Monday, April 26, 2021

Second Heaviest Snow This Late In The Season. When/How Did We Know?

I'm 5 days late with the late April snow recap.  Here are the snow amounts:  A few locations were close to 8 inches by Thursday morning.

April 21 snowfall


Seven Hills


Snow after March 20 is pretty common in northern Ohio.  Snow after April 20 is a rarity. Only two other years have had more than 2" after April 20.  1974 and 2005. The 2005 event was over a 48 hour period (see the map below).

April 23-25, 2005 snowfall.  Remember this? More than a foot of snow fell across a large part of northern Ohio.  In 3 days it was completely gone!

Signs were pointing to snow or at least a deep storm system with colder air back on April 5--two week prior.

The MJO was heading into favorable cold phases.

A recurving typhoon near the Philippines (which often times portends cooler than normal temperatures eastern US) gave us another good indication.

Eventually the long range models (back on April 8) picked up on this colder idea.

Animation of temperatures: April 10 to 22

Upper level pattern was pretty close to April 2005 snow event. That storm system was deeper.

What's the latest we've had snow? After cross-referencing hourly temperature data, the years are narrowed down to only a few.  Last year was the LATEST MEASURABLE SNOWFALL which broke the record set back in 1907.  Flurries were reported close to Memorial Day in 1907 and 1961 (Akron).

How quickly after late season snow do we see an 80° degree day? Earlier in April it took us around 7 days (6 days listed below) post snow to reach 80°.  Snow on April 1.  83° April 8.

Indications of a late month warmup were surfacing shortly after the colder mid-month pattern was showing up.  SOI composites (analog to similar situations in a La Nina) showed a weak, short-lived ridge of high pressure/warmth around April 26th.

Composite for BIG drop in SOI around April 11-13/La Nina

High temperatures across more than 15 states Monday-Wednesday this week will easily teach 80