Putting together a snow forecast is tough because the impact is high and the demand to know when and where is at the top of everyone's question list. It's truly impossible to know those answers even hours before. At this point we're watching the trends of the models and it's a wait and see game from run to run to see if we can see verification and consistency. That's not been the case with this storm so far... with the exception that most see the transitions and yield significant precipitation totals (rain, sleet & snow).
NAM 00Z compared to the NAM 18Z - MODEL DATA, NOT A FORECAST
When it comes to forecasting tough events it's not only helpful to look at what each model is saying, but also what they are trending toward. That means from run to run in the same model. Since the 00Z NAM is in let's take a look... you can see it brings in the colder air a little faster than the previous run (18Z). Allowing the transition from rain to snow to begin a little earlier (around midday in the latest run). This has consequently pushed the heaviest snow totals (at least in this one model) back farther to the south. Meaning the 12Z run was south, 18Z went north... and now the 00Z is back south a bit. 12Z runs in the morning will hopefully give some stability to the wobbly pattern.
Click on each set of runs to see the 00Z NAM compared to the 18Z NAM for the same time.
The difference in each are also noted. (courtesy: WeatherBell)
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