All About Wave DepressionsAdded : Friday at 10:02 If you go back around, say ten to fifteen years, then the one feature which most numerical weather models struggled with was wave depressions. Especially systems which formed as secondary low pressure areas to the South of the main system. These days, thankfully, the models seem to have no problem resolving them.
That's probably enough technical mumbo-jumbo for one morning, so take a look at the charts and we will show you what we mean.
If you look at the chart above you can see the primary low just West of Scotland. But notice the kink in the isobars to the West of the UK. This is a wave depression which has formed off the cold front of the primary low.
If you look at the rain chart for the same time you can see the wave depression a little clearer :-
AROME shows the wave depression coming in from the West later this evening :-
If we went back ten or fifteen years ago, then numerical models tended to get a little itchy with these systems and try to develop them into secondary lows way before they actually did. As forecasters there was this constant battle between looking at the charts and knowing that they were going to bust due to the poor handling.
If you look at the wave depression which comes into tonight and roll forward to the early hours of Saturday morning :-
You can see how all the mesoscale models keep it as a wave as it crosses England and Wales with some stronger winds to the South, but nothing like they would show had the system developed circulation.
Into Saturday evening and another wave depression comes in from the Southwest :-
Now, this little puppy has formed slightly further South. If the numerical models are right, then it could develop a little more than the one coming in tonight thanks to more upper level divergence than is available this evening.
ARPEGE shows this up well and closes circulation in the system
That could well bring some strong winds along the English Channel overnight Saturday and into Sunday. But, this is dependent on the circulation closing within the system. No promises just yet, but it's good to see the progress modelling has made in recent years and how it now handles that weakness far better than it did.
METEOROLOGIST : MARSH |