Model Output Discussion 31/03/14 onwards.

[Frosty.]

The Ecm 12z op run shows a changeable week ahead with some rain and showers for all of us but most of it concentrated across the northwest of the uk where it will also be cooler than elsewhere, the south & east will have decent fine and warm spells between weaker frontal systems but then it turns very unsettled and windier next weekend across all areas and much cooler eventually as a N'ly flow sets in for a few days but in the reliable timeframe, tomorrow looks good for central and eastern england with warm S'ly winds and lots of sunshine, some showery outbreaks further north and west, then a cold front sweeps through tomorrow night with a narrow band of rain on it but followed by a day of sunshine and showers on tuesday with a lot of dry and sunny weather further east and south again and feeling warm away from the northwest although a bit fresher than tomorrow.

[summer blizzard]

Could be looking at a transient plume around Mid-May..

 

The GFS at day 11 has this,,

 

 

The ECWMF has a positively tilted Jet supportive of building pressure.

[Frosty.]

Roll on summer, I hear it could be a scorcher :-)

We need to keep an eye in the sky for an unseasonally cool and very unsettled spell developing by the end of the week into following week if the ecm is right.

[Frosty.]

Why wish for very heavy T-Storms? The last thing we want is more flooding..stuff that, let's have a dry hot summer to make up for the rotton winter.

[davehsug]

Come on Frosty! Just as their is a large constituency here who believe that cold in the winter is useless without snow, there's an equally large one who believe that heat is useless without storms!

[knocker]

For a change a quick look at the southern United States. An area of low pressure is moving into the area bringing very dry and warm air and a high fire risk. There are red flag warnings out for Albuquerque and Las Vegas. Some temp records have already been broken.

 

 

[simshady]

Currently CFS are going for a warmish sort of summer, but a bit unsettled at times, trouble is will the evolution stick around?

The problem is that the CFS has to be taken with a large pinch of salt, especially at long range. From last May it was showing cold, snowy and blocked winter months and continued the theme right up to October when it started to gradually drop the idea. So even looking for trends with it is hard work.

[Frosty.]

The Gfs 00z op run shows low pressure anchored to the northwest of the uk this week which means the north and west, especially the northwest will have the most unsettled weather, cool to average temps, a lot of cloud and rain interspersed with sunshine and showers, breezier / windier at times. For the southeastern half of the uk it looks changeable rather than unsettled, warmer, drier, lengthy sunny spells between occasional rain and showers with temperatures in the mid to high 60's F range compared to the mid to upper 50's F for n.ireland & scotland. Things change by next weekend, low pressure swinging down across all areas with much more unsettled and cooler weather followed by a slow recovery next week but the run ends cool and very showery.

Edited May 5, 2014 by Frosty.

[Gibby]

HERE IS THE LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM TODAY MONDAY 5TH MAY 2014.

 

THE CURRENT GENERAL SITUATION. A Southerly flow is developing across the UK with an active front moving steadily East into western areas later today and further East tonight clearing Eastern Britain tomorrow morning. A showery WSW flow will develop thereafter.

 

GFS GFS continues to indicate the UK being under a broad West or SW flow with spells of rain and showers as Low pressure areas and attendant trough cross West to east over the UK through the next week or so. Thereafter indications of High pressure becoming a feature over the UK continues to be highlighted with this morning's ensemble charts suggesting this be of greater importance to Northern and Eastern parts while Low pressure remains a threat to Southern and Western areas at times.

 

UKMO UKMO is very unsettled this morning from later today to the end of day 6 with showers or longer spells of rain for all of the UK at times in a blustery West or SW breeze as Low pressure areas continue to cross west to East to the North of the UK.

 

GEM The GEM operational shows the same unsettled period shared by the other models and moves forward between Days 6-10 with drier and warmer conditions slowly developing from the South as High pressure from the Azores moves towards Southern England. In 10 days time this suggests that any further cloud and rain will continue only in the far North and NW.

 

NAVGEM NAVGEM loks unsettled and breezy with rain and showers throughout with Low pressure never far away from the UK in fairly average temperatures.

 

ECM today looks more optimistic again as we move out of next weekend and through next week as it has re-introduced the prospect that High pressure builds up from the SW later next week with some fine and warm weather possible for Southern areas at least. In the meantime though we have a lot of disturbed weather to get through with rain and showers in a blustery West or SW wind in association with Low pressure close to Northern Britain for the next week at least.

 

MY THOUGHTS  Through the period we have a very unsettled period to get through with showers or longer periods of rain with Low pressure close by to the North of the UK. Once again this morning GFS shows improvements later in this run and I can report that this has again spread to GEM and ECM's operational models this morning which of verified the trend would be for Southern Britain in particular to become dry, brighter and warmer later next week with any rain becoming more restricted to the far NW. However, we have to be mindful that this is still well over a week away and there is plenty of time for these weather improvement suggestions to evaporate as has happened a few days ago.

[knocker]

Yup by the middle of next week the ECM is looking a little more optimistic but the 500mb anomaly mean doesn't fill one with hope that this is a permanent arrangement. On Tuesday the cold air is to the NE still influencing the UK but this slips away as the heights build over the UK for the next couple of days. Not that warm. Back off to the southern States.

 

[Polar Maritime]

The GFS & ECMWF continues to show a quite a cool disturbed/mobile pattern from the W/N/W by the end of the week, With the Jet Stream moving South of the UK..

 

Edited May 5, 2014 by Polar Maritime

[Summer Sun]

A more promising end to ECM this morning with high pressure starting to move in

 

 

Temperatures still down initially but they soon recover

 

 

GEM shows the high slowly moving up from the Azores at day 9 with any rain shifted to the north by day 10

 

 

Then we have GFS which doesn't want to build pressure like ECM and GEM however GFS isn't a washout by any means

 

 

Respectable temperatures as well

 

 

Starting to wonder if we'll see a month of 2 half's more unsettled to start the month then becoming warmer and drier in the second half

Edited May 5, 2014 by Summer Sun

[Frosty.]

Ecm 00z T+240 hours is a PEACH with high pressure building north and becoming firmly established bringing progressively warmer and sunnier weather to most of the uk from mid may. In the meantime, a northwest / southeast split..most unsettled to the northwest with the best of the weather further southeast, less unsettled, more in the way of sunshine with temperatures on the warm side of average at times, predominantly rather cooler across the northwest. By next weekend it looks like very unsettled weather will reach all areas with cooler air and showers / longer periods of rain, some heavy and thundery, it may even turn a touch wintry across the far north as arctic air spreads south but then comes the recovery next week as we swap low pressure for high pressure by the second half of next week, at least across the southern half of the BI.

[IDO]

A comparison of the 10 day mean:

 

GEFS:   GEM:  ECM: 

 

All hinting at the same synoptics with the placement of the Atlantic trough the main separator; ECM the best for UK HP, GFS the worse.

 

GEFS at T300:   Still indicating a preference for a Scandi/Euro ridge.

 

The GEFS snapshot at T264 give a clear majority for a meridional flow with over 60% clustering the UK at least partially under a trough; of these the vast majority have us on the milder side of the trough: http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=264.

 

This then favoring the SE for a warmer flow in such a scenario, where the trough is more west based; mean 2m temps at D11: 

 

Last night's ECM 2m ensembles also suggesting some of the members heading into the warmer flow: 

 

The latest CFS London 2m also hinting at a temp rise from the cooler next 10 days: 

 

Though the UK HP is forecast to arrive in the last week of May (CFS), temps over 20c from around the 26th. Last week's ECM Monthly also had the UK under high pressure by the last week of May.

 

So maybe 7-10 days of a westerly flow followed by height rises to the NE/E leading to a MLB close to the UK for the last third of the month?

 

 

[Vorticity0123]

As mentioned above, it seems like a considerable shift in synoptic setup is forecasted, with a general dominance of low pressure over and just to the west of the UK anticipated in just a few days time. A detailed look at this transition will be given.

 

Current synoptics

 

Currently (as of May 5, 00Z), a north-south oriented stretch of high pressure cells is located from Tunis all the way up to Svalbard. In the 500 hPa pattern, this is shown as a weak upper level ridge extending toward Svalbard as well (indicated by the lighter green to yellow colours in the chart pointing northward in that area below). Furthermore, an active low pressure area is located to the southwest of Iceland (along with a 500 hPa trough). 

 

Current synoptics as analysed by the GFS. (as of May 5, 00Z)

 

On the satellite pictures, this low pressure area is also beautifully visible:

 

Satellite image of Europe (analysed as of 10:00 UTC). Courtesy: MetOffice.

 

Also note the frontal zone extending from just to the south of Iceland all the way via Ireland and Spain to the Azores. This rain maker will be the signal of the transition to a more unsettled period to come.

 

The result of the current synoptic situation is a weak southerly flow over the UK, yielding above-average temperatures. However, given that there is a weak pressure maximum in the high pressure stretch in central Germany, the origins of the air could be traced backward toward eastern France.

 

Forecasts

 

After today, low pressure activity will start to dominate the UK. Furthermore, the jet stream, previously fairy inactive over Europe, will be very active and pointed directly toward the UK, as can be seen below:

 

Netweather jet stream forecast (T120) as of May 5, 00Z. The contours indicate geopotential heights at 300 hPa (approximately 8 km height).

 

What can also be seen is that a large upper trough (isohypses dipping southward) is located just to the west of the UK, providing the ingredients for low pressure development toward the UK. The synoptics show quite some resemblance with what we have had all winter.

 

To elaborate on the ingredients for low pressure development, check the 850 hPa temperatures at T120 (from GFS) below:

 

GFS 850 hPa temperatures (T120, as of May 5, 00Z).

 

Just to the west of Nova Scotia, a rather sharp temperature gradient is present (sharp changes in temperature within a short distance). Cool upper air with 850 hPa temperatures down to -10*C just to the south of Greenland flows out over the Atlantic, and gets pretty close to upper air with 850 hPa temperatures of above 10*C. This temperature contrast fuels low pressure formation. More in-depth information about this process can be found in the link below:

 

http://www.globalchange.umich.edu/globalchange1/current/lectures/Perry_Samson_lectures/weather_patterns/

 

What is also remarkable is the low amount of uncertainty that the models exhibit over our area. This can be seen in the spaghetti plot of the GFS-ensembles below:

 

Spaghetti plot of all members of the GFS-ensemble at 500 hPa height. (T120, as of May 5, 00Z).

 

For the time being, only focus on the lines located over the UK. They indicate the location of the 5520 meter isohyps (the height at which a pressure of 500 hPa is measured). Note that even in 5 days out, all lines of the 5520 meter isohyps are very close together. This indicates that the location of the large upper trough can be considered very certain. (which is located to the north- and northwest of the UK).

 

Sources:

http://www.metoffice.gov.uk/satpics/latest_IR.html

http://www.wetterzentrale.de/topkarten/fsavneur.html

http://www.calctool.org/CALC/phys/default/pres_at_alt

http://www.netweather.tv/index.cgi?action=jetstream;sess=

Edited May 5, 2014 by Vorticity0123

[Frosty.]

The Gfs 06z op run in low res is showing potential for a hot plume extending north from southern europe during the mid month period with temperatures soaring well into the 20's celsius, it's a glancing blow on this run but the potential cannot be ignored, could be a late spring sizzler mid / late may.

[johnholmes]

A first class post from vorticity above, thank you.

The interpretation is much as Met Office for that period, along with the one from Gibby this morning, and both fit in with the 500mb anomaly charts although they are still not consistent between one another.

 

Obviously it is fun to do our own forecasts from the charts but for newcomers I would suggest both Gibby and Vorticity, amongst 1 or 2 others, are well worth reading. Clear and simple explanations on what the models are showing and predicting along with a personal prediction based on them.

[knocker]

This doesn't seem to me to support the build up of heights by the ECM.

 

 

[Frosty.]

A first class post from vorticity above, thank you.

The interpretation is much as Met Office for that period, along with the one from Gibby this morning, and both fit in with the 500mb anomaly charts although they are still not consistent between one another.

 

Obviously it is fun to do our own forecasts from the charts but for newcomers I would suggest both Gibby and Vorticity, amongst 1 or 2 others, are well worth reading. Clear and simple explanations on what the models are showing and predicting along with a personal prediction based on them.

one or two others? how rude

[phil nw.]

A quick look at the 12z UK and GFS confirms the unsettled westerly through this week.

 

It looks like more active fronts with quite widespread rain will move across later Thursday and into Friday as a cooler west/north westerly wind tucks in behind the cold front followed by showers.

 

 

the unsettled theme is modeled to continue into the week end at the moment unfortunately with GFS showing a cool and showery flow from the north west.

 

NB.

The 850hPa charts on the UKMO  charts on Meteociel look wrong after T72hrs so beware if you use them-up to T72hrs looks ok.

I have emailed them.

 

[Winter Cold]

Yess, more disapointing charts for mid May tonight from GFS. Next weekend is looking very unsettled:

 

 

 

UKMO also agrees:

 

 

No happy ending from GFS today either on the 12z, with the UK missing out on the high pressure warm fun:

 

[SylvainTV]

 

NB.

The 850hPa charts on the UKMO  charts on Meteociel look wrong after T72hrs so beware if you use them-up to T72hrs looks ok.

I have emailed them.

 

Thanks, I have fixed the problem. Make sure to refresh the page

[phil nw.]

Thanks, I have fixed the problem. Make sure to refresh the page

Thank you for a quick response Sylvain-much appreciated.

Edited May 5, 2014 by phil nw.

[Captain Shortwave]

Evening, lovely weekend I must say.

This coming week looks mixed or even unsettled in northern areas, though temperatures look reasonable for the time of year and even 20C could be reached on one or two days. Looks like most of the daytime precipitation looks to be in shower form so it shouldn't be too bad.

Unfortunately next weekend looks pretty rubbish at the moment with low pressure crossing the UK bring heavier rain and cooler conditions. 

Beyond that, still signs of pressure rising over the continent mid-month and perhaps further north and affecting the UK later on,

 

ECM coming out now and suggesting pressure will rise from the 13th

Surprisingly deep low in the Atlantic, would not be too surprised at a shallower feature and a more amplified pattern to be the reality.

Edited May 5, 2014 by Captain shortwave

[Summer Sun]

Very deep low in the Atlantic a week Tuesday but for the UK we have a a ridge of high pressure

 

 

By day 9 the low moves east with its centre NW of Scotland wettest and windiest weather for the north with the far south under the high

 

 

ECM ends with a NW flow for the UK as the deep low from earlier continues to move east