In the previous posting (read it here) I discussed some major changes across the higher latitudes of North America. The change had, at least temporarily, shut off the North American Monsoon. But as the atmosphere adjusted to those changes, the pattern of jetstream winds that developed last fall (2020) "bounced back" into place and a similar pattern returned. The heat across the high plains has been a bit more extreme than it had been earlier in the summer, but was actually expected for this exact period. However, I was not expecting it to persist more than 5 to 7 days and we're approaching that length of time. But at the same time I'm not too surprised as summer comes to a close and the atmospheric winds spin down before increasing again here in the next two to three weeks. And those that have been following my blog know that the "new" pattern will be developing within the next 5 weeks. I do have some evidence that it may actually start to develop in late September.
Here is a look at the jetstream (the solid arrows) from this morning....
One item to note is that the North American Monsoon has returned for one last gasp (the dashed green arrow), and has helped to bring more precipitation to areas of the high plains (mainly Colorado and Nebraska). Unfortunately many areas of Kansas and west Texas have missed out during this past few weeks (again the atmosphere is spinning down for now and this has impacted the weather). The map of rainfall for August through yesterday, the 25th, shows those that got it and those that did not.
But in reality it could be much worse if it weren't for good rains earlier in the growing season. Here is the latest drought map...
Some of you may have caught wind of a tropical system bringing rain to the high plains the first few days of September. Unfortunately that came from my agency that I work for and what was depicted is just not realistic - there just isn't predictability 10 days out for details such as were depicted. The chance that a tropical system will develop in the Gulf of Mexico is near 100 percent. It will even probably become a strong hurricane. But as is typical, the exact track is very much unknown as of this Friday afternoon. The earlier map from my agency had it moving towards western Kansas. I've been in the weather business since 1983 and the ONLY tropical system moving out of the Gulf of Mexico that impacted western Kansas directly during that time period was Alicia in 1983! Even going back 150 years - that is the ONLY one! Remnants of dying systems can bring precipitation but it is FAR more likely from remnants of Pacific systems.
Ok - does that mean it will be dry first week of September? Not necessarily because there could still be a disturbance move along the westerlies (the jet stream) coming in from the Rockies. There is a chance based on the pattern than got established. But at this point it doesn't look like there is widespread precipitation on the way. In fact, here is the outlook of rainfall through September 3 (from the Weather Prediction Center)...
Later in September? Yes I think so and in fact looking at the repeating pattern that started last fall, and even given the end of the patterns cycle is near, the last half of the month should have an increased probability of seeing at least a few good chances. One of the forecast models that has consistently been predicting a wetter than normal September and has this....
But - the bad news is the skill of this model for this time of year and pattern is extremely low (hence what you see in the bottom two panels of gray). But I would lean towards the probability of at least a couple of "wet" events - again based on the pattern and not what is depicted by the model.
More later on a possible early freeze.
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