Snowfall: Higher than Forecast?

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By Quincy Vagell on March 8, 2013, 11:35am Last modified: March 8, 2013, 6:59pm

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Snow blankets New Fairfield, Conn.

Snowfall amounts were higher than forecast in many areas, so what happened?

This was a very challenging forecast, right from the beginning. The storm evolved in a different way than the computer models were projecting 2-3+ days out.

However, there were some signs of the potential heavier snowfall amounts. Recall that the North American Mesoscale (NAM) computer model was projecting 8-14" yesterday afternoon for most of the state. Also, the NAM had showed a cumulative Wednesday-Friday snowfall total of 12-20" for northeastern Connecticut way back on Tuesday. [read more]

What changed?
1. Bands of heavy snow, that sometimes drop localized heavier amounts of snow than forecast, kept hitting the same areas. This band happened to set up over northeastern Connecticut. Banding can be difficult to forecast. Even in the northeastern part of the state, totals as of 11 a.m. ranged widely from 8 to 17+ inches. It was the highest elevations that have seen the highest snowfall totals.
2. Snowfall ratios were a bit higher than anticipated. Snowfall ratios determine how much snow can accumulate based on a specific amount of liquid. We assumed 10:1 inland and even lower on the shoreline, but it looks like ratios were greater than 10:1, especially in the hill towns. 
3. The storm simply over-performed. Meteorologiy is not a perfect science. It's simply not humanly possible at this time to get every forecast 100% right. It seems like almost every winter storm this year was either all or nothing! Either more snow than forecast are less.

It's been a tough winter to forecast for and the computer models haven't been the best.

One final note. The NAM has a reputation for being too heavy with precipitation/snowfall forecasts. Interestingly enough, the NAM showed 30" snowfall totals before the blizzard earlier this year and it also showed the potential for 12"+ with this current storm. 

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Quincy Vagell

Town: Marlborough, CT  

Reporting for WXedge since January 2012.

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