Flash Flood Events associated with Northeastern Cutoff Cyclones

Derek V. Mallia and Nicholas D. MetzUniversity at AlbanyDepartment of Atmospheric and Environmental Sciences35th Northeast Storms Conference, Saratoga Springs, NY7 March 2010

Outline:MethodologyClimatology of flash flood (FF) producing cutoff cyclones

monthly distributionmean location relative to moisture transportforcing mechanisms

Case Study250-hPa wind analysis500-hPa height and vorticity analysis850-hPa wind and precipitable water analysis

Conclusion

Data SourcesEarth System Research Laboratory (ESRL) daily compositesRapid Update Cycle (RUC20)Advanced Weather Information Processing System (AWIPS)Weather Event Simulator (WES)Geostationary Operational Environmental Satellite (GOES)Albany Radar (KENX)

MethodologyExamined warm season FF events that were associated with

convection (May through September)

FF event defined as one or more days under a similar weather feature with at least one FF report verified by the National Weather Service

A widespread FF event is defined as multiple FF reports that are separated by at least 40 km

An isolated FF event is defined as a one or more FF reports that occur within 40 km

Only events with a closed height contour at the 850 & 300 hPa levels were considered for the FF cutoff cyclone climatology

Cutoff cyclones had a minimum depth of 30 meters at 850 hPa and were cutoff for at least 24 hours

Methodology (cont.)

Dataset consists of FF and cutoff cyclone events that affected the Albany County Warning Area (CWA) between the years 2003 and 2009 that meet previous criteria listed

Methodology (cont.)

FF-Producing Cutoff Cyclone ClimatologyOut of the 39 FF days in the Albany CWA between 2003-2009,

11 were the result of cutoff cyclones

Out of these 11 FF days that resulted from a cutoff cyclone, 8 were considered widespread incidents while 3 remained isolated

Out of the 7 cutoff FF events, 3 resulted in multiple days of FF reports

Frequency of Cutoffs and FF Producing Cutoffs that affect the Albany CWA (2003-2009)

Num

ber o

f Cut

offs

Months

May June July August September0

2

4

6

8

10

12

14

16

18

- FF Producing Cutoffs

- Cutoffs

Precipitable Water Normals and Departures for Albany, NY

Prec

ipita

ble

Wat

er (m

m)

Months

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0

5

10

15

20

25

30

35

40

45

50

Normal

130% of Normal

170% of Normal

Mean 500-hPa geopotential heights for FF producing cutoff cyclones

Composite of flash flood producing cutoff cyclone events (m)N=11

Tom Wasula et al, 2009

Cutoff Cyclone Tracks

Mean 250-hPa vector winds for FF producing cutoff cyclones

Composite of flash flood producing cutoff cyclone events (m s1)N=11

Composite of flash flood producing cutoff cyclone events

Mean 850-hPa meridional winds for FF producing cutoff cyclones

(m s1)N=11

Composite of flash flood producing cutoff cyclone events

Anomalous 850-hPa meridional winds for FF producing cutoff cyclones

(m s1)N=11

Composite of flash flood producing cutoff cyclone events

Precipitable water anomaly for FF producing cutoff cyclones

(kg m2)N=11

Composite of flash flood producing cutoff cyclone events

Mean 700-hPa vertical motion for FF producing cutoff cyclones

(Pa s1)N=11

Neutral Type A Tilt

Tom Wasula et al, 2009

Forecasters beware when you see the following signs….

FF Producing Cutoff Cyclones: What to Look for…

Great Lakes track cutoff cyclone with a Neutral Tilt Type A

Anomalously strong meridional flow coming off the Atlantic Ocean which provides a sufficient moisture transport for storms

Forcing mechanism from either an upstream vorticity maximum, surface boundary, or favorable position in local jet max

Low to moderate amounts of instability and CAPE sufficient enough to cause a flash flood event

30 June–1 July 2009 Flash Flood Producing Cutoff Cyclone

Synopsis of the 30 June–1 July 2009 FF Event• Widespread FF event

• 13 reports total• Occurred in the following counties:

• Albany• Columbia• Bennington• Montgomery• Rensselaer• Saratoga• Schenectady• Ulster• Washington

• Multiple day event• Associated with cutoff cyclone over Lake

Ontario

30 June (Day 1)Consisted of 3 FF reports in the following counties (3 reports)

Bennington (1 report) Montgomery (1 report) Ulster (1 report)

FF reports occurred between 1700–2300 UTC

Significant severe weather event as there were multiple large hail and wind reports throughout the CWA

CAPE: 1,753 J/kgPWAT: 31.2 mmDewpoint: 17 CK index: 32Freezing level: 3,293 m

1500 UTC 30 June 2009

KENX Loop 1600-1800 UTC

1200 UTC 30 June 2009500 hPa Heights (dam), Absolute Vorticity (> 16 105 s1), and Wind barbs (kt)

1800 UTC 30 June 2009500 hPa Heights (dam), Absolute Vorticity (> 16 105 s1), and Wind barbs (kt)

2100 UTC 30 June 2009200 hPa Heights (dam), Wind Speed (kt), and Wind barbs (kt)

1800 UTC 30 June 2009Precipitable Water (mm), and 850-hPa Wind barbs (kt)

2100 UTC 30 June 2009Precipitable Water (mm), and 850-hPa Wind barbs (kt)

1 July (Day 2)Consisted of FF reports in the following counties (10 reports)

• Albany (2 reports)• Columbia (1 report) Rensselaer (1 report) Saratoga (2 reports) Schenectady ( 3 reports) Washington (1 report)

FF reports occurred between 1900–2200 UTC

Significant flash flooding

CAPE: 1,914 J/kgPWAT: 31.2 mmDewpoint: 18 CK index: 32Freezing level: 3,192 m

1500 UTC 1 July 2009500 hPa Heights (dam), Absolute Vorticity (> 16 105 s1), and Wind barbs (kt)

1800 UTC 1 July 2009500 hPa Heights (dam), Absolute Vorticity (> 16 105 s1), and Wind barbs (kt)

1500 UTC 1 July 2009200 hPa Heights (dam), Wind Speed (kt), and Wind barbs (kt)

1800 UTC 1 July 2009200 hPa Heights (dam), Wind Speed (kt), and Wind barbs (kt)

1500 UTC 1 July 2009Precipitable Water (mm), and 850-hPa Wind barbs (kt)

1800 UTC 1 July 2009Precipitable Water (mm), and 850-hPa Wind barbs (kt)

Conclusions:FF producing cutoff cyclones generally occur during June, July, &

August and track across the Great Lakes

Cutoff cyclone FF events often result in multi-day, widespread incidents due to slow progression of the cyclones and/or antecedent weather conditions

FF producing cutoff cyclones tend to occur near anomalously strong moisture transport with forcing for ascent associated with upstream vorticity maxima and upper-level jet stream

Neutral tilt Type A most favorable type of cutoff cyclone for flash flooding

AcknowledgementsJoe Villani; NWS AlbanyTom Wasula; NWS AlbanyNeil Stuart; NWS AlbanyRoss Lazear; University at AlbanyAlan Srock; University at AlbanyJonas Asuma; University at AlbanyKyle MacRichie; University at AlbanyKyle Griffin; University at AlbanyAnd my classmates!

Severe Weather Indices:Cutoff Case Avg.

*Widespread Case Avg.

*IsolatedCase Avg.

*Total Case Avg

CAPE (J/kg) 850 823 1046 938

K-Index 33.7 33.9 32.1 33

Total Totals 48 48 47 48

Freezing level (k ft)

13.0 12.9 13.6 13.2

PWAT (in.) 1.66 1.67 1.70 1.68

Dew Point (deg F) 68.3 67.8 68 67.9

Low level wind (kts)

18 19 15 17