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


НазваForecasting precipitation distributions associated with 500-hPa cool-season cutoff cyclones can be a challenge in the Northeast
Дата конвертації05.05.2013
Розмір542 b.
ТипПрезентации



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

  • 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



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

  • 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



0.5° GFS analysis 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


Analysis period:

  • 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



Analysis period:

  • 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



Each cutoff cyclone day was categorized by…

  • Each cutoff cyclone day was categorized by…

  • 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)


Each cutoff cyclone day was categorized by…

  • Each cutoff cyclone day was categorized by…

  • Precipitation amount observed

  • Tilt: negative, neutral, or positive



Each cutoff cyclone day was categorized by…

  • Each cutoff cyclone day was categorized by…

  • Precipitation amount observed

  • Tilt

  • 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










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

  • 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



















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

  • 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















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

  • 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





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