Glacier Point

It will continue north until it meets the next push of cold uppers coming in from the north / north-east. That looks to be around days 10-12, so yes scope for northern parts of the U.K but questionable how much it can dent the embedded cold airmass.

That blizzard next Friday is closer than that in reality. Once the upper flow around day 4 buckles poleward, the subsequent southward shift in the Atlantic jet due to the push of cold uppers leaves that as an eddy feature which has nowhere to go but just meander within sub 528 DAM air. The only questions are how far north it gets.

Worth noting that the 00z, 06z and now 12z GEFS is building back +ve height anomalies to our north and north-west beyond day 10. Indicative of the second tropospheric response to the stratospheric warming. If there is any breakdown, it won't be a long one.

Away from the impending brutalness, are we about to see another high amplitude MJO wave develop ? Currently quite a large convective signal across the Indian Ocean (different indices depicting different phase locations due to large aerial extent). Surface and particularly sub-surface temperatures very conducive in the Western Pacific. Rapid orbit into the higher aam states entirely feasible during March, with associated blocking signal persisting to the N/NE.

Thursday looking absolutely brutal cold with that wind chill. Attacks from the north and south lining up, northern one expected to win out which means we go into week 2 cold.

This is the sort of synoptic I would be looking for around the t300 mark. That's around the time our second downwelling pulse should be making itself felt. Not what those of us hoping to be going to Cheltenham the following week will be wanting.

Do think the idea of small 'cold' ridges appearing over Scandinavia and to our north is a sound one once this initial cold incursion wanes. And that's before our next proper influence from the strat warming is felt.

Not to get too carried away with at this stage, but EPS has an implicit snow threat from the south in one weeks time. Similar in evolution to ICON. Little upper level steering at that stage, so any system likely to meander.....

So far, text book. First tropospheric response will not be the last. Second and third waves, the latter with the most pronounced impact in the AO still likely, these timed around mid to final third March into early April. The MJO wave from January and February left a footprint in the Equatorial Pacific. Don't think this was oceanic Kelvin wave given its timing and duration.

Not sure why the angst GFS v EC placement of cold uppers. Both will be equally cold at the surface, and worth noting that there is no difference between EPS and GEFS mean ppn anomalies over the day 1-15 period. If anything EPS would be more likely to deliver something white (away from solely east facing coasts) for many beyond the day 12 mark. Angular momentum continuing to head down in response to eastward propagation of coupled convective waves in the Indian Ocean week 2. probably a stalled GWO phase 2 response. Strat warming will affect this composite, but broad scale signal for Euro trough there, as per EPS.

EPS and GEFS T850s are like chalk and cheese. I can guess the sort of issues that will be having on trading floors right now .... There is a continued shift towards a re-invigorated convective signal in the Indian Ocean. Phase 2 MJO. During December and January, such a trend would be what we have seen overnight from the GEFS and other operationals. However, we are not in December or January and we are nearly at March. That poses all sorts of seasonal wavelength issues. GEFS mean days 11-15 remains relatively consistent with the EPS and its previous runs, its just the 850 values being elevated. GWO phase 2 for March highlights the dichotomy in model interpretations right now.. Let's put that (tropical only) MJO composite against the GWO (tropics + extratropics) side by side for comparison. Model fog continuing I think, but thoughts would still be for a more genuine -NAO (and associated temperature signal) and more particularly the closer we get to the end of the month.

So, looks very much like a trend towards lowering AAM as we head into final third of the month. This looks like the synoptic evolution: > > > GWO phases 8 - 1 - 1(March) - 2(March) Phase 1 for Feb suggests too much flow going over the top of any ridge to sustain necessary advection west of cold uppers. Last five or six days of the month particularly problematic given rapidly altering wavelength and impacts of strat warming. Messy in a word, but reasonable sequence would take the NAO positive to negative.

If anything, these timescales may have come forward a touch on overnight data. Much more movement of tropical indices towards the Indian Ocean, favouring GWO phase 1 response. However, here's where I'm constrained by calendar monthly analysis. Composite for GWO Feb phase 1: Composite for GWO March phase 1: Surely it couldn't be that simple ? The compromise between the two would best fit - amalgamating both Feb and March dates gives: Not particularly helpful, but does suggest Euro trough is the key factor here. Model with best fit on this seems to be the GEM operational.

Just to put this to bed. Any uptick in solar would not have any impact on the set up here, in fact cooling of the outer layers would reinforce the blocking signal coming from above.

Thanks Alastair - I like it when which ever way you dice the assessments, you get the same end result. As per Ventrice's plot, week 2 looks good for convective wave to be centred with a bit more umph East Africa / West Indian Ocean ?

Tropical forcing will get impacted by the strat warming - most likely will get suppressed. Additionally, we have the convective coupling moving towards the far western Indian Ocean, negative frictional torque territory. Put the two together, and the engine house for aam will go into slow speed. We've also been in a solid Nina state for some period, which will have imprinted on the atmosphere. So some reduction in overall aam and negative tendency look the best place to look. I wouldn't go for a big -AAM target, maybe -1SD max given likely westerly additions through 30N-40N. Interestingly, the likely strat impacts in the high latitudes are best expressed through tropical analogues for African and West Indian Ocean convective centres. Some sense of choreography there ?

GEFS (as per EPS) still gunning for a monster ridge, initially to our N then across Greenland. Transition seems to be around day 9 or 10. Not convinced over any significant westward transfer of that blocking structure (remember how many times models have failed to pick up bits of residual trop vortex over the Canadian sector). All of which leaves us with high chance of cold + trough signal. Hmmmm

Couple of observations here.. The magnitude and longevity of the stratospheric warming may favour a slower, much more assured downwelling zonal wind signal. Even at day 15 GEFS struggle to get 10hPa winds to revert back to westerly. Think of it as a flushing through the atmosphere - ideally looking for the upper layers to begin to cool in response to downwelling. This argues for a tropospheric response later rather than sooner, more towards month's end (and well beyond). Like Brexit, the SSW has become the only game in town, but there are other factors we should have bandwidth for. Angular momentum rose dramatically in January in response to a major MJO wave. The GWO responded with a classical high amplitude orbit. However, phase 8 composites sifted for the La Nina years aren't what you would expect: Transference of this to current situation makes this tricky, but the idea of not all of the atmosphere being totally cooperative to stratospheric lead should not be discounted. That's the bad news out of the way. The MJO is forecast to be centred over Africa and enter the Arabian Sea during week 2. The idea that it will become weakened is sound given the theory that a SSW will impact the tropics and reduce the scope for wave development. So, a weakening tropical signal centred in phase 1 - 2 looks right. That translates to a loss in overall angular momentum and a more substantive negative tendency in angular momentum. Given we are still at relatively high levels of angular momentum, I would suggest a long phase 1 period upcoming, entering phase 2 final destination by months end into March. The composites for March phases 1 and 2 sifted for La Nina bear much more resemblance to what extended GEFS and EPS are suggesting: And factor in the impacts of the strat warming being timed at this time, which will likely excite this pattern. So bottom line is that expectations in the next ten days may need to be a little reigned in, but thereafter....a strong, convincing signal for a genuine -NAO pattern to take hold.

So 10 days after the warming date, we get first wave of tropospheric blocking developing: Next wave between days 20 and 30 although no detail on placement of that - so first week March. Peak effects around days 35-50 (mid March onwards). Spring looking on hold, and cold Cheltenham Festival beckoning. What have we learned so far ? Well, even though the warming was predicted by the models, they only managed to capture a tropospheric response until it was underway, so some way to go there in improving strat-trop modelling.

This is going to be a fantastic event to monitor. A top tercile magnitude MJO event in the Indian Ocean leads to a potential record strength reversal in zonal winds, leads to what tropospheric impacts ?

This feels like a long time ago now. GFS advertising around the 13th February as key date. That's 36 days after Indian Ocean coupled convective wave passage, so the timeline bang on and yet again another example of the slow time scales for stratospheric - tropospheric events.

Big swing in (synoptic) GEFS coming up in the extended..

I think we will look back at January's H500 anomaly and think how on earth was it not a frigid month ? Lack of cold pooling to our east doesn't seem so much of a potential barrier this time round, so is the EC op correct or more appropriately in the right ball park ? Looking at today's MJO synthesised plot, we are already in a phase 4 / 5 transition and heading towards phase 6. EC looks much closer to the mark on this, the GEFS dragging its heals a bit (low angular momentum bias?). Angular momentum, as expected, showing an upward trend. The key questions being the rate of injection of westerlies arising from the tropical wave shifting eastwards, and extratropical interaction. I suspect GEFS is too slow, EC closer to the mark on the tropics so we must assume more westerlies than being shown by the GFS products, and therefore greater prospect of more amplification commencing day 7 onwards as the GWO is shifted closer to a phase 4 transition. Interestingly GFS angular momentum shows a slowing of the westerly flow at mid latitudes from day 7. That's potential eddy signal which Scandinavian ridges are made of. Looking further ahead, we continue to see eastward migration of the MJO and every chance that it will enter phases 7 and 8 during early February. Synoptically, cold signal still there so getting some cold over or close to our shores will be crucial. So bottom line is I'm much more enthused by the EC signal albeit with some reduced strength from 12z EPS compared to last time around.

Models seem to be hitting a brick wall after day 10, large scatter developing thereafter

More appropriately, whereas the MJO and GWO were in sync for the Indian Ocean passage, they seem to be out of sync for the uptick in angular momentum likely. MJO for phases 4/5 compared to phases 3 and 4 of the GWO: <<MJO (look familiar to 06 GFS op?) << GWO