Analysis of Precipitation Distributions Associated with Two Cool-Season Cutoff Cyclones Melissa Payer, Lance F. Bosart, Daniel Keyser Department of Atmospheric

Analysis of Precipitation Distributions Associated with Two Cool-Season

Cutoff Cyclones

Melissa Payer, Lance F. Bosart, Daniel KeyserDepartment of Atmospheric and Environmental Sciences

University at Albany, SUNY

Neil A. Stuart and Thomas A. WasulaNOAA/NWS, Albany, NY

NROW XI

5 November 2009

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 and interaction with the complex topography in the Northeast

• Identifying signatures differentiating between precipitation distributions would help forecasters

Objectives

• Determine how synoptic and mesoscale features affect precipitation distributions through several case studies of difficult-to-forecast cutoffs as well as cutoffs associated with varying precipitation distributions

• Identify common signatures differentiating between various precipitation distributions

Data

• 1.0° GFS

• 2.5° NCEP–NCAR reanalysis data– Climatologies created for 1979–2008

• Standardized anomalies fields were created from the 1.0° GFS analyses with respect to climatology

• 6-h National Precipitation Verification Unit (NPVU) QPE

Methodology

• Cool-season: Oct 1–Apr 30

• Analysis period: 2004/05–2008/09

• Cutoff domain: 35–52.5°N, 90–60°W

• Cutoff criteria:– Duration > 12 h– 30-m height rise in all directions

• Precipitation domain: New England, NY, PA, NJ

• Heavy precipitation: > 25 mm of precipitation over the Northeast in a 24-h period from 1200 UTC to 1200 UTC

Case Study 1: 8–9 March 2008

• Fast-moving cutoff

• Widespread flooding event with some icing reported in the Adirondacks

• Numerical models showed considerable variability in forecasting the cutoff 3–8 days prior to the event

• Forecasts confined the heavy precipitation to coastal regions; however widespread heavy precipitation was observed throughout much of the Northeast

8–9 March 2008500 hPa Mean Heights (dam)

and Track of Cutoff

8–9 March 20082-day NPVU QPE (mm)

8–9 March 2008 Cutoff

080307/0000F000DT Potential Temperature (K, shaded), Winds (kt, barbs), and LL Relative Vorticity (black contours), 500 hPa Heights and Absolute Vorticity (inset)













1800 UTC 8 March 0000 UTC 9 March

6-h NPVU QPE (mm)


250 hPa Geo. Heights (dam, solid contour), Winds (ms-1, shaded), and Divergence (x 10-5 s-1, dashed contour)


500 hPa Geo. Heights (dam, solid contour), Absolute Vorticity (x 10-5 s-1, shaded), Absolute Vorticity Advection (x 10-5 s-1 3 h-1, dashed

contour), and Wind (kt, barbs)


700 hPa Geo. Heights (dam, solid contour), Temperature (°C, dashed contour), Q-vectors (arrow), and Q-vector Convergence/Divergence (K m-2 s-1, shaded)


Surface MSLP (m, solid contour), 1000–500 Thickness (m, dashed contour), and Precipitable Water (mm, shaded)


925 hPa Frontogenesis (K/(100 km * 3 h), shaded), Potential Temperature (K, solid contour), and Wind (kt, barbs)


Standardized Anomaly of Precipitable Water (SD, shaded), 850 hPa Geo. Heights (dam, solid contour), and Precipitable Water (mm,

dashed contour)

8–9 March 2008 Summary

• Three primary regions of heavy precipitation: – Precipitation maximum east of Lake Ontario due to lake effect– North-south band of precipitation in eastern New York and western New

England collocated with strong cyclonic absolute vorticity advection and favorable QG forcing for ascent associated with strong Q-vector convergence

– Heavy precipitation over Cape Cod and Maine associated with strong frontogenesis ahead of warm front

• Exit and entrance regions of upper-level jet streaks provided favorable forcing for ascent

• Anomalous Atlantic moisture advected by low-level jet contributed to heavy precipitation

Case Study 2: 2–3 February 2009

• Considered a forecast bust for the Northeast

• Numerical models exhibited large disagreement in the speed and track of the cutoff, which directly impacted forecasts of precipitation type and amount

• Heavy precipitation was forecast to occur with this event; however most locations received less than 5 mm

NCEP Global Ensemble Forecast System Valid 090203/1200

Source: Grumm et al. (2009)

t–90 h t–96 h t–108 h

2–3 February 2009500 hPa Mean Heights (dam)

and Track of Cutoff

2–3 February 20092-day NPVU QPE (mm)

2–3 February 2009 Cutoff














1800 UTC 3 February 0000 UTC 4 February

6-h NPVU QPE (mm)


250 hPa Geo. Heights (dam, solid contour), Winds (ms-1, shaded), and Divergence (x 10-5 s-1, dashed contour)


500 hPa Geo. Heights (dam, solid contour), Absolute Vorticity (x 10-5 s-1, shaded), Absolute Vorticity Advection (x 10-5 s-1 3 h-1, dashed

contour), and Wind (kt, barbs)


Surface MSLP (m, solid contour), 1000–500 Thickness (m, dashed contour), and Precipitable Water (mm, shaded)


850 hPa Equiv. Potential Temperature (K, solid contour), Equiv. Potential Temperature Advection (K 3 h-1, shaded), and Wind (kt, barbs)


Standardized Anomaly of Precipitable Water (SD, shaded), 850 hPa Geo. Heights (dam, solid contour), and Precipitable Water (mm,

dashed contour)

2–3 February 2009 Summary

• Precipitation forecast bust associated with phase error in the location of the surface cyclone which developed farther east than expected

• Exit and entrance regions of upper-level jet streaks provided favorable forcing for ascent along the coast

• Low precipitable water values (< 10 mm) contributed to the low precipitation amounts observed

Summary

8–9 March 2008:• Fast-moving cutoff

• Widespread heavy precipitation

• Rapid cyclogenesis occurred over NY

• Dual jet streaks over the Northeast

• Anomalous moisture advected by LLJ (PWAT +2 to +5 SD)

Forecast precipitation issues due

to rapid cyclogenesis

2–3 February 2009:• Cutoff stalled over the Great Lakes

• Precipitation confined to coast

• Cyclogenesis occurred off the East Coast

• Dual jet streaks off the East Coast

• Little moisture present in region (PWAT < +1 SD)

Forecast precipitation issues due to phase and intensity errors

Questions/Comments?

Slides Removed

Future Work

• Continue working on additional case studies

• Categorize cutoff days in order to identify common signatures differentiating between various precipitation distributions

• Develop conceptual models to delineate cutoffs which produce certain precipitation distributions to be used in the operational setting

Results

• 170 cutoff events identified – average region duration of 35.7 hours

• 384 cutoff days total– 164 days (42.7%) received precipitation > 25 mm (~1 in.) – 57 days (14.8%) received precipitation > 50 mm (~2 in.)



Standardized Anomaly of 850 hPa Meridional Winds (SD, shaded), 850 hPa Geo. Heights (dam, solid contour), and Wind (kt, barbs)


Documents

Analysis of Precipitation Distributions Associated with Two Cool-Season Cutoff Cyclones Melissa Payer, Lance F. Bosart, Daniel Keyser Department of Atmospheric