Case Studies of Warm Season
Cutoff Cyclone Precipitation
Distribution
Jessica Najuch
Department of Earth and Atmospheric Sciences
University at Albany, State University of New York
Advisors: Lance Bosart and Dan Keyser
NWS Focal Points: Tom Wasula and Ken LaPenta
Outline of Presentation
• Explain the motivation and focus behind my
research
• Look at my progress to date
• Climatology of monthly precipitation
distribution
• Climatology of monthly tracks
• Examine two case studies
• Discuss preliminary results and future work
Motivation
• Cutoff cyclones have diverse precipitation
patterns
• Flash floods are a consistent forecasting
problem
• National 30-year average for flash flood
deaths is 127
• Continuation of Matt Novak’s thesis but
focus on the Northeast
Arcade, NY June 26, 1998
Focus
• Stratify precipitation distribution relative to cutoff
cyclone tracks as identified in composites developed by
Matt Novak (2003).
• Map/understand cutoff cyclone precipitation
characteristics in composites especially in relation to
terrain.
• Document mesoscale precipitation signatures in case
studies representative of each of the composites.
Warm Season Composite Mean Cutoff Cyclone Tracks M. Novak (2003)
Focus Continued
• Understand role of terrain/low-level jet interactions in
determining the precipitation distribution in case studies
representative of each of the composites.
• Use composites to look for changes in orientation of the
cutoff in each case.
• Assess precipitation signatures in terms of shear/CAPE
profiles in selected case studies.
Progress to Date
• Created a climatology of monthly
precipitation distribution
• Hand drew the tracks of all 500 hPa closed
lows from 1980-1998
• Graphical and textural record of tracks
• Created and studied many composites for
two of four case studies
Climatology Of Monthly
Precipitation Distribution
• NCEP Unified Precipitation Dataset (UPD)
• 50 year dataset
• Each day a cutoff with precipitation passed
through a specified domain
• Months June through September
Outer Domain
inches/day
mm/day
inches/day
mm/day
inches/day
mm/day
inches/day
mm/day
inches/day
mm/day
Climatology of Monthly Tracks
• Used NCEP/NCAR reanalysis dataset
• Plotted 500 hPa geopotential height at 30m
intervals
• Tracked, by hand, cutoff cyclones at 6 hour
intervals 1980-1998
• Cyclone was considered cutoff where a
height minimum was surrounded by at least
one closed contour
Cases
1. 6/30/98-7/1/98
-Great Lakes Category of a Closed Low
2. 7/3/96-7/5/96
-Hudson Bay Category of a Closed Low
3. 7/18/96-7/19/96
-Great Lakes Category of a Closed Low
4. 7/29/96-8/2/96
-Great Lakes Category of a Closed Low
Case: 6/30/98 – 7/1/98
• Great Lakes Category of a closed low
• Produced all types of significant weather,
many tornadoes
• OH, WV, 6-10” of rain
• VT, NY flash floods
Tornadoes: 17
Hail: 64
Wind: 283
Maximum Precipitation:
Woonsocket, RI
3.58 inches
2-day precipitation plot (in) ending 12Z 1 July 1998
980630/1200F000
MSLP (hPa) and 1000-500 Thickness (dam)
250 Hght (dam) and Isotachs (m s1)
500 Hght (dam) and Abs. Vorticity (x10-5 s-1)
850 Hght (m) and Isotachs (m s-1)
980701/1200F000
MSLP (hPa) and 1000-500 Thickness (dam)
250 Hght (dam) and Isotachs (m s-1)
500 Hght (dam) and Abs. Vorticity (x10-5 s-1)
850 Hght (m) and Isotachs (m s-1)
Case: 7/3/96 – 7/5/96
• Hudson Bay Category of a closed low
• Flash flood producer
• Widespread heavy precipitation in eastern
NY, stretching northeastward into Maine
Maximum Precipitation:
Malone, NY
3.63 inches
960703/1200F000
MSLP (hPa) and 1000-500 Thickness (dam)
500 Hght (dam) and Abs. Vorticity (x10-5 s-1)
250 Hght (dam) and Isotachs (m s-1)
850 Hght (m) and Isotachs (m s-1)
960704/1200F000
MSLP (hPa) and 1000-500 Thickness (dam)
500 Hght (dam) and Abs. Vorticity (x10-5 s-1)
250 Hght (dam) and Isotachs (m s-1)
850 Hght (m) and Isotachs (m s-1)
960705/1200F000
MSLP (hPa) and 1000-500 Thickness (dam)
250 Hght (dam) and Isotachs (m s-1)
500 Hght (dam) and Abs. Vorticity (x10-5 s-1)
850 Hght (m) and Isotachs (m s-1)
Preliminary Results
• There is a general eastward shift of heavy
precipitation due to cutoff cyclones from June to
September
• Entrance/exit regions of low-level jets assoc. with
cutoff cyclones can strongly enhance heavy
precipitation
• Heavy precipitation normally falls either to the
right or left of track, not on track
• Cyclonic vorticity advection has much influence
on enhancing heavy precipitation
Future Work
• Continue producing the UPD climatology plots for
specific tracks and compare to monthly
composites
• Analyze precipitation patterns between cutoffs of
the same track
• Further analyze composites to see how speed and
direction of movement of lows affect precipitation
distributions
Future Work Cont.
• Obtain radar data to map/understand how precipitation
is associated with the composites for each case study
• Determine what percentage of monthly precipitation is
due to cutoff cyclones versus any other synoptic or
mesoscale feature
• Build a user friendly database of cutoffs from 19801998
• Put all of this research into one nice thesis!