Models, teleconnections and nowcasting

[knocker]

The EPS continues to indicate a strong vortex in the Arctic and the lessening of the amplification in the european sector. This doesn't portend anything, drastic initially,and in fact could even lessen the risk of cold incursions

 

[Blessed Weather]

A look at the 20th Dec 0z 500mb mean height anomalies for the 3 days ending 29th December from ECM and GFS op runs shows good agreement on the location of the tropospheric vortex, but otherwise some variation. GFS a tad more amplified than ECM over the Atlantic with the trough further east, coming up against the Euro ridge slightly further west, suggesting the GFS model is less clear-cut regarding a drier spell for the UK?

In another clear variance, the ECM has a stronger Siberian ridge and Aleutician trough combination, which is a favourable tropospheric pattern for generating Wave propagation into the stratosphere and disruption of the SPV. 

[knocker]

The 0600 gfs hasn't abandoned the idea of developing a low at the base pf the trough through Wednesday

Edited December 20, 2019 by knocker

[knocker]

Quite interesting to see how the 0600 gfs develops the low over 24 hours in the baroclinic environment of the south east quadrant of the upper trough

[knocker]

This evening's effort by the gfs

1800 Tues > 1800 Thurs

[knocker]

The most noted feature on the GEFS medium term mean anomaly is the strong ridge orientated across northern Russia. Thus the strong westerly upper flow diverges in mid Atlanticas one arm backs around this whilst the other continues around the European subtropical zone.The det run might struggle to sort the surface analysis

This Russian ridge weakens somewhat in the ext period but there are further developments upstream with a strong vortex and more am[amplification vis the east Pacific/ trough complex. Still a work in progress

 

 

Edited December 20, 2019 by knocker

[knocker]

The baroclinic zone around the trough/ridge boundary is still causing some headaches as noted on this evening's ecm over the Xmas period

[knocker]

The medium term EPS mean anomaly is in the same ball park as the GEFS with some obvious differences

Downstream there is some divergence of the upper flow in mid Atlantic resulting in a weaker flow running around the subtropical ridge over the UK. This indicating a relatively quiet period  but tending towards a N/S split

In the ext period there are some changes up stream with a more pronounced East Pacific ridge/trough combination allied with an intense vortex with trough extension south east.

Under this runs the strong westerly upper flow  across the Atlantic and then around the subtropical high. Nothing negatively anomalous about the Atlantic so a changeable scenario and it still portending a N/S split over the UK. Given the continuing differences still a work in progress

Edited December 20, 2019 by knocker

[knocker]

NOAA in the same ball park. Much really depends on the strength and orientation of the subtropical ridge, allied to the east bound energy

[knocker]

The North Atlantic 500mb and surface analysis for midnight

Apart from a few showers over western Scotland it is a dry start to the day in most places with some fog around but there is a line of rain associated with the occlusion that is steadily making it's way east across Wales and southern England at the moment which should clear the east coast by late morning. At the same time heavy rain associated with the deep low that is tracking quickly east will effect the south west and by 1800 most of Wales and southern England. But the strong winds will be in the southern quadrant of the low over France

The persistent rain will clear east this evening but showery stuff will linger along the southern periphery of England and down some western regions. Elsewhere dry with some fog patches

The complexity associated with the upper trough pertains on Sunday resulting in a day of sunshine and showers with longer spells of rain in the north west

Apart from some showers in the north west Monday will be a dry day but another low to the south west is tracking east and rain from the associated fronts will move across southern and central regions through Monday afternoon and evening

The rain will clear to the east so Tuesday a dry day with Showers/rain restricted to the areas effected by the two fronts at either end of the country. A rather cold day but  I will give the gfs temps a miss because the warm air in the south is rather dependent on the precise position of the front. But note the subtropical high is starting to ridge in the west

And by Wednesday the ridge has moved east to be over the country thus a dry day with some sunshine

Edited December 21, 2019 by knocker

[knocker]

But as can be seen the gfs continues to have a trough forming in the south east quadrant of the deep atlantic upper low with a surface low tracking north east to be over the SW approaches by midday Thursday.

Once the low clears to the south east we are back to a very transient ridge. Best left here I feel

[knocker]

The ext mean GEFS this morning is similar to last evening so further comment unnecessary

[knocker]

This morning's fax update for midday Tuesday has the front further north which fits better with the gfs temps and rain

Edited December 21, 2019 by knocker

[knocker]

The ecm also has the rogue trough Boxing Day

 

[knocker]

The EPS at day eight showing the WAA initiated  by the trough/ridge amplification

And in he ext period the weakening of th subtropical ridge over the UK as discussed last evening

 

 

[Blessed Weather]

Differences opening up with model forecasts of MJO progression. ECM staying in the neutral zone whilst GEFS and JMA showing progression from Phase 6 into Phase 7.

ECM  GEFS  JMA 

Phase 7 is supportive of high latitude blocking and also vertical Rossby Wave propagation into the stratosphere to disturb the SPV:

"It is clear that phases 7 and 8 are preferred during the 12 days preceding SSW"

Source: Observed connection between stratospheric sudden warmings and the Madden-Julian Oscillation

Are the GEFS members starting to react out at Day 10?

MJO Phase 6 and 7 Composites (rotated to match GEFS orientation below):

Ph 6  Ph 7 

GEFS perturbations:

 

Edited December 21, 2019 by Blessed Weather
Ph 6 composite added

[Griff]

17 minutes ago, Blessed Weather said:

Differences opening up with model forecasts of MJO progression. ECM staying in the neutral zone whilst GEFS and JMA showing progression from Phase 6 into Phase 7.

ECM  GEFS  JMA 

Phase 7 is supportive of high latitude blocking and also vertical Rossby Wave propagation into the stratosphere to disturb the SPV:

"It is clear that phases 7 and 8 are preferred during the 12 days preceding SSW"

Source: Observed connection between stratospheric sudden warmings and the Madden-Julian Oscillation

Are the GEFS members starting to react out at Day 10?

MJO Phase 6 and 7 Composites (rotated to match GEFS orientation below):

Ph 6  Ph 7 

GEFS perturbations:

 

This is fascinating stuff, many thanks for the comments too. Explanations are always appreciated (I get confused when models etc are posted without reason to accompany). Thanks, Griff. 

[damianslaw]

Good postings above, people need to keep an eye on these developments, MJO phasing hasn;t been conducive so far this season for high latt blocking, but if we are into phase 6 and then 7, a quick shift of heights advecting west would be line of travel and a deep longwave trough to our NE setting up, cold embedded air. 

[knocker]

Frontal surface on the Camborne midday sounding

[knocker]

Still no agreement between the ext anomalies this morning, in particular with the structure of the vortex over northern Canada and associated troughs, The disposition of the latter affecting the movement north of the subtropical high in the eastern atlantic as indicated on the GEFS Last evening NOAA was tending towards the EPS but the latter does go on to slattern the flow. The good news is there is no obvious likely encroachment of colder air

Edited December 22, 2019 by knocker

[knocker]

The 0600 ecm at t90

 

[knocker]

According to the gfs the evolution and quick devolution of the Thursday low as it becomes a non feature by Friday

[knocker]

The vortex and the cold over Alaska

[knocker]

The ecm has the center of the low 10mb higher than at midnight as it then moves east and fills rapidly

[knocker]

According to the ecm there is not a great deal of precipitation over the next ten days