Understanding Michigan snowfall. Jim Keysor - NWS Gaylord

Transcription

1 Understanding Michigan snowfall Jim Keysor - NWS Gaylord

2 Presentation Outline Topics Background information on lake effect Radar and lake effect snow Wind direction and lake effect Lake Enhanced snow Elevation and snowfall Snow-water ratio Where to find information Conclusion

3

4 Mean Lake/Air Temperatures (for Lake Michigan at Muskegon) 70 Lake Effect Snow Stable Season Lake Effect Rain Snow 60 F Lake Air 20 J F M A M J J A S O N D Month Air temperature Lake temperature

5 So What Happens? Imagine a cold air mass coming out of Wisconsin moving across a relatively mild Lake Michigan: As cold air moves out across a warmer body of water it picks up heat and moisture. As the air near the water becomes warm and moist it becomes less dense than the colder air above it. This creates buoyancy and causes the air to rise. Cold air Heat and Moisture Warm water

6 Formation of Lake Effect Precipitation The moist, rising air eventually cools to saturation (the relative humidity reaches 100 percent). Continued lifting leads to cloud formation. As these bubbles of buoyant air rise, they cool. Eventually, they cool to the point where its humidity reaches 100%. At that point, condensation occurs, resulting in cloud formation. Cold air Heat and Moisture

7

8 Lake effect snow and radar Heavy snow in Sault Ste. Marie, MI on this image 1 + per hour snowfall dbz

9 Radar and color curves

10 Surface wind, fetch and lake effect snow Fetch is the distance that an air mass travels over a body of water. Generally the longer the fetch, the more opportunity to pick up moisture/heat and develop into more intense lake effect snow

11 Typical northwest flow lake effect snow bands over Northern Michigan

12 Wind directions favorable for lake effect snow for Northwest Lower Michigan

13 Wind directions favorable for lake effect snow for Northwest Lower Michigan

14 Wind directions favorable for lake effect snow for Northwest Lower Michigan

15 Wind directions favorable for lake effect snow for Northwest Lower Michigan

16 Wind patterns when Lake Huron produces lake effect snow

17 Lake Enhanced Snow Lake enhanced snow is not pure lake effect, but is associated with regular snow-producing weather features (typically Alberta clippers or other low pressure systems) where the lake enhances snowfall. Lighter snowfall associated with storm system L 7 am EST 21 January 2005 Heavier lake enhanced snowfall January 2005 Strong/cold northeast flow off Lake Huron generated enough instability and added moisture to enhance snow totals

18 January 22, 2005 Lake Enhanced Snow Event

19 Another Factor That Can Enhance Snowfall Topography plays an important role in enhancing snowfall rates associated with lake effect snow bands. 100 feet of elevation change can result in an 8 to 12 inch increase in annual snowfall. Lake elevation=560 ft MSL Gaylord area=1400 ft MSL Traverse City area=600 ft MSL

20

21 Snow to Water Ratio Definition: Snow Water Ratio is a measure of how much water is in the snow if you melted it. System snow generally has snow to water ratios of 10:1 or 12:1 That means if you melt down 10 inches of snow, you get 1 inch of water Lake effect snow generally has snow to water ratios of 20:1 or 30:1 That means it takes 20 inches of lake effect snow to get 1 inch of water The average snow to water ratio in northern Michigan based on the past 30 years is 16:1 Snow to water ratios vary throughout the season, across the country and across northern Michigan

22 Average snow to water ratio s across the country Notice the drier snow ratios in northern Michigan

23 Snow to water ratio s in Michigan

24 30 Year study of average snow to water ratio s in northern Michigan

25 NWS Gaylord forecasts the snow ratio everyday during the winter months between November 1 st and April 1 st. You can refer to our snow ratio forecasts to determine how wet the snow is expected to be for an upcoming snow event. Go to our homepage: Finding daily snow ratio information Then click on the winter briefing page:

26 How to find snow ratio information Winter Weather Briefing Page

27

28 Daily snow ratio information On our NWS Winter Weather Briefing Page RECREATIONAL FORECAST FOR NORTHERN LOWER MICHIGAN NATIONAL WEATHER SERVICE GAYLORD MI 1100 AM EST SAT JAN MIZ SAULT STE. MARIE...PARADISE...TAHQUAMENON FALLS AND ENGADINE 1100 AM EST SAT JAN SNOW DEPTH...9 TO 11 INCHES..TODAY... SKY/WEATHER...CLOUDY. SNOW. MAX TEMPERATURE(F) WIND...EAST AROUND 5 MPH. SNOW AMOUNT...AROUND 1 INCH. WIND CHILL(F)...MINIMUM FOR THE PERIOD 22. SNOW RATIO...DRY/NORMAL (17 20 TO 1).

29 A few other things you can find on our webpage which you may find useful Hourly snowfall accumulation forecasts Lake effect snow maps with favored wind directions Recorded hazardous weather briefings

30 Hourly forecast charts which show hourly snowfall accumulation forecasts

31 Lake effect maps which show targeted areas with certain wind directions

32 How to find the Hazardous Weather Briefing on our web page This will take you to a 2x daily updated briefing

33 Weekly weather webinars Every Tuesday at 11 am during the winter, NWS Gaylord conducts winter webinars with road commissions, schools, EM s and MDOT in northern Michigan. These webinars last about minutes and include a summary of expected weather hazards over the next 7 days. There is also the opportunity to ask questions. If there is a specific storm in the near term, forecasters will provide detailed information on timing, locations, amounts. If you would like to be included on these webinars, please me james.keysor@noaa.gov

34 Winter Temperature Outlook

35 Winter Precipitation Outlook

36 Questions or want more information Jim Keysor Warning Coordination Meteorologist NWS Gaylord Ext 726