Forecasting Heavy Precipitation Associated with Cool-Season 500-hPa Cutoff Cyclones in the Northeast - Melissa Payer, SUNY Albany

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Transcript Forecasting Heavy Precipitation Associated with Cool-Season 500-hPa Cutoff Cyclones in the Northeast - Melissa Payer, SUNY Albany

Forecasting Heavy Precipitation
Associated with Cool-season
500-hPa Cutoff Cyclones in the Northeast
Melissa Payer, Lance F. Bosart, Daniel Keyser
Department of Atmospheric and Environmental Sciences
University at Albany, SUNY
Neil A. Stuart and Thomas A. Wasula
NOAA/NWS, Albany, NY
Eastern Region Flash Flood Conference
2–4 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
Composite: HP_neu_cutoff
m s–1
n=14
250-hPa wind (m s–1, shaded), 500-hPa geo. height (dam, solid contours), and
850-hPa potential temperature (K, dashed contours)
Composite: HP_neu_cutoff
σ
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)
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 2010 Cutoff Cyclone
mm
12–16 March 2010
500-hPa mean geo. height (dam)
and track of cutoff cyclone every 6 h
12–16 March 2010
4-day NPVU QPE (mm)
13 March 2010
mm
24-h NPVU QPE (mm) ending 1200 UTC 14 March 2010
13 March 2010: 250 hPa
1800 UTC 13 March
0000 UTC 14 March
m s–1
250-hPa geo. height (dam, solid contours), wind (m s–1, shaded), and
divergence (10–5 s–1, dashed contours)
13 March 2010: 250 hPa
1800 UTC 13 March
0000 UTC 14 March
σ
Standardized anomalies of 250-hPa zonal wind (σ, shaded)
and 250-hPa geo. height (dam, solid contours)
13 March 2010: 700 hPa
1800 UTC 13 March
0000 UTC 14 March
10−12 Pa m−2 s–1
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: 850 hPa
1800 UTC 13 March
0000 UTC 14 March
m s–1
850-hPa geo. height (dam, solid contours) and wind (m s–1, shaded)
13 March 2010: 850 hPa
1800 UTC 13 March
0000 UTC 14 March
σ
Standardized anomalies of precipitable water (σ, shaded), 850-hPa geo. height
(dam, solid contours), and precipitable water (mm, dashed contours)
13 March 2010: Radar
1800 UTC 13 March
dBZ
Base reflectivity (dBZ) and surface observations
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
14 March 2010
mm
24-h NPVU QPE (mm) ending 1200 UTC 15 March 2010
14 March 2010: 250 hPa
1200 UTC 14 March
1800 UTC 14 March
m s–1
250-hPa geo. height (dam, solid contours), wind (m s−1, shaded), and
divergence (10−5 s−1, dashed contours)
14 March 2010: 500 hPa
1200 UTC 14 March
1800 UTC 14 March
10−5 s–1
500-hPa geo. height (dam, solid contours), absolute vorticity
(10−5 s−1, shaded), and wind (kt, barbs)
14 March 2010: 850 hPa
1200 UTC 14 March
1800 UTC 14 March
m s–1
850-hPa geo. height (dam, solid contours) and wind (m s–1, shaded)
14 March 2010: 850 hPa
1200 UTC 14 March
1800 UTC 14 March
K (3 h)−1
850-hPa θe (K, solid contours), θe advection [K (3 h)−1, shaded],
and wind (m s–1, barbs)
14 March 2010: 925 hPa
1200 UTC 14 March
1800 UTC 14 March
K (100 km)−1 (3 h)–1
925-hPa frontogenesis [K (100 km)−1 (3 h)−1, shaded], potential temperature
(K, solid contours), and wind (kt, barbs)
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