Changes to Winter Weather Warning/Advisory Criteria for Upcoming Winter Season

 

Winter Weather Warning and Forecast Changes at  the National Weather Service in Marquette
The National Weather Service in Marquette will be making some changes to their winter weather warning and advisory products for this upcoming winter weather season.  Any questions and comments should be directed to Matt Zika, Warning Coordination Meteorologist, via e-mail or phone (matthew.zika@noaa.gov, 906-475-5782 x726).
Snowfall Warning and Advisory Criteria
Currently, the WFO Marquette snowfall hazard methodology for issuing winter weather warnings and advisories focuses mainly on snow amounts. The current warning and advisory criteria do not take into account the fact that different snow/water ratios, snowfall rates, and time of the day/year all play a role in the impacts the winter storms have on the public. Through research conducted at the National Weather Service in Marquette where the number of weather related incidents were correlated with individual snowfall events from last winter, it was found that snowfall intensity and the water content of the snow is just as important (if not more so) than the storm total snowfall itself. The research showed that snow events with high water content (wet snow) usually result in more weather related incidents during the snow event.
Therefore, to better serve the public during winter events, the National Weather Service in Marquette will be running a test for the 2008-2009 Winter using some different criteria for its winter weather warning and advisory products. The changes can be seen in the table below. Although there are not significant changes to warning criteria, the snowfall warning criteria has been lowered for non-lake effect snow or system snow cases, since those cases typically have much higher water content than lake effect snow cases. Most of the adjustments have been made to the winter weather advisory criterion for snow. Once again, due to the high water content of system snows (non-lake effect snow), the advisory criteria has been lowered to snow amounts averaging 3 inches to less than 6 inches in 12 hours. In addition, snowfall rates have been taken into account.  If snowfall rates of 1 inch per hour are expected to last for 2 hours or more a winter weather advisory will typically be issued especially if this heavy snow is expected during the day time. There will no longer be a geographic breakdown for snowfall criteria for northern Upper Michigan vs. southern Upper Michigan. Lastly, the National Weather Service in Marquette will start issuing Special Weather Statements to highlight locally significant winter weather, especially in situations where the snowfall or snow rates are not expected to reach warning/advisory criteria thresholds. These statements will be issued mainly during the daytime when sociological impacts are greatest.
 
 
NWS Marquette Revised Winter Hazard Criteria
Type of Warning/Advisory
Current Criteria (used in 2007-2008)
Proposed New Criteria (for use in 2008-2009)
Blizzard Warning
Visibility in Snow and or Blowing Snow ≤ ¼ mile
Sustained Winds or Frequent Gusts  ≥ 35 mph
Duration ≥ 3 hours
No changes planned 
Winter Storm Warning for Heavy Snow
(System snow with snow/water ratios < 20 inches of snow to 1 inch of liquid)
Northern Upper MI
8 inches in 12 hours
10 inches in 24 hours
Southern Upper MI
6 inches in 12 hours
8 inches in 24 hours
≥6 inches in 12 hours
≥10 inches in 24 hours
≥3 inches of snow with sustained winds ≥25 mph and visibility < 1/2sm, but not reaching Blizzard Criteria
Lake Effect Snow Warning
(Lake effect snow with snow/water ratios ≥ 20 inches of snow to 1 inch of liquid)
Northern Upper MI
8 inches in 12 hours
10 inches in 24 hours
Southern Upper MI
6 inches in 12 hours
8 inches in 24 hours
≥8 inches in 12 hours
≥12 inches in 24 hours
Winter Weather Advisory for Snow
(System snow with snow/water ratios < 20 inches of snow to 1 inch of liquid) 
Northern Upper MI
≥4 inches but <8 inches in 12 hours
Southern Upper MI
≥3 but < 6 inches in 12 hours
≥3 inches but < 6 inches in 12 hours
Any snowfall with rates ≥ 1 inch/hour, for 2 hours or more, even if total snowfall is < 3 inches
Forecaster discretion (i.e. heavy snow band affecting Holiday travel, etc)
Lake Effect Snow Advisory
(Lake effect snow with snow/water ratios ≥ 20 inches of snow to 1 inch of liquid)
Northern Upper MI
≥4 inches but <8 inches in 12 hours
Southern Upper MI
≥3 but < 6 inches in 12 hours
≥4 inches but < 8 inches in 12 hours
Any snowfall with rates ≥ 1 inch/hour for 2 hours or more, even if total snowfall is < 4 inches.
Forecaster discretion (i.e. heavy snow band affecting Holiday travel, etc)
Significant Winter Weather Alert (Special Weather Statement)
N/A
Any snow with rates ≥ 1/2 inch/hour or more during the daytime (6am-6pm LT)
Enhanced snowfall during an ongoing advisory or warning situation that may affect commerce or increase winter weather danger
Forecaster discretion


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