Model Output Discussion - 1st February Onwards 12z--->

[Frosty.]

They will get lots of praise now and rightly so, the sun feels strong already and with another dud of a winter in the bin, I'm liking these spring charts. Hope we get a long mild settled spell this month.

Nice 6z

Edited March 1, 2015 by Frosty.

[Paul]

ANOTHER POLAR LOW

 

Hi all

 

You probably remember the polar low forum at the end of January that went 'viral' on that night.  The interest then was in how much snow people would get and the low track in a general N-NW flow.  Well look at the satellite images for today and the observations over Ireland. Another polar low is tracking east, just leaving the Dublin area as I speak. Looks set to give a good dump over the Peak district this afternoon, though many places will see just rain/sleet.  Just goes to show how common these features are. Any old unstable airmass to depth will do, with a bit of PVA at height, just like today.

The models have picked this up quite well over the last 12h or so, especially Euro4, latching onto the differential wind flow at height, and developing the feature.

Don't know quite where to post this but I'll also post it in the model section as I have mentioned the model output above.

 

It's not a polar low, just a standard, albeit small low pressure system - been modelled for a couple of days now. 

 

[Captain Shortwave]

Voice of reason, similar looking charts in early March before have given chilly days under persistent fog, initialy it could be very mild from the SW but rather cloudy with moist atlantic air but when the high moves over us it will turn cooler esp at night, strange to see charts get praise when just 6 weeks ago they would be called dire.

The models are starting to come to a decision to position the high just to our south east over the weekend and into the following Monday.

GFS 6z for instance

Whilst the winds are from the south/south west they are originating from Iberia/France which should be dry enough to bring some sunny spells, especially in southern areas.

Temperatures again in the mid-teens, in fact widely to 16C, possibly a degree or so higher in favoured spots.

Edit - Forsty' images above say it all.

 

Cooler in the north as fronts pass over the top of the high. As I said this morning the temperatures will drop off a little after next Monday as the next high builds in from the west and a cold front pushes south through the country introducing cooler air.

Plenty to be positive about if you like pleasantly warm weather, even if it doesn't last too long.

Edited March 1, 2015 by Captain shortwave

[I remember Atlantic 252]

 

spring1.gif spring2.gif

 

spring 3.gif spring4.gif

 

thats good agreement, that we will most likely get some very pleasant mild weather at last!

 

it might not be very sunny ( although it might) , but the mildness will feel great!

 

what a great outlook for the first day of spring!

 

Agree but it's not exactly going to come off! can guarantee it will downgrade to low pressure with westerlies

[IDO]

Agree but it's not exactly going to come off! can guarantee it will downgrade to low pressure with westerlies

 

The UKMO update is promising: "Becoming mild across the country and very mild in parts of the south and east".

 

ECM looking to have some mild members as well: 

 

GEM ensembles showing very warm uppers next weekend:

  

 

As others have said, it will be a brief warm spell, but should remain dry for the south till well into week 2:

 

GEFS mean pressure stays over 1028 hpa from Wednesday till D16 for London, and the precipitation amounts reflect that: 

 

[Frosty.]

I know it's risky to write off the chances of wintry weather in early spring but given the current expert view and the medium / longer range models, I'm writing wintry weather off once the next few chilly unsettled days subside midweek. I'm officially throwing in the towel and accepting the growing evidence supporting generally mild anticyclonic conditions becoming the main weather type through weeks two and three at least.

[Milhouse]

Well the first spell of springlike warmth is approaching and to make it even better it looks like the peak of the warmth will coincide with the weekend. No doubt there will be the familiar hum of a distant lawnmower.

 

The ECM mean is very supportive of a light and very mild southwestwerly resulting in some very mild/even pleasantly warm temperatures. After initially going off the idea, the GFS is back showing a more pronounced rise in pressure.

 

 

 

[mushymanrob]

Agree but it's not exactly going to come off! can guarantee it will downgrade to low pressure with westerlies

I refer you to post 1605 above by john holmes

[mushymanrob]

I know it's risky to write off the chances of wintry weather in early spring but given the current expert view and the medium / longer range models, I'm writing wintry weather off once the next few chilly unsettled days subside midweek. I'm officially throwing in the towel and accepting the growing evidence supporting generally mild anticyclonic conditions becoming the main weather type through weeks two and three at least.

Well i wouldnt throw in the towel just yet, whilst a proper wintry freeze is highly unlikely theres still time yet for more cold and frosty weather. With high pressure expected to be a major player it wouldnt take much of a synoptic shift to put spring on hold.

[Frosty.]

Well i wouldnt throw in the towel just yet, whilst a proper wintry freeze is highly unlikely theres still time yet for more cold and frosty weather. With high pressure expected to be a major player it wouldnt take much of a synoptic shift to put spring on hold.

No mushy my towel is thrown. The final straw for me was that debacle the other day but this isn't a moan, it's just acceptance and as you know mushy, between april and october we share similar views and it's just arrived a little early this year. I'm now hoping the upcoming anticyclonic outlook will bring a sunny high and pleasant temperatures, it's looking good, even the north looks like joining in as time goes on but next weekend shows a north west / south east split, heavy pulses of rain for the north west but drier and brighter for the south east and mild. Edited March 1, 2015 by DiagonalRedLine
Fixed problem of quote not showing properly.

[Winter Cold]

It does seem that the brief warm spell has come out of nowhere, just as some of our cold spells did at short notice over the winter. Look at how much the METO update has changed in 48-72 hours; from talk of cold to very cold to mild to very mild!

 

Crazy place this UK of ours isnt it, but much fun all the same

 

Having said that, all the chopping and changing probably means we still havent found the final solution yet.....

[John Badrick]

ame="mushymanrob" post="3176865" timestamp="1425224418"]

No mushy my towel is thrown. The final straw for me was that debacle the other day but this isn't a moan, it's just acceptance and as you know mushy, between april and october we share similar views and it's just arrived a little early this year. I'm now hoping the upcoming anticyclonic outlook will bring a sunny high and pleasant temperatures, it's looking good, even the north looks like joining in as time goes on but next weekend shows a north west / south east split, heavy pulses of rain for the north west but drier and brighter for the south east and mild.

That's what I like to see frosty, a bit of reverse psychology!

[Frosty.]

That's what I like to see frosty, a bit of reverse psychology!

I better stay on topic, it's not reverse psychology this time, it's a genuine acceptance of the milder anticyclonic outlook which I expect the models to strengthen further during the weeks ahead.

PS..Thanks DRL :-)

Edited March 1, 2015 by Frosty.

[Eugene]

It does seem that the brief warm spell has come out of nowhere, just as some of our cold spells did at short notice over the winter. Look at how much the METO update has changed in 48-72 hours; from talk of cold to very cold to mild to very mild!

 

Crazy place this UK of ours isnt it, but much fun all the same

 

Having said that, all the chopping and changing probably means we still havent found the final solution yet.....

 

 

Trust me we have.

 

However this doesn't preclude further cold spells this Spring, this anticyclonic spell could be a precursor to a cold spell.

 

Spring isn't one warm season unlike Summer and sees great variation in conditions.

Edited March 1, 2015 by Eugene

[Interitus]

ANOTHER POLAR LOW

 

Hi all

 

You probably remember the polar low forum at the end of January that went 'viral' on that night.  The interest then was in how much snow people would get and the low track in a general N-NW flow.  Well look at the satellite images for today and the observations over Ireland. Another polar low is tracking east, just leaving the Dublin area as I speak. Looks set to give a good dump over the Peak district this afternoon, though many places will see just rain/sleet.  Just goes to show how common these features are. Any old unstable airmass to depth will do, with a bit of PVA at height, just like today.

The models have picked this up quite well over the last 12h or so, especially Euro4, latching onto the differential wind flow at height, and developing the feature.

Don't know quite where to post this but I'll also post it in the model section as I have mentioned the model output above.

You are correct about the potential vorticity advection (PVA). This midday chart from the NOAA FIM model is not particularly clear but shows a stream of positive relative vorticity (i.e. cyclonic) feeding from the Atlantic into Ireland at this time

 

 

 

More interesting though is this chart from the same model showing the pressure of high vorticity stratospheric PV2 air, indicative of tropopause height -

 

 

This shows a very low tropopause down to below 500mb feeding over western Ireland. This was confirmed by the radiosonde measurements from Valentia which shows very dry isothermal layer from about 530mb, beneath the jet stream which peaked at around 300mb at this time.

 

 

So it looks like the PVA and low pressure is related to a tropopause fold, mixing high pv stratospheric air into the troposphere beneath the jet stream.

 

[IanR]

Trust me we have.

 

However this doesn't preclude further cold spells this Spring, this anticyclonic spell could be a precursor to a cold spell.

 

Spring isn't one warm season unlike Summer and sees great variation in conditions.

Spot on, April especially is the month that, depending upon the synoptics, can deliver full on mid summer type conditions ,  or throw you back to mid winter type conditions 

[summer blizzard]

Euro's a beauty.

 

[Scorcher]

Euro's a beauty.

 

 

Yes very nice indeed...at first glance. But I'm not sure about cloud amounts in that setup. I know it's hard to tell, but does anyone have any idea?

[ANYWEATHER]

Diurnal Temps scream out from both gfs and ecm as high pressure takes control later in the week. Question is , how much cloud will there be???   If skies are clear at this time of year , very cold nights are replaced by some warm sunshine. Some interesting temperature ranges if skies are clear, about the only interest from the models in the near Mid -range....    

[knocker]

You are correct about the potential vorticity advection (PVA). This midday chart from the NOAA FIM model is not particularly clear but shows a stream of positive relative vorticity (i.e. cyclonic) feeding from the Atlantic into Ireland at this time

 

 

 

More interesting though is this chart from the same model showing the pressure of high vorticity stratospheric PV2 air, indicative of tropopause height -

 

 

This shows a very low tropopause down to below 500mb feeding over western Ireland. This was confirmed by the radiosonde measurements from Valentia which shows very dry isothermal layer from about 530mb, beneath the jet stream which peaked at around 300mb at this time.

 

2015030112.03953.skewt.parc.gif

 

So it looks like the PVA and low pressure is related to a tropopause fold, mixing high pv stratospheric air into the troposphere beneath the jet stream.

 

Interesting. I note that on the Valentia ascent there is a second tropopause at 250mbs. On the Castor Bay midday there is only one at 450mb. I'm not well versed on tropopause folds so does this mean the stratospheric disruption is more complete on the Castor Bay ascent? The jet is running south of CB.

 

Alicia Bentley's site is very good for charts.

 

EDIT

I see this fits with your second chart so is this an indication of the fold along that narrow band of the jet?

 

http://www.atmos.albany.edu/student/abentley/realtime.html

Edited March 1, 2015 by knocker

[Summer Sun]

ECM has the high lasting a lengthy time once it gets in, remaining pleasant by day after the main surge of milder air over the weekend in any sunshine and cold overnight with any mist / fog patches burning away fairly quickly in the strengthening sunshine

 

Edited March 1, 2015 by Summer Sun

[Milhouse]

The ECM has winds switching round to a more easterly direction later on dragging in slightly colder air but with upper air temps still above zero i would expect temperatures to be still in the range 8-12c. The main surge of mild air is still set to arrive this weekend before temperatures drop back as cooler air comes into the mix.

[Frosty.]

Nice Ecm 12z tonight, watching those 850's rocket makes me pine for summer heat waves, from late spring, they would bring temperatures of 25 Celsius + which is what we can look forward to a little later this spring. Anyway, this run shows pressure rising steadily so tap that barometer next weekend. Spring will have sprung by next weekend which looks much milder nationwide. :-)

Edited March 1, 2015 by Frosty.

[IanR]

you know spring weather is imminent when frosty gets on the other bus    

[mushymanrob]

Of course the really mild and pleasant weather expected next weekend wont last, before more normal spring/march conditions return... So what! Anything above the norm is welcome by me!