Verification of the 2013-2014 Winter Forecast

Hello everyone, this is a look back at my 2013-2014 winter forecast, and an analysis of how well it performed against what we observed from December 1, 2013 to March 1, 2014.

Temperature Verification

In my Final 2013-2014 Winter Forecast, I projected that we would see the core of the cold centered in the Northern Plains, Upper Midwest, Great Lakes, Midwest, Ohio Valley and into the Central Plains. The forecast also called for warmer than normal temperatures in the Southeast, while average conditions were to prevail over the southern Plains and the Northeast. My projection had the West US in for back and forth temperatures, ending up around normal.

Actual temperature anomalies for December - January - February 2013-2014

Looking back at what actually happened this past winter, we saw the core of the cold in the Upper Midwest into the Midwest itself, with still well-below normal temperatures in the Northern Plains, Ohio Valley, Great Lakes, and Southern Plains. This part of the forecast verified quite well, with the only trouble spot being the Southern Plains, which ended up a bit cooler than forecasted. The Northeast observed overall normal conditions, verifying that part of the forecast. The Southeast did end up a bit warmer than normal, but not as much as I thought it would be. The main trouble spot was in the West, where we saw warmer than normal temperatures instead of the average conditions I predicted. This can be attributed at least partially to the drought, as well as the persistent ridge in the Gulf of Alaska.

On a self-grading scale, I might put this forecast at an A-minus, maybe down to a B-plus.

Precipitation Verification

For the precipitation forecast, I anticipated above normal precipitation from the Central Plains into the Midwest and Great Lakes, believing that was where we would see the primary storm track. I also believed a drier than normal winter was in store for the Southeast, with neutral conditions in the East and West.

This part of the forecast actually busted quite badly. The Central Plains saw below normal precipitation rather than the above normal precipitation that was forecasted, though we did see verification in the Great Lakes. Overall, the East Coast didn't stray too far from what I thought would happen, ending up only slightly above normal overall compared to my projected average conditions. The West US definitely busted hard, with a serious drought taking over instead of my forecasted average conditions. The Southern Plains also ended up drier than normal, while the Southeast did not.

On a self-grading scale, this portion of the forecast likely deserves a D-plus.

Snowfall Verification

The snowfall forecast called for snowier than normal conditions over the Plains, Upper Midwest, Midwest and Great Lakes. The rest of the country was pegged for average conditions, with the East Coast possibly in line for some big storms.

I do not have a verification image, but I can affirm that the Midwest and Great Lakes regions verified accurately in this portion of the forecast. The East Coast ended up a bit snowier than I thought it would, and the West definitely got much less snow than what is considered average.

I would put the accuracy of this forecast at a B even.

Overall Forecast Verification

The overall forecast called for some big snowstorm potentials in the Northeast, with a warm and dry winter in the Southeast. The risk for a warm and dry winter existed in the Southern Plains, with a cold and snowy winter outlined for the North Central US. Slightly below average temperatures were anticipated for the Rockies, while a warmer than normal winter was projected for the Pacific Northwest. I feel verification of this graphic went better than I actually thought it would, with most areas seeing at least partial verification of this winter forecast.

For the overall forecast, I believe a grade of B-plus would be appropriate here.

What did you think of the accuracy of this forecast? Comment below with your thoughts!

Andrew

April 12-16 Potentially Major Storm System & Cold

Tropical Tidbits

Model guidance indicates we will see a trough drop through Japan on the morning of April 6th, in the wake of a stronger system just before it. You can read about that storm on this post. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. In this case, we see can expect a storm system in the United States, likely accompanied by a brief cold spell, in the April 12-16 time period, 6-10 days after the expected April 6th intrusion in Japan. The post title indicates this may be a potentially major storm due to the deep negative height anomalies in the above forecast, but that may be more for the cooler weather.

Projected PNA Index on top left
Projected NAO index on top right
Projected WPO index on bottom left
Projected EPO index on bottom right

Shown above is a chart of four panels, each showing the projected anomaly of a different oscillation in the atmosphere. Let's begin with the top-left panel, the PNA. The Pacific North American (PNA) index deals with 500mb height anomalies in the West US and into the Northeast Pacific. When we see high pressure dominating this area, we deem it to be a positive PNA. When we see storminess over the aforementioned regions, a negative PNA is in place. The positive PNA tends to lead to cold and stormy weather in the Central and East US, while the negative PNA provokes high pressure and warm weather across the same areas. We see the PNA is to be positive during this expected storm system, which does support the idea that this storm will bring along cooler conditions with it. A potential storm track in the positive PNA is one that goes through the South Plains, which could create severe weather, before shooting north into the Midwest or Ohio Valley.
We see the WPO (West Pacific Oscillation) and EPO (East Pacific Oscillation) are both projected to be negative during the April 12-16 time period, adding to the chances that we see cooler weather during this timeframe.

To summarize:
• There is the potential for a storm system in the US in the April 12-16 timeframe.
• Cooler than normal conditions may arrive during this time period.
• Severe weather is a possibility. Exact locations are unknown.

Andrew

Long Range Outlook for April 2014

Today's post will look at the expected weather pattern for the month of April, 2014.

We currently see tropical forcing located over the Indian Ocean, specifically southeast of the subcontinent of India. This forcing is associated with a convectively-coupled Kelvin Wave (CCKW), which will begin progressing east in future days. Currently, the placement of the CCKW supports cooler than normal weather, which we have been seeing recently, and should continue to see in the next few days, probably into about April 9th or 10th.

Specialized maps from the Australian Bureau of Meteorology indicate we will see this CCKW push east in coming days, taking the tropical forcing with it into a pattern that should bring more seasonal, possibly even above normal temperatures to the United States.

Typically, when we see enhanced tropical convection entering the western Oceania region, we tend to see the weather pattern favoring warmer than normal weather in the United States. On the Madden-Julian Oscillation scale, this would mean movement into Phases 5 and 6.

500mb height anomalies for Phase 5 MJO events in April (left)
500mb height anomalies for Phase 6 MJO events in April (right)

Temperatures for March-April-May for all eight MJO phases

If we take a look at mid-level height anomalies for MJO Phases 5 and 6, as well as temperature anomalies for phases 5 and 6, we see that the pattern decisively supports seasonal to slightly above normal temperatures. Even though it won't be a Madden-Julian Oscillation wave going into western Oceania, the tropical forcing from the CCKW should suffice to bring about these seasonal temperatures.

Despite this, a recent spike in East Asian mountain torque anomalies means we're likely to see those warm temperatures dampened a bit. In the winter, positive East Asian mountain torque values indicate the perturbation of the upper Arctic, and these +MT events can bring about sudden stratospheric warmings. In this specific case, though, we can just expect those warmer temperatures to be tempered some by this positive mountain torque event in East Asia. These warm CCKW-induced temperatures should come about in the general mid-April timeframe, but again, watch for cold shots in response to the positive East Asian mountain torque in the not-too-distant future.

Moving along, we can look ahead into late April by examining outgoing longwave radiation (OLR) plots from Paul Roundy at Albany. Looking specifically at the bottom plot, valid for April 20th to 27th, we see strong negative OLR anomalies (enhanced tropical convection) present in western Oceania, the same place where the CCKW is expected to travel in just a couple days. If this chart is to be believed, we may expect seasonal to warmer than normal temperatures for the end of April, as these negative OLR anomalies are in the typical Phase 5 and 6 MJO phases, which, as we looked at above, bring about warmer than normal weather in the US.

To sum up, here is a graphical representation of expected temperature anomalies across the month of April.

Andrew

April 10-14 Potentially Major Storm System

I'm monitoring the April 10-14 timeframe for some stormy weather.

Tropical Tidbits

The image here shows a GFS forecast map, valid on the morning of April 4th, earlier today. We observed a negatively-tilted storm system hitting Japan this morning, and if you've been reading this blog lately, you know that that means we're in for a storm here in the US in just a few short days. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. With this negatively tilted storm hitting Japan on April 4th, we're watching April 10-14 for a storm system in the United States.

There's a reason why I keep bringing up the negatively-tilted aspect of this trough in Japan. We may expect a negatively-tilted trough here in the US around April 10-14 in response, and there's a reason why the negative tilt is concerning.

USA Today

As the graphic shows, there are two types of tilts to a trough- positive and negative. The positive tilt trough sees the jet stream bending towards the southwest, as the Energy Pocket, also known here as the 500mb maximum vorticity, pushes in that direction. The negatively tilted trough indicates the system has reached maturity, as the vorticity maximum now pulls the system to the southeast. The mature storm now produces more vigorous storms, hence why we are concerned more when a negatively tilted trough comes around, compared to a positively-tilted trough. Since we might expect a negative trough to impact the US in the April 10-14 timeframe, it's plausible we also see a decent severe weather event in response to the negative tilt.

It's a bit too far out to tell an exact track for this storm, but as always, I'll update the situation in the next day or two with new information on this storm.

Andrew

Record-Breaking Kelvin Wave Begins Hitting Ocean Surface

We continue to see the record breaking Kelvin Wave pushing to the surface, and anomalously warm waters are now appearing from the subsurface.

Water temperatures from the coast of Ecuador across the Equator are decidedly warmer than normal as of March 26th, as the chart above from the Climate Prediction Center shows. We see an arm of warmer than normal sea surface temperature anomalies (SSTAs) extending from about the 100W longitude line westward to roughly 140W. This noticeable warming comes as the strongest Kelvin Wave in history begins to push to the surface, in what could result in one of the stronger El Nino events on record.

The image here shows temperature anomalies on a depth by longitude layout on the bottom panel of this graphic, and the Kelvin Wave is clearly marked. As of March 31st, the water temperatures maxed out as high as 6.35 degrees Celsius above normal, confirming that this Kelvin Wave does appear to be the strongest one on record. This body of warm water provoked by the Wave is beginning to push to the surface, and this is already observed well by the extension of warm water to the surface around the 160E longitude line. I expect sea surface temperatures to continue to gradually rise in response to the agitated Kelvin Wave as it begins its trek to the surface.

We have been seeing the telltale El Nino signal in the Southern Oscillation Index for some time now. The chart above shows observed values of the Southern Oscillation Index averaged across a 30 day time period, shown since roughly December 2011. We have seen a roller-coaster pattern, as the atmosphere has been undecided on whether it will declare a La Nina or El Nino, until recently. As the chart shows, the SOI has completely tanked in recent days, to levels approaching -15. Values below -8 are considered resembling of an El Nino, while SOI observations above +8 are considered indicative of a La Nina. With the SOI being as low as it has been, there's little question in my mind that along with this Kelvin Wave, and taking into account the predicted conditions in the Equatorial Pacific in coming weeks, that we are entering into an El Nino.

A spread of global model projections of the El Nino-Southern Oscillation (ENSO) phenomenon all agree on at least a weak El Nino forming by August 2014, but even this seems a bit weak to me. I fear that model guidance is underestimating the current Kelvin Wave, and the El Nino may be a fair bit stronger by August 2014 than what is being shown here.

Updates on this unfolding situation will be provided on a weekly or bi-weekly basis, depending on the new information available.

Andrew