Thursday: Clouds mixed with sunshine and rather windy. High in the low to mid 40s. NW winds around 10 to 15mph. (Catskills scattered snow showers, mid 30s).
Thursday Night: A fair number of clouds and breezy. Low in the upper 20s. NW wind at 5 to 10mph.
Friday: A mix of clouds and sun, cold and breezy. High in the mid to upper 30s. NW winds at 5 to 10mph.
Wednesday saw some serious warmth across the Hudson Valley… at least in terms of mid December. Poughkeepsie’s high of 52° was a full 12 degrees above average.
The next several days are looking uneventful… for complete details, please check out the 5 day forecast. As a rule, we will include all the forecast details you need there. Our goal with the 5 day, is to give you more information than you might get with a traditional 5 day forecast… so you don’t have to infer what we’re thinking. For example, if you check the 5 day, you’ll see in the commentary for Sunday that the coastal storm is no longer expected to develop. Hopefully this will be more useful.
So with that said, what we want to focus on is why the storm threat for this weekend has all but vaporized. We’ve seen a LOT of energy come into the western US over the past week or two. With a very strong Pacific flow in the jet stream, the computer models have struggled to figure out how the jet stream would respond further east. So here comes a very detailed look at the progression of the pattern. (Fair warning, this may not be everyone’s cup of tea… but we try to tell a story, so we hope you enjoy…)
The following maps are all European 500mb upper air pattern maps (basically the jet stream). Lets start by looking at the upper air pattern for Wednesday 12/17 (yesterday). The first image is the European model forecast from Saturday:
We’ve labeled the features we want to focus on. Last Saturday, the European model believed Wednesday would have a noticeable upper low over Michigan (A) and a rather strong low over California (B). The result also helped amplify the ridge in between, over the center of the country. Well… what actually happened?
The above image is the European’s initial conditions (actual observations) from Wednesday morning. Notice that both features, A & B are noticeably weaker than in the first image (from Saturday). The ridge feature in the central US is also weaker and flatter. So basically… the projected features from Saturday were all weaker than forecasted. That is due to the jet stream off the Pacific Ocean (southern branch of the jet stream) being faster and stronger than anticipated. It prevented the features from developing as much as originally thought.
Now… the differences are noticeable, but not stark. But like a snowball rolling down the hill… the impacts down the road are amplified. So now, lets look at the forecast for this coming Sunday 12/21. First… the projection from last Saturday’s run of the European model:
Ahhh… what could have been (sigh). Feature #1 shows a deepening Upper Low pressure just off the coast of Virginia. Feature #2 is a strong ridge over the central US, that acts like a pendulum, and helps to steer feature #1 up the east coast. Feature #3, is a piece of energy digging into the SW US, helping to amplify the ridge just enough to put the final touches on the painting of a very snowy picture for the Hudson Valley.
However, remember… this forecast was based on an upper level pattern that had stronger features than what actually came to pass. So taking that into account… what does the new projection look like for Sunday?
You would never guess that this image, is a projection for the same moment in time as the previous one… everything is different. The intensifying upper low in feature #1 has vanished. The reason? Because features #2 and #3 are faster and flatter (weaker) than originally projected. Notice how both #2 and #3 are further east by several hundred miles? The ingredients for the east coast storm (#1), never came together. The energy in the southern branch of the jet stream was too fast, and the energy in Canada never links up with it, to phase off the east coast. So you have small, seemingly insignificant differences… and when the snowball rolls down the hill 5 days later… the end result is completely different.
And THAT is how you go from major east coast storm, to nothing… in about 48 hours.
We hope you made it through the nerd-fest. When things don’t pan out the way we were thinking… we like to try and tell the story and explain why. Plus, it can be interesting to see how all the pieces come together. If any one little ingredient changes, the whole recipe can be ruined. We hope you enjoyed the explanation… thanks for your support, and have a great Thursday!