Significant Arctic Outbreak Threat Rising for Late January

Model guidance is combining with the long range tools commonly used on this blog (namely the Typhoon Rule) to portray the country's best shot at true wintry weather to end the month of January.

We'll start off with the Typhoon Rule.

Tropical Tidbits
Click on any image to enlarge

The above image shows the GFS forecasted 500mb geopotential height anomaly forecast in the West Pacific region, valid for the morning of January 17th. In this image, we see warm colors, indicative of positive height anomalies / typically warm and quiet weather, but we see a much different picture over Japan. In Japan, a strong upper level low is impacting the country, sliding to the east as it does so. Notice how the center of this upper level low appears to go directly over far northern Japan.

The Typhoon Rule can be used to predict weather phenomenon in the United States. The rule of thumb indicates that weather phenomena impacting Japan is reciprocated in the US about 6-10 days later. So, if we see a strong (and very cold) upper level low crossing northern Japan on January 17th, we can extrapolate this upper level low to "re-appear" in the US on a January 23-27th timeframe.

Does this solution have any support from ensemble guidance? Let's find out.

Weatheronline

The image above shows 500mb geopotential height values (not anomalies) from the prestigious ECMWF ensembles set, valid on January 25th. These types of charts are generally used to identify the presence of large-scale ridges or troughs. In this image, we see a very pronounced depression in the contour lines, bringing the 520gpdm line all the way down just south of the Canada/USA border. This depression of contours shows the presence of a strong upper level low, which is actually centered all the way up in northern Canada.

The strong upper level low is being forced southward due to that strong ridge of high pressure developing along the West Coast. Other guidance eventually does much bigger things with that ridge even further down the road, but we'll get to that a little later on in this post. For now, the takeaway from this forecast is very cold conditions might be on deck for the late January period. I have discussed this end-of-the-month timeframe for some cold weather in earlier posts, but its significance is quickly becoming more realized.

ESRL

Next up, we'll analyze the ensembles off of the ESRL agency, a physics-based modeling branch of the NOAA body. In this image, showing 500mb geopotential anomalies for January 26th, we see a similar layout as the ECMWF ensembles showed. Strong negative height anomalies are developing in the Central and East US as the ridge along the West Coast continues to build and push northward. In these sorts of situations, the ridge may force itself so far north that it becomes a 'blocking' mechanism.

What is 'blocking'? My favorite example is to imagine a highway, with traffic moving along at an even pace. That's a good representation of the atmosphere during 'normal' flow. Now, imagine something happens on the highway that forces the cars to stop - a back-up, perhaps. The cause of this 'back-up' is analogous to the blocking ridge of high pressure; the ridge forces itself towards the North Pole and blocks the atmospheric flow from moving things along. This has been known to produce flooding, long-lasting cold, or intense warmth, depending on the season and who is affected.

ESRL

The upcoming pattern is very similar to that shown by the negative phase of the West Pacific Oscillation (WPO). In the image above, we see typical temperature (bottom panel) and 500mb geopotential height anomaly (top panel) values for a positive WPO phase. Notice how stormy conditions persist just west of the Bering Sea during a +WPO phase, leading to warmth across most of the Central and East US.

To see the typical conditions during a negative WPO phase, just flip the color scale. We then see intense ridging just to the west of the Bering Sea, leading to sustained cold flooding the Central and East US. The eventual alignment of this ridge into the waters near the Bering Sea, as the GFS ensembles are indicating, would lead to this -WPO pattern.

The final (and what I consider the most surprising) part we have to go over is the analog forecast.

CPC

This image shows projected 500mb geopotential height anomalies, valid for about 11 days from today, based on the top ten analogs (dates with the atmospheric pattern similar to the one forecasted to occur 11 days from today) produced at the Climate Prediction Center. In this image, we can see that strong ridge along the West Coast of North America into Alaska, resulting in below-normal anomalies over the Central and East US, eastern Canada, and into Greenland. Just for kicks, let's see what the top analog of 20090118 (January 18, 2009) shows, since it has been deemed the most similar to the forecast down the road.

ESRL

Above, we see temperature anomalies from January 16, 2009. I went back two days as the cold wave had already pushed east by January 18th; we want to get a diagnosis of the cold wave itself. This graphic is in units of Kelvins, but we can easily convert to Fahrenheit.

The core of the cold extends from southeastern Minnesota into far western West Virginia. A spot of values below -17.5 degrees below normal (Kelvin) shows up along the border of Indiana and Ohio. Let's see how -17.5 degrees below normal in Kelvins translates to Fahrenheit. Doing the math, that area saw temperatures 32 degrees (Fahrenheit) below normal for this cold wave, deemed the most similar to what we could see to end January. That's very impressive; for a scale of how impressive it is, consider that the average temperature in Richmond, Indiana (very close, if not inside that -17.5 Kelvin anomaly) to end January is 37 to 38 degrees F. In this cold snap, temperatures likely dipped down to just above zero, with even colder conditions to the north.

By no means does this mean we'll see something as cold as what happened on January 16, 2009, but it gives you an idea of the type of pattern that's coming down the pipe to end January.

To summarize:

- Model guidance and the Typhoon Rule are in agreement concerning a potentially significant cold blast at the end of January.

Andrew