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Model Output Discussion - What does April have in store?

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21 minutes ago, Leo97t said:

I can see the next two months being unbelievably warm and dry and sunny. Loads to look foward to 

Way too early to say there's loads to look forward to..it's encouraging but it's too early to celebrate!👍

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Good Evening!  It never ceases to amaze me the British weather Summer last weekend , Winter this weekend!   The upcoming week looses the strong winds but cold uppers and a slack area of pressure. Means one thing Convective  skies , slow moving Thunderstorms,  and cold clear nights leading to some frosts  The Bank holiday weekend is still very uncertain....

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ecmt850.096.png

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7 minutes ago, ANYWEATHER said:

Good Evening!  It never ceases to amaze me the British weather Summer last weekend , Winter this weekend!   The upcoming week looses the strong winds but cold uppers and a slack area of pressure. Means one thing Convective  skies , slow moving Thunderstorms,  and cold clear nights leading to some frosts  The Bank holiday weekend is still very uncertain....

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I would say there is a fair chance the bank holiday weather is uncertain, and a  fair chance it will be fair! 😉I reckon icon has the right idea though! 

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Hints of the Nino pattern of plume-favourable ridges coming and going, uncertain how quickly and strongly it will establish. A gradual increase in % time under HP over the next few weeks makes a lot of sense. So GFS 12z not a bad guide overall. ECM possibly a little too vigorous with the Atlantic trough (as usual these days).

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Indications from Ensembles that central core heights of ridge development through early May will be perhaps just a tad too far to the west to allow a surge of continental air, hence always at risk of atlantic disturbances invading or making a passing blow to northern parts - a good place to be all the same, but not a pattern conducive to any notable heat for the time being at least.

 

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Posted (edited)

 Maybe we're not getting that warm and dry BH after all ….

 

viewimage.png

Edited by 38.5*C

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Love Norwich. Love weather. Love this forum. Looking forward to an eventful summer:  bring on the storms.:oldsmile:

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UKMO 0z goes all Arctic blast on us

image.thumb.png.31e6879fb7ec0c8807af8f87757e94e2.png

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Posted (edited)

The upcoming pattern change is essentially about high pressure developing over the Arctic leaving the subtropical high struggling to amplify in the vicinity of the UK, trapped between the large trough that has developed in the west/central Atlantic and the one over Scandinavia, associated with the vortex lobe. Put simplistically, will the ridge over the UK resist the energy from the west and keep Atlantic systems at bay?. The answer is probably partially

gfs-nhemi-z500_anom-6409600.thumb.png.a5cc2e97cc35b8ffd58364bd700b8470.pnggfs-nhemi-z500_anom-6841600.thumb.png.e6771448ac1820b8570d7af7570e012f.png

The Atlantic surface analysis for midnight and the Camborne sounding

PPVA89.thumb.gif.5e3c575aa77fe389e880ad99e2a8c2c9.gif2019042800.03808.skewt_parc.thumb.gif.3b2ca7da3933f51c46e81dcf5eebfb53.gif

At the moment there is still some rain  around in the south east from the occlusion but that should clear quite quickly, but bits and pieces may linger in the far south east, and it will remain quite cloudy for a while in central and eastern regions but when the cloud does start to dissipate it will be quite warm in places. But thicker cloud from the upper warm front was evident in the west at the beginning of the night and this will be reinforced during the day as the surface front struggles east and patchy rain/drizzle will effect western Scotland, N. Ireland, west Wales and the south west by 1800

PPVE89.thumb.gif.15c0add7cddca4c1c2c916f751bdf572.gif439347604_maxs.thumb.png.5483c0c5f679b1404403499b1330a501.pngp15.thumb.png.1d2b0f80ca1bc6b2491923f29d82357e.png

The patchy rain/drizzle will continue overnight as the front stalls but there may be the odd fog patch in eastern regions under clearer skies

PPVG89.thumb.gif.8d0683b16a731035ffd63ca3223aa03c.gif

Although the warm front is weakening the cloud and patchy rain/drizzle will persist through Monday in Wales, the south west, and possible N. Ireland  whilst the rest of the country will be dry and relatively sunny.

PPVI89.thumb.gif.3a94235ee1d40fd6fb506d48eb5bf7fd.gif76570235_maxm.thumb.png.25bdf47b37fa85a37b1a8a73cac21fa6.pngp14.thumb.png.fb20e3dd23851e2d0930d7dce9eae27e.png

Patchy drizzle in the west eventually clears leaving a generally sunny and quite warm day on Tuesday but a cold front does track across Ireland bringing some more light rain to western parts by late afternoon

PPVJ89.thumb.gif.512d45647e0ca5a719c3cfa530cf305d.gifPPVK89.thumb.gif.80073c8f151263723aa9b2e60c052371.gif

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The front will continue to move east across the country on Wednesday bringing rain to most areas and a marked west/east temp variation.

PPVM89.thumb.gif.731122af5477d5673ae5dfc7d26c4dad.gif1506411924_rainwed.thumb.png.4e23dd5923d7e1b2f4eaeaa64011b90d.png1937313270_maxwed.thumb.png.ecc62ca9763f15dd698e06d81c98420f.png

And Thursday is really the tale of a N/S split with the latter staying dry and quite warm whilst in the north a shallow wave, that has formed on the fronts trailing west around the ridge, has brought rain and quite a breeze to the north as well as much cooler temps.

PPVO89.thumb.gif.233d3c50dd5dda3a215828bfc4f9c87a.gif1388205292_rainthurs.thumb.png.5ffd71ffb8a1fab70662ab5bc55d99b1.png651065400_maxthurs.thumb.png.dbda2cd754dbaafc692369a33376ffb1.png

Edited by knocker

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Posted (edited)

From here the upper trough continue to move east across the Atlantic against the quite resilient ridge, with the Scandinavian trough paying quite close attention on Friday, reaching this position by 1800 Monday.

gfs-nhemi-z500_anom-6895600.thumb.png.288c7c706e3a69f467ea6600b7359159.pnggfs-nhemi-z500_anom-7165600.thumb.png.8e8a9a96ad0c651c13d1fbeaa5903471.png

On the surface this translates to patchy rain and colder air flooding south on Friday but the trough to the north east moves away resulting in the next three days being dry, albeit with,a complication arriving in the south west on Monday. But this is according to the gfs and not set in stone at this range

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Edited by knocker

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And just to illustrate the uncertainty next weekend vis the energy distribution. The ecm has much more amplification but with the subtropical high ridging strongly to the west of the UK this brings the trough in the north east > east into play resulting in a cold northerly plunge down the UK over the weekend with temps below average, way below on Saturday. The ridge does nudge east on Monday.

t132.thumb.png.59fabc0fb20461f25707cb514953243d.pngt162.thumb.png.b6d33f8e0f60297178bb05f45dc1162d.pngt186.thumb.png.62da630d318673043bc77b1233869fb9.png

 

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The uncertainty over the upcoming weekend from gfs and ecm is quite frankly astonishing.🤣

h850t850eu-8.png

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So, expectations (GFS expectations!) for the upcoming BH have taken a bit of a dive...?

FV3: image.thumb.png.c86672e8ebba45555ee758ad55ae65d4.png image.thumb.png.4da180e7f1a5166a12b4f0c6b2d2027b.png

GFS:image.thumb.png.fd13afa0873f358b505b5ee3cdfdae30.pngimage.thumb.png.7964fe26fa7de97de5c3fa3caeba30a0.png

Not only has the initial threat of a nasty-feeling Arctic blast increased, so has that of LP from the SW; so the fine 'spell' may be somewhat truncated?

GEFS ensembles are nowt special: image.thumb.png.348a0f36fb879c6e9aa95aa514f4746e.png

No rain to speak of, where it's most needed, either: image.thumb.png.0b87bf52f2576ef6b2c3280c57291659.png

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Posted (edited)

The temporary amplification of the ecm appears to be linked to  lot of movement in the North Pacific and the consolidation of high pressure over the Arctic before settling down again That is not to say it is correct

t150.thumb.png.6b3d5ebe4c514ea209f79b18356e2ba1.png6-11.thumb.png.00c0e35f08f56767613ae066790dff97.png

 

Edited by knocker

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A very decent Ecm 00z ensemble mean both early and especially later.🌞👍

EDM1-48.GIF

EDM1-168.GIF

EDM1-192.GIF

EDM1-216.GIF

EDM1-240.GIF

EDM0-240.GIF

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Posted (edited)

Weekend not starting too well:image.thumb.png.3d0d9e75e7fe9297e947db9001173678.png                                                                              image.thumb.png.d2cb78fda1310c75f96b2cab1cb93c0a.png

Monday: where have all the yellows gone?  image.thumb.png.0fb7deb38c469fde4d658338368f2502.png                                                                              image.thumb.png.cc2da5644130df7f1cbf92d700b25233.png

Edited by Ed Stone

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Well not a lot to say about the 6z operational except the end is the best bit.😁

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A big swing towards a colder bank holiday weekend at the end of the coming week looks like a total contrast to easter when the UK was seeing temps into the 20s

gefsens850London0.thumb.png.881c7a61703c357aa155138abb67b635.png

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Posted (edited)

Looking at the GEFS 6z next weekend could still be pleasantly warm and anticyclonic.😉🌞

GFSP03EU06_156_1.png

GFSP13EU06_156_1.png

GFSP13EU06_180_1.png

GFSP19EU06_180_1.png

GFSP20EU06_180_1.png

Edited by Frosty.

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The 06Z GEFS ensembles are something to behold. Or not!

Av temp:image.thumb.png.8f82e6e743e18da0ba3314e42225be19.png PPN: image.thumb.png.56a28524f42aa04629787ec552501291.png

Don't venture outside, on May 11!:shok:

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5 minutes ago, Ed Stone said:

Don't venture outside, on May 11!:shok:

I think I'll risk it Ed..nae problem😜🌞🔥😎

GFSP19EU06_324_2.png

GFSP19EU06_324_1.png

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15 minutes ago, Frosty. said:

I think I'll risk it Ed..nae problem😜🌞🔥😎

GFSP19EU06_324_2.png

GFSP19EU06_324_1.png

Risk it for a Swisket?:yahoo:

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Cfs setting us up for a promising weekend with settled and warmish conditions, pretty much ties in with other senior forecasters predictions. I will take that any day.... Tbh May in general is looking pretty positive especially the mid and final 3rd parts! 

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The clusters certainly have the trough to the NE taking closer order at t144 and less so over the next two days  It's very much a knife edge scenario with the precise position of the amplification of the ridge paramount

ec-ens_nat_z500scenarios_2019042800_144.thumb.png.7675070fdf9fb20fa98d6439c46787f2.pngec-ens_nat_z500scenarios_2019042800_168.thumb.png.510bcf9ecb5aefb0fd4f3f45f71d28c9.pngec-ens_nat_z500scenarios_2019042800_192.thumb.png.6cb12a40434dea413512ba420bea715d.png

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On ‎25‎/‎04‎/‎2019 at 15:48, Tamara said:

On this basis, assuming active tropical >extra tropical forcing sustaining angular momentum tendency through the greater part of May c/o weak El Nino circulation and aligned with w/QBO, increasingly inhibiting Atlantic and Greenland blocking heading towards the important seasonal wavelength setting as Spring turns towards Summer, then whilst such a pattern will inevitably sustain backwards and then forwards once more-  its not unreasonable to hypothesise further re-setting of the Atlantic trough and downstream W/European ridge and re-cycling of increasingly warm patterns from an ever warming continent as the days keep growing longer.

In the shorter medium days 5 to 10 period, its a case of seeing how the models resolve the ridge placement now that the ejected trough is backed west into the Atlantic. This will determine how much cooler air advection comes south before the suggested higher heights close to Greenland fade in the longer term and hopefully set up a mid latitude ridge as day 10 ensemble means are trying to converge on.

The shorter term is the easier bit to update on. Alas, the seasonal warming across the Arctic looks to make the pivotal difference to the amplification wavelength and latitude of the ridging and put the UK  just enough on its "wrong" side with a much cooler start to the B/H weekend than seemed possible.. Such fine lines here....

Hopefully a recovery of temperatures as the polar flow gets cut off and feeling much more seasonal to round off the long weekend

Thereafter much hinges on how sustained the westerly wind bursts across the Pacific are c/o the tropical cycle propagating eastwards during the first 10 days of May and discussed in thorough detail in the full post from which the above quotes are extracted from.. 

That post dealt with the upside to the possibilities. This one equally deliberately looks at what can, and might, go wrong.     Wrong at least for those of us hoping for warmth.

Seasonal models are most unreliable with atmosphere and ocean trends during the Spring but start to gain greater reliability once more heading towards May. These forecasts are generally becoming less supportive of El Nino than they have been, with indications it will not last far into summer.

What is important here is not so much the base state per se, but the travel of direction of the relationship the atmosphere adopts to it and takes the lead. A downward spiral of Pacific SST's implies westerly wind bursts scrubbed out at the expense of strengthened trade winds and consequentially - an associated falling angular momentum trend with the amplification wavelength dictated well upstream in the Pacific rather than our closer downstream European sector

 

1399646985_3.4zone.thumb.GIF.a78b946b73ac0d4d40f108726d6025ac.GIF

 

The MJO looks due to return to the Western Hemisphere later in May at the end of its cycle, and much will depend on how successfully the tropical wave will imprint the standing wave in the Pacific as it passes through the region and provide maximum upside to angular momentum before it starts to fall back again as it completes.

Any shortfall in this, lends itself to a collapse of AAM tendency at the most pivotal time as seasonal wavelengths attune to summer changeover. Cautionary caveat attached to any CFS forecast and associated model biases, but based on the programmed evolution of the forthcoming tropical cycle, this prediction has good enough credibility and is fully consistent with the daily updating trends.

image.thumb.png.01b74d0c70a79fea17d5bdee3707ffa1.png

 

In any shortfall scenario (should it verify) the baseline for global momentum would fall below that of the low point just arrived at in April  which in itself followed the descent from the late winter "peak" of this weak El Nino.

image.thumb.png.0110c7ec02e03cfe68289f25534c696e.png

Such a situation lends itself to a quite different scenario outlined in the above post with the Atlantic trough and Western Europe/Scandinavian ridge scenario reversing to an Atlantic ridge and downstream trough.  Therefore cool, changeable and showery rather than any warm/very warm plume scenarios.

Clearly its far too soon to know exactly how this is going to play out - so no need for any undue suspicions just yet. Its too close to call and  warm scenario A could yet still prevail.

However, May as often is the case, looks set to be a crossroads month for the high season that follows it. So its worth in my opinion looking at possible things to look out for in the modelling in the coming few weeks, and the scenarios and different pathways that might start evolving as we get nearer and nearer to the start of summer proper.

 

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