Forecasting Heavy Precipitation Associated with Cool-season

500-hPa Cutoff Cyclones in the Northeast

Melissa Payer, Lance F. Bosart, Daniel KeyserDepartment of Atmospheric and Environmental Sciences

University at Albany, SUNY

Neil A. Stuart and Thomas A. WasulaNOAA/NWS, Albany, NY

Eastern Region Flash Flood Conference2–4 June 2010

NOAA/CSTAR Grant NA07NWS4680001

Motivation

• Forecasting precipitation distributions associated with 500-hPa cool-season cutoff cyclones can be a challenge in the Northeast

• Forecast uncertainties often arise due to variation in cutoff speed/location and interaction with the complex topography in the Northeast

• Identifying signatures differentiating between precipitation distributions would help forecasters

Objectives

• Create composites of cutoff cyclones categorized by tilt, structure, and precipitation amount

• Investigate the 12–16 March 2010 cutoff cyclone that produced widespread flooding in the Northeast by examining conventional synoptic and dynamic fields

• Identify signatures differentiating between various precipitation distributions

Data

• 0.5° GFS analysis data

• 2.5° NCEP–NCAR reanalysis data– Climatologies created for 1979–2008

• Standardized anomalies fields were created from 1.0° GFS analyses with respect to climatology

• 6-h National Precipitation Verification Unit (NPVU) QPE

• NEXRAD base reflectivity

Methodology

• Analysis period:– Cool season (Oct–Apr)

– 2004/05–2008/09

• Cutoff cyclone domain: 35–52.5 °N, 90–60 °W

• Cutoff cyclone criteria:– 30-m height rise in all directions

– Duration >12 h

• Precipitation domain: New England, NY, PA, NJ

• Days were defined as the 24-h period from 1200 to 1200 UTC

Methodology

• Analysis period:– Cool season (Oct–Apr)

– 2004/05–2008/09

• Cutoff cyclone domain: 35–52.5 °N, 90–60 °W

• Cutoff cyclone criteria:– 30-m height rise in all directions

– Duration >12 h

• Precipitation domain: New England, NY, PA, NJ

• Days were defined as the 24-h period from 1200 to 1200 UTC

Composite Methodology

Each cutoff cyclone day was categorized by…

1) Precipitation amount observed: heavy precipitation (HP), light precipitation (LP), or no precipitation (NP)

– HP: > 1% of precipitation domain

received 25 mm (n=100)

– LP: < 1% of precipitation domain

received 25 mm (n=250)

– NP: no precipitation observed in

the domain (n=34)

Composite Methodology

Each cutoff cyclone day was categorized by…

1) Precipitation amount observed

2) Tilt: negative, neutral, or positive Scalora (2009)

Composite Methodology

Each cutoff cyclone day was categorized by…

1) Precipitation amount observed

2) Tilt

3) Structure: cutoff or trough

cutoff: presence of 250-hPa zonal wind standardized anomaly of −2.0 σ or below on the poleward side of the cyclone (i.e., purely separated from the background westerly flow)

trough: does not meet the cutoff criteria (essentially a closed low embedded within a large-scale trough)

Note: Since there were so few NP cutoff cyclone days they were not separated into cutoff/trough

Average Location of Cutoff Cyclones

m s–1

Composite: HP_neu_cutoff

250-hPa wind (m s–1, shaded), 500-hPa geo. height (dam, solid contours), and 850-hPa potential temperature (K, dashed contours)

n=14

Stand. anom. of precipitable water (σ, shaded), MSLP (hPa, solid contours), 850-hPa wind (>30 kt, barbs), and precipitable water (mm, dashed contours)

σ

Composite: HP_neu_cutoff

n=14

Cyclone-relative Composite Summary

12–16 March 2010 Cutoff Cyclone

• Long duration event (cutoff cyclone in domain for ~84 h)

• Widespread flooding occurred throughout southern New England

• High winds were also observed with this event — 64 kt wind gusts were observed at Kennedy International Airport around 0000 UTC 14 March

• Models did well forecasting precipitation would occur but the forecast amounts were lower than observed and they didn’t capture the terrain influences

12–16 March 2010500-hPa mean geo. height (dam)

and track of cutoff cyclone every 6 h

12–16 March 20104-day NPVU QPE (mm)

12–16 March 2010 Cutoff Cyclone

mm

13 March 2010

24-h NPVU QPE (mm) ending 1200 UTC 14 March 2010

mm

13 March 2010: 250 hPa

250-hPa geo. height (dam, solid contours), wind (m s–1, shaded), and divergence (10–5 s–1, dashed contours)

1800 UTC 13 March

m s–1

0000 UTC 14 March

Standardized anomalies of 250-hPa zonal wind (σ, shaded) and 250-hPa geo. height (dam, solid contours)

13 March 2010: 250 hPa

σ

1800 UTC 13 March 0000 UTC 14 March

700-hPa geo. height (dam, solid contours), temperature (°C, dashed contours), Q vectors (>5 x 10−7 Pa m−1 s−1, arrows), and Q-vector

convergence/divergence (10−12 Pa m−2 s−1, shaded)

13 March 2010: 700 hPa

10−12 Pa m−2 s–1

1800 UTC 13 March 0000 UTC 14 March

13 March 2010: 850 hPa

850-hPa geo. height (dam, solid contours) and wind (m s–1, shaded)

m s–1

1800 UTC 13 March 0000 UTC 14 March

Standardized anomalies of precipitable water (σ, shaded), 850-hPa geo. height (dam, solid contours), and precipitable water (mm, dashed contours)

13 March 2010: 850 hPa

σ

1800 UTC 13 March 0000 UTC 14 March

13 March 2010: Radar

Base reflectivity (dBZ) and surface observations

1800 UTC 13 March

dBZ

13 March 2010 Summary

• Heaviest precipitation (>100 mm) observed in northern New Jersey and southern New England

– Favorable forcing for ascent downstream of upper-level cutoff in the region of a shortwave trough

– Weak Q-vector convergence

– Strong (>70 kt) low-level southeasterly jet advected Atlantic moisture

– Precipitable water of +1 to + 3 σ above normal along the coast

• Low-level flow interacting with topography suppressed precipitation in the Hudson Valley

24-h NPVU QPE (mm) ending 1200 UTC 15 March 2010

14 March 2010

mm

250-hPa geo. height (dam, solid contours), wind (m s−1, shaded), and divergence (10−5 s−1, dashed contours)

14 March 2010: 250 hPa

m s–1

1200 UTC 14 March 1800 UTC 14 March

500-hPa geo. height (dam, solid contours), absolute vorticity (10−5 s−1, shaded), and wind (kt, barbs)

14 March 2010: 500 hPa

10−5 s–1

1200 UTC 14 March 1800 UTC 14 March

14 March 2010: 850 hPa

850-hPa geo. height (dam, solid contours) and wind (m s–1, shaded)

m s–1

1200 UTC 14 March 1800 UTC 14 March

14 March 2010: 850 hPa

850-hPa θe (K, solid contours), θe advection [K (3 h)−1, shaded], and wind (m s–1, barbs)

K (3 h)−1

1200 UTC 14 March 1800 UTC 14 March

14 March 2010: 925 hPa

925-hPa frontogenesis [K (100 km)−1 (3 h)−1, shaded], potential temperature(K, solid contours), and wind (kt, barbs)

K (100 km)−1 (3 h)–1

1200 UTC 14 March 1800 UTC 14 March

14 March 2010 Summary

• Heaviest precipitation (>80 mm) observed in northern Massachusetts and coastal New Hampshire

– Favorable forcing for ascent within the entrance and exit regions of an easterly upper-level jet poleward of the cutoff cyclone

– Strong low-level southeasterly jet continued to advect Atlantic moisture

– Quasi-stationary region of frontogenesis developed along coastal New England

• Lobe of cyclonic absolute vorticity moving westward contributed to heavy precipitation (>25 mm) in New Jersey

Conclusions

• Long-duration cutoff cyclone associated with widespread heavy precipitation and flooding primarily caused by…

– Advection of anomalous moisture (+1 to +3 σ) by a strong (>60 kt) southeasterly low-level jet

– Favorable forcing for ascent in the entrance and exit regions of an easterly jet poleward of the cutoff cyclone

– Presence of a quasi-stationary region of low-level frontogenesis that developed along coastal New England

• Signatures contributing to heavy precipitation for this event agree well with the composite for the heavy precipitation, neutral tilt, cutoff category