Let's talk this afternoon about a couple of things that aren't getting a lot of press 3-4 days in advance of the East Coast's Valentine's Day Storm. All images on this page our courtesy our pro site.

First, the temperature of the ocean. Since the beginning of the season, some here at AccuWeather have warning that "unusually heavy" snowfall could result from unusually strong Nor'easters this season. Why?

Above are the "sea-surface temperatures" as of yesterday morning (in Celsius) (PRO). While meteorologists don't fully understand the ocean-land interactions yet, the idea is that the SSTs off the Northeast coast are warmer than usual this year, so storms (which feed on warm water) could get some extra energy (we see this happen with hurricanes). The warm water could also increase the snow intensity as the winds blow from east to west above the storm (kind of like lake-effect). Here are what the temperature "anomalies" (or "differences from normal") looked like yesterday morning.

The water is more than 2 degrees above normal off the coast of Massachusetts. While that doesn't sound like a lot, it can make a big difference if the storm tracks over that area. We'll just have to wait and see.

Next, model confidence. Let's take a look at this morning's GFS Ensembles (PRO). As I've said before, what Ensembles do is run the forecast several times with slight changes (within the error tolerance of the initial conditions the model starts out with). What you get from this is basically the model's confidence in it's own forecast. Generally the confidence decreases as you go out farther in time, and decreases with extreme weather, but not always.

Let's look at what meteorologists refer to as the "540 line". This is actually the line at which the 500mb pressure level in the atmosphere is located at 5400 meters. We use this to gauge where snow will fall -- there are other factors, of course, but especially in the days before models could actually tell you what winter precipitation was where, the 540 line was the dividing line between rain and snow.

The map above shows each different Ensemble "member"'s forecast for Tuesday morning. Notice that they are all reasonably close together, indicating the model is confident in its forecast. If precipitation were falling, the "540" rule would indicate that it would only be snow to the northeast of the line. But move forward to Valentine's Day morning...

Now the different members are disagreeing with each other, indicating that the forecast is less confident. The 540 line might be all the way in northwestern Pennsylvania, or it might be off the East Coast.

We could also look at the "0-degree line", meaning: Where will the temperature be below freezing (zero Celsius) on Valentine's Day morning. Because the cold air is moving in from the west, areas to the left of the line will be below freezing and whatever precipitation is falling will freeze to the ground. Unfortunately for our big storm, the range of locations for this line ranges from... east of the major cities to west, so the model is not confident enough yet to say whether Philly, New York or Boston will see freezing precipitation.

Look at the lines even further out and you can see why they call these "Spaghetti Plots."

One final way to look at the GFS model's confidence is to plot the actual forecast map over top of a "confidence map." This is called a "Mean/Spread Combination" (PRO). The Remember, the lower the pressure is, the stronger the storm will be and ultimately the pressure at your location will determine how close you will be to the heavy precipitation. Below, the map shows a 998 mb (29.76") low pressure system off the coast of Nantucket. But the "warmer" the colors underneath, the less confident the model is. In fact, at Nantucket, the confidence is +/- 7 mb, meaning that the pressure there could be anywhere form 991 mb (29.26", a much stronger storm) to 1005 mb (29.67", a much weaker storm). This could make a big difference in the amount of snow that falls.