Glacier Point

T180: Three jet streaks in play across the North Atlantic. Ridge number 1 there beneath the poleward streak. T222: Trough carving through Texas, next amplification coming through

Your challenge Nick answered by another question. How many in that period have had Modki / weak / moderate end Ninos / low solar / coming after strong sustained weakening of the SPV ?

Agree with this Nick, although it's noticeable how much sub-tropical flow we get into the SW Atlantic through days 5-12 which is in line with tropical forcing signals. That, allied to the Euro trough gives a strong below average signal for us care of repeated ridge building in the Atlantic. If we get the cold entrenched, these become self reinforcing for cold. The impacts of the SSW this time are a lot more nuanced and subtle, but they're clearly having a big impact in the pattern.

Blocking features are not necessarily Greenland Highs. Within the context of a deep cold trough across NW Eurpe, you don't need strong blocking features. These are however still potentially on the table for the week 3 period, and would represent the icing on the cake. We go below average on the 16th, and remain there after.

Extended EPS T2s and T850s dipping at the very end of the run, which would be against model bias to drift back to climatology. I'm struck at the moment by the Scandinavian trough and daughter vortex over Canada. Perfect mirroring of the stratospheric pattern. This is a clear influence which does not fit troposheric drivers. Between the two features, uncertainty abounds, but you can't escape the model trend for deep cold uppers forecast within the Canadian vortex. That should, against other signals, continue to remove the Greenland High option. I think more +ve height anomalies and a more likely mid Atlantic ridge rebuilding but not necessarily Greenland Highs are of the order, and tonight's EC run will be viewed with interest - there could well be a very slow downwell of the stronger -U wind anomalies from the warming to come which might be the trigger, although I'd like to see some more NAM plots to get a proper handle on this. The tropical wave signal is moving extremely fast. By week 3, we could well be back to Dateline convection and Eastern Pacific. Again, good signal for sustained cold. Other features catching my eye: the deeply negative state of the Arctic Oscillation (not unexpected for the second half of the winter); and, related to this, the ridge extending into the Arctic from Alaska modelled to break off and move towards Siberian sector. With the clockwise rotation developing in the Arctic lower tropospheric flow, this shows signs of moving towards Svalbard by month's end. With the European trough embedded, that makes for some interesting permutations for February.

...and there's a difference between low tropospheric heights over Greenland with a deeply entrenched SPV and without it. The latter instance results in rapid changes in the lower circulation pattern.

Absolutely want to see the upper strat u wind resume westerly to aid in flushing through the -u wind signal

CFS weeks 3 and 4 identical to EC:

Look again Nick. STJ becoming evident across N Atlantic with split flow and ridge signal off the Eastern US

Effectively the -U wind signal waxes and wanes as it downwells appearing as a series of nodes at descending heights. It is a good signal if you're looking for tropospheric blocking, and would be difficult to model correctly *If* the GFS is correct.

and a hint on nodal propagation going on there ....

Interesting to note the key phase around days 8-9 when a tropical wave forces a ridge over the Southern US and enhanced sub-tropical flow develops in the SW Atlantic. That seems to be the trigger to the sudden slowing in the mid latitude flow, but likely to be related to downwelling zonal wind signal.

Significant adjustments to the eps tonight, much more amplified in the North Atlantic and across North America. Still got some catching up to do with the GEFS, and confirms it takes the EPS 2 days to react to GEFS when it switches. All model suites now carving out a deep trough across Scandinavia and West Russia in the extended. Significant as it cannot be attributed to upstream ridging or nascent polar blocking. First impacts of downwelling being felt?

.. back to views out of hotel windows in Torquay.... Unless and until upstream Pacific flow is resolved, and until strat downwelling takes place, out to day 10 will have a strong mid latitude high component for NW Europe.

GFS, GEFS and GGEM starting to find some consistency on the building Alaskan ridge around day 10. That allows ridge development in the North Atlantic. Notably end of GFS (p) and op also starting to develop sub-polar lows days 12+ across the NH, suggestion of slowing zonal winds aloft.

Noted difference between EPS and GEM/GEFS over handling of Pacific trough and downstream ridge over Alaska. GEM/GEFS more amplified on the trough and less flat across the North Atlantic.

wQBO extends down to just above 50hPa I think, but will be ‘footprinted easterly below that, so reduced shearing. The GSDM has to my eye been typically low amplitude (reduced tendency in AAM) in response to potential drivers through reduced equatoward eddy flux, but that should change in the coming 2 week period to allow for more extreme tendencies to develop. Polar field = all layers 1000hPa up to 1hPa, typically viewed as cross section

... all of a sudden, some notable model output beginning to appear... Progression of mjo towards favourable tropical forcing phases not to be overlooked here.

With the central warming date set at 1st Jan, earliest trop response seems to be 13th onwards. To restate - Stratospheric. Timescales. Are. Extremely. Slow. I suspect we may be at the longer end of the envelope for trop response (so more like 15-20 day) given that the duration of this warming event is extremely long. For downwelling signature I would normally look for a reorganisation of the upper SPV. That's clearly not evident just yet, and it may well be we are reliant on a massive -U wind signature muscling its way down. In the meantime, we are in what is a clear teleconnective phase, one where the (enso lead) pattern wants to go cold, but is prevented from doing so by the atmospheric field over the polar region not being conducive. A clear cut signal for mid latitude highs. The unfavourable AO state is being driven by constructive interference from the stratospheric warming and tropical forcing in the Pacific. looking at the tropical forcing signal for weeks 2 and 3 with a return of forcing to the far Indian Ocean, that would suggest a slowing and retraction of the Pacific Jet. We therefore have a plausible favourable time line for downwelling stratospheric signal and tropical forcing opening up end week 2 into week 3. For those on the 2001/02 bandwagon, no propagation, I offer this. This was one of my analogues that performed well during the summer and early autumn. Atmospherically it punched above its weight during the autumn with AAM running well ahead of the enso indices. However, this analogue was rejected for the winter as it fell at the complete opposite end of the solar cycle, and could not mirror the enso values experienced this winter. Additionally, and crucially, I cannot see this analogue holding a candle the scale and extent of the major mid winter warming we are about to embark upon. That gives me a 70% chance of downwelling taking place, but more likely on a much longer time scale that many are anticipating. the broad scale evolution looks to remain as mid latitude high retrogressing north and northwards over time.

Agree with timings there Nick. Warming date looks to be 31st December and split on 3/4th January. That gives 11th January as first real opportunity to gauge any impacts on the tropospheric pattern. Suspect that the continued warming forecasts are a hindrance to fast downwelling. It's all related, but the destruction of the SPV is possibly constructively interfering with the tropics. That MJO signal for week 1-2 is well beyond what we would expect for an +ENSO pattern. As the atmosphere choreographs itself, an MJO in Phase 8/1 and downwelling -U wind continues to be the end destination. Expectation would however be for the MJO to weaken significantly through phase 7 but regain intensity in phases 8 / 1.

Take a look further down. 12z op likely to be a significant outlier synoptically in our quadrant based on this. Placement of the vortex west of Greenland the vital thing here. GFS likely to have it too far east and north here.

..think you'e going to like the 06z GEFS ! Whilst the fixation with 10 hPa layer is understandable, analysis of 50 hPa layer proving to be most useful at this stage, particularly regarding ridge development.

06z Parallel much more aligned to what EPS and GEFS means are showing (and also splits the SPV). Not wholly surprising the op GFS turbo charges the +NAO and +AO in low resolution. Week 2 tropical modelling looks not uninteresting as a starting point to migrate the mean ridge NW.

12z eps doubles down on that split idea. Now clearly apparent on the means. We sit here waiting for downwelling.