Yes we could still be still in winter right up until the middle of May... as there could be snow up until then, even more usual during April.
When is the start of spring.
I find the following rhyme, courtesy of Flanders and Swann, quite useful:
January brings the snow,
Makes your feet and fingers glow.
February's ice and sleet,
Freeze the toes right off your feet.
Welcome, March, with wint'ry wind,
Would thou wert not so unkind.
April brings the sweet spring showers,
On and on for hours and hours.
Farmers fear unkindly May,
Frost by night and hail by day.
June just rains and never stops,
Thirty days and spoils the crops.
In July the sun is hot,
Is it shining? No it's not!
August, cold and dank and wet,
Brings more rain than any yet.
Bleak September's mist and mud,
Is enough to chill the blood.
Then October adds a gale,
Wind and slush and rain and hail.
Dark November brings the fog,
Should not do it to a dog.
Freezing wet December, then...
Bloody January again!