By John Ruggiano

October 8, 2007

From December 1, 2007 Through March 31, 2008 (D,J,F,M)

A Weak/Moderate La Nina, is on tap for much of the Winter !

Let me begin with some general thoughts on La Nina, and then We’ll get into more details as I progress into the writeup. A La Nina like pattern is underway this Fall for much of The USA, and continues to influence the weather. For much of the East: Warmer than Normal temperatures, and Very Dry weather have been the general rule for September, and this continues into October. This is quite typical with a majority of La Nina type patterns. So the question is what will happen next, as we approach the winter months, of December through March.

A Weak, Moderate, and Strong La Nina, all have different implications on one’s weather, but then we have other factors and variables, such as the PNA, NAO, AO, and other signals, that can alter the outcome of a typical La Nina Pattern. As many of you know, I’m not a very big analog fan, nor do I use them often. It’s just not my style in forecasting. So don’t expect me to post maps, from every month on certain past years. I do like to use some past years as guidance in showing a general reflective pattern, but not to be mistaken with using specific numbers, as some other forecaster’s like to do.

A typical pattern, associated with a Weak/Moderate La Nina Winter Season, here in the USA.

Well since I’m going with a Weak/Moderate La Nina type winter, let’s get into some typical pattern’s that apply. For the most part, The “PAC JET” is quite strong and is driven into the NW States with Colder than Normal Temps and Above Normal Precip, thus a stormy pattern for that region. The flow then moves eastward into the Northern Rockies and Plains, bringing big mountain snows, and Colder temperatures, with an associated trough.

As we head on Eastward, the main flow then effects, The Upper Midwest & Great Lakes regions, with a wide variety of weather. In general more cold shots and snowstorms are likely along and north of the Jet Stream. Here is where the Northern Branch likes to interact most often, because the PAC JET becomes slightly weakened after crossing the Rockies. This is were the Northern branch, finds a weak spot to move in, and tries to take over the flow. This can usually lead to some phasing and Big Midwest and G/L storms to develop. AKA: The Witch of November (The Wreck of the Edmund’s Fitzgerald)

For The East: Now comes the tricky part and where variables are a huge factor. The Atlantic signal, AKA as the NAO must be in it’s “NEG PHASE” for Colder than Avg Temps, and Above Avg Snowfall, to evolve for the M/A regions. Further North into New England, the NAO can be Neutral, and they’ll still have a descent winter up there. In this “NEG PHASE” parts of the Northeast could be looking at several chances for significant snowstorms, from what we call : Miller B’s. These storms form near the NC/VA Coast’s, and are spun off as secondary systems from a dying TN/V or OH/V storm. With a “NEG NAO” these storms usually move Northeastward up the East Coast, and can intensify into a Nor’easter, this occurring mainly for The New England States.

Parts of the Northern Mid-Atlantic can also get some descent snow and cold from these Miller B’s. There’s also the strong Clippers with the Northern branch, that can dive Southeastward to the M/A coast. With a trough in place, They can quickly intensify, and produce 2″ to 4″ or even 3″ to 6″snow events for parts of “The M/A Region”. I like to call these storms “Virginia Quickers”

For The Southeast: There’s the dreadful “SE Ridge” and “Displaced Jet Stream” to the north (Typical of a La Nina Pattern) which are the main culprits, if you like cold and snow. For the most part “Above Avg Temps” and Drier conditions can be expected. These conditions are also common for the South Central US and parts of the SW States. So basically the southern 1/3 of the country, is warmer than average and drier than Normal for a good majority of the winter season.


Let’s begin with the good news. For all the snow and cold lovers, this winter season will be best for the following locations: The mountains of the PAC NW, The Northern Rockies, The Northern Plains, Upper Midwest, The Great Lakes, and into Parts of The Northeast. This winter season will be one, where if you’re north of the main Jet, you’ll be “Slightly colder” and more Stormy at times. Along and near this flow, or Storm track, will be an awesome battle zone. The result will be “ICE STORMS” as overrunning will be common along this setup zone. My best estimate for potential Ice Storms, will be from the Central Plains, into the Midwest, The Ohio Valley, and into the Northern Mid-Atlantic States, and also Southern New England. Temperature contrasts along this boundary, will be quite steep at times.

Now if you’re along and south of this zone, Warmer than Normal Temperatures and Below Average Precip can be expected. The best chance for these conditions will be from the SW States eastward to The SE States, or basically the Southern 1/3 rd of the Nation. Also there will likely be some Severe Weather outbreaks, even during the heart of winter from Texas into the Deep South. This mainly because of a big extreme in temperatures, and storm development near the Central US and Midwest.

The Pattern will be quite progressive and active for a good part of the winter. I’m also forecasting the winter to start on time this year, as this is very common with most La Nina’s. The NAO will likely be “Neutral” to “Slightly Negative” in the beginning, and then level off as we approach the second half, to a more neutral or positive phase. A majority of the second half of winter, or should I say February and March, will depend on how the La Nina signal holds up through the winter season. In most cases if it does hold up, we should begin to enter a milder and less active pattern. Being there’s some uncertainty, I’ll take the middle road and hold to more of an average consensus. If the La Nina weakens considerably and or collapses, this could result in a pattern of cooler and more stormy conditions for parts of the M/A and SE states, during this later time frame.

For the I-95 Corridor in the M/A and NE regions, the best chance for snow and cold will be from late December into late January. February will also be good game for some snow, mainly in portions of the Northern M/A and Northeast Cities. A couple of Ice Storms, and or Mixed events, will also be favorable, for late December, and again from Mid January into Early February. DCA and Southward, will likely miss out on the biggest snow and Ice events, for a good part of the winter season. The storms that effect these areas, will likely track near or just north of the Northern M/A States. One or two of these storms will likely dive, and redevelop further south, in VA or NC (The Miller B Storms, I’ve mentioned earlier) These types of storms are the only hope for bigger snows, and a colder weather pattern, near and south of the DCA area. A “NEG NAO” must be in place for a La Nina Pattern, to produce any good snow chances there. I see very little chance in this pattern for a “Miller A” developing in the GOM, and moving up the coast. The Southern Stream or Subtropical Jet, will be very weak or non existent this winter season.

So to sum it all up, I’m forecasting temperatures to be “Slightly Above Avg” and Snowfall to be Below Normal for the Northern M/A and parts of New England.
For “Northern” and “Interior New England”, They’ll have “Near” to Slightly Below Avg” Temperature. Snowfall will be Near to Slightly Above Avg.

Further South: From much of Virginia into the SE States, temperatures will be “Above” to “Much Above Average”. Snowfall values will be Below Normal for the “Central” and “Lower M/A States” with Well Below Snowfall Normals for much of the SE States and South Central States.

My Forecast for PHL: (Philadelphia, PA)

Forecast Period: December 1, 2007 through March 31, 2008.

Mean Temperatures: +2.2 (Above Average)

Mean Temperature Range: +1.0 to +3.0

Total Snowfall: 12″ to 18″ (Below Average)

The Monthly Breakdown:


Temps: +1.0 to +2.0 (Slightly Above Avg)
Snowfall: 2″ to 3″


Temps: +2.0 to +3.0 (Above Avg)
Snowfall: 6″ to 8″


Temps: +1.0 to +2.0 (Slightly Above Avg)
Snowfall: 3″ to 5″


Temps: +1.0 to +2.0 (Slightly Above Avg)
Snowfall: 1″ to 2″

Selected I-95 Corridor Cities
BOS (Boston, MA)

Temps: 0.0 to +2.0 (Slightly Above Avg.)

Total Snowfall: 28″ to 36″ (Below Normal)

NYC (New York City, NY)

Temps: 1.0 to +3.0 (Above Avg)

Total Snowfall: 18″ to 26″ (Below Normal)

BWI (Baltimore, MD)

Temps: +1.0 to +3.0 (Above Avg)
Total Snowfall: 10″ to 16″ ( Below Normal)

DCA (Washington DC)
Temps: +1.0 to +3.0 (Above Avg)

Total Snowfall: 8″ to 14″ (Below Normal)

RIC (Richmond, VA)

Temps: +2.0 to +4.0 (Above to Much Above Avg)

Total Snowfall: 4″ to 8″ (Much Below Normal)


Temperature Map: (Click map to enlarge)

Snowfall Map: (Click map to enlarge)

Main Storm Track: (Click map to enlarge)