2007-2008 Winter Outlook

Here we go…in the spirit of it being fashionable to put together Winter forecasts, I will provide mine. I will also include some of the reasoning I used to come up with it.

First, I have to state that this is tough. Because moisture is so scarce in the winter months and how little moisture is required to produce snow, winter predictions can get way out of control with the impact of just one big storm.

The seasonal norm for this area is around 20 inches a year of snow and 4 inches of rain December through February. This forecast is using this range. Depending on temperature, if any of this rain turns to snow, then it can really affect the totals as one inch of rain on average can translate to 10-12 inches of snow!

That said, only January really provides an average temperature norm that would be conducive for a normal expectation of snow. The reason for this is both the high and low temp norms are constantly within the range of freezing, though the high temps average just a hair above. This would likely translate to 90% availability for snow during an average January day if the moisture were present with a frontal or other trigger.

http://www.crh.noaa.gov/eax/?n=kcrecnorm-jan

It is this same reasoning that factors December and February into the same equation, but more at 60% availability – about half the day cold enough, and half the day too warm.

http://www.crh.noaa.gov/eax/?n=kcrecnorm-dec
http://www.crh.noaa.gov/eax/?n=kcrecnorm-feb


This is all based on norm temps. Norms are established over many years, but clearly there are anomalies that factor into each year. These anomalies can be caused from many different factors, including frontal passage or other upper atmospheric movements. It is factoring in these norms and anomaly patterns that must go into this type of winter forecast analysis.

So…temp is one ingredient; the other is moisture. As shown above, winter is very dry. As an example, this October, we had one day that would have made up the norm rainfall for an entire winter! In establishing a forecast, one must look back at the norms and anomalies to determine precipitation.

All this said, it would be easy enough to say we will have 20 inches of snow and seasonal temperatures, but based on different concepts and theories; there are some hints as to what may be different. Oddly, as norms are set, it isn’t normal for every year to be “normal.” Does that make sense? Each year is just a small slice of the overall norm, so it is expected that each month will have some funny business going on that over time averages out.

Storm track changes, ocean water anomalies [El Nino/La Nina] and other large scale pattern shifts can dramatically affect a given year’s winter output. For the use of this forecast, I am using all of these as factors.

So…high level, here we go….

I am expecting a somewhat warmer than normal winter. This is based off of observations of a persistent Pacific zonal flow, a weak La Nina event and extrapolation from the last three months of data which I believe to be in this years recurring cycle. This does not bode well for a white winter for us. But, this is not to say we should lose hope. I believe we will have several nice snow days with several inches at a time -perhaps one event where 6-12 inches is possible. In general, I am expecting about normal precipitation, but perhaps a bit more rain than snow based on temps.

In addition, I am expecting to see two cold air outbreaks, but several streaks of above normal temps. For every one cold streak, I expect to see two warm streaks.

In coming up with specifics for this forecast, I took the last three months of data and applied it to what I believe the recurring cycle duration is for this year. In addition, I then trended these events with associated outputs to days within the subsequent cycle. After this, I applied where I expected to see the warm and cold streaks and applied climate data to the overall data set.

It was in doing this, I able to target specific parts of the month were I expect certain events. I cannot specify exact days, but can get specific enough to get to weeks within a month.

So before I get to the details, I will redefine what I believe this years recurring cycle to be:

27-Aug to 21-Sep Phase 1 Cycle 1

22-Sep to 17-Oct Phase 2

18-Oct to 12-Nov Phase 1 Cycle 2

13-Nov to 8-Dec Phase 2

9-Dec to 4-Jan Phase 1 Cycle 3

5-Jan to 30-Jan Phase 2

31-Jan to 25-Feb Phase 1 Cycle 4

26-Feb to 23-Mar Phase 2

24-Mar to 19-Apr Phase 1 Cycle 5

20-Apr to 15-May Phase 2

16-May to 10-Jun Phase 1 Cycle 6

11-Jun to 6-July Phase 2


In using this cycle, it helps to define the outputs of the recurring storms within the cycles. For example, if a storm recurs within an expected dry phase, it may bring cooler temps, but likely be low or absent of precipitation. The converse is also true.

Each cycle I believe is an average of 50 days this year. Last year we saw it vary from 42-48 days, and I would expect this cycle to be from 48-52 days. I will stick to 50 days for the purpose of my forecast.

As each phase is defined within a cycle, we will have storms that cycle. Where storms cycle is very important. These seasonal paths are called long waves. These long waves will establish themselves as an extension of the jet stream and in relationship to upper air entities such as high and low pressure centers. This year, I am noticing a pattern brings storms near this area in two different methods..and really isn’t too unusual…

One path is for upper level lows brought into the Four Corners region by sliding down a ridge in the Eastern Pacific. These storms will likely cut-off especially as the flow is so zonal this year. This track is very tough to find as cut-off lows will normal wonder around until a follow up trough or “kicker” comes behind it to push it along or absorb it. From what I have analyzed this year, I believe this track to be south of Kansas into Oklahoma and Arkansas. This could bring snow if we can get into the “comma head” of the system. Location will be everything with this track. Too far south, we get nothing..too far north we get rain or get dry-slotted.

The second path is for upper level lows to drop in from Alberta and slide through South Dakota/N. Nebraska. This is another tricky path as it can do the same as the one mentioned above..but there is a difference. I expect these to be much more frontal thus bringing more of a rain look due to lack of cold air ahead of the boundary.

So..I have defined what I believe to be the overall outlook, the cycle definitions, and the storm tracks. Now I will define where I think we will find below and above average temperature streaks.

Each of these streaks are forecasted to be about 7-15 degrees below/above mean temperatures.

Cold streaks
5-8 days after each Phase 1 begins. Lasting for about a week.


Warm streaks
11-13 days after Phase 2 begins. Lasting for about 3 days.
and
Last 5-7 days in Phase 1

Last but not least, here is where I think we will see most of our snow…

You will see the majority of the snowfall fall during Phase 2 of the cycles. We will get this chance twice for snow. Also, there is one chance for smaller amounts in Phase 1, but it will be more of the zonal flow reducing significant snowfall. As we enter each Phase 2, I will have information on our snow chances.

To reiterate, all in all, I am going for 16 inches of snow and 5 inches of rain. I am going for a two cold air outbreaks with four warm streaks. I expect we will see longer periods of dryness in Phase 1 as the flow is more zonal.

Whew. I think this is valid, though I suspect parts may end up suffering to do misinterpretation. I believe the cycle to be solid along with the cold/warm streaks.

A lot of work to see if we can just get some white stuff, huh?