Sunday, October 19, 2008

October 21-22nd First Snow Possibilities


First snow possibilities....
The area in light blue is basically a zone where I feel that the potential exists for a trace to 1 inch with isolated 2 inches. These amounts though would be in the mountains ONLY.....

Since it would be quite difficult to make a map that shows ONLY mountains accumulations I have decided to use a zone......

Wednesday, October 15, 2008

PNA/NAO/AO defined and whats needed for a good winter!

A little information needs to be clarified on the PNA and NAO...

A positive PNA will put a ridge on the west coast and a trough along the east coast....
A strongly negative NAO will cause suppression..
A weak negative NAO will be ideal to not cause suppression.....

QUOTE
During a positive PNA pattern, the simulated and observed eastern U.S. jet shifts to the southeast, coinciding with cold, dry conditions in the Northeast. This shift and intensification of the upper-level jet stream during a positive PNA pattern coincides with a greater frequency of cyclones and anticyclones along a distinct southwest-northeast track. Despite increased cyclone activity, total wintertime precipitation is below normal during a positive PNA pattern because of enhanced stability and subsidence over land, along with lower-atmospheric moisture content. Lower surface air temperatures during a positive PNA pattern result in enhanced simulated cloud cover over the Great Lakes and Atlantic Ocean due to increased thermal contrast and fluxes of sensible and latent heat, and a reduction in clouds over land. Interactions between the PNA and North Atlantic Oscillation (NAO) patterns impact the Northeast winter climate. Observed frontal passages through New York are most abundant during a negative PNA and positive NAO pattern, with a zonal upper-level jet positioned over New York. A positive PNA pattern is frequently characterized by an earlier observed Great Lakes ice season, while the greatest lake-effect snowfall occurs during a positive PNA and negative NAO pattern. The NAO pattern has the largest impact on northeast U.S. temperatures and the eastern U.S. upper-level jet during a positive PNA pattern.


PNA/NAO
As you can see it is the NAO pattern which has the largest impact on Northeast US temperatures......
Now lets look at the AO..

QUOTE
The Arctic Oscillation (AO) involves not just the Atlantic but the full band of winds that encircles the North Pole at about 55°N. When this vortex tightens (a positive AO index), it tends to lock Arctic air over the pole. When the vortex loosens (negative AO), frigid air masses can dive more easily into North America, Europe, and Asia. This pattern is also called the Northern Annular Mode, in parallel with its Antarctic counterpart, the Southern Annular Mode.

Pretty simple actually....
A Negative AO means colder air can discharge south
A negative NAO largest impact on the Northeast temps. Necessary for blocking.
A positive PNA Ridge on West coast ..trough in east.
A Negative PNA in Tandem with a Positive NAO means milder and wetter conditions

Some of our biggest storms come with a negative NAO and Positive PNA....
So essentially what you want is a slightly negative NAO or neutral ...a positive PNA or neutral...and a negative AO....

Now look at this chart...

This is showing all Nino, La Nina, and neutral years...from 1948 thru 1993...
Reduced: 75% of original size [ 540 x 466 ] - Click to view full image
Attached Image
As you can see Neutral years are not too shabby for the cities listed here. this is the mean over those years.

Most of the ocean-atmosphere indicators suggest that ENSO-neutral conditions are likely to continue not only during the Sep-Oct-Nov season in progress, but through most of the remainder of 2008 and early 2009.

The chances of an el nino developing are at or about 30%...so thats a 70% chance of not occurring this winter....

So all and all this should show you and tell you what you need for the winter in the Northeast and Mid Atlantic....

I have issued my forecast back in March of 2008 and it will not be altered. Also keep in mind a positive NAO in October correlates to a Negative NAO with historical data for DJF...


--------------------
A Colder then normal Winter for the Mid Atlantic? Weak La Nina? Stay tuned to updates.