Climatology and Predictability of Cool-Season High Wind Events in the New York City Metropolitan

and Surrounding Area

Michael LayerSchool of Marine and Atmospheric Sciences

Stony Brook UniversityStony Brook, NY

Outline

• Motivation • Data & Methods• Climatology Results• Model Verification Results• Conclusions

Motivation

2007-2013

Counts StatisticsWarnings Events Scores

Total Verif NOTVerif Total Warned NOT

Warned POD FAR

OKX 422 123 299 191 150 41 0.785 0.709

• Poor verification statistics for High Wind Warning events

Source: NWS Performance Management [available online at https://verification.nws.noaa.gov/]

Motivational Questions• What synoptic regimes and meteorological

conditions are common to non-convective cool-season high wind events?– Height and MSLP pattern evolution– Low level winds and stability

• What atmospheric mechanisms might be responsible for the generation of high surface winds?

• How well does an ensemble forecast system improve the prediction of NCWEs as compared with deterministic forecasts?

Data & Methods

Observational data• RUC 13 km analyses

– 1-hr temporal resolution– Available 2008-2013

• NARR 32 km analyses– 3-hr temporal resolution– Available 1979-2013

• ACARS profiles– Variable temporal resolution– Available 2005-2013

• ASOS METARs– 5-minute temporal

resolution– Available 2000-2013 for 6

primary climate sites

Data & Methods• Climatology study period: 2000-2001 through 2012-2013

“cool seasons” (15 September – 15 May)• Model verification study period: 2009-2010 through 2011-

2012 seasons• Use 5-Minute ASOS observations to find observed High Wind

Warning criteria (Sustained wind 35 kts or higher and/or wind gust 50 kts or higher)– Observations >=9 hours apart are separate events– Exception: Regime change (frontal passage)

• Exclude convective events • Bin events into 3 common types

– Pre-cold frontal– Post-cold frontal– Nor’easter/coastal storm

Event Type Classification• Pre-cold frontal (PRF)– 14 observed events – 1 false alarm

• Post-cold frontal (POF)– 32 observed events – 4 false alarms

• Nor’easter/Coastal storm (NEC)– 14 observed events– 7 false alarms

Observed PRF events

Observed PRF events

Observed POF events

Observed post-cold frontal events

Observed NEC events

Observed NEC events

Large-Scale Synoptic Summary• Pre-cold frontal (14 observed events)

– Trough deepening and going negatively tilted over the Great Lakes, ridging over the W. Atlantic/SE Canada

– Simultaneous strengthening of negative and positive height & MSLP anomalies, oriented in a WSW-ENE direction

• Post-cold frontal (32 observed events)– Trough deepening and going negatively tilted over the NE U.S./SE

Canada– Rapidly strengthening negative height & MSLP anomalies

• Nor’easter/Coastal (14 observed events)– Trough deepening and going negatively tilted over the Great Lakes,

ridging over the W. Atlantic– Simultaneous strengthening of negative and positive height &

MSLP anomalies, oriented in a SW-NE direction

Diurnal Climatology of High Winds

Influence of Height Gradient

PRF Vertical Profiles

NEC Vertical Profiles

POF Vertical Profiles

Larger-Scale vs. Smaller-Scale Factors• Diurnal factor insignificant except for POF events• Correlation between maximum height gradient & maximum

wind/gust is positive but not significantly positive• LLJ strength/height cannot solely differentiate between an

observed event vs. a false alarm• PRF profiles

– Stable low-levels– Strong LLJ signature

• POF profiles– Weak low-level stability– Weak LLJ signature

• NEC profiles– Moderate low-level stability– Strong LLJ signature

SREF Ensemble Verification

• Verification of the previous version of SREF (October 2009 – August 2012)

• 32 km horizontal resolution, 21 members, 4 different model cores

• Two daily model runs (09Z and 21Z)• Verified against RUC analyses and ACARS profiles• Four forecast lead time periods

– 1st period: 1-6 hour – 2nd period: 9-24 hrs– 3rd period: 27-48 hrs– 4th period: 51-72 hrs

2nd Period Verification

2nd Period Verification

2nd Period Verification

2nd Period Verification

Verification Summary

• The SREF as a whole has a high bias in low-level (875-1000 hPa) wind forecasts

• The WRF-ARW core has the largest error in over-predicting the LLJ

• SREF ensemble provides a significant improvement in skill over the deterministic (control) members

Conclusions• Highest FAR with NEC events• Lowest POD with POF events• Large-scale synoptic evolutions can be used as

pattern recognition/analog tools• Height/pressure gradient and LLJ height & strength

cannot solely determine an event vs. a non-event• Analyze wind profile & low-level stability plus other

factors (if applicable)• SREF over-predicts LLJ, but still provides improved

forecast skill over any of the 5 control members