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Model output discussion - August hot spell - how hot, how long?


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It's going to be tough to get any warmth for the BH holiday. We start with a southerly tracking low, pulling in cooler air from the NE, and then the north

UW120-21.GIF?23-18

And I forgot to mention the likelihood of a lot of rain on this one too. Tough seven days ahead unless you like wind and rain.

Most Ecm ensembles this morning, surprisingly, were still clinging to the idea of a height rise for at least the southern half of the UK between 2nd and 6th September - even if just a short-lived one.

ec-ens_nat_z500scenarios_2020082300_276.

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Astonishing rebound in momentum transport that is behind the current spectacular synoptics and associated high impact weather. Both the heat, and also the powder keg potential for thunderstorms.

*** USING THE ECM TO FORECAST TEMPERATURES IN A HEATWAVE - A REVIEW *** I often make predictions based on models several days ahead, and then I find it useful to revisit these predictions after t

The reality is that NWP is wholly congregated on, but susceptible to be blindsided and over preoccupied by, the re-ignition of the low frequency tropical convective standing wave across Africa and the

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Well the 0z operational models were all awful, so far I think the 12z are better, how many times have we seen that, GFS looks as good as one might reasonably expect around the turn of the month, some amplification on UKMO might lead to a brief settled spell, and GEM better than this morning’s run. 

I think we need to get beyond the Tuesday low, before firming up predictions about the bank holiday weekend and beyond, though.  

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Models showing a generally very unsettled picture for the foreseeable, further wet and windy conditions, limited dry sunny weather and with a southerly tracking jet, cool for all, notably so by the weekend as we pull in a cool N/NW flow. Late August can often do this, then we see an abrupt change of fortune come early September.

Longer term - no obvious signal for a quick exchange to something more settled, there is much activity in the atlantic at present, and the jet is invigorated, coupled with uncertainties with expected high tropical storm activity, its not clear how things pan out, but the odds perhaps favouring a continuation of the unsettled theme as we start Autumn.

 

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Tonight’s ecm up there with one of the worst ever for summer? 3 different deep lows affecting the UK in the space of 8 days. Dreadful. AAM rises slowly being pushed back too.

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Good Evening! Very interesting  weather coming up ,damaging gales and heavy rain by early midweek and then models show some ground frost as far south as southern England by The weekend...Indeed a very interesting August   !!!

h850t850eu-6.png

ecmt850.168-2.png

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Coldies will be hoping that winter starts with the same pattern as Autumn.   Still no signs of the normal September settled spell / Indian summer unfortunately. 

D5C52A0E-E0BE-45E7-832E-07EAA45D5BDF.png

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The GEFS give a good picture for the next week and it's not looking very pretty:

image.thumb.png.e6544e8193148352f594c613f6aed4b7.png

Downward trend on the 850's with some hefty spikes on the precip line - in summary, cool, wet and windy.  So the next week gives us an early taste of autumn, then all eyes to the period after.  Hopefully September will see summer out with a bang!

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Latest icon  seems to have ramped the winds up slightly  for Tuesday   getting more inline with the usually ott aperge    High ground of wales bearing the brunt with winds possibly hitting 120   130 kmph

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1 hour ago, Tim Bland said:

Coldies will be hoping that winter starts with the same pattern as Autumn. 

D5C52A0E-E0BE-45E7-832E-07EAA45D5BDF.png

Really?..... a mobile and unsettled in a strong mean westerly upper flow?

 

sept.gif

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On 22/08/2020 at 20:48, carinthian said:

The very last day of summer months ends on a very cool note for much of Northern and Central Europe. Forecast 850mb height temps of 4c and negative dew points would be cold enough for some snowfall in the Alps. Models showing the Swiss Valais and Western Austrian Alps predicted for early snowfall . Based on the height to temperature values, snow level could be as low as 2000m. Fascinating end to August.

C

winteroverview_20200822_12_204.jpg

The models continue to show widespread unseasonal weather this weekend over much of Europe with falling temperatures. A lot of rain expected over the Eastern Alps, especially along the boundary of the the warm and cooler air mass as indicated by the tighteness of the thickness lines as per the chart above. The latest snow forecast model confirming new snow by Sunday morning as indicated in the above post for peaks in the Western Tirol, Voralberg and parts of the Swiss Alps Valais.

 

 

111a69a06540b911_eed11950b67e74ec@2x.jpg

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16 minutes ago, Steve Murr said:

^^^ Your comparing an apple to orange using that chart V the other chart.

Not even on the same timestamp.

I wasnt comparing the other cherry picked chart to the NOAA, i was pointing out the NOAA and indeed the current GFS and ECM suggest an unsettled start to Autumn, westerly driven...is that really what "coldies" want to see at the start of winter? Im not a "coldie", i dont care, but id have thought coldies would be looking for some sort of northern blocking, not a transitory ridge that soon collapses before a raging zonal pattern sweeps in.

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A complex conundrum on the ECM clusters this morning. The problem is, by D8, there's quite a split on the ensembles with two Atlantic troughs as opposed to just one trough.

ec-ens_nat_z500scenarios_2020082400_192.

The runs with one trough generally lead to a NW/SE split in the weather by D10 with the ridge possibility for the SE half, but the runs with the extra trough (generally further east) provide varying solutions for how the ridge builds in, depending upon the clearance of the first trough.

ec-ens_nat_z500scenarios_2020082400_240.

Given the uncertainties by D8/D10, there doesn't seem too much point in analysing D11-D15 in much detail, expect to note that the second Atlantic trough starts to progress towards the UK during this timeframe but seems to be weakening as it does, which yields yet more widely different options

ec-ens_nat_z500scenarios_2020082400_300.

So not really sure where this is going by D8 and beyond, but, if there is a crumb of comfort, it does not look like the Atlantic is simply going to roll-over everything in front of it in the way it is this week 🙂

 

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This probably doesn’t have a snowball’s chance in hell of verifying but I’m showing it anyway!..actually there a few other GEFS 6z members which flirt with the idea 💡 of early September heat, more so across the near continent..so, you never know!!!😜:shok:🔥

BD951BE2-8D13-4427-A3A2-F85F016D4E4F.thumb.png.18ed2a9a1e2e646804285ee7f5bd0454.png48A0D5F8-2A2D-4D11-9CB5-EC65FCBF1DFC.thumb.png.c8d6f7ccf443e53e623b851a892913d1.png

Edited by JON SNOW
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4 minutes ago, JON SNOW said:

This probably doesn’t have a snowball’s chance in hell of verifying but I’m showing it anyway!..actually there a few other GEFS 6z members which flirt with the idea 💡 of early September heat, more so across the near continent..so, you never know!!!😜:shok:🔥

BD951BE2-8D13-4427-A3A2-F85F016D4E4F.thumb.png.18ed2a9a1e2e646804285ee7f5bd0454.png48A0D5F8-2A2D-4D11-9CB5-EC65FCBF1DFC.thumb.png.c8d6f7ccf443e53e623b851a892913d1.png

with hurricanes/TS bumping the jet a bit more north it wouldn’t surprise me if this could actually happen from the lag effect from the current 2 storms affecting it 

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The 06z GFS is showing this @276:

gfs-0-276.thumb.png.97a52ccc9b68d3859560655acece9ed7.png

This scenario would produce temperatures into the mid-high twenties in the south while the north will be cooler, and I think we may see more charts like this as we head into September. FI at this stage though.

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The BBC app is showing a max of 13C here on Friday and NE England could be even cooler in a NE wind- struggling to reach 12C by midday in some parts of the north.

I'm struggling to recall a day that cool in August before? Certainly without constant rain anyway.

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Well the GFS 12z is a breath of fresh air, T144:

099D1289-C8A6-4812-8EDC-41BED50420F5.thumb.png.d126d4807cfc12b1eb5643b45f2f1f51.png

Ridge pushing in, T192:

4FF1E62D-42D0-42EB-AC07-434A3CE3A2A9.thumb.png.08573d81bca477d84dcb930993a8a861.png

Leading to more settled conditions T240:

36E1B10B-1D4D-44E1-8A5A-BB9A374FB955.thumb.png.d1283fbacfbb1e41a212317a3bb57b2b.png

And finally this T300:

F1DC1019-57CB-4568-836A-27C250781E0F.thumb.png.54ae2655c0724e699fe2798e900c708c.png

Despite this week, it is not a given that September will start with rubbish weather at all.

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Until this morning it was showing wet and windy with a cyclonic northwesterly for the first weekend of September so I certainly won't be getting excited just yet. I think more likely is a transient spell of more settled weather at some point in that first week among the overarching changeable period we are now in. All seems a bit reliant on tropical developments and a miraculous shunting of the jet northwards.

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2 hours ago, Scorcher said:

The BBC app is showing a max of 13C here on Friday and NE England could be even cooler in a NE wind- struggling to reach 12C by midday in some parts of the north.

I'm struggling to recall a day that cool in August before? Certainly without constant rain anyway.

I remember a similar cool spell in late August 2018 around the bank holiday, maxima was in the low teens in the north of England.

 

Ive just checked the BBC Weather app now and its showing a max of just 12C for my location on Friday and a low of 5/6°C on Sunday morning! Brrrrrr! 🥶
 

 

Edited by East Lancs Rain
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