This mechanism is referred to as the Typhoon Rule, and states that weather patterns found at the 500mb level can replicate themselves over North America 6-10 days later after they appear over Japan. We see forecasted 500mb height contours and anomalies (with legend on the right) in the left-hand panel, with the ensemble ‘spread’ on the right image. The image above shows the GFS Ensemble forecast for the Pacific-North American (PNA) index, which is based along the West Coast of North America. Shown above is a near-analysis of the meteorological environment over eastern Asia for the morning of January 17th. At this time, we saw a storm system skirting the eastern coast of Japan, intensifying somewhat as it did so. At this time, the winter storm discussion remains preliminary. However, as I was sifting through the data I wanted to include in this post, I came upon the realization that this data indicated a threat for a potentially major winter storm around the Thanksgiving timeframe.

We’ll start off with the long range thoughts, and then go into the major winter storm threat. THURSDAY: After a frigid start early, mostly sunny and turning a bit milder in the afternoon. We’ll start with the teleconnections, with the Arctic Oscillation up first. Similarly, if stormy weather is found in the Arctic landmass, the North Atlantic Oscillation is declared to be positive. In the positive phase, high pressure anomalies are found along the West US and into Southwest Canada. The image at the top of this post displays a widening of contour lines under the number 3. When you get the expansion of these lines, it is typically demonstrative of high pressure anomalies present in the area. Let’s say that on November 26th, a certain number of ensembles are showing a relatively similar forecast. This tells us that the ensembles are uncertain as to how likely this particular factor is to actually occur, and results in a wider spread of ensembles.

This ridge in the West results in cooler weather for the Plains and Midwest, as the CMC ensembles depicted, but that then leads to some slight ridging over the Ohio Valley. This image shows the cold front creating a traditional squall line as a cooler air mass moves in over the area. The ECMWF’s proposition of a cold air mass across the entire Bering Sea would suggest more of a long-term cold weather period, across a big chunk of the nation. This has been the case in the last few days for some in the United States, but with the big cold snap coming into the heart of the nation starting today, that warm weather trend will be quickly reversed. In the image above, valid September 17th, we see a swath of negative height anomalies overtaking Japan as a rather strong upper level low scrapes the nation to the north.

Once again using this Typhoon Rule, we see the forecast on September 21st calling for continued deep troughing over Japan, now pushed deep into the country. Now shown above is a two-panel forecast from the ECMWF ensemble system. Still, this part of the forecast must be monitored closely for the discrepancies described above. The image used above is a forecast from the GFS ensembles, but the part I disagree with is for its forecast in the Northeast Pacific, not over Japan. If you are above 500 ft, you will see some very light accumulations. Also this will serve as your protection against the wide temperature variation in South Texas as it is usually made up of thick material. But going farther south along the Cascades toward Oregon and snow levels are up to 5,500 feet by the time you get to like Lewis County. I hope you get to come. This is where a tire repair kit would come in handy. 24 hours ago, we were expecting supercells to form out ahead of the cold front, with a weak squall line come with the cold front. This was not expected 24 hours ago.

Regardless of which index wields more power, it is agreed on that the Arctic Oscillation does play at least some role in the US’ weather, and this is why it bears watching. The NAO has a positive and negative phase, like the Arctic Oscillation. It is like going from old analog TVs to high definition. High temps return to the low 40s Thursday and the mid to upper 40s to close out the work week and the weekend. The NAO is determined by pressure anomalies in and around Greenland- if there is abundant high pressure in Greenland, the NAO is determined to be negative. The current, pronounced easterly pressure gradient (4 to 5 mb from Tucson to Deming NM) led to winds occurring much of the night across most of the city. KimberlyLake – thank you so much for voting up and taking interest in Ilha Berlenga. I was taking a look at the long range this morning, and decided it was time to do a post on what my thoughts for the middle and end of November are. Even though this is definitely a long range forecast (and thus shouldn’t be seen as high-certainty), the premise is concerning. By now, the cold front has hit a warm air mass and has created a defined squall line as seen in the picture.