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Model output discussion-mid Autumn and beyond


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The GEFS 500mb mean anomaly at 0600 pretty much as expected and clarifies my early comments vis the oo det run once I got them sorted properly of course

gefs_z500a_5d_nh_41.thumb.png.0b211e7e57e88f6e6af62faf5065ee74.png

 

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Thanks knocker. Useful to come over to this thread for a dose of reality rather than seeing P14 of the 18z GFS run which shows cold weather at 300 hours, when we all know that it's standard wet, windy

Hi Malcolm, I just saw your post after doing mine above. Yes this thread seems under used which is a shame.The idea of this one as you probably know is for any members to post what hopefully

Finally getting time to check how the 500 mb anomaly charts have been over the past week. They have not consistently but generally gone from suggesting trough domination to one that now has ridging as

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The ecm has high amplification upstream as a strong Pacific jet swings around the intense Aleutian low and then joins ranks with the subtropical jet exiting the south east US across the Atlantic This facilitates the movement of a deep upper trough into mid Atlantic as the high pressure migrates west over Greenland which is also helped by energy running around the north and into eastern Europe.All of which slowly moves the UK from an easterly into a slack pressure area/

T144.thumb.png.119fc2377ef5c8e471455b4364ba493c.pngT192.thumb.png.b0a6b2df604f8d4ff9ae89cafec1c84e.png

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Little doubt that the UK will see below average temps in the coming week but around day 6 seems to be a focal point as to whether we see colder air dragged further south and west-or not.

Modeling at T144hrs showing trough disruption heading for the southern UK as the high over Iceland starts to edge west..

UN144-21.GIF?18-18gfsnh-0-144.png?12ECH1-144.GIF?18-0

Later frames of both GFS and ECM show  the jet pulled a little too far north to deepen the cold with the weakening of northern heights, but it's a borderline situation and could well change as we get closer.

 

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1 hour ago, knocker said:

The ecm has high amplification upstream as a strong Pacific jet swings around the intense Aleutian low and then joins ranks with the subtropical jet exiting the south east US across the Atlantic This facilitates the movement of a deep upper trough into mid Atlantic as the high pressure migrates west over Greenland which is also helped by energy running around the north and into eastern Europe.All of which slowly moves the UK from an easterly into a slack pressure area/

T144.thumb.png.119fc2377ef5c8e471455b4364ba493c.pngT192.thumb.png.b0a6b2df604f8d4ff9ae89cafec1c84e.png

This evening's NOAA anomaly illustrates quite well the point I was attempting to make with the above

610day_03.thumb.gif.439110061efaf451915ce073a0a45cb4.gif

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Moving forward with the gfs into the weekend and next week the pattern continues to be about energy flows and the precise pressure distribution with the southern flow promoting low pressure in the Atlantic under the elongated high cell. This balancing act initially has the UK in a col with temps around average before a light north easterly sneaks around the high cell with temps a little below average.

gfs_z500_vort_natl_27.thumb.png.49c74f44ed74d4536f7eb1a4909ca13a.pnggfs_z500_vort_natl_33.thumb.png.0bf889f6009902f37251477fb7c43a0e.png

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The updated fax for midday Thursday and the ecm 24 hour follow up

PPVL89.thumb.gif.2b877c92fc086462f88eb98516bbc166.gifT108.thumb.png.1156e5f3dba3e6631ec9f6d80785c400.png

After that it is a familiar story of the energy flows with initially the trough dominating the Atlantic forcing the elongated high pressure to the north to track east where eventually it's supported by some ridging of the European high. Given that by the end the evolution is markedly different to the previous run and the northern arm of the energy is starting to track south east one would think this is transient and best ignored without support./

t144v.thumb.png.e528e372d6f5f35643584a8175653dc0.pngt174v.thumb.png.713b19b6d063a43e51fedd9f7785055e.pngt210v.thumb.png.ef7d228402058449fbd15ccfec632d6a.png

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A strong Pacific jet in the 180kf range with a very amplified up stream pattern featuring  an Alaskan ridge/cold trough eastern N, America with the subtropical jet exiting the south east US across the Atlantic. This energy promotes low pressure on this gfs run which impacts the UK at the beginning of next week as the high cell is relegated west

gfs_z500_vort_natl_25.thumb.png.65b33043c30679afcb065f56e8c497ad.pnggfs_z500_vort_natl_35.thumb.png.3b38006acb75798eaf1b8654b9f1f1a4.png

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The ecm differs from the gfs this evening when just post t144 the energy exiting the south east US tracks a tad north east,.Ergo instead of running under the high cell, which in conjunction with the northern energy, then relegates the high cell west, it splits it resulting in cut off cell to the east.

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Although tonight’s GEFS and EPS medium term mean anomalies are not in agreement in some areas they are both in the same ball park indicating a quite significant pattern change.

The significant features now indicated are an Aleutian low/Alaskan ridge complex with a very strong north Pacific jet hitting the buffers with the subtropical jet running under the radar , exiting the south east US seaboard, and across the Atlantic to the UK.  Both agree on the loss of the north Russian vortex and east European trough, albeit keeping negative anomalies over Europe

The contentious area is mainly around the vortex returning to north Canada/ NW Greenland whilst the high pressure retrogresses and weakens and this is a bit messy.

So as an overview this would portend an upper westerly flow tending to changeable weather with temps near average.

8-13.thumb.png.50832b34062527fb9c77af64676924b9.pnggefs_z500a_5d_nh_53.thumb.png.14801fd100f39da5d2820cacfb53b613.png

Looking quickly at this evening's NOAA it would appear also to be in the same ball park

814day_03.thumb.gif.e6ad3285689b1428e9e6c2a4aa39f0b7.gif

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Moving into next week it is still all about the energy distribution, imo of course, well illustrated by looking at the NH 250mb wind profile at T168 (and maybe worth a glance at the post above) A very strong north Pacific jet hitting the buffers of the Alaskan ridge and then aiding and abetting the subtropical jet as it swings across the Atlantic.

gfs_uv250_nh_29.thumb.png.2b484ad833e283cb925fc10e6a753358.png

So in a nutshell the UK stays in a cool easterly to begin with which the becomes a col before a quite cold transient northerly. By day ten a trough dominates the mid Atlantic and northern Europe.

gfs_z500_vort_natl_41.thumb.png.feb6fd7c5c338a4c4f640ac3e8c3e2d3.png

 

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The general point made above equally applies to the ecm and the downstream difference in detail will be down to the ecm interpretation of the energy distribution. For example towards the end of the run the ecm again has the Atlantis trough nudging a tad north and disrupting the elongated high cell which promotes the Azores to ridge north to phase with th east section of the disconnect. All of which sets up a south easterly again after a period in a col. temps remaining below average

t204.thumb.png.6236b5d662969eec943a95779791098a.png

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At T120 at the end of the short range there is the usual two energy flow conundrum south and north of the high cell with the former gaining some traction with a surface low now over France. This maintains the easterly with showers along the east of the country with temps around average.

gfs_z500_vort_natl_21.thumb.png.cf4846530ef1f635fda9716d8073e5bc.png

Over the next two days the energy flows working in tandem and slowly force the high cell west over Greenland which initially pushes low pressure a tad north increasing the easterly flow over the UK with rather more in the way of unsettled weather with temps around average or a tad below, But by T168 the northern arm has dropped an upper trough into northern Scandinavia which, on the surface, has introduced a light north easterly element in the north with temps generally a little colder with showers still along the eastern fringes

gfs_z500_vort_natl_25.thumb.png.813fb3e58e83fc80e42edb81747b49d6.pnggfs_z500_vort_natl_29.thumb.png.b209d10d9fb8aab67406dcbfc54b2818.png

By T192 the battle is still raging and although the southern arm a.k.a. the subtropical jet, has facilitated the formation of a deep depression in the atlantic there is now minimal longitudinal movement so colder air has filtered down from the north over the UK which is in no mans land, Possibly snow showers in the north on a quite cold day

gfs_uv250_nh_33.thumb.png.90e1ea83fa5154b1196c666794f6f210.png

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21 minutes ago, mb018538 said:

Strange that despite there being some impressive northern blocking the flow across the northern hemisphere is fairly flat.

Well yes and no. It is very amplified over North America and it would appear that the combination of the strong Pacific jet after it hits the buffers of the Alaskan ridge, and the subtropical jet, ensures a strong twin westerly flow exiting the south east seaboard across the Atlantic.before diverging. I suppose that if the block weakens and tracks too far west, which appears to be the suggestion, then the flow would become more zonal.

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