It is not that long ago, maybe four or five years, that a great white egret sighting in Dorset was quite unusual and would create a bit of a stir but not any more. They have been seen quite regularly on the Somerset levels for a while now and I understand that they are now starting to breed there so to have over wintering birds in Dorset is no longer that surprising. It remains to be seen whether their colonisation of Britain is as dominant as their smaller cousin, the little egret.
The weekly reports chart show the frequency at which this species is being seen with records during the non-breeding months from around week 26 (mid-July) through to week 17 in early April. They are pretty much absent from 18 through to 25 presumably whilst away breeding so it will be interesting to see if that gap is maintained this coming summer or whether we start to get sightings as younger birds stay with us or even if they start to breed here.
It will be seen that there is a big jump in reports during the late summer and autumn. That is not directly because of a major influx of birds but because a small number of long staying birds are being reported regularly from Longham Lakes, Lodmoor/Radipole and from around Poole harbour. There could be about ten birds present during the 2018/9 winter but, although more common now they are still a notable bird and attract lots of reports. Reports during 2018 are about 50% up on 2017.
Records are mainly from coastal locations as the distribution map clearly illustrates and this, of course, reflects their preferred feeding habitat in shallow waters near reed beds.
In the winter of 2018/9 your best bet for seeing one would seem to at Longham lakes where three or four birds are regularly reported.