The Use of Ensemble and Anomaly Data during the 13-16 May 2006 New England Record Rain

Event

Neil A. Stuart Richard Grumm Walter DragNOAA/NWS Albany, NY NOAA/NWS State College, PA NOAA/NWS

Taunton, MA

Northeast Regional Operational Workshop VIIIAlbany, 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 1996 May 2006

Type A – Atlantic Flow Wind Anomalies

October 1996 May 2006

Type B – Gulf/Tropical Origins Wind and PW AnomaliesOctober 2005 June 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 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: Http://eyewall.met.psu.edu

Questions?