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Lake-Effect Snow 1

Instructors:

Dan Bikos

John Weaver

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Topic:

Archived Training

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Developed:

2000

Other Contributors: Greg Byrd, Tom Niziol, Ed Mahoney, Dick Wagenmaker, Julie Adolphson, Jim Ladue, Jeff Waldstreicher, John Quinlan

Introduction


The material in this session is designed to increase your theoretical understanding of lake-effect snow as well as improve lake-effect snow forecasting skills. The unique characteristics of the eastern and western Great Lakes will be examined with case studies for both regions.

Training Session Options


NOAA/NWS students – to begin the training, use the web-based videoYouTube video, or audio playback options below (if present for this session). Certificates of completion for NOAA/NWS employees can be obtained by accessing the session via the Commerce Learn Center

  1. Audio playback (recommended for low-bandwidth users) – This is an audio playback version in the form of a downloadable VISITview and can be taken at anytime.

    Create a directory to download the audio playback file (32 MB) from the following link: http://rammb.cira.colostate.edu/training/visit/training_sessions/lake-effect_snow_1/lake-effect_snow_1_audio.exe

    After extracting the files into that directory click on either the visitplay.bat or visitauto.bat file to start the lesson. If both files are present, use visitauto.bat

Talking Points


Slide number Talking points
1 Title slide – showURL button goes to LES student guide page
2 Objectives
3

Conceptual diagram of Lake-effect snow

  1. cold air over warm water – latent/sensible heat fluxes mixed upward
  2. mixed layer deepens
  3. frictional convergence on lee shore
  4. possible additional lift from topography
4

Ingredients for Lake-effect snow

  1. Instability – Used to look at temperature difference between the lake and 850 mb temperature being 13 degrees Celsius or greater to develop LES bands. Now we look at paramaters like lake-induced CAPE.
  2. mixed layer depth – may be as or even more important than instability
  3. wind direction and fetch – want to maximize fetch so that more fluxes get into the boundary layer
  4. speed – calm winds will not allowing vertical mixing of fluxes.  shear – details in slide 19
  5. microphysics – heavy snow events are favored with particular snow crystal types
  6. upstream lakes – conditions downstream air mass
  7. orography – forced ascent from topography results in heavier snow
  8. synoptic influence – watch for cyclonic vorticity advection (raises the inversion height), secondary troughs (changes the wind direction) etc.
  9. ice/snow cover – inhibits the fluxes from mixing upwards
5 Typical synoptic setup – Hudson Bay low, cold advection pattern at low levels, deep mixed layer in the sounding
6 Ideal LES sounding – illustrates deep PBL, little directional shear and strong cap. Concentrate on the sounding below 500 mb since that is where most of the “action” occurs.
7 Nakaya Diagram show snow crystal type as a function of temperature and supersaturation. Yellow area denotes most favored area for dendritic growth, graupel and riming. Graupel forms in regions of rapid ascent. Riming of frozen crystals occurs in supersaturated layers (most efficient on dendritic aggregates. Dendrites form near -15 degrees Celsius. Supersaturation (riming) occurs most easily when the initial relative humidity is high (see next slide)
8 For these lake-effect snow cases the pre-event 850 mb dewpoint was greater than 80% for all heavy snow events, and less than 80% for all trace cases. This illustartes the importance of starting with a relatively high RH in the PBL to achieve riming. 
9 John Quinlan (NWS Albany, NY) has trained the spotters in his CWA to take observations of snow crystal type. The data from this study confirm that dendrites, and aggregates (especially when rimed) produce the greatest snowfall totals.
10 The following 3 diagrams illustrate the importance of fetch (assume environmental conditions favor LES development and the only changing parameter in these 3 slides are PBL wind direction). Click the arrow button to go between the 3 frames in this slideFetch 1 – In southwesterly PBL flow – The angle of  the wind with respect to the major axis of the lake is less than 30 degrees and the fetch is maximized , therefore a single intense bands occurs off Lake Erie. For Lake Ontario the fetch is not maximized and the angle of the wind with respect to the major axis of the lake is greater than 30 degrees, therefore multiple bands occur.
10 Fetch 2 – Imagine a trough moves in from the west, changing the wind direction to westerlies starting in the west. The snowband on Lake Erie is pushed towards the shoreline towards the region which still favors a single band. The Lake Ontario band transitions to a single band due to the longer fetch and decreased angle the wind makes with the long axis of the lake.
10 Fetch 3 – The trough has crossed over the area, leaving westerly flow across the domain. The Lake Erie snowband develops multiple snowbands due to the decreased fetch and the increased angle the wind makes with the long axis of the lake (greater than 30 degrees). The Lake Ontario snowband develops a single intense band due to the wind flowing parralel to the long axis of the lake, maximizing the fetch.
11 Topography of the Great Lakes – note areas in your CWA where snowbands may be enhanced by upslope flow. Also note bays and peninsulas (see slide 22)
12 Types of lake-effect snowbands
13

Multi-sensor view of a single band. showURL goes to a GOES multi-channel view of another single band case. Interesting phenomena of single bands:

  • strong winds on either side of band. weak to no wind right under the band in the zone of maximum convergence and heavy snow.
  • 90 degree wind shifts as band crosses the region.
  • thunder and lightning
  • snow that is charged in thunderstorms – may be more adherent because of the charge
  • “snowspouts” (similar to waterspouts)
  • mesolows or meso-waves that propogate along a steady state band and cause tmeporary oscillations.
14 Picture of a single intense band at night. Single intense bands often produce lightning.
15 Multi-sensor view of a multiple band. Note the cloud shadowing off Isle Royale (on Lake Superior) and enhancements off northern Michigan and the peninsula over southwest Lake Superior.
16 One of the first satellite views of a multi-lake band. Clevland, OH received 18″ of snow from this event. The snowband crossed over the minor axis of Lake Erie, however, the snowband originated off Lake Huron.
17 Meso-vortices. The band associated with the vortex over Lake Michigan deposited 6″ of snow in one hour on the shoreline of Wisconsin.
18 Morphology of the eastern Great Lakes.

Since lakes Erie and Ontario are elliptical a major axis exists. This means that the flow directions needs to be parallel to the major axis for the maxium fetch. Lake Erie usually freezes over in January (inhibiting the fluxes altogether), while Ontario remains mostly unfrozen.

19 Directional shear less than 30 degrees allows an enhanced confluent zone and conditioning over a deep layer for single band development. PBL depth generally greater over the eastern Great Lakes due to either upstream conditioning in northwest/west flow or conditioning from warmercontinental air mass over lower latitudes in southwest flow.
20 Morphology of the western Great Lakes
21 Directional shear less important over Superior and Huron because the lakes are wide and a major axis does not exist.

PBL depth generally shallower over western Great Lakes because source region is from colder higher latitudes with no upstream large bodies of water.

22 Bays – Focused land breezes from shorelines generate convergence near the center of the bay.Convergence zones can be advected by boundary layer winds. See example of Saginaw Bay snowband on next slide

Shorelines – Surface friction over land backs winds relative to those over water setting up convergence line along downwind shore.

Peninsulas – Surface friction over land also backs winds on peninsulas setting up convergence at the tip of the land mass.

showURL goes to an example of a Saginaw Bay snowband

23 Pretend it is 16:30 UTC 22 December making a forecast through 12:00 UTC 23 December
24 BUF CWA
25 GOES-8 Infrared (IR) imagery from 12:15 to 16:30 UTC 22 December 1999. Eta 500 mb height forecast from 12:00 UTC. Notice Hudson Bay low, multiple bands on western Great Lakes (indicating cold advection), short wave trough shown in IR imagery between lakes Huron and Erie. This short wave trough is not depicted in the 500 mb height forecast (or the 700 mb height – not shown). Note the snowbands over Lake Ontario which breakup as winds back in advance of the short wave (fetch decreases).
26 RUC 12 hour forecast of 850 mb temperatures and winds superimposed on lake surface temperatures.
27 GOES-8 visible imagery from 14:01 to 16:31 UTC 22 December 1999 with surface observations superimposed. Note enhancements associated with the short wave trough over Lake Erie. Also note veering winds at Toronto (CYYZ) with passage of the short wave. Wave clouds over the higher terrain in southwest New York often precede lake-effect snow development in an unstable environment (Reinking et al., 1993).
28 12:00 UTC 22 December 1999 soundings for Buffalo (green) and Detroit (cyan)plotted from the surface to 625 mb. The mixed layer at BUF is relatively shallowand dry. However the upwind sounding (DTX) indicates cold advection at low -levels will occur and conditioning by Lake Erie will likely moisten the PBL as wellif the winds back to southwest.
29 ETA forecast 850 mb heights, temperatures and winds from 12:00 UTC 22 December through 18:00 UTC 23 December in 6 hour increments. Cold advection from the west is evident. Winds southwesterly through most of the period except veer to west/southwest following the passage of the short wave and beginning at 12:00 UTC 23 December as the long wave trough moves east. Notice the initial short wave (seen earlier in IR imagery) is dampened by the model.
30 Bufkit output of Eta model forecast from 12:00 UTC 22 December 1999. Right – cross section valid at BUF showing relative humidity, temperatures and lake-induced equilibrium level (LIEL). Left – model sounding valid at 00:00 UTC 23 December with equilibrium level (EL) shown. Notice the LIEL and EL are at different levels. The EL is computed from the Eta using the surface based temperature and dewpoint while the LIEL uses the user-defined lake temperature and dewpoint. The LIEL is frequently higher than the EL and is generally more accurate during lake-effect snow periods.

To investigate the cloud microphysics note the height of the forecast -15 degree Celsius isotherm is where the relative humidity is relatively high (70%). This is close to 80% and remember this is only model guidance! For graupel considerations need to assess region of maxium ascent. One rule of thumb is to use the halfway point between the surface and lake induced equilibrium level as an estimate of the level of non-divergence. In this case this would be at about 1.3 km at 00:00 UTC (the beginning of our forecast period).

31 Bufkit output of Eta model forecast from 12:00 UTC 22 December 1999. Right – loop of model soundings valid at BUF with EL (equlibrium level) and lake-induced CAPE shown (the top of which is the lake-induced equilibrium level – LIEL). Left – locator charts based on using a mean wind layer from approximately the top of the friction layer to 850 mb. Note the output for the lake-induced CAPE and LIEL and how much they differ from the same parameters from the Eta.
32 Morning loop (14:37 – 16:29 UTC) of BUF radar reflectivity in clear air mode. Snow is already occuring in southwest NY and a snowband is evident over Lake Ontario. The snowband does extend further east (as seen in the visible satellite imagery) but the radar beam overshoots the low tops of lake-effect snowbands.
33 Radar reflectivity from BUF and TYX (Montague, NY) for the period 2:42 through 8:30 UTC 23 December. This may be seen more easily by zooming in (click on the zoom button and click the cursur in western NY. A single band off Lake Ontario is nearly stationary, higher reflectivites can be seen to the northeast of the band as well over regions of higher terrain where upslope flow enhances the snowband. The single band off Lake Erie remains south of Buffalo then moves southeast later in the loop.
34 The Lake Erie snowband dropped the most snow just south of Buffalo. Off Lake Ontario you can see a secondary maximum further northeast due to upslope flow.
35 Note the extreme gradients over short distances. The observations of 40 and 14close together are in the town of Redfield, NY where 40″ fell on the north side oftown and 14″ on the south side!
36 The 00z Eta run (cross section valid for BUF) showed an ideal environment for the development of dendrites with riming occuring. The -15 degees Celsius isotherm is colocated with the 90% RH contour during the overnight hours.
37 Eta output from 00z showing 850 mb height and winds forecast valid 00:00 through 12:00 UTC 23 December. Note the change in wind direction between 06z and 12z over Lake Erie. The winds veer which causes the snowband to miss the city of Buffalo by moving it southeast.
38 IWX CWA
39 IR imagery with the standard enhancement curve overlaid with Eta forecast 500 mb height field from 12z 25 January 2000. The nor’easter catches your eyes first. Note the Hudson Bay low, cold air upwind of Lakes Michigan and Superior (enhancements over Ontario) and high amplitude trough moving towards Lake Michigan. The winds turn to northerly behind this trough which is a favorable fetch for Lake Michigan.
40 Lake Surface Temperatures with 850 mb forecast wind and temperature
41 Visible imagery with observations – There are multiple bands over Lake Superior in the morning. A snowband over Lake Michigan is developing, winds are probably northerly already over the lake.
42 The 12z 25 January 2000 soundings from Alpena, MI (Yellow) and Lincoln, IL (Red).The sounding locations are not ideal (not close to the IWX county warning area).The Alpena sounding only reflects a short fetch from upwind lakes and Lincoln is away from theGreat Lakes but does show northwest winds which will change to north after passage of highamplitude trough.
43 12z 25 January Eta forecast 850 mb heights, temperature and winds valid through 00z 27 January. Cold advection (temperature drops 6 degrees Celsius across IWX CWA in 18 hours) with northerly flow across the major axis of Lake Michigan.
44 Workstation Eta (6 km horizontal resolution) showing mean sea-level pressure and 1000 mb winds. The mesoscale model shows the developing convergence and lower pressure on the south end of Lake Michigan.
45 Workstation Eta showing 850 mb omega and winds. Rising motion is depicted in a single band across the south end of Lake Michigan. The band starts on the eastern edge of the lake then moves west.
46 Workstation Eta forecast precipitation (mm in 3 hour intervals). This field can sometimes be different than the omega field due to downwind displacement of snowflakes. In this case the 850 mb flow was around 35 knots, blowing the snow inland an appreciable distance.
47 GOES-8 visible imagery from 17:45 through 21:15 UTC 25 January. The single band location agrees well with that forecast by the workstation Eta mesoscale model output. Note the feature oriented northwest to southeast moving southward on Lake Michigan. This feature can be followed after dark by using the GOES 3.9 um imagery (next page).
48 GOES-8 3.9 um imagery during the late evening and overnight hours. The disturbance over Lake Michigan seen in the visible imagery can be tracked after sunset. This disturbance moves along the snowband and acts to disrupt it resulting in a temporary letup to the snow in northern Indiana on the Lake Michigan shoreline.
49 IWX radar reflectivity from about 00:00 to 12:00 UTC 26 January. Note the temporary breakdown of the snowband due to the southward moving disturbance we saw in the satellite imagery on the previous slides. This illustrates why satellite data should continue to be monitored along with the radar data during lake-effect snow events.
50 IWX – observed snowfall for the forecast time period
51 Summary

References/Additional Links


Train the Trainer


Slide number Talking points

1

Title slide – showURL button goes to LES student guide page

2

Objectives

3

Conceptual diagram of Lake-effect snow

a) cold air over warm water – latent/sensible heat fluxes mixed upward

b) mixed layer deepens

c) frictional convergence on lee shore

d) possible additional lift from topography

4

Ingredients for Lake-effect snow

a) Instability – Used to look at temperature difference between the lake and 850 mb temperature being 13 degrees Celsius or greater to develop LES bands. Now we look at paramaters like lake-induced CAPE. 

b) mixed layer depth – may be as or even more important than instability

c) wind direction and fetch – want to maximize fetch so that more fluxes get into the boundary layer

d) speed – calm winds will not allowing vertical mixing of fluxes.  shear – details in slide 19

e) microphysics – heavy snow events are favored with particular snow crystal types

f) upstream lakes – conditions downstream air mass

g) orography – forced ascent from topography results in heavier snow

h) synoptic influence – watch for cyclonic vorticity advection (raises the inversion height), secondary troughs (changes the wind direction) etc.

i) ice/snow cover – inhibits the fluxes from mixing upwards

5

Typical synoptic setup – Hudson Bay low, cold advection pattern at low levels, deep mixed layer in the sounding

6

Ideal LES sounding – illustrates deep PBL, little directional shear and strong cap. Concentrate on the sounding below 500 mb since that is where most of the “action” occurs.

7

Nakaya Diagram show snow crystal type as a function of temperature and supersaturation. Yellow area denotes most favored area for dendritic growth, graupel and riming. Graupel forms in regions of rapid ascent. Riming of frozen crystals occurs in supersaturated layers (most efficient on dendritic aggregates. Dendrites form near -15 degrees Celsius. Supersaturation (riming) occurs most easily when the initial relative humidity is high (see next slide)

8

For these lake-effect snow cases the pre-event 850 mb dewpoint was greater than 80% for all heavy snow events, and less than 80% for all trace cases. This illustartes the importance of starting with a relatively high RH in the PBL to achieve riming. 

9

John Quinlan (NWS Albany, NY) has trained the spotters in his CWA to take observations of snow crystal type. The data from this study confirm that dendrites, and aggregates (especially when rimed) produce the greatest snowfall totals.

10

The following 3 diagrams illustrate the importance of fetch (assume environmental conditions favor LES development and the only changing parameter in these 3 slides are PBL wind direction). Click the arrow button to go between the 3 frames in this slide

Fetch 1 – In southwesterly PBL flow – The angle of  the wind with respect to the major axis of the lake is less than 30 degrees and the fetch is maximized , therefore a single intense bands occurs off Lake Erie. For Lake Ontario the fetch is not maximized and the angle of the wind with respect to the major axis of the lake is greater than 30 degrees, therefore multiple bands occur.

10

Fetch 2 – Imagine a trough moves in from the west, changing the wind direction to westerlies starting in the west. The snowband on Lake Erie is pushed towards the shoreline towards the region which still favors a single band. The Lake Ontario band transitions to a single band due to the longer fetch and decreased angle the wind makes with the long axis of the lake.

10

Fetch 3 – The trough has crossed over the area, leaving westerly flow across the domain. The Lake Erie snowband develops multiple snowbands due to the decreased fetch and the increased angle the wind makes with the long axis of the lake (greater than 30 degrees). The Lake Ontario snowband develops a single intense band due to the wind flowing parralel to the long axis of the lake, maximizing the fetch.

11

Topography of the Great Lakes – note areas in your CWA where snowbands may be enhanced by upslope flow. Also note bays and peninsulas (see slide 22)

12

Types of lake-effect snowbands

13 Multi-sensor view of a single band. showURL goes to a GOES multi-channel view of another single band case. Interesting phenomena of single bands

  • strong winds on either side of band. weak to no wind right under the band in the zone of maximum convergence and heavy snow.
  • 90 degree wind shifts as band crosses the region.
  • thunder and lightning
  • snow that is charged in thunderstorms – may be more adherent because of the charge
  • “snowspouts” (similar to waterspouts)
  • mesolows or meso-waves that propogate along a steady state band and cause tmeporary oscillations.
14 Picture of a single intense band at night. Single intense bands often produce lightning.
15 Multi-sensor view of a multiple band. Note the cloud shadowing off Isle Royale (on Lake Superior) and enhancements off northern Michigan and the peninsula over southwest Lake Superior.
16 One of the first satellite views of a multi-lake band. Clevland, OH received 18″ of snow from this event. The snowband crossed over the minor axis of Lake Erie, however, the snowband originated off Lake Huron.
17 Meso-vortices. The band associated with the vortex over Lake Michigan deposited 6″ of snow in one hour on the shoreline of Wisconsin.
18 Morphology of the eastern Great Lakes.

Since lakes Erie and Ontario are elliptical a major axis exists. This means that the flow directions needs to be parallel to the major axis for the maxium fetch. Lake Erie usually freezes over in January (inhibiting the fluxes altogether), while Ontario remains mostly unfrozen.

19 Directional shear less than 30 degrees allows an enhanced confluent zone and conditioning over a deep layer for single band development. PBL depth generally greater over the eastern Great Lakes due to either upstream conditioning in northwest/west flow or conditioning from warmer
continental air mass over lower latitudes in southwest flow.
20 Morphology of the western Great Lakes
21 Directional shear less important over Superior and Huron because the lakes are wide and a major axis does not exist.

PBL depth generally shallower over western Great Lakes because source region is from colder higher latitudes with no upstream large bodies of water.

22 Bays – Focused land breezes from shorelines generate convergence near the center of the bay.
Convergence zones can be advected by boundary layer winds. See example of Saginaw Bay snowband on next slide

Shorelines – Surface friction over land backs winds relative to those over water setting up convergence line along downwind shore.

Peninsulas – Surface friction over land also backs winds on peninsulas setting up convergence at the tip of the land mass.

showURL goes to an example of a Saginaw Bay snowband

23 Pretend it is 16:30 UTC 22 December making a forecast through 12:00 UTC 23 December
24 BUF CWA
25 GOES-8 Infrared (IR) imagery from 12:15 to 16:30 UTC 22 December 1999. Eta 500 mb height forecast from 12:00 UTC. Notice Hudson Bay low, multiple bands on western Great Lakes (indicating cold advection), short wave trough shown in IR imagery between lakes Huron and Erie. This short wave trough is not depicted in the 500 mb height forecast (or the 700 mb height – not shown). Note the snowbands over Lake Ontario which breakup as winds back in advance of the short wave (fetch decreases).
26 RUC 12 hour forecast of 850 mb temperatures and winds superimposed on lake surface temperatures.
27 GOES-8 visible imagery from 14:01 to 16:31 UTC 22 December 1999 with surface observations superimposed. Note enhancements associated with the short wave trough over Lake Erie. Also note veering winds at Toronto (CYYZ) with passage of the short wave. Wave clouds over the higher terrain in southwest New York often precede lake-effect snow development in an unstable environment (Reinking et al., 1993).
28 12:00 UTC 22 December 1999 soundings for Buffalo (green) and Detroit (cyan)
plotted from the surface to 625 mb. The mixed layer at BUF is relatively shallow
and dry. However the upwind sounding (DTX) indicates cold advection at low –
levels will occur and conditioning by Lake Erie will likely moisten the PBL as well
if the winds back to southwest.
29 ETA forecast 850 mb heights, temperatures and winds from 12:00 UTC 22 December through 18:00 UTC 23 December in 6 hour increments. Cold advection from the west is evident. Winds southwesterly through most of the period except veer to west/southwest following the passage of the short wave and beginning at 12:00 UTC 23 December as the long wave trough moves east. Notice the initial short wave (seen earlier in IR imagery) is dampened by the model.
30 Bufkit output of Eta model forecast from 12:00 UTC 22 December 1999. Right – cross section valid at BUF showing relative humidity, temperatures and lake-induced equilibrium level (LIEL). Left – model sounding valid at 00:00 UTC 23 December with equilibrium level (EL) shown. Notice the LIEL and EL are at different levels. The EL is computed from the Eta using the surface based temperature and dewpoint while the LIEL uses the user-defined lake temperature and dewpoint. The LIEL is frequently higher than the EL and is generally more accurate during lake-effect snow periods.

To investigate the cloud microphysics note the height of the forecast -15 degree Celsius isotherm is where the relative humidity is relatively high (70%). This is close to 80% and remember this is only model guidance! For graupel considerations need to assess region of maxium ascent. One rule of thumb is to use the halfway point between the surface and lake induced equilibrium level as an estimate of the level of non-divergence. In this case this would be at about 1.3 km at 00:00 UTC (the beginning of our forecast period).

31
   Bufkit output of Eta model forecast from 12:00 UTC 22 December 1999. Right – loop of model soundings valid at BUF with EL (equlibrium level) and lake-induced CAPE shown (the top of which is the lake-induced equilibrium level – LIEL). Left – locator charts based on using a mean wind layer from approximately the top of the friction layer to 850 mb. Note the output for the lake-induced CAPE and LIEL and how much they differ from the same parameters from the Eta.
32 Morning loop (14:37 – 16:29 UTC) of BUF radar reflectivity in clear air mode. Snow is already occuring in southwest NY and a snowband is evident over Lake Ontario. The snowband does extend further east (as seen in the visible satellite imagery) but the radar beam overshoots the low tops of lake-effect snowbands.
33 Radar reflectivity from BUF and TYX (Montague, NY) for the period 2:42 through 8:30 UTC 23 December. This may be seen more easily by zooming in (click on the zoom button and click the cursur in western NY. A single band off Lake Ontario is nearly stationary, higher reflectivites can be seen to the northeast of the band as well over regions of higher terrain where upslope flow enhances the snowband. The single band off Lake Erie remains south of Buffalo then moves southeast later in the loop.
34 The Lake Erie snowband dropped the most snow just south of Buffalo. Off Lake Ontario you can see a secondary maximum further northeast due to upslope flow.
35 Note the extreme gradients over short distances. The observations of 40 and 14
close together are in the town of Redfield, NY where 40″ fell on the north side of
town and 14″ on the south side!
36 The 00z Eta run (cross section valid for BUF) showed an ideal environment for the development of dendrites with riming occuring. The -15 degees Celsius isotherm is colocated with the 90% RH contour during the overnight hours.
37 Eta output from 00z showing 850 mb height and winds forecast valid 00:00 through 12:00 UTC 23 December. Note the change in wind direction between 06z and 12z over Lake Erie. The winds veer which causes the snowband to miss the city of Buffalo by moving it southeast.
38 IWX CWA
39 IR imagery with the standard enhancement curve overlaid with Eta forecast 500 mb height field from 12z 25 January 2000. The nor’easter catches your eyes first. Note the Hudson Bay low, cold air upwind of Lakes Michigan and Superior (enhancements over Ontario) and high amplitude trough moving towards Lake Michigan. The winds turn to northerly behind this trough which is a favorable fetch for Lake Michigan.
40 Lake Surface Temperatures with 850 mb forecast wind and temperature
41 Visible imagery with observations – There are multiple bands over Lake Superior in the morning. A snowband over Lake Michigan is developing, winds are probably northerly already over the lake.
42 The 12z 25 January 2000 soundings from Alpena, MI (Yellow) and Lincoln, IL (Red).
The sounding locations are not ideal (not close to the IWX county warning area).
The Alpena sounding only reflects a short fetch from upwind lakes and Lincoln is away from the
Great Lakes but does show northwest winds which will change to north after passage of high
amplitude trough.
43 12z 25 January Eta forecast 850 mb heights, temperature and winds valid through 00z 27 January. Cold advection (temperature drops 6 degrees Celsius across IWX CWA in 18 hours) with northerly flow across the major axis of Lake Michigan.
44 Workstation Eta (6 km horizontal resolution) showing mean sea-level pressure and 1000 mb winds. The mesoscale model shows the developing convergence and lower pressure on the south end of Lake Michigan.
45 Workstation Eta showing 850 mb omega and winds. Rising motion is depicted in a single band across the south end of Lake Michigan. The band starts on the eastern edge of the lake then moves west.
46 Workstation Eta forecast precipitation (mm in 3 hour intervals). This field can sometimes be different than the omega field due to downwind displacement of snowflakes. In this case the 850 mb flow was around 35 knots, blowing the snow inland an appreciable distance.
47 GOES-8 visible imagery from 17:45 through 21:15 UTC 25 January. The single band location agrees well with that forecast by the workstation Eta mesoscale model output. Note the feature oriented northwest to southeast moving southward on Lake Michigan. This feature can be followed after dark by using the GOES 3.9 um imagery (next page).
48 GOES-8 3.9 um imagery during the late evening and overnight hours. The disturbance over Lake Michigan seen in the visible imagery can be tracked after sunset. This disturbance moves along the snowband and acts to disrupt it resulting in a temporary letup to the snow in northern Indiana on the Lake Michigan shoreline.
49 IWX radar reflectivity from about 00:00 to 12:00 UTC 26 January. Note the temporary breakdown of the snowband due to the southward moving disturbance we saw in the satellite imagery on the previous slides. This illustrates why satellite data should continue to be monitored along with the radar data during lake-effect snow events.
50 IWX – observed snowfall for the forecast time period
51 Summary
  • Talking points – these may be used by local offices in tandem with the visitview training session (run in local mode – “visitlocal.bat”). The talking points may be printed out to easily review the session in detail at any time. The web page version contains talking points embedded in each slide (useful for printing).
This course is Basic

An understanding of the basics of lake-effect snow is assumed. See references section below (especially by Fenelon and Byrd) to go into more detail of basic concepts. More experienced forecasters of lake-effect snow will find this to be a basic course while inexperienced forecasters of lake-effect snow may find this to be intermediate.

Contact