In a time where technology rules over traditional forecasting techniques, one could make the assumption that putting out a seasonal forecast must be a piece of cake. With what seems like new forms of guidance coming out monthly, more ensembles, sophisticated SST (sea surface temperature) detection, and a wide array of studies into various types of oscillation patterns, among other things, forecasting for the winter of 2001-2002 should be money in the bank right? Guess again! If anything, advances in technology have put more strain on meteorologists and their traditional forms of forecasting seasonal patterns and pattern changes across the globe. But on the flip side, many forecasters now have a scapegoat to blame when their forecasts turn out to be inaccurate, i.e., computer generated forecasts, whether daily, seasonal, or annual. On more than one occasion last winter, I was appalled to see a local meteorologist actually blame “the models for their ineptness” in seeing a change in a forecast prior to a large storm affecting the region. These computer generated schemes are good for ‘guidance’, but not for etching a forecast in stone. However, without guidance (technology), meteorologists are forced to use some of the older, more time demanding methods to make a forecast. Point is, it is not a good idea to solely use computer-generated guidance to make an assumption/forecast. One must find a happy medium that lies between guidance and one’s own knowledge of how the atmosphere works in order to derive a solid forecast. Throw into the mix the relatively recent incorporation of the popular ENSO (El Nino Southern Oscillation) and many other lesser-studied oscillation features into forecasting, and one can only imagine the complexity of compiling a seasonal forecast.
Here at SNUWW, we provide seasonal outlooks based upon recently recurring weather features in the Northern Hemisphere, jet stream and 500mb level trends, and clues from the tail end of last season. Many disagree with the method of comparison with late winter 2001, but I firmly believe that recognizing these ‘clues’ can be beneficial in a seasonal outlook. As for jet stream and 500mb trends, it is important to pay attention to any amplification in the flow this time of the year. Yes, these features do change over time, but spotting a persistent, flat, deep upper-level low over the Hudson Bay or an absence of energy in the Southern stream early in a season could help a forecaster to consider a progressive pattern for part of the winter. Using recent surface features also tends to provide clues as to where the ‘hot zones’ may be in terms of storm development during the winter months.
In my opinion, the keys in any given season are the trends, whether at the surface or upper levels. For instance, winter 97-98 featured a storm track from the Western Gulf into the Great Lakes for much of the winter. Therefore, those that spotted that trend were able to forecast a warmer than normal winter for many places East of the Appalachians. The trend in 95-96 was for upper energy to explode once hitting the coast. The rest is history. So, trends are very important in helping to arrive at a forecast.
Rainfall totals for the month of October are below average (2-4” below in some cases) for many East of the Appalachians. This is reminiscent of last year at this time when we saw similar dry conditions in the region. On the other hand, much of the Midwest had above normal precipitation for the month of October. Is there a correlation between this trend and the upcoming winter? Perhaps, in that the Midwest may be in the path of at least two possible storm tracks, one coming from Colorado or another from East TX/LA through MI/OH. That would leave parts of the East above normal temperature wise during this sort of pattern. Again, not too say either of these storm tracks will be predominant, but they could appear a few times this winter.
Another recent trend that may or may not be coincidence, are the bouts of above normal temperatures in parts of the Mid-Atlantic and northeast followed by below normal temps much of the fall. As is often the case as we approach mid/late fall, there is a real battle going on between developing bitter cold in higher latitudes and retreating early fall warmth. As a matter of fact, several tornadoes accompanied a strong cold front in the Midwest just last week. It’s seems later than normal for seeing this type of activity still across parts of the country. Like last season, I expect to see bitter cold days balanced by above normal days in the temperature department. If you recall last year, there was a stretch where we struggled out of the upper teens for highs. Then we saw days where the temperature topped off in the mid 40s. I expect similar for this winter, but colder days balanced by warmer days. I.e., a few stretches with teens for highs, and a few stretches with highs reaching close to 50.
But what type of pattern would allow temps in the teens for highs in our area? The answer, a pattern that features blocking at high latitudes. By blocking, I mean an area of raised heights at the 500mb level, usually prevalent over Greenland (Greenland Block) and Western Canada (Rex Block or thumb projection). Through much of the fall, blocking near Greenland was persistent in one form or another. In recent weeks, it has become less prevalent, but still showing hints of re-emerging strongly during mid November. Time will tell if blocking will be a persistent feature this winter, but this type of pattern would feature a negative NAO = troughiness in the East and generally colder than normal with the polar Vortex being suppressed into the Eastern US. Often, yet no always, this pattern will yield lower pressures near the East Coast in response to the PV headed south.
Another feature that I have noticed recently is when there has been a deep trough in the Eastern US, a closed low often tried to pinch off near the base of the trough as energy rotated around. A closed low hasn’t cutoff yet, but with this trend, it seems to me as we head deeper into fall and the beginning of winter, we will indeed see these systems start to close-off and spin up storms along the coast. This actually ties in with the ‘trends from the end of last winter’ theory.
From March all the way through late May (not continually), the Eastern US saw quite a number of closed 500mb lows develop or migrate south from Canada. This in turn carved out a broad trough and kept conditions cool and moist in the East. As stated above, there are subtle hints that we may see this type of pattern emerge early this year. If that were the case, I’d expect to see a storm track from the Southeast US or just off the Coast near the Gulf Stream to the Outer Banks and then either out to sea or up the coast from there.
Another trend that caught my eye at the 850mb level is plenty of CAD (cold air damming) signatures already taking shape at this time of the year. Last year we repeatedly saw weak lows at 850mb forming near the upper Ohio Valley, forcing warmer Atlantic air into the coastal plain. Thus far the pattern has featured a high-pressure area over the Ohio Valley with a NE flow along the East Coast. Not sure how this will hold up during the winter, but interesting to see a different orientation to the flow thus far at that level. There is a notable difference in the orientation and flow to the pattern at this level in the atmosphere.
The other feature that may or may not be related at all to last season is the amount of cold air present in Canada and Siberia. This is something that was not seen this early in the seasons of 97-98 and 98-99, two mild winters in our area. This leads me to believe that cold air intrusions will be plentiful, but they will also be balanced by warmer than normal days when the pattern shifts. Another ‘clue’ I gather is that it will be another late winter for parts of the Northeast. Late meaning colder air hanging on later in the season like last year when parts of the Northeast saw snow into April.
Just to touch on ENSO very quickly. As we know, the El Nino Southern Oscillation plays a role in our weather, whether folks continue to disagree on that fact or not. However, this winter we should NOT have to worry too much about El Nino or La Nina. Right now, ENSO is in a neutral phase. It is expected to remain neutral through mid winter and perhaps trend toward a warm phase late in the season. Any changes in the neutral phase of ENSO should be minor and should not severely impact the weather across the US.
So what is going to happen this winter? Will it be colder and snowier than last? Does a blue moon on Halloween mean that the entire Northeast will be up to their ears in snow? I do think this winter has the potential to be colder than last winter on average in the Northeast. This does not necessarily mean that I think it will be snowier.
Factors that discourage me from forecasting above normal snowfall are a quasi-zonal flow and a shearing component off the Southeast Coast. One thing about this pattern so far is that it has been somewhat progressive. No large storms to speak of. No cutoff lows. No Blue Norther yet (although parts of the upper Plains picked up some cold air and snow the third week of October, but no arctic outbreak plunging into Texas just yet). As for the shearing, there has been some sort of Southwesterly wind component paralleling the Gulf Stream off the Southeast Coast for the past few months. I am not sure if this is normal or not, but I’ve watched 2 or 3 tropical systems and one non-tropical system get sheared apart off the Southeast coast in recent months. With the other elements in place for systems to possibly develop in this area (negative NAO, amplification in the East, etc), shearing or a zonal flow would be the snow lover’s nightmare. We saw this scenario two years ago when it seemed every system trying to develop off the Southeast coast was either sheared or kicked out to sea. I think there are 1-2 large storm systems (Nor’easters) likely this year as long as this scenario doesn’t hold true and rip them apart.
Factors that encourage me to forecast above normal snowfall are Greenland Blocking, active Southern jet developing, and below normal fall precipitation. As crazy as it seems, I am a believer that below normal precipitation will be replenished with above normal precipitation over time, whether it be over a prolonged period or in one shot. Being similar to last year in this respect, one must consider that October is notoriously a dry month in the area. However, I’ve noticed that when we are below the already low total for the month, we make up for it during the winter whether with rain OR snow.
That leads me finally to the forecast. This winter will feature several storm tracks: 1) Colorado to New York State (during zonal and positive NAO patterns), 2)Colorado to South Texas to Ohio Valley (secondary development near Hatteras possible), 3) Eastern Gulf of Mexico across Florida to Outer Banks and either up the coast or out to sea, 4) Outer Banks and out to sea or up to Nova Scotia, and 5) Montana to Indiana to DelMarVa peninsula (clipper with possible coastal development on occasion). I will put out a map depicting this in the next few days.
As for temperatures, as stated earlier, there is quite a contrast between temperatures in Canada and across the Southern US at this time. Temperatures across Northern Canada are actually running a few degrees colder now than last year at this time. This leads me to believe we will see a few intrusions of frigid air into our region, with the interior Northeast bearing the brunt of the cold air masses. Expect our area to get hit with the ‘motherlode’ of cold air at least once this season.
And now the million dollar question…. will we see more snowfall than usual this year? As stated above, chances are better than normal of our region being impacted by 1-2 large-scale storm systems. What scares me is that large systems are notorious for bringing with them rain along the coastal plain in our area. We should also see at least 3 minor snowfalls from Alberta Clipper systems. For now, I am going for a near normal winter in terms of snowfall. It only takes one or two large storms to throw a wrench into that forecast however.
My annual breakdown of how I think things will pan out (hey why not, we averaged 70% accuracy doing this with last winter’s outlook): NAO goes full negative by the middle of November and alternates in two week to 20 day cycles (on average) from negative to positive. Accompanying the negative phase will be below normal temperatures with increased likelihood of coastal cyclogenesis along the East Coast. Remember, just because the NAO swings negative with blocking near Greenland does not ‘always’ guarantee a snowstorm in the East. By Thanksgiving, the area has seen the first flakes of winter with the first accumulating snows arriving in the second week of December. Pattern relaxes and goes zonal towards the 3rd week in December. Next push of Arctic air arrives late in December being reinforced by Alberta Clippers in the first week of January. Good chance for one of the potential big systems affecting the Northeast early in January. Overall, January will be average with the annual ‘thaw’ coming late in the month. First weeks of February will be the coldest period of the year for us with a few light snows thrown into the mix. Next chance for a big storm seems destined for the third week in February with a return to positive NAO by early March. Another snow event likely into mid March when the pattern goes negative once again, before conditions finally start thawing out by the third week of the month. Perhaps one late shot of cold air in the last week of March or early April in response to the NAO headed negative once again.
Again, my thinking is for a normal winter more or less, comparable to last season. I do think on a few instances we see snow to rain or rain to snow, as the periods of cold will be sandwiched with periods of above normal temps. Rather than basing this winter on why it will be ultra cold and snowy, I did just the opposite and weighed my outlook on why I think this winter will NOT be cold and snowy. However, I found NO conclusive evidence leaning in either direction. So, a call for near normal average conditions seems the logical route to take. Good luck to all this winter, forecasters and weather enthusiasts alike. Here’s hoping that all those winter forecast and white winter dreams pan out. God Bless and have a happy and safe Winter 2001-2002.
Email: Steve
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