Back in early fall I was pretty excited about what I thought were the makings of a pretty decent winter. The first place I always start when making a 3 month forecast is the sea surface temperatures. What they are, and what they are projected to be in the heart of the winter season.
I do that because 70 percent of the earths surface is comprised of water....lots and lots of oceans and water. They provide the moisture and latent heat for storms. Water also has a far different specific heat than land which means it heats and cools at a much slower pace than land masses. That means big concentrated bodies of warm or cold water can have a tremendous influence on how long wave jet stream patterns evolve and hold for long periods of time.
The ENSO (El Nino Southern Oscillation) is a climate driver that everyone focuses on to predict what a winter might look like. More likely you have heard of it in terms of El Nino. La Nina, or La Nada. To determine what state it's in, or will be in for extended periods of time during the winter, we look to the sea surface temperatures of the tropical Pacific near the equator. In general, a vast west to wast expanse of warm surface water covering the central and eastern Pacific signals an El Nino. Conversely, cool water implies a La Nina and near normal SST signals constitute La Nada or neutral conditions. Strong forms of El Nino or La Nina are well known to produce significant impacts on our winters by consistently positioning the polar and sub-tropical jet streams in ways that determine how much cold air we have access to as well as the amount of moisture available for rain and snow.
This year most forecasts showed a weak Modoki El Nino much of winter. The Modoki is different than the traditional El Nino because the warm waters are further west in the central Pacific (in a region known as 3.4). Further east towards South America the water is cooler than average which is not the case in the full fledged version of El Nino. Also in the western Pacific the waters cool again. You end up with warmth in the middle and cool on either side. You can see the SST differences in the graphic below.
That unique structure brings with it a different winter weather result. With the Modoki, instead of a split flow with limited cold air and snow, the polar jet has more access to the Midwest that can get you cold and snow with more phasing. Certainly a much more traditional winter. With models showing and projecting this pattern in the tropical Pacific through winter I felt this was a key consideration. See the difference between El Nino winters left and El Nino Modoki on the right.
The other thing I really liked for cold was the "warm blob" returning to the north Pacific. Above normal temperatures there have a decided advantage of producing a persistent ridge off the west coast. That buckles the jet allowing the polar jet the ability to freely and frequently dig into the central and eastern U.S. That was a key player in the harsh winters of 2013-14 and 2014-15.
In October the blob was alive, large, and well. It was also projected to be in play the majority of winter. That was the second really big factor that I felt was strongly in favor of a cold winter,
The third and final consideration was sea surface temperatures in the eastern Indian Ocean extending to the east of Australia. They were projected to stay cool like they are in the graphic above in blue. To me that was the final nail in the coffin as it would keep the MJO in the cooler phases during the heart of winter. It all makes great sense.
Problems arise when you make a forecast based on a forecast and the forecast fails. In the depiction of current SST anomalies below you can see I was good in the north Pacific and the central and eastern tropical Pacific.
Things went really bad though in the western tropical Pacific. All that area from the Indian Ocean to the east of Australia that was below normal and expected to stay that way did the opposite. A huge warming took place, especially near Tahiti and the region northeast of Australia. Warm water there induced convection (thunderstorms) that kept the MJO cycling in warm stages such as 3, 4, 5 and 6. That promoted a strong zonal flow aloft over southern Canada that kept the EPO (eastern Pacific Oscillation positive) and thwarted any attempts by arctic air to make any deep or prolonged attacks. The western ridge never developed in a way that could consistently deliver cold air.
That was a major and unforeseen problem that annihilated the projected Modoki. Look hat happened to temperatures when the Modoki El Nino existed from mid October to early December. Temperatures were at extremely cold levels to start. Then the Modoki died and so did winter from December 15 to the present.
Last but not least I think the warmth in the Atlantic was also an issue. Much to the surprise of forecasters SST there stayed very warm. That brought a consistent and powerful ridge to the SE United States that also provided resistance to cold air masses. Too much warm water in the wrong places did winter in.
Also if you look at the amount of above normal water in the oceans compared to cool it wins the ratio by roughly 70 to 30 percent. That is going to add a lot of water vapor to the atmosphere and its what climate change is all about. Water vapor will produce less range in average temperatures but more fuel for extreme weather events and storms. We are seeing it now. I also think it is going to make it harder and harder for us to experience the type of winters that I remember in my younger life. We'll get one now and then but it's my belief those will be the exceptions as opposed to the rule.
A CLIPPER TUESDAY NIGHT IN THE NORTH
Okay, now that we have confirmed my winter temperature forecast was a bust and why, here's an update on a weak clipper that could bring a bit of snow to my northern counties Tuesday night.
Even before that event (which is nothing to write home about), a small short wave and its associated warm advection may bring some rain or snow showers Tuesday morning. Nothing to be concerned about as temperatures will be above freezing and any snow would be up around HWY 20 north and not likely to accumulate in that part of my area. Even if it did highs will get well into the 40s and that would melt it in a heart beat.
The actual clipper itself slides through Tuesday night and is gone very early Wednesday. There is a chance some places near and north of HWY 20 could pick up an inch of slushy accumulation. If some banding develops just north of HWY 20 a few spots could see isolated bursts that drop a quick 1-2". Those types of accumulations should be isolated based on Monday night's models. With the warm ground temperatures travel issues should be limited and confined to areas near and north of HWY 20. Even if snow is confined to grassy and elevated surfaces, it will rapidly melt as temperatures quickly warm to the 40 degree mark once it ends on Wednesday. Here's the raw date on what models are showing for snow totals. I would lean toward the EURO.
The 12K NAM
The 3k NAM
After the clipper conditions warm again for the weekend and it seems likely that highs will reach the 60s Sunday, if not as early as Saturday in my western and southern counties. Both days look dry so some fine springlike weather is on the table for both Saturday and Sunday! Roll weather...TS
A BRAND NEW WEATHER SCHOOL PLANNED FOR APRIL 4TH
We are pleased to announce that we are offering a new edition of Weather School called Severe Weather 101 for Saturday April 4th. We have devoted the entire afternoon to the formation of severe storms with a strong emphasis on tornadoes. We'll do some simulations and take you inside several classic historic tornado outbreaks that have impacted Iowa and Illinois. I think you'll be really pleased with the sessions. We hope you can join us for all things severe weather! For all the details click on the banner below or contact Carolynswettston@yahoo.com