The Use of Ensemble and Anomaly Data during the May 2006 New England Record Rain Event Neil A. Stuart Richard Grumm Walter Drag NOAA/NWS Albany, NY NOAA/NWS State College, PA NOAA/NWS Taunton, MA Northeast Regional Operational Workshop VIII Albany, NY 1 November 2006

Overview – Heavy rain events studied October 1996 > 12” of rain in part of southern and eastern New England Major flooding in eastern MA, NH and ME

Overview – Heavy rain events studied October 2005 Phase I 8-12” of rain interior northeast U.S. and New England Major flooding in eastern NY, and much of western and central New England

Overview – Heavy rain events studied October 2005 Phase II 8-12” of rain for large part of New England Major flooding across the New England Region

Overview – Heavy rain events studied May 2006 > 12” of rain in eastern New England Major flooding in eastern MA, NH and ME

Overview – Heavy rain events studied June 2006 > 12” of rain in the interior northeast U.S. Major flooding in interior PA, NY

Overview Compared May 2006 with 3 other cases Two large scale patterns identified that support flooding warm season rains No cold season cases with snow melt involved No weakly-forced, localized summer time convective flood events Focus on widespread synoptic scale events Newly developed forecast products to evaluate heavy rain potential

Type A – Atlantic Flow MSLP and PW Anomalies October 1996May 2006

Type A – Atlantic Flow Wind Anomalies October 1996May 2006

Type B – Gulf/Tropical Origins Wind and PW Anomalies October 2005June 2006

One more important note about October 2005 Transition from Gulf/Tropical event to Atlantic flow event Note the PW anomalies and timing of rainfall distributions

Some selected guidance products Short Range Ensemble Forecast Probability of 2.00” of rain in 36 hours Short Range Ensemble Forecast Probability of 2.00” of rain in 84 hours

Some selected guidance products 12Z 10 May 2006 SREF Plume Diagram – Precipitation Accumulation for Boston, MA 12Z 11 May 2006 SREF Plume Diagram – Precipitation Accumulation for Boston, MA 12Z 12 May 2006 SREF Plume Diagram – Precipitation Accumulation for Boston, MA

Conclusions 2 Types of events Type A – Atlantic flow Upper system cut off from steering flow = slow moving system Anomalously strong southeast low-level flow – –Anchored surface high pressure in SE Canada – –Strong surface low pressure in Great Lakes or Ohio Valley in weak steering flow – –Extreme 850 hPa U and V wind anomalies (≥ |4SD| for U, V or both directions) Anomalously high Precipitable Water values (≥ 1.5SD) Persistent long-duration combination of extreme low- level wind anomalies and Precipitable Water

Conclusions (cont.) Type B – Gulf and Tropical Origins Slowly moving large scale upper trough approaching from the Midwestern U.S. Smaller short wave(s) of energy track in weak flow on eastern side of upper trough Extreme S to SW 850 hPa wind anomalies associated with smaller short wave(s) (≥ 4SD V winds) Extreme Precipitable Water anomalies (≥ 1.5 SD, but often ≥ 2.0 SD with tropical cyclones or remnants) Often associated with tropical system or its remnants in the late summer and autumn

Conclusions (cont.) Clues in Medium Range and Short Range Ensemble Forecast Model Guidance (MREF and SREF) Co-location of anomalously high precipitable water and 850 hPa wind maximum Probability for 2.00” of rain and spread for 36 hours or time period that spans the entire event Areal extent of 2.00” probability contour less important as the fact it exists Any probability above 50% lends very strong confidence of 2.00” or more Can at least double local rainfall amounts depending on expected intensity, duration and orography Spread shows # of members forecasting ≥ 2.00” – Accounts for masking of areal extent in probabilities Plume diagrams - time sequence of QPF for each ensemble member - affects confidence in QPF forecast Be careful to consider the NWP model characteristics – SREF mainly NAM/WRF and MREF is GFS

Thank You! Real-time anomalies, plumes and probabilities can be found at: Questions?