Cold Season 500 hPa Cutoff Cyclone Precipitation Distribution and a Case Study Tony Fracasso Department of Earth and Atmospheric Sciences University at Albany, State University of New York Lance Bosart, Dan Keyser, and Anantha Aiyyer NWS Focal Point: Mike Evans (Binghamton, NY)

Research Goals To determine how precipitation in the Northeast US varies in association with 500 hPa cutoff lows during the cool season (October–May) Find what characteristics cutoff cyclones exhibit between similar tracks, based on B. Smith (2003) Document mesoscale precipitation signatures in several case studies representative of cutoff composites

How Often is a Cutoff Observed?* * In the Outer Domain of study (1948–1998)

Outer Domain

Cool Season Mean Cutoff Cyclone Tracks B. Smith (2003)

Climo Results Monthly composites of average daily precipitation and monthly precip as a percentage of climo when a 500 hPa low was present (1948–1998) Average daily precip and storm-relative average daily precip for four preferred cutoff tracks (1980–1998)

Results of First Composites Avg. daily precip. amounts are a max in November, decrease throughout the winter, then somewhat increase through spring. Higher amounts are located directly over and just to the east of higher elevations and also near the coast; lower amounts are located over lower elevations and further from the coast. Gradient of amounts decreases through the cool season.

Avg. Daily Precip. in./day mm/day Oct. and Nov Composite

Avg. Daily Precip. in./day mm/day Dec. and Jan Composite

Avg. Daily Precip. in./day mm/day Feb. and March Composite

Avg. Daily Precip. in./day mm/day April and May Composite

Results of First Composites Avg. daily precip. amounts are a max in November, decrease throughout the winter, then somewhat increase through spring. Higher amounts are located directly over and just to the east of higher elevations and also near the coast; lower amounts are located over lower elevations and further from the coast. Gradient of amounts decreases through the cool season.

Results of Second Composites Over 50% of the normal precip. is associated with cutoffs in October, November, March, April and May. Significant seasonal variations. Higher (lower) amounts to the East and North (West and South).

% of Climo % Oct. and Nov Composite

% of Climo % Dec. and Jan Composite

% of Climo % Feb. and March Composite

% of Climo % April and May Composite

Results of Second Composites Over 50% of the normal precip. is associated with cutoffs in October, November, March, April and May. Significant seasonal variations. Higher (lower) amounts to the East and North (West and South).

Precipitation Distribution by Track Categorized cutoffs by individual track: –Mid-Atlantic –Southwest –Clipper –Hudson Bay Average daily precip and storm-relative average daily precip

in./day mm/day

in./day mm/day Note: Circle indicates average starting position; “X” indicates average ending position, 24 h later.

in./day mm/day

in./day mm/day Note: Circle indicates average starting position; “X” indicates average ending position, 24 h later.

in./day mm/day

in./day mm/day Note: Circle indicates average starting position; “X” indicates average ending position, 24 h later.

in./day mm/day

in./day mm/day Note: Circle indicates average starting position; “X” indicates average ending position, 24 h later.

Results of Track Composites Mid-Atlantic and Southwest tracks are the wettest; Clipper and esp. Hudson Bay tracks are much drier All tracks except Southwest have the most precip falling near its 24 h ending location Coastal areas (esp. MA) consistently receive the most precip for each track

Case Study: May 2003 Three phases: 1)“Southwest track”—slowly moves from Michigan into Canada (23–25) 2)Stationary stage—meandering in Canada north of Toronto (26–27) 3)Exiting phase—travels south into PA then hooks back toward the Northeast to exit the area through Maine (28–30) Quite a cool environment for late May

Four-day (96 h) precipitation total (inches) from 12Z 23 May to 12Z 27 May. Cutoff track is plotted, with daily 12Z locations indicated by the day number

Four-day (96 h) precipitation total (inches) from 12Z 27 May to 12Z 31 May. Cutoff track is plotted, with daily 12Z locations indicated by the day number

Tracking of three vorticity maxima centers, every 12 hours: A begins 00Z/24, ends 00Z/28 B begins 00Z/25, ends 12Z/26 C begins 12Z/25, ends 00Z/30

00Z 24 May 2003 – 500 hPa Heights (dam) and Abs. Vorticity (x10 -5 s -1 )

12Z 24 May 2003

00Z 25 May 2003 B

12Z 25 May 2003 B

00Z 26 May 2003 A B

12Z 26 May 2003 B A

00Z 27 May 2003 A C

12Z 27 May 2003 C A

12Z 26 12Z 27

00Z 28 May 2003 C A

12Z 28 May 2003 C

00Z 29 May 2003 C

12Z 29 May 2003 C

U.S. Radar loop 00Z 23– 23Z 29 May 2003

Results of Case Study Three phases: “Southwest” track  stalled  resumes and increases forward speed Most precip fell near the coast and when the cutoff was “dead” (similar to composite Southwest track avg. daily precip map) Precipitation mainly linked to three vort maxes rotating around cutoff

Observed Southwest Track Composite

New Insights to Cutoffs in General… Vital source of precipitation to the Northeast Have many flavors – mobile cutoffs, dormant cutoffs, decaying cutoffs, etc. Influence can be most pronounced on its edges (boundaries) Reliable prediction of vorticity maxima is crucial to the forecast

Future Work Use data from 1999–present for monthly composites and especially track composites thanks to UPD’s extension to 31 December 2002 and CPC data Examine common synoptic scale features among similar tracks Expand outside the Northeast to the rest of the US