Cesair

Gwahaniaethir rhyngddi ac eirlaw, er cânt y ddau eu cymysgu â'i gilydd yn aml. Pan fo cesair yn disgyn yn ystod storm o daranau, fe'i gelwir yn 'storm o gesair' (hailstorm). Gall cesair bwyso mwy nag 0.5 kg.

Cesair

Enghraifft o'r canlynol	math o ffenomen meteorolegol
Math	dyodiad
Lliw/iau	gwyn
Deunydd	Iâ
Achos	Atmospheric convection, cumulonimbus
Yn cynnwys	hailstone
Ffeiliau perthnasol ar Gomin Wicimedia

• 20 Awst 1939: Un o'r cawodydd cesair trymaf a brofais erioed y bore yma a ddaeth gyda tharannau

Meddai’r meteorolegydd Huw Holland Jones:
Interesting...records show that Aug 1939 was warmer than usual, Average Tx for month at Ross on Wye was 21.1°C, Tn 11.7°C. but not a wet month, with High Pressure much of the month. A hot spell of weather started on the 14th, and by the 19th daily temps were 25°-26°C in South Wales, and still 16°C the following night. On the morning of the 20th a thundery low had formed over N. France and the humid warm air in its circulation spread across S. Britain (and S. Wales) resulting in many thunderstorms (and the ones at Esgerdawe ). By the 21st fine weather had returned, and continued right through till the end of September. War was declared on Sept 3rd (ironically one of the few wet days that fine September) [Tx = uchafswm Tn = isafswm]

• 10 Mehefin 2011: “wrth gerdded draw am Lyn Eiddew Mawr ar ddiwrnod hynod o braf, tua diwedd y pnawn dyma gythgiam o gymylau bygythiol yn hel tua'r de ac yna fel o'n i'n mynd am Ddolgellau be welais i ond cawod o eira/cenllysg di cwympo ar y llethrau uwchben Arthog”.

Mae’r llun yn dangos sut mae cawodydd cenllysg yn gallu bod yn lleol iawn.