November 13-16 Potential Winter Storm

There is a very slight chance of a winter storm that may impact the Plains, Midwest and Northeast.

The European model had previously been showing a major snowstorm in the Plains, Midwest and Northeast from the November 13 to November 16th period. This came as the model projected a storm system to develop in the southern Plains that then moved north and east to spread snow across the aforementioned regions. The model has since lost the idea of the major storm, but with other guidance also showing the potential for snowfall in these regions in roughly the same idea (which we will discuss later), we are gong to look at the mid-level atmospheric set-up to determine if that forecast is even realistic.

The mid-level synopsis for this time frame from the 0z ECMWF shows a deep trough across the Plains, which in turn has provoked slight ridging in the East that gradually increases to a staunch high pressure system on the Maine border with Canada. This does have some merit- with model guidance in agreement on stormy weather prevailing over quiet weather on the West, the potential for high pressure ridging in the Southeast grows. That said, with the idea of a storm system arriving in the Plains, it wouldn't be difficult to imagine that the storm would then make a beeline for the Midwest and Plains, before possibly pushing north or east. This would only be possible if we see the colossal ridge in the Bering Sea break down in the day or two leading up to this projected storm.

Ensemble guidance confirms the widely-expected idea that a massive ridge will blossom in the Bering Sea in the next several days. When that happens, a very meridional (wavy) pattern will evolve throughout the eastern Pacific and North American regions. This huge ridge in the Bering Sea will lead to some decent troughing activity across the waters in the far northeast Pacific, with this resulting in ridging across the Rockies in North America.

Two or so days later, models agree that the ridge will start to flatten out across the northern Pacific, and it is here where the potential for this storm system arises. When that ridge flattens our, it is expected that the aforementioned troughing anomalies in the northeast Pacific combine with negative height anomalies in the Arctic to create an elongated negative height anomaly zone, and this would be expected to carry the storm system. As the elongated negative height anomaly zone moves east into the Rockies and Plains, previously-entrenched ridging over the Canadian Maritimes flexes its muscles once again, and provokes a situation akin to the one shown in the second image on this post.

Based on all of this information, and accounting for trends in the GFS and its ensemble set, I'm really unenthusiastic about this storm. While it technically can happen, and there is a chance, bear in mind that chance is very low. I do think there will be a chance for some snow during this timeframe as the pattern attempts to switch to a more winter-like pattern, but as of now, I'm not seeing a major winter storm in the forecast for the Plains, Midwest and Northeast.

Andrew

Spike in October Sunspots Raises Concerns for Warm Winter

New data concerning the monthly averages of sunspots has come in for October, and the results show a spike in sunspot values for that month. If we go by the acknowledgement that sunspot spikes precede a warm weather trend by 2-3 months, it's possible we see a solidly warm start to winter, possibly extending beyond December.

As the graph above shows, sunspot values jumped up for the month of October. While they are still below normal in the grand scheme of things, my concern now is that we see a decisively warm start to winter. For an example, see the fall of 2011 in the graph above. A very similar situation unfolded- a spike in sunspot numbers in October preceded the winter of 2011-2012, and we all know how that winter actually ended up. I'm not saying this winter will be like 2011-2012, but this sunspot spike does increase the potential for a warmer winter.

The chart above shows a composite of winters following a spike in sunspot numbers. This chart tells the story, with a clear trend for warmer weather over much of the United States as a result of these sunspot spikes. To fit the criteria, the winters of 2001-2002, 2005-2006 and 2011-2012 were picked solely as a result of the fall spike in sunspots, with other atmospheric patterns (i.e. ENSO, PDO, AMO etc.) not taken into account. That said, the aforementioned patterns, among many others, will alter the temperature pattern for this winter. But this composite does give us an idea of the potential consequences of a fall spike in sunspots.

Andrew

Analysis of October Snow Cover and its Impacts on This Winter

There has been an emerging idea that the amount of change of Eurasian snow cover below 60N in October can give excellent clues on the prediction of the Arctic Oscillation for the following winter. Judah Cohen, who made the Snow Advance Index (or the SAI), says that if snow cover ends up higher at the end of October than at the beginning of the month, the chances of a negative Arctic Oscillation greatly rise. On the other hand, a negative change anomaly from October 1 to November 1 then influences the potential for a positive Arctic Oscillation, and thus warmer weather for the US in winter.

Now that October has passed, let's take a look at the graph of October snow cover for the 35N-55N latitude region.

Taking a look at this graph, we see a definitive above normal snow cover trend for the month of October. The graph suggests snow cover began around normal, and ended well above normal. This tells me that the Arctic Oscillation may very well be negative this winter, as Cohen's SAI would deduce.

I'm not fully sold on the idea of a sustained negative Arctic Oscillation for this winter. For one, the Quasi-Biennial Oscillation (a wind-related oscillation that affects the stratospheric and tropospheric weather patterns, particularly in the Arctic) is in a weakening positive state. The positive QBO state means that the polar vortex is more likely to be seen as stronger in the winter, and a stronger polar vortex fits the definition of a positive Arctic Oscillation. If you've seen my Final 2013-2014 Winter Forecast, you also know that Michael Ventrice was able to fit the QBO into eight phases, each of which has different effects on the northern hemisphere. We are currently entering Phase 6 of the QBO, which enhances the strength of the polar vortex, per the QBO phase composite included in that forecast. A ridging pattern in the Southeast also appears possible based on this QBO composite, but the point is that the negative AO that may be induced by this snow cover anomaly may need some time to deal with the unfavorable QBO. I expect we see some down right cold weather in the end half of winter, and this could very well be when the AO is at its lowest points.

Andrew

Pattern Change Coming for Early November

Ensemble guidance is indicating that the weather pattern over the Pacific waters and over North America will be changing in coming days.

The GFS Ensembles above show the development of intense troughing in the western US, along with high pressure in the East SU US as a byproduct. This comes as the overall pattern in the Pacific also appears to be in line for changes, including the troughing pattern being replaced by a more persistent ridging pattern. Longer range model guidance indicates that this ridging in the pacific will strengthen, but it is possible we see the West US troughing evolve in the waters west of the coast of California. This would be good news for those in the Central and East US who want the cooler fall weather, as offshore troughing could incite ridging in a portion of the Rockies, which could then lead to some cooler weather in the Central and East US. The Central US would be more likely to see this cold weather, as it is possible some slight ridging would appear in the East US. This trend is partially shown in the GFS ensemble temperature departure forecast for 9 days out:

Andrew

Halloween Potential Major Storm System

There is the potential for a major storm system in the Plains and Great Lakes during the Halloween timeframe.

There are currently two different model projections, so we'll start with the ECMWF model. The sea level pressure forecast for the morning of Halloween shows deep pressures across northern Minnesota and Wisconsin, with a tight pressure gradient across the eastern Midwest and Great Lakes. This tight gradient is suggestive of a high wind field in those regions, and the ECMWF confirms this with 5000' wind speeds peaking just over 50 knots in Michigan, Wisconsin, Illinois and Missouri on Halloween. This translates to some awfully gusty winds for the aforementioned states, and windy conditions across the north central states in general. As far as precipitation, the ECMWF hints at non-accumulating snowfall across the upper Plains, and overall precipitation isn't horribly more impressive. This would be more of a big wind event rather than a big winter storm.

The GFS model keeps this storm system further south, with the lowest pressure centered over southern Wisconsin and northwestern Illinois/northeast Iowa. The GFS actually follows the ECMWF with low to practically non-existent snowfall over the upper Plains, but differs from the model with a rather high amount of precipitation falling across the southern Plains and parts of the Midwest.

I'm thinking that a compromise between the two models may be appropriate, with wind being a pretty good portion of the storm, but some wet conditions also arising in the Midwest and southern Plains. With the Pacific North American (PNA) index rising to a weak-moderate positive during this storm, but the North Atlantic Oscillation (NAO) in a strong positive phase, expect the storm to go through the upper Midwest.

Andrew