Quick resume of some wet weather approaching on Wednesday for the whole of the UK. The current cool pool is being nudged out of the way East on Tuesday by a vigorous return of an Atlantic jet stream blowing across the UK W-E during Wednesday and ushering a wedge of Tropical air. As the warm humid Tropical air from the SW meets the cool Polar air the warmer less dense tropical air will be forced to rise, cool and condense over a wide area and produce persistent and occasionally heavy frontal rain. This is a classic active warm front and occluding from the NW. The warm sector will brush across the SE during the day raising temps from 8c to 15c during the afternoon despite the rain! Rain totals for the SE may approach 10mm for the day but the heaviest rain will fall further NW along this extensive warm occluding front.
A point to note is that, despite the classic text-book mid latitiude depression having a warm and cold front, it is usual for one front or the other to be more vigorous. In this case, it seems the warm front is the more active, although the front is occluding as the cold fronts catches up the warm and lifts the warm sector up.
On Thursday, a much drier and more pleasant day, any sunshine could raise Tmax to near 20c in Reigate! By that stage despite being a relatively warm W/SW flow, the air mass is probably more accurately described as a modified polar maritime, coming in behind the occlusion, nevertheless, the SE will sit in warmer air than of late.
Here is an animation, courtesy of NMM netweather that shows the transition from cool polar pool to warmer SW flow in the next few days.
sirgeogy