Een goeie analyse van komende potentiële onweer
Bericht van: Marcus (Sleidinge) - moderator - , 01-08-2004 22:59
Opgesteld door een zeker MVH op TWO.
Natuurlijk voor England maar met een fasesprong van 12 à 24 uur kan het ook voor ons min of gelden.
OK, so now that the general info is out of the way, lets get down to business. Starting with this mornings FAX chart;
http://www.wetterzentrale.de/pics/brack0a.html
http://www.wetterzentrale.de/pics/brack1.html
http://www.wetterzentrale.de/pics/brack1a.html
http://www.wetterzentrale.de/pics/brack2.html
http://www.wetterzentrale.de/pics/brack2a.html
On a somewhat pessimistic view, I have seen similiar synoptic patterns in years gone by and the end result has been a damp squib, mainly because you can only forecast and discuss what is currently being shown by the meteorological information, but when the event in question actually arrives its generally less intense than what was overall expected. However as I have just mentioned you can only discuss and forecast what is being shown by the information and that the outcome of this event is likely to be some excellent convective activity.
All eyes will be on Southwest England overnight tonight and through into tomorrow Monday morning. As can be seen by the 12z Monday chart the trough essentially signals where the main thermal plume will be and the main thunderstorm activity. So Southwest England, South and Western Wales, through into Ireland and later in the day and overnight into Tuesday, possibly into Eastern Wales and also Western Scotland. Forecast soundings for Southwest England (Exeter 15z Monday), signal an atmosphere that is likely to initially produce what is known as mid-level instability. This is a process that allows altocumulus castellanus (ACCAS) to develop (then high based CB's) in association with a stable or conditionally unstable lower part of the atmosphere, but the mid and upper levels of the atmosphere are completely unstable. In association with upper forcing and possible nocturnal cloud top cooling thunderstorm activity could well persist throughout the night in some parts, but the overall frequency is likely to reduce compared with Monday daytime.
Into Tuesday and the main plume pushes further Eastwards. Tuesday overall is what I believe will be the main day for thunderstorm activity across a large portion of the UK. Significant upper troughing pushing in from the West will push significant amounts of upper forcing over the UK, just aiding the thunderstorm development in conjunction with surface heating and possible convergence zones. The cold front on the Tuesday 12z chart could well act as a focal point for thunderstorms, but the cold front in this instance will simply be a boundary between much fresher air and the humid and thundery airmass. A forecast sounding (00z GFS, personnally modified) over Central England at 18z on Tuesday shows a highly impressive atmosphere in relation to the deep instability present. SBCAPE values are likely to be between 1000j/kg and 1500j/kg, and depending on surface temperatures and dew points could be higher than that. LI values are generally around -5C. Wind profiles aren't that impressive, but coupled the deep instability with more dynamic features including the cold front then organisation is possible, with multicell activity a solid possibility. Throughout this thundery period the chances of supercell activity is limited, this is simply because the extreme dynamic processes that are needed to create supercell activity aren't present.
Tuesday night into Wednesday could be a very special night indeed for some with the upper forcing, nocturnal cloud top cooling and continued humid and high surface temperatures likely to aid in keeping a good rash of night-storms going. As ever saying exactly where, is open to significant uncertainty. Behind the cold front on the 00z Wednesday FAX chart, the thundery weather will likely have cleared and it will turn much fresher. By Wednesday the uncertainty in general over the pattern is high, because the cold front becomes a warm front inassociation with warm air advection. Anywhere to the East of this front will be at a continued risk of thunderstorm activity, however of notice is the reduction in 1000-500mb thickness values. The 564dam has moved away from the UK, so in general at the moment Wednesday should be a fresher or at least a cooler day for many.
The main uncertainties are;
The speed at which the thundery activity will cross the UK - Overall confidence is high on the main activity starting in the Southwest and West of the Country and then gradually moving Eastwards across the UK over the period of 36 to 48hrs. If this process slows down then the thunderstorm risk could be higher into Wednesday than if the process is quicker.
The thunderstorm distribution - In this situation its always important to find the main thermal plume (located by the trough on the FAX chart) and this is likely to be the main region of activity, not always but its a good start of picking out the main regions. Because of the intense heat and humidity effecting the UK, then home-grown airmass storms could also add to the thunderstorm activity in association with the plume.
Thunderstorm intensity - With the forecast soundings signalling SBCAPE values in excess of 1000j/kg and cloud tops towards 35,000ft to 40,000ft (overshoots), then the overall intensity of some of the storms is likely to be high. Torrential downpours leading to flash flooding, large hail (1-2cm), strong convective windgusts (35 - 45KT) and obviously intense and frequent lightning will all combine in some cases to produce quite extreme convective weather. The overall threat of any tornadic activity as with the supercell activity is low at the present time.
Thunderstorm persistence - During the daytime in association with surface heating thunderstorms could persist for the majority of daylight hours in some parts, but by night the uncertainty is greater. As mentioned earlier, because of significant upper forcing and possible nocturnal cloud top cooling, some significant night-storms are possible, more especially on Tuesday night through into Wednesday.
So all in all, plenty to monitor, watch and enjoy if you like convective weather, or even if you don't really!. As mentioned at the beginning of the post, all further information from myself on the up coming event will remain directly within this thread. More information on the end of the week will be available once this convective threat has moved away.
Natuurlijk voor England maar met een fasesprong van 12 à 24 uur kan het ook voor ons min of gelden.
OK, so now that the general info is out of the way, lets get down to business. Starting with this mornings FAX chart;
http://www.wetterzentrale.de/pics/brack0a.html
http://www.wetterzentrale.de/pics/brack1.html
http://www.wetterzentrale.de/pics/brack1a.html
http://www.wetterzentrale.de/pics/brack2.html
http://www.wetterzentrale.de/pics/brack2a.html
On a somewhat pessimistic view, I have seen similiar synoptic patterns in years gone by and the end result has been a damp squib, mainly because you can only forecast and discuss what is currently being shown by the meteorological information, but when the event in question actually arrives its generally less intense than what was overall expected. However as I have just mentioned you can only discuss and forecast what is being shown by the information and that the outcome of this event is likely to be some excellent convective activity.
All eyes will be on Southwest England overnight tonight and through into tomorrow Monday morning. As can be seen by the 12z Monday chart the trough essentially signals where the main thermal plume will be and the main thunderstorm activity. So Southwest England, South and Western Wales, through into Ireland and later in the day and overnight into Tuesday, possibly into Eastern Wales and also Western Scotland. Forecast soundings for Southwest England (Exeter 15z Monday), signal an atmosphere that is likely to initially produce what is known as mid-level instability. This is a process that allows altocumulus castellanus (ACCAS) to develop (then high based CB's) in association with a stable or conditionally unstable lower part of the atmosphere, but the mid and upper levels of the atmosphere are completely unstable. In association with upper forcing and possible nocturnal cloud top cooling thunderstorm activity could well persist throughout the night in some parts, but the overall frequency is likely to reduce compared with Monday daytime.
Into Tuesday and the main plume pushes further Eastwards. Tuesday overall is what I believe will be the main day for thunderstorm activity across a large portion of the UK. Significant upper troughing pushing in from the West will push significant amounts of upper forcing over the UK, just aiding the thunderstorm development in conjunction with surface heating and possible convergence zones. The cold front on the Tuesday 12z chart could well act as a focal point for thunderstorms, but the cold front in this instance will simply be a boundary between much fresher air and the humid and thundery airmass. A forecast sounding (00z GFS, personnally modified) over Central England at 18z on Tuesday shows a highly impressive atmosphere in relation to the deep instability present. SBCAPE values are likely to be between 1000j/kg and 1500j/kg, and depending on surface temperatures and dew points could be higher than that. LI values are generally around -5C. Wind profiles aren't that impressive, but coupled the deep instability with more dynamic features including the cold front then organisation is possible, with multicell activity a solid possibility. Throughout this thundery period the chances of supercell activity is limited, this is simply because the extreme dynamic processes that are needed to create supercell activity aren't present.
Tuesday night into Wednesday could be a very special night indeed for some with the upper forcing, nocturnal cloud top cooling and continued humid and high surface temperatures likely to aid in keeping a good rash of night-storms going. As ever saying exactly where, is open to significant uncertainty. Behind the cold front on the 00z Wednesday FAX chart, the thundery weather will likely have cleared and it will turn much fresher. By Wednesday the uncertainty in general over the pattern is high, because the cold front becomes a warm front inassociation with warm air advection. Anywhere to the East of this front will be at a continued risk of thunderstorm activity, however of notice is the reduction in 1000-500mb thickness values. The 564dam has moved away from the UK, so in general at the moment Wednesday should be a fresher or at least a cooler day for many.
The main uncertainties are;
The speed at which the thundery activity will cross the UK - Overall confidence is high on the main activity starting in the Southwest and West of the Country and then gradually moving Eastwards across the UK over the period of 36 to 48hrs. If this process slows down then the thunderstorm risk could be higher into Wednesday than if the process is quicker.
The thunderstorm distribution - In this situation its always important to find the main thermal plume (located by the trough on the FAX chart) and this is likely to be the main region of activity, not always but its a good start of picking out the main regions. Because of the intense heat and humidity effecting the UK, then home-grown airmass storms could also add to the thunderstorm activity in association with the plume.
Thunderstorm intensity - With the forecast soundings signalling SBCAPE values in excess of 1000j/kg and cloud tops towards 35,000ft to 40,000ft (overshoots), then the overall intensity of some of the storms is likely to be high. Torrential downpours leading to flash flooding, large hail (1-2cm), strong convective windgusts (35 - 45KT) and obviously intense and frequent lightning will all combine in some cases to produce quite extreme convective weather. The overall threat of any tornadic activity as with the supercell activity is low at the present time.
Thunderstorm persistence - During the daytime in association with surface heating thunderstorms could persist for the majority of daylight hours in some parts, but by night the uncertainty is greater. As mentioned earlier, because of significant upper forcing and possible nocturnal cloud top cooling, some significant night-storms are possible, more especially on Tuesday night through into Wednesday.
So all in all, plenty to monitor, watch and enjoy if you like convective weather, or even if you don't really!. As mentioned at the beginning of the post, all further information from myself on the up coming event will remain directly within this thread. More information on the end of the week will be available once this convective threat has moved away.
"Koersen, dat is stampen en afzien tot ge niet meer weet van welke parochie ge zijt." (Briek Schotte)
