1. Lake Effect Snow Forecasting
Zachary Hiris & Phil Pascerelli
Special Thanks to Jim Sullivan (Ohio Univ. ‘16)

2. Basics
Lake-effect snow (LES) is snow which develops on the downwind side of a major body of water (lake)
Driven by heat and moisture differences between the lake and the air above
Can produce extremely heavy snow rates for long durations of time

3. Basics
The basic ingredient absolutely needed for significant lake effect snow?
Sfc.-850mb▲C ≥ 13°C - Why?
Indicates an absolutely unstable lapse rate from the lake surface to 850mb level! (Holroyd 1971)
Absolute instability in the low levels is indicative of lift- and therefore the development of clouds (cloud streets) eventually developing into lake convection
Allows for lake induced instability to develop!
More on this later

4. Other Basic Ingredients
Deep Moisture Layer
Moisture in the boundary layer is absolutely needed- Lake-effect will NOT survive without background moisture
At least 1.5km deep, with <70% Humidity
Generally a good LES setup has moisture depth to at least 2-3km (7-10kft)
Wind Shear
Winds in the moist (boundary) layer ideally fall within 15-30kts
Directional shear within the layer should be less than 30*, speed shear <15kts
Any stronger shear tears apart a single band, and multiband setup is more likely
Fetch/Wind Direction
Short fetch leads to less moisture, less lake effect
Can be affected by ice cover later in the season
Typically- minimum fetch needed for flurries is 80 km, 160 km needed for significant lake effect
Strong convergence can negate this (see Oct. surprise event)

5. Wind Direction 240-270° 270° 280° 290-300° 300+°
Must know wind direction and what this wind direction means for downstream locations
BUFKIT is your friend here!
Quiz… What are the ideal winds for LES for the following cities?
Tug Hill & North (Watertown, Lowville)?
240°-270°
Pulaski/Mexico?
270°
Oswego?
280°
Fulton/Syracuse
290°-300°
South of Syracuse
300° °
270°
280° °
300+°

6. Lake to Lake Connections
Often times, a “link” or connection to a lake further upstream will enhance boundary layer moisture before reaching Lake Ontario
Most common?
Lake Huron
Georgian Bay
Occasionally Hudson Bay (possibly happened Oct. this year)
Important to look for these connections
Basic method- follow the moisture on any model page
Winds- were 850mb/700mb winds generally uniformly coming from an upstream lake?
Look at 925mb/850mb RH plots to track upstream moisture
Often times can help spark lake snows even with significant ice cover

7. Favorable Synoptic Pattern
Lake effect is most prevalent directly after the passage of a cold front
Why?
Strongest period of Cold Air Advection (CAA), generally uniform winds from the West/Northwest, background moisture
Trough over Canada
Location of 850mb/700mb low (generally my standard)is key
Closer to Lake Surperior/Huron - WSW (240) flow
Closer to the NY/VT/NH border- WNW ( ) flow
Reinforcing Cold Shots/Fronts
Also can cause subtle wind shifts that can move the band
Increase in lift can produce heavy snow rates

8. Sources of Lift/Convergence
Land Breeze
Caused by temperature difference between the surface temperature and the lake surface temperature
Leads to the creation of a mesolow that will enhance convergence at the surface
Frictional Convergence
On the lee side of the lake faster air hits the slower air that is over land
On the shore that is to the right of motion of the band, slower air over land is deflected into the band by the pressure gradient.
Other source of lift- orographic lift (Tug Hill), convergence- thermal convergence

9. Tieing it Together- Case Study #1
November 17-21st, 2014
Over 80” fell in the southern suburbs of Buffalo
Massive single band which remained stationary for hours at a time
First “event” shown to the right

10. Case Study #1- Buffalo Sounding
Things to consider…
Lake Sfc. Temps: 9C
850mb Temp near -15C
Delta T’s = 24C!!
Produced massive amounts of Lake Induced CAPE
Lake Induced Equilibrium Levels of up to 20kft!

11. Case Study #1- Buffalo BUFKIT (Niziol)

12. Case Study #1- The Results

13. Case Study #2
February 3-12, 2007
10 day event that caused 121 inches of snow to fall in Parish, New York
Most Oswego County saw at least 80 inches of snow
Note the repeated cold fronts/surface troughs moving through the region

14. Case Study #2 Sounding
This sounding was just taken after the initial cold front passed Buffalo, New York
This sounding shows the 850 mb temperature to be near -18° C and the average temperature of the surface of Lake Ontario was 3.52 °C
The Boundary Layer is up to 600 mb
The combination of cold 850 mb temperatures and deep boundary layer allowed for the development of a strong band over the lake
Generally WSW winds promoted a band of snow just south of Buffalo
Winds over Lake Ontario were more West-WNW

15. Case Study #2 Results

16. Using Standard Computer Model Output
Look at basic maps
500mb heights/vorticity, 700mb RH/Winds, 850mb Temp/RH/Wind, Sfc. Temps/Wind
Should give you a general idea of the synoptic situation
Think- where is the upper level low? Is the 850mb low in a favorable placement for 240 winds or 280?
Is the pattern favorable for lake effect snow development?

17. Computer Model Output- Soundings
Standard SkewT/logP for the Oswego area
Note- it’s not a BUFKIT sounding- raw soundings can help too!
What are some important features you can see from this skewT?

18. Using BUFKIT- Example Sounding
Important Features
Left Panel
Right Panel

19. Additional Tips- Courtesy of Jim Sullivan
700mb wind/RH, 850mb temp/wind and SLP/10m wind plots are your friends
Deep moisture to 700mb or higher can mean a big event. Lake-850mb temp differentials. Wind direction at 850mb is often good clue for where bands will setup. Surface pressure/wind plots can help identify important features that can enhance convergence.
Best lake effect snow tends to occur before passage of a surface trough and associated shortwave aloft
Tends to be a period of ascent ahead of shortwave trough. Often associated with a period of heightened inversions and deeper moisture. Surface convergence along/ahead of surface trough can intensify bands.
Look for sources of low level convergence.
Surface high building in, surface trough (lake aggregate or associated with a shortwave)
The NAM seems to do a better job of picking up on lake modification to an airmass and seems to more accurately predict low level flow than the GFS

20. Model Forecast Tips - ZH
In most LES cases, the snowfall : liquid ratio is much higher than the standard 10:1. Typically, most LES cases are much closer to 15-20:1, if not higher.
Do NOT use the NAM/GFS for your precipitation forecasts. LES does not show up well in lower resolution guidance (i.e. >5km grid spacing), and QPF forecasts are essentially useless. Use these models for pattern recognition and BUFKIT!
When Equilibrium heights are >15kft, and Lake Induced CAPE is >750 jkg-1, typically very heavy snow rates are possible (>2”/hr). This will not always show up on high-resolution models
Lake effect snow is very difficult to predict- don’t be discouraged if your first forecasts aren’t perfect!

21. Helpful Links Buffalo’s Locally run 4-Panel WRF Oswego WRF
Oswego WRF
College of Dupage Website
Good for satellite, radar, mesoanalysis, and forecast models
Penn State E-wall
WeatherBell.com
Also has the HRRR, RAP, RGEM, etc
Be careful using snowfall plots