# Presentation: 091388

## Finger Lakes Rain/Snow Bands: A Summary of Research

- Michael L. Jurewicz, Sr.
- WFO Binghamton, NY

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## Cosgrove Study (continued)

- Sensitivity Runs

- Land-water array was altered at 2.5 km resolution to take out both Lake Ontario and the Finger Lakes separately
- Results implied that the largest Finger Lakes (Cayuga and Seneca) could support lake effect snow on their own given otherwise favorable conditions
- Other smaller Finger Lakes could only enhance snowfall originating from larger Great Lakes

## LATER RESEARCH

- Watson et al.  (1998)

- Two additional events were looked at (January 10-11, 1996 and November 27, 1996)
- Penn St.-NCAR Mesoscale Model Version 5 (MM5) was used for numerical simulation with topography built in
- Model again captured temporal and spatial evolution of band development well
- Overall, quantitative comparisons were better

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## RECENT RESEARCH (Continued)

- Strategies/Goals

- Identify common synoptic/mesoscale settings
- Identify most important meteorological variables/thermodynamic processes that trigger significant banded precipitation
- Categorize events by type and intensity
- Create forecast graphics/tools to detect these events more accurately prior to their occurrence and improve subsequent snowfall forecasts

## ATMOSPHERIC SETUP

- Common Large Scale Elements

- Highly amplified pattern with sharp mid level troughing along the East Coast and ridging over the Midwest
- Leads to meridional flow through a deep layer that maximizes fetch length along north-south water bodies
- Pre-existing low level moist layer with depths to at least 800 mb is an IMPORTANT component
- Highest pcpn totals when the cap is AOA 700 mb

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## GENERAL OBSEVATIONS

- Comparison by Type

- Cayuga Lake vs.  Seneca Lake
- Snowband cases vs.  Warmer Rainband situations
- Events vs.  Non-events

## MORE SPECIFIC BREAKDOWN

- Cayuga vs.  Seneca

- Of the most recent events included in the study, 8 involved mainly Cayuga Lake bands and 4 had Seneca Lake bands
- In general, Cayuga Lake bands produced more pcpn and were longer lived
- Better upstream Lake Ontario fetch
- Slightly longer fetch length for the lake itself
- More favorable downstream topographic influences
- Due northerly wind often signals faster approach of ridge axis and lowering cap levels in Seneca cases

## ADDITIONAL COMPARISONS

- Snowband vs.  Rainband

- Rainband events in this study showed less organization and longevity, thus having less pcpn
- Interesting considering warmer water temps/better latent heat flux potential earlier in the season
-  Synoptic enhancement for these examples was better in the snowband events
- Snowfall tends to bring more attention/better spotter response, thus making such events easier to analyze

## EVENTS VS.  NON-EVENTS

- Comparisons

- Main factor to look at is amount of antecedent moisture
- In addition to 12 positive cases studied, several “no- shows” were investigated
- Given similar instability, synoptic, and shear parameters, main difference was depth of moist layer

## WHAT ACTUALLY HAPPENED?

- Tabulations

- Of the 12 Finger Lake snowband cases interrogated since 1996, the majority (7) have produced “minor” accumulations - 1" to 3"
- Primary reason is narrow “window of opportunity” for development between passage of 500 mb trough and approach of low level ridge axes
- However, 5 of the events did produce NWS Advisory criteria amounts (>4"); with one of them into the Warning threshold (>7")

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## SIGNIFICANT EVENTS (continued)

- More Common Elements

- Ideally, presence of mid-level short wave to enhance upward motion and elevate capping inversion
- Tendency for best development to occur between 03z and 11z
- Same noticed in many larger scale lake effect bands
- Lack of turbulent mixing from daytime heating may allow for greater organization to be achieved
- Deep moisture/high precipitation efficiency can make up for a relative lack of instability or other of the above mentioned ingredients

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## MORE MM5 STUFF

- Strong suspicion that higher resolution model runs would improve precipitation output
- For now, combo of using appropriate MM5 mass fields and interrogation of BUFKIT hourly model sounding data works best for assessing potential

## CONCLUSIONS/FUTURE GOALS

- Latent heat flux from the Finger Lakes themselves and topographic influences both appear to be critical factors
- Prior model runs altering the realistic land-water array plus objective results of this study so far are supportive of such thinking
- Future sensitivity runs are needed to better quantify heat/moisture transfer processes between the larger Finger Lakes and Lake Ontario