region. Then the development of an easterly jet north of the cyclone which developed along the north-south frontal zone. This transition from a Maddox Synoptic to Frontal type produced two periods of heavy rainfall which the guidance predicted quite well. The data in Figure 14 illustrated the problem with interpreting QPF, it is the time the forecast ends at. In Figure 14a, the heavy rainfall was forecast to move north of the region of significant flooding. The accumulated images showed the regions where the forecast indicated that the heaviest rainfall should have fallen. These data captured the time wind and threat for heavy rainfall. One of the more impressive features in Figure 14 was the 4 inch mean contour in Figure 14d. Though an underestimate, it showed the high threat for excessive rainfall in the 32km SREF and in the correct general area. A higher resolution model would likely have shown higher QPF values. Clearly, it would be of considerable value to know the climatology of heavy rainfall in the SREF and thus know when the SREF is forecasts a record event. An important piece of forecast information that is missing in the forecast process. Figure 15 showed the probabilities of exceedance of key parameters associated with heavy rainfall. Based on studies by Grumm and Hart (2001) and Stuart and Grumm (2006 & 2009) these exceedance images were developed. A limited set was shown here, however, these data illustrate the potential to show the threat of weather events by type based on past histories. A comparative image for the high and heavy rainfall event of March 2010 is shown in Figure 16. These data showed a large area encompassed by the -2.5SD u-wind anomalies and the +2.5SD total 850 hpa wind anomalies. The event of March lacked the surge of high PW air found in the March events. The earlier event also had a deeper surface cyclone. Figures 15 & 16 illustrate the value of ensembles to focus on identifying high probability outcomes of specific weather event types. This could be accomplished for a range of weather event types over the entire globe. One thing that could improve these data is the ability, especially with the QPF fields, to compare the current forecasts to the models internal climatologies. This would allow the forecaster to determine if an event will potentially be meteorologically and climatologically significant and meteorologically and climatologically significant relative to the forecasts systems internal climatology. 5. Acknowledgements The National Weather Service Office in Taunton, MA for data and insights into the event.

9 Figure 5. As in Figure 3 except for 250 hpa winds (kts) and wind anomalies. 6. REFERENCES Colle, B.A., F. Buonaiuto, M.J. Bowman, R.E. Wilson, R. Flood, R. Hunter, A. Mintz, and D. Hill, 2008: New York City's Vulnerability to Coastal Flooding. Bull. Amer. Meteor. Soc., 89, Colle, B.A., K. Rojowsky, and F. Buonaiuto, 2010: New York City Storm Surges: Climatology and an Analysis of the Wind and Cyclone Evolution. J.Appl. Meteor. Climatol., 49, Doswell,C.A.,III, H.E Brooks and R.A. Maddox, 1996: Flash flood forecasting: An ingredients based approach. Wea. Forecasting, 11, Doty, B. E., and J. L. Kinter III, 1995: Geophysical data and visualization using GrADS. Visualization Techniques Space and Atmospheric Sciences, E. P. Szuszczewicz and Bredekamp, Eds., NASA,

10 Graham, RA. And R.H. Grumm 2010: UTILIZING NORMALIZED ANOMALIES TO ASSESS SYNOPTIC SCALE WEATHER EVENTS IN THE WESTERN UNITED STATES. Wea. Fore,25, Inp ress. Grumm, R.H. and R. Hart. 2001: Standardized Anomalies Applied to Significant Cold Season Weather Events: Preliminary Findings. Wea. and Fore., 16, Grumm, R.H., and R. Hart, 2001a: Anticipating Heavy Rainfall: Forecast Aspects. Preprints, Symposium on Precipitation Extremes, Albuquerque, NM, Amer. Meteor. Soc., Grumm, R.H., and R. Holmes, 2007: Patterns of heavy rainfall in the mid-atlantic. Pre-prints, Conference on Weather Analysis and Forecasting,Park City, UT, Amer. Meteor. Soc., 5A.2. Grumm, Richard H. 2000, "Forecasting the Precipitation Associated with a Mid-Atlantic States Cold Frontal Rainband", NWA Digest,24, Hart, R. E., and R. H. Grumm, 2001: Using normalized climatological anomalies to rank synoptic scale events objectively. Mon. Wea. Rev., 129, Junker, N.W., R.H. Grumm,R.H. Hart, L.F Bosart, K.M. Bell, and F.J. Pereira, 2008: Use of normalized anomaly fields to anticipate extreme rainfall in the mountains of northern California.Wea. Forecasting, 23, , M.J. Brennan, F. Pereira, M.J. Bodner, and R.H. Grumm, 2009: Assessing the Potential for Rare Precipitation Events with Standardized Anomalies and Ensemble Guidance at the Hydrometeorological Prediction Center. Bull. Amer. Meteor. Soc., 90, Lackmann, G. M., and J. R. Gyakum, 1999: Heavy cold-season precipitation in the northwestern United States: Synoptic climatology and an analysis of the flood of January Wea. Forecasting, 14, Maddox,R.A., C.F Chappell, and L.R. Hoxit. 1979: Synoptic and meso-alpha aspects of flash flood events. Bull. Amer. Meteor. Soc., 60, Neiman, P.J., F.M. Ralph, G.A. Wick, J. D. Lundquist, and M. D. Dettinger, 2008: Meteorological characteristics and overland precipitation impacts of atmospheric rivers affecting the west coast of North America based on eight years of SSMI/satellite observations. J. Hydrometeor., 9, Neiman, P.J., F.M. Ralph, A.B. White, D.E. Kingsmill, and P.O.G. Persson, 2002: The Statistical Relationship between Upslope Flow and Rainfall in California's Coastal Mountains: Observations during CALJET. Mon. Wea. Rev., 130, Ralph, F. M., G. A. Wick, S. I. Gutman, M. D. Dettinger, C. R. Cayan, and A. B. White, 2006: Flooding on California s Russian River: The role of atmospheric rivers. Geophys.Res. Lett., 33, L13801, doi: /2006gl Stuart, N. and R. Grumm 2009, "The Use of Ensemble and Anomaly Data to Anticipate Extreme Flood Events in the Northeastern United States", 33,

11 Stuart, N.A., and R.H. Grumm, 2006: Using Wind Anomalies to Forecast East Coast Winter Storms. Wea. Forecasting, 21, Figure 6. As in Figure 3 except for NAM 00-hour forecasts of mean sea-level pressure (hpa) and pressure anomalies valid at valid at a) 0000 UTC 29 March, b) 0600 UTC 30 March, c) 1200 UTC 30 March, d)1800 UTC 29 March, e) 0000 UTC 30 March, f) 0600 UTC 30 March, g) 1200 UTC 30 March, h 1800 UTC 30 March and i) 0000 UTC 31 March Return to text.

12 Figure 7. As in Figure 6 except NAM 850 hpa winds and v-wind anomalies. Return to text.

13 Figure 8. A s in Figure 7 except for 850 hpa winds and u-wind anomalies. Return to text.

14 Figure 9.As in Figure 8 except NAM PW forecasts for the times shown. Return to text.

15 Figure 10. GEFS ensemble mean forecasts of PW and PW anomalies valid a 1200 UTC 29 March 2010 from forecasts initialized at a) 1800 UTC 25 March, b) 0600 UTC 26 March, c) 1800 UTC 26 March, d) 0000 UTC 27 March, e) 0600 UTC 27 March, f) 1200 UTC 27 March, g) 1800 UTC 27 March, h) 0000 UTC 28 March and i) 0600 UTC 28 March Return to text.

16 Figure 11. As in Figure 10 except for GEFS 850 hpa winds and total wind anomalies. Return to text.

17 Figure 12. As in Figure 11 except showing the mean total accumulated QPF (mm) from the GEFS for the forecasts ending at the times presented in Figure 10. Return to text.

18 . Figure 13. GEFS forecasts of QPF from forecasts initialized at (left) 1200 UTC 28 March and (right) 0000 UTC 29 March Data shown include (upper panels labeled a) the probability of 4.00 inches or more QPF in the 48 hour period ending at 0600 UTC 31 March. Lower panels (b) show the ensemble mean QPF and each member s 4.00 inch contour. Return to text.

19 Figure 14. NCEP SREF initialized at 0900 UTC 29 March 2010 showing the probability of a) 12 mm of QPF in 12 hours, b) 25 mm in 24 hours, c) 35mm in 30 hours, d) 50mm in 36 hours for the period ending at 0000 UTC 31 March Shading shows probability and contours in 4 inch increments are drawn where applicable. Return to text.

20 Figure 15.As in Figure 14 except SREF probability forecasts valid at 1500 UTC 30 March 2010 showing a) the probability of 850 hpa u-winds of -2.5SD or lower anomalies, b) the probability of the 850 hpa wind being +2.5 SDs above normal, d) the probability of the precipitable water being +2SDs above normal along with the 6.25 and 25mm contours, and d) the probability of the mean sea level pressure anomalies -1.5SDs or lower and the 996, 1008 and 1020 contours.

21 Figure 16. As in Figure 15 except valid at 0000 UTC 14 March 2010 for the rain event of March Return to conclusions.

22 Figure 17. No longer used QPF for 13 March event.

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