Saturday, February 22, 2014

My Forecast for Wednesday's Storm System

The time has come for me to make a forecast for what I think will happen Wednesday. When I started this blog the purpose was to give advanced notice to potential storm development and the reason behind why I thought they would occur. In some cases this means I will end up being wrong, but I much rather make a real forecast than just wait till the last second and Nowcast when every model is in agreement. 

So lets talk about Wednesday. Right now I am forecasting a moderate to potentially significant snowfall event for the Mid Atlantic Tuesday night into Wednesday. Do I have model agreement? Absolutely not, in fact every models is out to sea except for the European which is just off shore. Now this is not just me wishcasting let me explain why I think this event will occur. 

We are going to see a major pattern change next week. Take a look at the cold arctic air in place over our region just ahead of this storm system as seen by the cooler colors...(all images can be clicked to make bigger)

This is the result of an arctic high pressure system in place over our region at this time. Just to our south over the Gulf States notice the warm air. This boundary between warm and cold air creates what is called a baroclinic zone. Storms usually like to form on these gradients between warm and cold air and you can clearly see that is present ahead of the storm on Wednesday. 

Now lets look at the jet stream structure for this time period. I am using the European model because it has been extremely consistent in its last few runs...

We have a few ingredients here that are important to look at. For one we have a ridge of high pressure in the west. This causes the jet stream to rise in that region which results in the jet stream sinking over our area. This brings in the cold air. You also have a Negative NAO which is the high pressure system seen over Greenland (orange color) which sharpens trough over our area. To add, you have a low pressure center located around 50 North 50 West which historically has been a big precursor to east coast storms. This 50/50 low basically helps drive the storm up the coast as opposed to out to sea. So now that the foundation is laid, we need energy to form a storm. Lets take a look at where the energy is expected to be.

There are two clear disturbances in the jet stream in the image above. You have a very sharp disturbance coming off the northern branch of the jet stream and also a lot of sub tropical moisture flooding into the southern part of the country as seen on the bottom circle. The 1 million dollar question is do these two disturbances combine in the right spot to spawn a decent storm. We already know we have the other factors discussed above in place. So now it all comes down to timing.

This is where I am using my experience from watching storms develop all winter and how the modeling has handled them. There are a few things I want to point out:

1. This is a Miller A type storm. Miller A storms develop near the Gulf of Mexico and come up the coast. I have noticed that the European model this winter has handled these types of low pressure systems the best compared to the GFS and even the Canadian. There has been very good consistency with the European model in the last few runs which are all showing a moderate snow event. 

2. Most models have underestimated the strength and how far south the northern disturbances have dug all winter. The reason the GFS is taking this storm out to sea is it keeps the northern energy flatter which means it does not dig enough to combine with the southern energy. I believe this is an error. 

3. The Northern energy has not even hit land yet. It is still out in the Arctic Sea.. Weather models are based on data inputs. The data sampling is scarce out in the open water. It is my opinion that once this northern energy hits land up in Northwest Canada tomorrow night the models will begin to get a better handle on this system and correct in line with my ideas. 

So when it is all said and done I expect a moderate storm to develop Wednesday and potentially become significant. If when the energy hits land tomorrow the models start to catch on to my ideas, I will give snowfall estimates if necessary. 

In any event even if this forecast ends up busting, it will become brutally cold by the end of next week. Heading into march that split flow in the Jet Stream I discussed in my Video Sunday will be come even more prominent giving us more shots at winter storms. I mentioned on twitter yesterday that all leading climate indicators are showing this can be a brutal March. In fact even if we had little snow so far this winter I would be saying now that March has the opportunity to fill that gap. 

That's all for now. 

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