For the last couple of days I’ve been talking about the difficulty in forecasting Sundays rainfall so I’ve decided to take a closer, more detailed look at the various different computer model forecasts to try and pin down exactly where this rainfall is likely to fall. Lets take a look at the GFS and UKMO rainfall predictions for Saturday evening at 6PM

GFS Rainfall Prediction


UKMO Rainfall Prediction

As you can see there’s some fairly large differences between the two models even at this very short timeframe. The UKMO model is keen to bring the rainfall in across Wales and South-West England whilst the GFS model is only just bringing the rainfall into the far South-Western corner. Taking a look at the GFS ENS rainfall however, which is a collection of different runs, it does seem to fall inline with what the UKMO is predicting.

GFS ENS Rainfall Prediction

Through Sunday morning and into the afternoon, the models have the rainfall moving Northwards and even clearing the far South by around lunch time

GFS ENS Sunday 6AM
GFS ENS Sunday 12PM

The rain then seems to pivot around this area as it becomes lighter, rainfall once again beginning to effect Southern areas

GFS ENS Sunday 6PM

The ECM Rainfall Prediction for Extreme Rainfall tends to agree with this forecast, placing some fairly large rainfall totals across Wales heading in a South-Easterly direction

ECM Rainfall

So I think with this in mind, during Saturday evening we’ll begin to see the first signs of some rainfall moving up into South-West England and Wales, it’ll generally be quite light and patchy at first but as the night progresses it’ll begin to turn heavier, spreading across much of Southern England and into the Midlands by morning, the system will continue to head North, sitting across the Midlands around lunchtime bringing some fairly heavy rain to some areas, drier for a time across the far South but as the rain begins to  weaken showers will begin to develop further South, particularly across Central Southern England. A weather warning is likely to be issued on Saturday along with a detailed forecast for the double bank holiday. The map below highlights areas expected to see the highest rainfall totals based on the charts above.

RED ZONE: 10-15mm likely throughout the course of Saturday night and during Sunday, localised flooding is possible in some areas.

YELLOW ZONE: 5-10mm likely throughout the course of Saturday night and during Sunday, localised flooding is possible but considered unlikely.