Case Studies of Warm Season Cutoff Cyclone Precipitation

Distribution

Jessica NajuchDepartment of Earth and Atmospheric Sciences

University at Albany, State University of New York

Advisors: Lance Bosart and Dan KeyserNWS 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

Cases1. 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: 17Hail: 64Wind: 283

Maximum Precipitation:Woonsocket, RI3.58 inches

2-day precipitation plot (in) ending 12Z 1 July 1998

980630/1200F000

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)

980701/1200F000

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)

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) 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)

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 1980-1998

• Put all of this research into one nice thesis!