Analysis of short term synoptics & forecasts

ninebeanrows

Here is a thread for some detail to be posted away from the mother thread.

Please only post charts details and forecasts etc and do not post general responses, put those in the main thread, this will allow for people to easily access what the lads on here think and other forecasts without having to trawl through the other thread.

Thanks alot.

I will post up some thoughts shortly.

Other thoughts on the charts more than welcome.

ninebeanrows

Here is the forecast precipitation for tomorrow morning.

It comes across from Northern England and enhances over the Irish sea during the early morning.

Saturday Morning Snow

Southeastern areas looks most at risk.

2-5cms likely.

nacho libre

precipitation keeps going through tuesday- however the risk is, as my grandfather used to say, "the longer the snow falls the greater the chance it'll turn to rain". so by tuesday there may only be snow at higher levels.

JanuarySnowstor

My thoughts are that most of the East & South will see persistent snow from Sunday to Tuesday with little respite. Further North and West will see some showers also. Away from coastal regions, favoured spots could see as much as 15cm's esp for Dublin & Cork.
This is almost a guaranteed risk and very likely to cause severe disruption.
Monday looks like a bank holiday to me:D

Moving on from Tuesday and a definite trend of milder air moving into the mix turning ppn more sleety or even back to rain. Considering ground temps are so low a day or two of freezing rain is very possible. This could in fact lead to even larger disruption as ice is slow to thaw throughout Wed / Thurs. Then once/if the ice does thaw there looks like being a large risk of disruptive flooding.

So all in all probably the most noteworthy week's weather ahead that any of us have ever seen
Extraordinary times!!

Supercell

It's funny, I pay to heat my house, and then I pay to chill my food to warmer than outside in my fridge.
Western.

Snowaddict

Good Evening Everyone,

The following is an analysis of the potential snowfall event, indicated as developing later on Sunday & into Monday.

Synopsis & Evolution

Confidence & Risk 65% - 70%

At present, a slack Easterly airflow covers Ireland. An Anticylone of 1035mb in intensity, continues to strengthen over Scandinavia.



Over the next 24 Hours, a slightly stronger Easterly flow will develop over Ireland. This will lead to a significant wind chill factor, with ''real-feel'' temperature values between -6 and -10. At present, an area of low pressure centred between Corsica & Northern Italy, of 995mb in intensity, is advecting a deep cold pool westwards. A complex frontal feature associated with this area of low pressure spreads Northwestwards towards the UK & Ireland over the coming 36 Hours.



T+48 12.00 - Sunday

A strong Easterly wind persists over Ireland, while a complex frontal feature begins to arrive from the Southeast. Associated snowfall, at first rather light in nature, should arrive in Southern & Southeastern areas, sometime shortly after 12 Hours on Sunday, between 12.00 & 17.00 Hours. During the course of Sunday, outbreaks of snow should develop more widely over Southern, Southeastern & Eastern areas. Pressure will fall to 1020mb overnight, particularly across the southern half the country, allowing for an intensification of the precipitation. At this point, it is largely expected that all precipitation will be snowfall, apart from some possible exceptions along extreme coastal fringes. 850mb temperatures at 12 Hours Sunday will range from -8 to -10.





T+60

Overnight, the frontal feature will straddle the southern half of the country, with strong Easterly winds persisting. While Dam Heights will gradually begin to increase above 528DAM, towards 529 & 530 - this shouldn't be a problem immediately because we will be dealing with a continental influence. It may, however, add to the marginality element in exposed coastal locations. At this point, outbreaks of snow, light to moderate in nature, should straddle many Eastern, Southeastern, Southern & Southwestern areas of the country.

Counties at risk at this timeframe include:

Kerry, Cork, Limerick, Tipperary, Waterford, Wexford, Wickow, Kilkenny, Carlow, Southern Laois, Kildare, Dublin, Meath & Louth.



T+72

At 12 Noon Monday, the boundary line of the complex frontal feature lies to the North of the country. An Easterly, backing Southeasterly airflow persists over Ireland. At this time, 850mb temperatures continue to support snowfall across the country, although marginality may become more prominent in exposed coastal areas. Equally, precipitation may continue to fall as snow in many areas, due to the level of embedded cold. Areas most at risk include large portions of the East, Southeast and South, with the risk diminishing in the Southwest. Blizzard conditions are possible over High ground in particular, and possibly to lower levels at times. Precipitation will generally fizzle out later on Monday into the East of the country. 850mb temperatures continue to support snowfall in Eastern areas in particular. A slight thaw is possible in the far Southwest later in the day.



Summary

There is a High Risk - 65% - 70% - of outbreaks of persistent light snowfall developing in the above areas later on Sunday & into Monday. While conditioins may become increasingly marginal in some areas on Monday, as discussed above, many areas should see snowfall during this period if the current NWP Guidance verifies. Total accumulations possible in this period range from 3CM to 8CM at lower levels, with in excess of 10CM possible at higher elevations. Disruption to Transportation is possible during this period. A gradual slight thaw may occur in the far Southwest & exposed areas much later on Monday, although 850mb temperatures remain largely supportive of snowfall, particularly further East, until Wednesday on the latest ECMWF Guidance.

SA

Su Campu

These the next three days' events all stem from the upper low currently cutting off over the Mediterranean. Enhanced PVA from the shortwave trough swinging westwards over England and southern Ireland tomorrow is the energy focus for tomorrow's event.

This shortwave then itself cuts off and elongates, forming the basis for the Sunday/Monday event.






Saturday's Event
PVA early Saturday morning kicks off convection over the Irish Sea from about 6am, but with a tongue of 1°C 850ThetaW values, any precipition will be initially sleet below 100m along the eastern coastal counties. These wet bulb values then fall to -3°C, ensuring that all levels will get snow. But with forecast soundings indicating a strong cap above at 700hPa throughout tomorrow, convection will be very shallow, with max cloudtops of 10,000-11,000ft. This will limit precipitation considerably, giving less than 2cms in most places.





Moderate northeasterly 700hPa winds will generate convection from Isle of Mann southwards, so the east-southeastern third of the country should see shower activity up to around midday. The upper trough clears the southwest late tomorrow night/early Sunday morning, and starts to elongate and rotate, generating stage 2 of the process.


Sunday/Monday

The current upper warm front, located at around 700hPa over France and Germany today, approaches Ireland from the southeast by Sunday afternoon.


It is being caused by widespread isentropic lift of a much warmer southerly airstream air over the northern European cold airmass. It is generating widespread light to moderate snowfall over much of central Europe this evening. By Sunday though the frontal gradient has diminished somewhat, and precipitation is now being generated at upper levels by the upper cut off low to our southwest. With conditions Monday becoming slightly less conducive for snow, there is the chance of this upper precipitation melting in the lower levels of the atmosphere, and falling as freezing rain Sunday night and Monday morning, causing, as Snowaddict said, cause for concern. Precipitation accumulations at this stage look to be about 2-3mms liquid water equivalent....giving possibly over 5cms snow down to about 500ft , and treacherous driving conditions at all levels where freezing rain occurs. But later Monday precipitation of a less wintry nature looks like intensifying in the southwest, giving heavier rain at low levels, and heavier snow above 1200-1500ft in the southwest.

WolfeIRE

Hi all,

Just a quick follow up to my ensembles review at 9.45pm:
http://my.boards.ie/vbulletin/showpost.php?p=63883507&postcount=1655


I am have been looking at some of the other less utilised models (probably less utlised for a reason).


All in all it appears at this stage that South Munster and East Leinster will see snowfall on late Sunday afternoon/early evening. This will continue to spread NW throughout the evening and night. There is no doubt that temps will rise somewhat the further south as Monday morning progresses but not significantly so. Snow may very well continue to fall in the southern third of the country, and most likely two thirds, into Monday afternoon before dissipating.

These ensembles all indicate that precipitation will be relatively light except for in the SW and in the initial stages in the SE. Accumulations from Sunday to Monday midday would be closer to 2-4cm in coastal areas and 5-8cm elsewhere. Higher ground and areas well inland are most at risk of higher accumulations.


Precipitation does looks like fizzling out as it tracks very slowly North (or perhaps as it stalls halfway across the country). I have mentioned my thoughts on the next system in the earlier thread.


GFS
Sunday, 6pm – Snow for the southern third of the country and much of the east coast. Precip will push further north and west as the night goes on.
http://expert.weatheronline.co.uk/daten/proficharts/en/2010/01/08/basis18/euro/prec/10011018_0818.gif
http://expert.weatheronline.co.uk/daten/proficharts/en/2010/01/08/basis18/euro/t850/10011018_0818.gif

NAE
Similar scenario at Sunday 6PM. Precip heaviest in South/South West
http://expert.weatheronline.co.uk/daten/proficharts/en/nae/2010/01/08/basis18/euro/prec/10011018_0818.gif

NOGAPS
Sunday, 6pm – precip covering a everywhere south of the line from Dublin to Clare/S Galway
http://expert.weatheronline.co.uk/daten/proficharts/en/nogaps/2010/01/08/basis12/euro/prec/10011018_0812.gif

CMC
Sunday 6pm – precip is lighter but may extend further north than above models.
http://expert.weatheronline.co.uk/daten/proficharts/en/cmc/2010/01/08/basis12/ukuk/prec/10011018_0812.gif
upperair temps favourable
http://expert.weatheronline.co.uk/daten/proficharts/en/cmc/2010/01/08/basis12/ukuk/t850/10011018_0812.gif

The very consistent UKMO fax charts places has precip most likely affecting all of Leinster and Munster, and parts of South Connaught.
http://expert.weatheronline.co.uk/daten/proficharts/en/ukmonws/2010/01/08/basis12/ukmoan/10011100_0812.gif


Finally to something next Thursday (this is for some light relief as it could not possibly happen....could it?)

This continental wind pattern mixed with these upper air temps meeting with this beast from the Atlantic could lead to massive snowfall, particularly the further N and E you are. Should the winds swing more easterly or NE by this time then snowfall would be more certain for all.

Please note that all of the above is just my reading of ensembles. These ensembles are updated a number of times a day and therefore will require further analysis tomorrow.

Wolfe

EDIT:

This HIRLAM speaks for itself.

embee

edit : sorry, wrong thread!

Irish Steve

WolfeIRE wrote: »

Precipitation does looks like fizzling out as it tracks very slowly North (or perhaps as it stalls halfway across the country).
Wolfe

Something similar happened to us in the UK in the mid 70's. A front tracked up over the West country (to about Wiltshire) over a 24 hour period, then the cold air won, and 24 hours later, it got pushed back again.

It dumped significant snow over Somerset in both directions, which resulted in complete paralysis of transportation for about 4 days until the army and others were able to start clearing things. The house we were living in at the time was on the edge of the road, and directly outside the window, we could see tarmac. Between us and the pub opposite, about 18 Ft away, there was a 6 Ft high snowdrift, and visible tarmac the other side of the road.

My car was parked on the ground beside the house, and after the second pass of the front, it was not visible, as there was over 4 Ft of snow on the patch of ground.

On the other side of the house, with the way the drifting went, we opened the door, and the snow bank was above the top of the door, all we had was an imprint in the snow of the shape of the door. It took about a week before things got back to normal, helped by the introduction of a significantly warmer air mass off the Atlantic, which brought a rapid thaw and consequent flooding in some areas.

Steve

Redsunset

Latest GFS 00z run.

Early Sleet then snow showers kick in fairly early moving west from irish sea and perhaps making inland somewhat.








859mb temp really dipping across irish sea moving west.






From early sunday morning it's showing good south east/east snow shower potential.







Enclosed in a -8 / -10 upper air cold pool.





Sun night into monday we seem to be threading water as the very cold feed of air is shut off from the east so we 're holding on to what cold we have at this stage






A few coastal areas are looking not so supportive of snow but a wintry mix.





So just to summarise up to this period on this run.

Plenty of snow showers east/south east get going early sat morning spreading west but fizzling out quickly as they do.

The main event sunday looks like strong snow potential for all in precip areas but then turning to wintry mix in coastal regions as we head in to the wee hours of monday.
Thats my view on the given charts just up to this point because it will change again so not going any further.

MT has already mentioned about a sloppy mess setup and he might not be far out,but i can;t see that happening until tuesday away from the coasts

WolfeIRE

EDIT wrong section

Snowaddict

Good Afternoon,

Confidence & Risk - 90%

[Note: Conifdence & Risk refers to the overall event taking place, not the nature of precipitation as this is extremely difficult to forecast]

The latest 12Z UKMO NAE Guidance has now become available & indicates that persistent but relatively light snowfall will gradually develop from mid morning tomorrow morning, spreading across many parts of the country during the afternoon. There are indications that conditions may be more marginal in coastal areas of the East & Southeast, however it is impossible to predict with certainty marginality in this circumstance. Again, prior to the arrival of the main area of precipitation, relatively light snow showers are possible in both Eastern & Southern areas.

UKMO - NAE - 12Z - Sunday 06.00



UKMO - NAE - 12Z - Sunday 12.00



For the total land area being affected by this event, conditions are not being indicated as marginal, until Monday, in the majority of areas.

UKMO - FAX - T+24



At 12 Hours Sunday, an Anticyclone of 1039mb is centred over Scandinavia. A complex frontal feature extending into the UK & Continental Europe approaches from the East/Southeast. Moderate Easterly winds persist across Ireland, with 850mb temperatures generally ranging -8 to -9. 850mb temperatures will rise slowly later overnight & into Monday, especially further Southwest. DAM Heights will remain at or below 528 until about 6PM Sunday, slowly rising overnight and into Monday, from the south as the main complex frontal feature moves slowly northwards.

UKMO - FAX T+36

A large portion of the country remains under supporting 528 DAM Air, an area from Wexford, through Wicklow and Dublin has DAM air with values of 529, indicating the risk of marginality. Winds remain moderate to strong, Easterly in direction.



UKMO - FAX - T+48

At 12 Hours Monday, the latest UKMO Fax Chart has the majority of the country under 528 DAM air, even those areas which have had slightly warming DAM air at T+36.



Summary

In summary, there are no changes to the forecast in light of the latest Guidance. Light snow showers are possible (Risk 70%) in Eastern and Southeastern areas from mid morning tomorrow, becoming more widespread & persistent towards 12 Noon. During the afternoon they will gradually spread to the rest of the country. There is the risk of precipitation turning to more of a wintry mix, especially along Eastern & Southeastern coasts, later tomorrow.

Total Accumulations of 2CM - 10CM are possible, accumulations highest in the South & Southeast & over High Ground. Those living on High Ground should be aware of possible disruption of transportation due to snowfall.

SA

M.T. Cranium

In the longer term, looking at Tuesday, the models generally agree that the frontal zone well south of Ireland from Sunday through Monday will edge northwards and a strong wave will form south of Cork, moving in a north to NNW direction. With the thickness support shown to be around 540-546 dm, it's difficult to imagine that this won't turn to a steady rain across the south at some point on Tuesday. There may still be sleet or snow in the mix further north and at highest elevations of the south, but given this guidance, the south should be on alert for localized flooding as higher temperatures (albeit briefly) and rain could combine to melt snow on the ground (including additional amounts to be expected now to Monday) producing two types of flooding, urban ponding (due in part to drainage being clogged by ice and slush) and small stream overflow especially in poorly drained lower-lying areas.

The effects of this liquid precip further north, however, may be more along the lines of adding to ice accretion in the long run, so the main impacts will vary south to north, flooding in some areas, more slippery conditions possible further north.

Any changes in my thinking on this situation will be found in the forecast thread as warranted by updating model output. I rather hope I'm wrong about the thaw and flooding, but at least it would clear the roads and pavements eventually.

inabina

are we seeing the end in sight of this cold spell? Eagle says temps likely to get above 4C by end of week.

Musicman2000

I think its a wait and see event:)

inabina

i couldnt handle it if this cold spell came to an end. looking at the weather and looking at this site, I really dont have a positive feeling. its coming to an end i fear.

Su Campu

On Thursday I said next Tuesday would mark the breakdown, and that now does indeed look to be the case.

Snowaddict

Su Campu wrote: »

On Thursday I said next Tuesday would mark the breakdown, and that now does indeed look to be the case.

Indeed Su Campu, although it's quite clear the breakdown won't be straightforward, as was suggested last Thursday. It was also suggested that an area of positive height anomolies would persist to the North/Northeast & this is quite evident on tonight's Guidance - quite clearly seen on ECMWF.

In addition, it's uncertain as to how positive the NAO/AO/PNA will trend over the coming medium term, PNA being important upstream of course.

There are some indications pointing to a warming at the 30mb level at the moment within the next 10 days. Global Angular Momentum is down and will continue to be so.

SA

greysides

I took a spin around some high country roads today and was happy with the traction of the compacted snow. I'm not looking forward to the frozen thaw water that we'll be driving on soon enough!

The compacted snow gives an insight into snow driving conditions elsewhere. Normally when it snows it is followed by rapid thawing and ice formation.

We could learn to cope with the current conditions which are more favourable to getting around than our normal post-snow hangover.

nacho libre

Snowaddict wrote: »

Indeed Su Campu, although it's quite clear the breakdown won't be straightforward, as was suggested last Thursday. It was also suggested that an area of positive height anomolies would persist to the North/Northeast & this is quite evident on tonight's Guidance - quite clearly seen on ECMWF.

In addition, it's uncertain as to how positive the NAO/AO/PNA will trend over the coming medium term, PNA being important upstream of course.

There are some indications pointing to a warming at the 30mb level at the moment within the next 10 days. Global Angular Momentum is down and will continue to be so.

SA

hi sa, what's global angular momentum when it's at home?? also is the warming at the 30mb level a good/bad sign if you are a cold lover? thanks.

Snowaddict

nacho libre wrote: »

hi sa, what's global angular momentum when it's at home?? also is the warming at the 30mb level a good/bad sign if you are a cold lover? thanks.

Hi Nacho,

It broadly refers to the interaction of various meteorological & geophysical influences throughout the world. For example, Mountain Torque Events, Tropical Convection Activity etc.

Regarding the 30mb Level, we need a warming of this level if we are after cold weather, as it supports the development of Blocking Highs. The wintry outbreak last February was brought about by a Major Midwinter Warming at the 30mb level.

SA

Su Campu

Snowaddict wrote: »

Indeed Su Campu, although it's quite clear the breakdown won't be straightforward, as was suggested last Thursday. It was also suggested that an area of positive height anomolies would persist to the North/Northeast & this is quite evident on tonight's Guidance - quite clearly seen on ECMWF.

In addition, it's uncertain as to how positive the NAO/AO/PNA will trend over the coming medium term, PNA being important upstream of course.

There are some indications pointing to a warming at the 30mb level at the moment within the next 10 days. Global Angular Momentum is down and will continue to be so.

SA

I think the breakdown IS as straightforward. After Tuesday the chance of snow becomes non-existant for 95% of the Irish territory, with just the highest peaks not showing a thaw by Wednesday/Thursday.

Put the models aside for a moment, no point getting caught up in reading them, the big picture upstream is the key, and it's being put in the lock right now. The global pattern 90° phase shift I spoke of is taking shape. The positive anomalies to the northeast are going to push the scandi even farther to the east by mid week. Zonality will be established over the Atlantic with the setting up of the broad Icelandic low.
Geopotentials are on the rise in North America, eventually putting a stop to the New Foundland low that's been generating Nor'easters there one after the other, feeding the NA high and locking us in that scenario for the past few weeks. I see us possibly becoming NAO +ive for the rest of the month of January - after that I don't know.

Su Campu

Interesting satellite pictures this afternoon as system moves westnorthwestwards over Ireland.

The 500hPa southeasterly jet streak from the cut off upper low giving the energy to the system is clearly visible as jet fibre above the vast overcast blanket, extending from southwestern England to the far west of Ireland. Another feature visible is the enormous swathe of low cloud and fog covering England, France and into Germany and the low countries.





The 12Z Camborne sounding shows the development of this streak nicely. Also visible is the warming at mid and lowers levels, with 850 theta W of +2°C confirming the snow marginality present to our southeast.

http://weather.uwyo.edu/cgi-bin/sounding?region=europe&TYPE=GIF%3ASKEWT&YEAR=2010&MONTH=01&FROM=0912&TO=1012&STNM=03808

Today's FAX analysis shows the 700hPa warm front lying from central England back to western Russia. Divergence of the 700hPa wind vectors is leading to a weakening of the frontal gradient, and tomorrow's 06Z FAX shows it as a decaying front.



This frontolysis leads to a reduction of precipitation tonight over England and Ireland, and give a brief lull before the arrival of heavier precipitation linked to the movement of the upper trough northwards over us tomorrow evening. This will start tomorrow morning as snow above 250m, moving northwards throughtout the day, with the heaviest falls in the western half of the country, giving several cms of snow above 250m in the central areas above 250m, and above 400m in southern areas by tomorrow night.

Tuesday see the arrival of the low to southern areas, with its occluded front giving decent rainfall across the southern half of the country.



Wednesday sees this low move northwards along the western half of the country, clearing quickly and introdicing mild southwesterlies Thursday and Friday, turning southerly for the weekend.

M.T. Cranium

This seems like the best thread to place a few notes on the developing low pressure system and warm fronts expected to arrive Tuesday.

The clearing line visible on satellite now reaching into parts of Kerry is not the warm front of this system, what it represents is the southern edge of the mid-level cloud mass which represents a dissolving frontal wave moving retrograde (east to west) across Ireland on Sunday. So it might warm up slightly in some places when this clearing moves in simply because there was some very cold air trapped in an inversion layer over Cork and the southwest, which accounted for their heavier snow yesterday. But this is still a stale variant of arctic air that had its origins in central and eastern Europe days ago. The leading edge of the warmer maritime polar air mass is off to the south of Ireland around 49 N and is really just starting to take shape this morning; a ship report at 47N 18W approx gives us SE winds at 40 knots and a temperature of 10.5 C, dew point 4.4 C. That's the warm sector of this low forming up, while the K1 buoy closer to Ireland near 49 N 13 W has seen light southerly winds developing and as usual is close to the sea surface temp at about 10 C but the dew point there is still closer to zero and this shows that the dynamic warm front is not quite through that location yet.

What this means is that the warmer air as evidenced by higher dew points is still 250-300 miles southwest of Valentia and Cork, and on its way to arrive possibly about 0600h. The strong winds and heavy rain should begin about 0300 before this surface front moves through, and the associated cold front will be occluding the system fairly quickly just about then, so most places further north will only see one frontal passage, the occlusion, which will tend to terminate a period of strong SE winds and heavy rain.

The track of the low is likely to bring it quite close to Valentia about 1200h and then in a generally NNW direction back out to sea around the Shannon estuary 1500h and west of Galway Bay about 1800h. All this time, this low will be weakening so that the strongest winds are likely in the south and southeast around 0900-1200h Tuesday.

Su Campu

Tommorrow's storm didn't even exist 18 hours ago, but is set to deepen to between 960 and 970 hPa off the west coast tomorrow afternoon, depending on what model you look at. The NAE is the most agressive with it at 960hPa at 15Z tomorrow, the GFS has it as 970hPa, but one thing is common with them all - this system is a true cyclonic bomb, ie. its core pressure will have decreased by more than 24 hPa in 24 hrs. The wind field from such systems can be quite impressive, especially on its eastern flank where the movement of the system adds to the windspeed observed.

Formation
At 6am this morning a kink started forming in the isobars along the polar front, caused by divergence in the left front quadrant of a 200kt+ (230mpth+) jet streak on the 300hPa jetstream. Divergence means a spreading out of the flow, so when this occurs in the upper atmosphere, air from below is forced to rise to fill the relative void, causing pressure at the surface to fall, and setting in motion a period of pressure falls as the air continues to rise to compensate for the upper divergence. In this case the divergence aloft is strong due to the strength of the jetstreak, hence this system is going to be a humdinger by tomorrow.

6am this morning






24 hours later (06am Tuesday)


At this stage the vertical velocity (speed at which the air is rising inside the system) is shown below to be around 46hPa per hour (or around 0.25mph - may not sound much, but for these systems is enormous). This rising motion is the reason for the heavy rain rates we'll experience tomorrow.



At 18Z this evening the UKMO analyse it as a 983hPa low to the southwest of Ireland, turning towards a northerly direction as it deepens and occludes tonight. Ship in the area are already reporting up to 38 knot (43mph) mean wind speeds



By tomorrow afternoon all areas will be affected by up to 40 knot mean windspeeds, with gusts of up to 70 knots possible in the south and west.