Bitter weather on officially the first day of spring caused chaos for commuters and students, with roads blocked and schools and colleges closed.
An elderly woman was found covered in snow on a pavement in the Knighton area of Powys at 0500GMT.
The woman - believed to be in her late 80s or 90s - was taken to Hereford hospital where she was said to be in a critical condition.
High winds blew the roof off a house in Aberystwyth, and there have been a number of accidents on the M4 in south Wales.
Five jacknifed lorries blocked the A483 between Llandovery and Builth Wells.
In north-east Wales, snow has continued to fall heavily and the main A55 is down to one lane in places.
Police there urging people not to drive unless the journey is absolutely necessary.
Clearing roads in the Denbighshire area has been hampered because the local authority normally uses agricultural contractors who are unable to help because of foot-and-mouth restrictions.
No serious accidents have been reported so far and most roads are passable with care.
The A 4109 Glyneath to Banwen road has been closed, and many in mid Wales have been badly affected, including the main A470 which is passable only with care.
The following roads in mid Wales have been closed : the A44 at Forest Inn between Llandrindod Wells and Radnor; the B4358 between Beulah and Llanafon near Llandrindod Wells; the A494 at Llanbedr Duffryn Clwyd.
In north Wales, there have been problems reported on the Crimea Pass above Blaenau Ffestiniog and at Tal-y-Llyn pass south of Dolgellau.
Police say all routes are passable with care, but travelling is very difficult on high ground around Wrexham and Ruthin, and there is poor visibility around Holywell.
The following schools have told BBC Wales they will be be closed on Wednesday:
South Wales
In Merthyr Tydfil : Cyfarthfa High School, Pen-y-Dre High School; Vaynor and Penderyn High School, Cefn Coed, Pantysgallog Primary School; Edwardsville infants and junior school; St Aloysius Primary, Gurnos. Elsewhere : Trinant Primary, Caerphilly; Newbridge Comprehensive; Georgetown Primary School in Tredegar; Abertillery Primary School; Blackwood Primary School; Griffithstown Junior School in Pontypool; Coleg Gwent's Ebbw Vale campus; Ysgol Gyfun Gwynllyw, Pontypool; Nanyglo Comprehensive; Bedwellty Comprehensive; Rassau Primary Ebbw Vale; Garnlydan Primary in Ebbw Vale Ebbw Vale Comprehensive School Deighton Primary Tredegar; Abertillery Comprehensive - closed for most pupils, but open for year 10 and 11 pupils who are sitting a GCSE exam
North Wales
Ysgol Rhyd Galed Groes near Denbigh; Ysgol y Gader, Dolgellau;. Ysgol Hooson, Rhosllanechrugog, Wrexham;Ysgol Maes Garmon in Mold; Ysgol Belmont in Buckley; Ysgol Berwyn in Bala; Ysgol Llanllechid in Bethesda; Llanfechain and Llangedyn, near Llanfyllin, Montgomeryshire; Ysgol Gynradd Rhos Ellig, Flint; Ysgol Cerig y Dreidion near Corwen; Ysgol Gynradd Capel Garmon near Llanrwst; Ysgol Ysbyty Ifan, Conwy; Llanarmon yn Ial; Llanferres;Grainanrhyd;Cefn Meiriadog; Llangollen; Clocaenog; Carrog; Corwen; Bryneglwys;, Llandegla; Rhuallt;
And the atrocious weather conditions are expected to continue, with snow in some parts predicted to reach 10cm on higher ground.
Temperatures as low as minus 1C have been recorded in Exmoor and the wind chill is making it feel between -6C and -8C across southern England.