I have been pondering this amber warning for heavy rain on Tuesday and Wednesday issued by the UKMO yesterday and looking at the latest NWP forecasts for rainfall accumulations. It’s difficult to be that precise, because the ARPEGE chart from wxchart.com is not displaying each 0.1° grid point for rainfall accumulations, but because this is an orographic rainfall event, wouldn’t the highest rainfall be on the western slopes of the Pennines with the highest totals across the northwest of England? So why does the warning cover so much of south Yorkshire? Obviously the rivers running down from the Pennines (the Don, Swale, Ure and Calder) will be running wey high but wouldn’t the rain shadow effect will reduce the amount of rain that fell east of the Pennines by at least 50%? Perhaps the Pennine watershed will not prevent a lot of the rain that does fall to run off to the east.