3/12/17 – Storm update and some QPF talk

WEATHERBUDDHA SAYS: I don’t really have much to add from yesterday’s post. I stated that I believed the NAM was a bit too far West and the Euro & GFS are a bit too far Southeast. I believe the storm will split the difference. This storm is going to be so powerful that the determining factor between who gets a 12-15″ vs who gets 18-24″ is virtually impossible to predict. Here’s part of the reason why:

I’d like to take a minute and talk about snowfall ratios and QPF. (Quantitative Precipitation Forecasts). QPF is essentially the liquid equivalency of the snow/ice that will fall. If a storm is forecast to drop an inch of liquid and the temperature is between 28-34 degrees, the ratio is around 10:1. If the temperature is 20-27, expect 15:1 ratios. 15-19 degrees = 20:1 ratios!!! (Information obtained from NOAA at the link below…slide 4). The faster the storm strengthens, the colder the storm will become, and the higher the snowfall ratios will go. This QPF forecasts with this storm range up to around 2 inches!

Let’s say you’re in a QPF area for 1.5 inches of liquid. If the temperature is 30 degrees, that means you’re going to get about 15″ of snow…however, if the temperature crashes into the teens because the storm rapidly intensifies, that 15″ of snow just became 30″!

I do believe this storm will rapidly intensify and that temperatures will quickly fall into the teens and low 20’s. Expect fluffy powder over the top of whatever your location starts with (I’ll explain below). Furthermore, the faster the storm strengthens, the windier it will become and then blowing and drifting will become a problem.

For the reasons stated above, I am going to refrain from posting a snow map at this time…because honestly it would just be guesswork. With that being said, here are my best estimates based on current information, model data, history of storms like this, and my gut.

– If you live pretty much anywhere in PA (even in the areas in the western part of the state that comparatively speaking “aren’t getting much”), 6-8″ is likely.

– If you live around and east of I-81″ (especially in the Poconos down into the Lehigh Valley) you’re looking at 1-2 feet of snow…with some places upwards of 30 inches or more as temperatures fall!

– Areas like Philly, Baltimore, Washington DC, into Atlantic City may start as rain/sleet and change to snow. They may STILL end up with 18-24″ of snow because this storm needs to be treated like a winter hurricane. The most intense precipitation will be on the Northern and Western side of the storm.

Questions/Comments: Go!