sebastiaan1973

Cohen: And as I discussed two weeks ago (see 27Nov_blog), a Canadian warming almost always transitions to either a stretched PV or an SSW. This time I am anticipating an SSW to follow. It is of my opinion, much of the winter will likely hinge on the nature of this SSW that is predicted to begin the last week of December. I think the models were slow to appreciate the magnitude of the energy transfer from the troposphere to the stratosphere. Where the energy leaves or diverges it creates cold, low pressure and the westerly winds increase or in this case in the troposphere. Where the energy enters or conerges it creates warm, high pressure and the westerly winds decrease or in this case in the stratosphere. That is why I believe that the weather models both showed a more robust weakening of the PV simultaneously predicting more low pressure and less high latitude blocking in the troposphere and milder temperatures across the continents. But if the SSW starts to go sideways and has little or limited (in both time and/or space) impact, I see little reason anticipate anything but an overall mild period for a more extended period. Once an SSW rolls over prematurely it is my experience that it takes many weeks for a chance at another one. Given so much uncertainty I will refrain to say much more today other than to expect greater than usual model volatility in the lead up to the SSW and even beyond. But I will leave you with two teasers. First the quasi-biennial oscillation (QBO) has a long history as an in and out fad and recently it is back in. This winter it is easterly and according to the most recent research that favors a more robust tropospheric response to an SSW and overall colder temperatures across the NH post the SSW. Second all the weather models are for now predicting a PV displacement, but this is still an evolving situation. The weather models are converging on a dominant wave-2 in the troposphere for late December (for example see Figure with ridging centered near the Urals and western North America and troughing in the North Pacific and North Atlantic. My personal favorite PV disruption, the PV split, is thought to be favored when wave-2 dominates the tropospheric pattern. AO/PV Blog Update | Verisk's Atmospheric and Environmental Research (aer.com) https://www.aer.com/science-research/climate-weather/arctic-oscillation/

Cohen: And as I discussed two weeks ago (see 27Nov_blog), a Canadian warming almost always transitions to either a stretched PV or an SSW. This time I am anticipating an SSW to follow. It is of my opinion, much of the winter will likely hinge on the nature of this SSW that is predicted to begin the last week of December. I think the models were slow to appreciate the magnitude of the energy transfer from the troposphere to the stratosphere. Where the energy leaves or diverges it creates cold, low pressure and the westerly winds increase or in this case in the troposphere. Where the energy enters or conerges it creates warm, high pressure and the westerly winds decrease or in this case in the stratosphere. That is why I believe that the weather models both showed a more robust weakening of the PV simultaneously predicting more low pressure and less high latitude blocking in the troposphere and milder temperatures across the continents. But if the SSW starts to go sideways and has little or limited (in both time and/or space) impact, I see little reason anticipate anything but an overall mild period for a more extended period. Once an SSW rolls over prematurely it is my experience that it takes many weeks for a chance at another one. Given so much uncertainty I will refrain to say much more today other than to expect greater than usual model volatility in the lead up to the SSW and even beyond. But I will leave you with two teasers. First the quasi-biennial oscillation (QBO) has a long history as an in and out fad and recently it is back in. This winter it is easterly and according to the most recent research that favors a more robust tropospheric response to an SSW and overall colder temperatures across the NH post the SSW. Second all the weather models are for now predicting a PV displacement, but this is still an evolving situation. The weather models are converging on a dominant wave-2 in the troposphere for late December (for example see Figure with ridging centered near the Urals and western North America and troughing in the North Pacific and North Atlantic. My personal favorite PV disruption, the PV split, is thought to be favored when wave-2 dominates the tropospheric pattern. AO/PV Blog Update | Verisk's Atmospheric and Environmental Research (aer.com) https://www.aer.com/science-research/climate-weather/arctic-oscillation/

Yep. You can find them here https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml

Windplume for De Bilt, I guess there will be almost the same for the south of England. Almost entirely west or southwest winds.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019JD030911 Thans to Blessed Weather I found this piece of intresting information. The MJO propagates more slowly eastward with a prolonged period of active convection farther into the western Pacific & In general, boreal winterMJO activity is enhanced when the equatorial lower stratospheric winds at 50 hPa are in the easterly phaseof the QBO.

Cold Scandinavia in January.

Latest MJO by EC46. The MJO is close by entering phase 6 (I guess tuesday). As that the moment the amplitude will change (right now forecasted in COD).

HI, this is a chart from 7 of december. Dennis, we see the MJO with little amplitude through phase 6,7. In phase 8 it gets better. But that is over almost a week when it comes there.

I guess a lot see the importance of the coming phase 6,7 and 8 of the MJO. I guess we have to wait until we get to phase 6 to get a real picture of the amplitude. Perhaps than we see soon a cold cluster in the plume. Right now, in the latest EC46 the MJO gets in COD when it reaches phase 6.

I suppose we have to wait until the MJO i getting out of phase 5, till we see a real change in the forecast (couple of days) if the MJO has enough amplitude.

This must be one of the highest UK barometer values. It would be a record for the time of the year in the Netherlands (around 1048 hPa), beating a record from 1905 (!)

Mother nature is excellent in spoiling our cold winter weather Over here in the Netherlands we hope to get an easterly with temperatures dropping below zero, so we can skate. In Belgium * south of the Netherlands they mostly want snow.

More ice & water is cooler than normal . Text below from: https://en.ilmatieteenlaitos.fi/ice-conditions/?41IwWJ2g4eC6q7wAZNe7q6_q=mode%3D1%26lang%3Den New ice is forming in all sea areas. In the northern Bay of Bothnia 15-35 cm thick fast ice and thin level ice to Keila, Ajos and Oulu 3. Farther out, new ice and thin drift ice to Malören, Bothnia buoy and approximately to 30 nautical miles south-west of Merikallat. Off Raahe, thin level ice to Heikinkari. Farther out, drifting new ice to Nahkiainen and Ulkokalla. In the southern Bay of Bothnia thin level ice and new ice in the inner archipelago. In the Quark thin level ice in the archipelago and from Vaasa to Storhästen. Farther out, drifting new ice and new-ice formation to Ensten. In the Sea of Bothnia, in the Archipelago Sea and in the Gulf of Finland thin level ice and new ice in the inner archipelago. Farther out ice formation. In the Lake Saimaa thin ice, new ice and ice formation. Icebreakers: Kontio assists in the Bay of Bothnia.

A good update from ECMWF.

A tweet by World Climate Service. We heading to a Modoki El Nino.

We often hear/ read that Russian anticyclones are destructive for our winter chances, no cold available. in my opinion this is not true. It all depends what the synoptic setting is in the Western Atlantic. As. GEM240h shows.

Altough we do need a split for the biggest impact.

And while a technical SSW is difficult to forecast with precision at extended leads, the expectation based on the composite analogs remains that one will indeed take place between approximately Christmas and January 8, along with a major winter storm in the vicinity of the holiday week. This impending disruption of the polar vortex is not only significant due to the sensible implications for later December and into January, but also the balance of the winter season given the unexpected prevalence of the negative NAO through the early portion of December. Having the NAO average negative prior to the vortex even weakening makes it extremely likely that December will end up featuring a negative NAO in the monthly mean. This represents a significant deviation from warm ENSO climatology and offers invaluable as to how the rest of the season may evolve. Research conducted by meteorologist Eric Webber confirmed that El Niño events that feature a greater incidence of negative NAO in December are more likely to exhibit additional episodes of high latitude blocking, leading to a colder and snowier outcome for January through March over the Eastern US. A nice read -> https://easternmassweather.blogspot.com/2023/11/december-preseason-impressions-appear.html And the Tweet where he writes about: https://twitter.com/webberweather/status/1728115422648562170?s=20 Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4966707

And while a technical SSW is difficult to forecast with precision at extended leads, the expectation based on the composite analogs remains that one will indeed take place between approximately Christmas and January 8, along with a major winter storm in the vicinity of the holiday week. This impending disruption of the polar vortex is not only significant due to the sensible implications for later December and into January, but also the balance of the winter season given the unexpected prevalence of the negative NAO through the early portion of December. Having the NAO average negative prior to the vortex even weakening makes it extremely likely that December will end up featuring a negative NAO in the monthly mean. This represents a significant deviation from warm ENSO climatology and offers invaluable as to how the rest of the season may evolve. Research conducted by meteorologist Eric Webber confirmed that El Niño events that feature a greater incidence of negative NAO in December are more likely to exhibit additional episodes of high latitude blocking, leading to a colder and snowier outcome for January through March over the Eastern US. A nice read -> https://easternmassweather.blogspot.com/2023/11/december-preseason-impressions-appear.html And the Tweet where he writes about: https://twitter.com/webberweather/status/1728115422648562170?s=20

And while a technical SSW is difficult to forecast with precision at extended leads, the expectation based on the composite analogs remains that one will indeed take place between approximately Christmas and January 8, along with a major winter storm in the vicinity of the holiday week. This impending disruption of the polar vortex is not only significant due to the sensible implications for later December and into January, but also the balance of the winter season given the unexpected prevalence of the negative NAO through the early portion of December. Having the NAO average negative prior to the vortex even weakening makes it extremely likely that December will end up featuring a negative NAO in the monthly mean. This represents a significant deviation from warm ENSO climatology and offers invaluable as to how the rest of the season may evolve. Research conducted by meteorologist Eric Webber confirmed that El Niño events that feature a greater incidence of negative NAO in December are more likely to exhibit additional episodes of high latitude blocking, leading to a colder and snowier outcome for January through March over the Eastern US. A nice read -> https://easternmassweather.blogspot.com/2023/11/december-preseason-impressions-appear.html And the Tweet where he writes about: https://twitter.com/webberweather/status/1728115422648562170?s=20

This is some serious cold. Anomaly chart for temperature at 2 meter.

Will this impact our weather?

Will this impact our weather?

Perhaps the model is better in the development to a positive NAO, than a negative NAO (blocking seems to be more difficult for models)

Excellent setup for disturbing the stratosphere.