"Its still early and a LOT can change". You have heard that phrase a lot lately, mainly because it is so true. The track of this storm is so important for totals, especially this time of year when we are dealing with a great deal of moisture and a lot of mild air nearby. The storm that is approaching for Thursday night into Friday will produce rain and snow. The snow zone is almost always off to the Northwest of the circulation, as illustrated below.
The center of the storm is just like the center of the water whirl pooling down the drain in your bathtub, no lift there, so no precipitation. The lift out ahead of the storm, usually East and Southeast is in the warm sector and the lift to the West and North of the center is in the cold sector. So, it is very important to where the center moves, as to where the rain and snow will fall.
Now that you have a better idea of rain versus snow, let's talk track. The latest information in this ever-changing storm is that more of the models are agreeing on a track that will put the Twin Cities on the colder side of the storm for a longer period of time, hence more snow.
Here are two model outlooks for this storm for early Friday. As you can see, both centers of circulation of south of the Twin Cities, therefore more snow for us. Also, look closely at that yellow line running down the center of the maps. That is the 5400 height line, I.E. the rain/snow line. The Twin Cities is off the West of that line, hence colder, hence more snow possible.
FRI STORM POSITION NAM (NORTH AMERICAN MESOSCALE) MODEL
FRI STORM POSITION GFS (GLOBAL FORECAST SYSTEM) MODEL
You can also notice that the band of precipitation off to the Northwest of the circulation is in a slightly different location with each model, one a bit farther North than the other. So the track is very important.
As of noon Wednesday, here is what our in house computer models, plus another computer model, are predicting for snow totals. This is as of noon Wednesday and will most likely be tweaked, but it definitely raises confidence that snow, and heavy snow at that, will fall in our neck of the woods.
GFS MODEL SHOWING 6"-12" FOR THE METRO
IN-HOUSE ADONIS MODEL SHOWING 7.1" IN THE METRO
IN-HOUSE MICROCAST MODEL SHOWING 7.1" IN THE METRO
EARLIER RUN OF IN-HOUSE MICROCAST SHOWING LESS SNOW
From this information we can place the metro in the 6-12 inch range for snow totals AS OF NOON WEDNESDAY, but as you have learned, the path can easily change those totals.
We can also look at the total storm moisture for the same storm. This is also known as the QPF (Quantitative Precipitation Forecast). The 3 day QPF with this storm is below.
QPF FOR TOTAL MOISTURE THROUGH FRIDAY
See the light blue band across the Twin Cities? That is indicating over an inch of water. The general, yet not finite, rule of thumb is that 1" of water equals 10 inches of snow. So, when you do the math, you get over 10 inches of snow, if it all falls as snow. Once again we go back to the track.
I hope this helps you better understand things when we talk on air about the system and how it is coming together. Stay tuned, as a lot can change over the next 36 hours.
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