You probably all are tired of hearing me talk about a pattern change and that winter will finally grip the area. Well, I'm going to stick to it. With everything I have seen, I really do not have a doubt that a pattern will finally get set in stone. The reason computer models have had such a bad time with the pattern is because, if you haven't already noticed, the pattern has been changing every week. Last week, the jet stream was highly variable with more of a north-south motion instead of west-east motion, which is what caused the "mini ice storm" that many areas saw last Wednesday night and Thursday. When the jet stream is in a meridional pattern, which is when the jet stream is variable and has rather large longwaves in the upper atmosphere, strong surface storms tend to result, due to large areas of unbalanced winds (I would like to elaborate on this, but it really is complicated to a lot of people if you don't remember high school Physics.). Right now, the jet stream is highly zonal, which means the jet stream is very flat and not variable. When the jet stream is zonal, disturbances move rather quickly across the United States, and they are not able to produce strong storm systems. When the jet stream is in zonal pattern, mild Pacific air can easily flood the United States. When I talk about Pacific air, I mean mild air that is dry, not moist. The air mass is dry because of the drying that the air mass undergoes as it moves over the Rocky mountains. This week, I expect a rather quiet pattern as the jet stream remains quite zonal and the disturbances will be relatively weak. Even with that, there will be some rain Tuesday night, with rather light amounts of rainfall in the range of 0.10 to 0.25 inches of rainfall. The latest NAM is forecasting even lighter amounts with only 0.01 to 0.10 inches likely overnight Tuesday. The time frame for this rainfall event will be from the late evening hours Tuesday night to the early morning hours Wednesday. It will probably not be a widespread rainfall event with most areas not picking up much rain, because of its showery nature. As for temperatures, they will likely be well above normal for this time of year with highs in the lower 50's tomorrow. After the weak surface cold front moves through Wednesday morning, temperatures will only hit the mid 40's Wednesday, with a gradual trend toward much cooler temperatures by the end of the week. By the end of the week, the weather pattern looks to shift into a more favorable pattern for snow and possibly cold weather. The first step for the change in the upper levels to happen is a strong shortwave forecasted to move out of Northwest Canada and into the United States by Thursday and Friday. This will begin to develop into a positively tilted trough over the Central states. This is where the forecast gets tricky. By the time the trough begins to develop, the PNA index is expected to sky rocket at the same time. This means that a rather strong West Coast ridge will develop, leading to significant troughing over the eastern United States. If the trough would be negatively tilted, a major longwave trough would develop leading to a significant snowstorm across many regions and a massive arctic outbreak. Instead the ridge will try to complicate things further. It will attempt to close off the trough located over the plains, which at the same time will lead to significant development of possibly a rather large storm system, with three types of precipitation possible (freezing rain, sleet, and snow) by Saturday. If cold air is involved in the system more than currently expected, a widespread heavy snow and strong winds will develop north of the surface cyclone, right in the heart of our area, with sleet, rain, and freezing rain mixing in at times. If a more northerly solution verifies, than expect rain, possibly heavy, changing over to heavy snow and sleet in the comma cloud behind the system, with heavy snow accumulations farther north into Canada. This also depends on if the storm system becomes significantly strong, as positively tilted troughs are notorious for producing weaker storm systems. After that, a significant trough is expected to develop across the United States, especially in the East, and cause an arctic wave to move through after the system on Sunday, possibly bringing temperatures below normal. This trough will become more negatively tilted with time, possibly leading to a second significant storm system by Monday. In the long range, cold waves will become more frequent with the possibility of a rather significant and severe cold wave by mid February. Stay tuned for further updates.
No comments:
Post a Comment