Friday, November 25, 2011

Weather Explained: Arctic Oscillation (AO)

Arctic Oscillation Positive/Negative phases.
Positive Phase on the left, Negative Phase on the right.
The Arctic Oscillation is an oscillating index based in the Arctic Circle region.
When the Arctic Oscillation is in a positive phase, a vortex in the upper regions of the Northern Hemisphere is strong and locks in cold air to keep it up north. This keeps the cold air up north as stated, and does not let the US get colder air.

When the Arctic Oscillation is in a negative phase, the vortex weakens, and the cold air locked in releases itself to more southerly regions of the North Hemisphere, typically affecting North America.

The AO can be a key player in winters when determining cold weather, and is an index that should be watched closely.

Weather Explained: Aleutian Low

The Aleutian Low is a semi-permanent low pressure system that sets up over the Aleutian Islands, Alaska. Below is an example of the Aleutian Low.
The Aleutian Low is most intense during the winter months, and can send energy towards North America that can eventually affect the US.

We are not publishing too much information on the Aleutian Low because we do not have enough information on it at this time.

Weather Explained: LRC

What is the LRC?

The LRC (Lezak's Recurring Cycle) is a pattern eagerly followed by many meteorologists and can be a key instrument in determining a winter forecast. Here are the guidelines:

-Pattern sets up between October 1 and November 10.
-Between this time, a certain atmospheric feature occurs that will reoccur over the winter, spring and into summer over a 40-60 day cycle.
-Pattern is never the exact same each year.

So, as an example, let's say a huge rainstorm came through the Ohio Valley on October 17th. Then, on November 30, another huge rainstorm came through the Ohio Valley. This may be considered a part of the LRC, if atmospheric conditions (similar strength, effects on atmosphere) agree with the October 17th storm.

MJO Forecast Unfavorable For Winter Weather

MJO Forecast
MJO Precip. Anomalies for Phases 3 and 4

MJO Temp. Anomalies for Phases 3 and 4
The MJO, a strong influence of weather in the winter season, is not looking favorable for the next several days for the US. The GFS and ensembles have the MJO moving into Phases 3 and 4. Phases 3 and 4 would mean the following effects for the US:

1. Warm for Much of US
2. Cool for SE in Phase 4, Cool for SW in Phase 3.
3. Dry for Midwest, Ohio Valley, Upper North US for both Phases
4. Wet in West US, Southeast in Phase 3.
5. Wet in NW, NE in Phase 4.