Model Output Discussion - 15th April Onwards

[samadamsuk]

Morning all -

Outlook looking slightly more promissing imo, but I think it could go anyway and output will flipflop.

The situation at 24h is our typical current pattern of an icy northerly blasting down from the north and mixing with warm continental temps over us, but at 96h a cold pool which is probably the remnants of our last deep trough currently sat under the atlantic high out near the madeira islands, is responding to the aproaching lower heights and tracking east towards iberia.

This interacts with a surge of warm air from africa, resulting with reinforced upper air trough trough and a cut off low west of Iberai at 144h, with at the same time the flow to our north cut off and so the jetstreaming running from our SW to NE resulting from the feed of cold air from our north loosing it's punch (modeled for a while) with WAA and a ridge building up the southern side of the greenland trough.

HP takes stretches up across the north of the UK and put's us in a warm easterly, with the HP taking shape as the Iberian cut off interestingly detatches from the northern low heights over northern europe at 168h, and joins a weakly defined trough with the heights spilling out of greenland in the mid-west atlantic. An interesting switch which as we get further out into FI detatches from the western trough again and sits in the position of the original madeira cold pool, unattached from any troughs although there is a line of relatively low hights stretching into central southern europe, and a huge high pressure stretching from russia to the labrador coast. The polar air deflected over the top into central asia, and our air coming from a warm, but not hot northern/central europe.

If this played out, I believe we'd be looking at a very interesting thundery and increasingly warm June! But of course, the next runs are coming out now and it'll all change completely!

Cheers, Sam

Edit: Sorry - should mention this is my interpretation of the current GFS - not a cross model look at things!

Edited May 14, 2012 by samadamsuk

[johnholmes]

The overall trend on the 500mb anomaly charts over the past 3-5 days has been at the same mixed but fairly consistent.

If that sounds a bit odd then hopefully this explanation will help.

What all 3 variations have shown is the shifting of the long term position of the upper trough in the UK vicinity. Its not gone but its overall position is being predicted to change. The overall concensus seems to be for some kind of upper trough possibly even an actual cut off low to develop in the western Iberia area. Coupled with this are the signs of 500mb heights rising somewhere north, most suggest NE, of the UK. This was first indicated by the NOAA output about 5 days ago and has been increased as time has gone by. NOAA still shows the upper trough but now as a less pronounced feature extending towards Iberia and with a slacker flow into the UK. Two out of the 3 suggest that 500mb flow to be south of west, and that over several days now rather than the north of west pattern for so long a feature of the UK weather.

Just how the actual 500mb pattern will be 7-10 days down the line is still not certain by any means but I would suggest the 'cold' upper trough pattern we have had will be probably replaced by a more anticyclonic set up at least for the last few days in May with the axis of the upper ridge probably to our NE. What the actual 500mb flow into the Uk is going to be is not clear. It may be south of east or south of west. Its direction and how near the upper ridge is will be important for the actual weather that occurs at the surface.

Looking at the flow over north America and its generally predicted to be relatively 'flat' compared to what it has shown for several weeks (or at least for the majority of that time). This MIGHT suggest that the pattern over the UK is going to be fairly changeable.

I would imagine, IF this post from me is anywhere near correct that the outlooks from UK Met MAY start to show some of these ideas over the next few days.

I hasten to add that post very early June I have no idea how the upper pattern will evolve.

Just looking at the MJO actual=close to the origin and between 7 and 6 and the forecast (again I'm not a great believer in its ability to predict 500mb patterns when its very close to the origin) its predicted to be 8/1. Most of these late May into early June show blocking of some kind but a minority show troughing roughly west-east across most of the Atlantic into southern Scandinavia.

So a more settled end to May into very early June but pretty uncertain beyond that with perhaps the higher probability favouring an unsettled flow off the Atlantic rather than from more northerly areas which would at least suggest higher temperature values?

Edited May 14, 2012 by johnholmes

[phil nw.]

As it`s quiet in here at present it seems like a good time to start a new thread as this one is now pretty long.

So closing this shortly.