Polar Vortex freeze coming to SOMa this weekend? Snow storm next week?
ridski said:
There’s a Washington Post article today talking about a PV shift to the east coast, and possible snow storm, but my usual go-tos for weather forecasting say nothing about this. Any clues as to what’s happening? Should we pull in all our plants already?
Plants should not be put outside until May 15 — no matter how tempting to do so— especially tempting these days when getting outside to garden is good medicine!
mtierney said:
ridski said:
There’s a Washington Post article today talking about a PV shift to the east coast, and possible snow storm, but my usual go-tos for weather forecasting say nothing about this. Any clues as to what’s happening? Should we pull in all our plants already?
Plants should not be put outside until May 15 — no matter how tempting to do so— especially tempting these days when getting outside to garden is good medicine!
May 15th is the 'official' last frost date. Most years, it occurs much earlier.
I watch the long term forecast, and then use my judgment. I have moved my cooler growing orchids (which can tolerate temps down to 30F) out already. I will cover them with plastic from Friday through Sunday AM, just in case.
I was raised by a mother who has never stopped announcing to any and all that only fools plant anything in the ground before Mother’s Day.
Although there is no freeze watch here at this time, overnight lows this weekend (May 8 - 10) will be in the 30s. If you have your house plants out, you might want to bring them in this morning before the rain.
There is no snow in the forecast for the immediate MAPSO area.
WxNut2.0 said:
FYI, it’s not the polar vortex. Just a dip in the jet stream.
Don't tell me, tell the washington post. Like I said, I couldn't even read the article.
ridski said:
WxNut2.0 said:
FYI, it’s not the polar vortex. Just a dip in the jet stream.
Don't tell me, tell the washington post. Like I said, I couldn't even read the article.
Many meteorologists have tried to tell them. That particular author is well-known to mislead people, including WaPo, about his qualifications and with his writing.
The technical definition of the polar vortex is a quasi-stationary feature that occurs somewhere around 30,000 meters above the ground. It is quasi-stationary in the sense that it exists in the winter and doesn't really move too much. By this point in the year though the polar vortex is typically no longer in existence as winter is over. The vortex itself has very little impact on tangible weather and is at this point mostly a buzzword.
That said, what is happening here is all about the jet stream. The jet stream is a completely normal current of wind about 20,000 feet above the ground that dictates the weather nearer to the surface that is constantly morphing and evolving. The evolution of the jet is exactly why the weather at the surface changes, as the configuration/strength of the jet stream is what leads to things like nor'easters. Typically there are two (sometimes three but we'll ignore the third for now as it's pretty rare that it becomes established) "branches" of the jet stream; the subtropical jet (the southern branch) and the polar jet (northern). You can think of the location of these two branches as 1. the areas that will experience noteworthy weather; and 2. especially in the case of the (northern) polar jet stream, the delineator of cold air from warmer air. Both jets act to delineate warm from cold air, however the polar jet stream is effectively the barrier that prevents air from the north pole from spilling out over the continental US. Some scientists have argued that the subtropical jet is actually a good delineator of the tropics from the mid-latitudes, which means that meteorologically speaking, NJ is technically tropical during the summer. But that's a different discussion for a different day.
During the transition seasons (spring and fall) especially, the jet stream can become extremely wavy, meaning that the current of air itself is not simply flowing from west to east, but rather has all kinds of dips and waves associated with it. These waves are known as troughs and ridges, which correspond to low and high pressure respectively. Underneath a trough the air is cold, and underneath a ridge it is warm. Sometimes when the jet becomes "too" wavy, little troughs can break off in the form of a localized vortex that acts to sequester the cold air inside. These local vortices can be extremely cold, especially when they were originally a part of the polar jet. That's exactly what is happening here; a small vortex has broken off the main wave train and has traversed south and east, carrying extremely cold polar air within it. This little piece is known as a "tropospheric polar vortex" (TPV), with the word "tropospheric" being extremely important here. The troposphere is the lowest layer of the atmosphere, and is the one we reside within. The normal polar vortex that is often referred to resides within the stratosphere. These TPVs are fairly common during the winter, though not as common this time of year. As a result of this TPV, we will likely experience record breaking cold air and perhaps a few flakes that more than likely won't stick. As the TPV moves north and east however, it may induce another buzzword phenomenon, a "bomb-cyclone" over the North Atlantic.
All in all this is a fairly interesting phenomenon that we may not see again for some time. For the true weenies out there, as of a couple of days ago this particular TPV was characterized by geopotential height anomalies on the order of -4.5 sigma, meaning that for this location and time of year the odds of occurrence are mind-numbingly low.
I hope this explains it.
TL;DR: The polar vortex isn't making it cold. A dip in the jet stream is allowing cold air from the polar regions to make its way south and impact the area. The polar vortex is a buzzword.
from Bob Roe: Meteorology is so cool. Literally cool tonight. With satellites, and radar and computers that allow complicated atmospheric physics data to be analyzed, weather reports are so much more accurate. One of my favorite weather alerts was a couple of years ago when a small tornado hit Springfield. The alert was that it was headed towards Maplewood. All our cell phones went off with the alert advising us to take cover. Instead we all went out the front door to see if we could see the tornado. It did not make it to Maplewood and dissipated very quickly.
RobertRoe said:
from Bob Roe: Meteorology is so cool. Literally cool tonight. With satellites, and radar and computers that allow complicated atmospheric physics data to be analyzed, weather reports are so much more accurate. One of my favorite weather alerts was a couple of years ago when a small tornado hit Springfield. The alert was that it was headed towards Maplewood. All our cell phones went off with the alert advising us to take cover. Instead we all went out the front door to see if we could see the tornado. It did not make it to Maplewood and dissipated very quickly.
For all the jokes about meteorologists being wrong, its pretty astounding to think that we can predict the future at all.
from Bob Roe: I really like how the Weather channels can show a radar picture of a thunder storm and then point out a small hook section of the cloud rotation that may develop tornadoes. Totally amazing. Spring is usually the most frequent time of tornadoes in the south and Midwest. My dad from southern Illinois had a tornado cellar, but he said one never hit their town when he lived there.
RobertRoe said:
from Bob Roe: I really like how the Weather channels can show a radar picture of a thunder storm and then point out a small hook section of the cloud rotation that may develop tornadoes. Totally amazing. Spring is usually the most frequent time of tornadoes in the south and Midwest. My dad from southern Illinois had a tornado cellar, but he said one never hit their town when he lived there.
The first time the hook echo was recognized was in Illinois: https://www.news-gazette.com/news/tornadoes-hook-echo-discovered-here-years-ago/article_cc5a6a2e-a968-5e0c-be7d-ada419641841.html
There’s a Washington Post article today talking about a PV shift to the east coast, and possible snow storm, but my usual go-tos for weather forecasting say nothing about this. Any clues as to what’s happening? Should we pull in all our plants already?