Friday, January 11, 2013

Special: Flu Outbreak May Experience Spike Soon

Source: CNN
Everyone's heard of the sudden flu outbreak that has been ravaging the country, and the second to worst part is, the peak isn't in sight. The worst part is, it may get worse. And fast.

The above map shows the current spread of the flu. All states are in some form of flu alert, with many states bypassing all levels and skipping to 'High' infectivity rates, with big states like Pennsylvania, Texas, Colorado and Illinois on that list, just to name a few. Questions are arising like: Why is the flu so bad? Why is this year so horrible compared to others? And why is the peak still weeks away? While we can't answer all of those, there is one issue we have to face: this outbreak could get worse in coming weeks.

The answer? Cold weather.

The flu virus is a wintertime virus because it thrives in cold and dry conditions. This winter, while not particularly cold, is carrying a stronger flu virus than normal, explaining the severity and spread of the virus. This outbreak appears to be on the fast track to getting worse. This is due to an impending breakdown of the Arctic and resulting cold outbreaks. Yes, plural.

Forecasts agree that the first cold shot will be on the way in coming days, so the next week or two could see a fair spike in numbers of infected patients. However, the real surprise comes after December 20th. You see, a permanent low pressure system that sits in the Arctic will be forced south as high pressure builds in that region. As a result, anomalously colder weather will be shoved into the United States, only enhancing the favorability of conditions for the flu virus. With this Arctic air comes further decreasing of the air's humidity, again boosting favorable conditions for the flu virus to divide and conquer.

So in conclusion, incoming colder weather will hit in waves and should persist through February starting in Late January. This could very well heighten the spread of the flu virus all over, something no one needs at this time of year.

Andrew

Polar Vortex Could Collapse South into US

New signals are showing that the polar vortex could collapse south into the United States in the next 10-14 days.

Shown above is the 10 day forecast from the ECMWF ensemble prediction system, or just the EPS. The ensembles are forecasting 500 millibar height anomalies for this timeframe, where low pressure systems are shown in cool colors and high pressure formations are in warmer colors. The big green spot on the Canada-US border is the polar vortex itself- the low pressure entity which practically drives the Arctic to retain its cold powers. If this thing drops south like it did in 2009, cold to a very similar degree could be observed across parts of the nation.

Also key to this forecast is the presence of high pressure on the west coast of Canada and in the Pacific Northwest into the Southwest US. This is commonly known as the Pacific-North American (PNA) index, and is a driver of storm tracks and cold weather within the United States. When the PNA is in its negative phase, low pressure anomalies begin to build and persist in the West US (negative height anomalies, negative PNA), resulting in high pressure and warm air in the East US. Storms are then diverted into the Plains or way into the South. In the positive PNA, high pressure builds into the West, and low pressure evolves across the East, bringing higher potential for cold and snow to the central and east sections of the States. I find it very possible that the PNA could go positive after its been so negative recently- a huge low pressure system pushing south into the US means physics must respond with above normal height anomalies in the West US, and all of the sudden there's a positive PNA in the area.

The ECMWF Ensembles, despite the fact they are at the top of the most reliable models and ensembles of the world, are still prone to errors that strike the other global models, so do not take this as written in stone. It certainly is a good sign to see the ensembles agreeing on this- you need all the help you can get after last winter (even after last month)!

Andrew