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

Tuesday, April 20, 2021

Late April Snowfall: How Rare is this?

Yes, it's April 20 and we are talking about accumulating snow!

Sure we've seen late season snow before. It snowed in mid-April in 2019.

...and it snowed in May 2016 (under an inch).

In fact 16 of the last 20 years has featured measurable snowfall after the first day of spring. Over the last 30 years April has featured snowfall almost half of the time. But snow that need shoveled after April 20 is something else entirely.

Below is a calendar of each day starting on March 20 showing the snowfalls for each day. Notice how the frequency of snow drops significantly once we make it through the first 10 days of April. Interestingly we've only had 3 snow events greater than 2" after April 20th. Two of those occurred in 2005. (I remember driving home from work during that big snow on the 24th).  The other one was on May 6, 1974.  We've had snow in May but never more than 2 inches.

The late April snow in 2005 was historic for northern Ohio.  Look at the similarities between this year's pattern and 2005. Position of storm center is close.  2005 was much deeper.

Bigtime cold across the Great Lakes and New England (April 2005)

Much of northern Ohio saw more than a foot of snow that year in late April

This time the overall pattern was showing signs of stronger weather systems by the 3rd week of April (shades of blue).   My tweet from April 5th below.

The cold was building a week ago in central Canada as this temperature animation below shows. This loop is from April 15 to April 29.  Not much warmth here.

Snowfall accumulation is much different this time of year due to warmer ground and road surface temperatures.  These numbers are mainly for grassy surfaces.  Snowfall on roads and sidewalks will end up being under these levels. Sun angle is much higher so any sunshine will accelerate snow melt Wednesday and Thursday. 

Snowfall forecast could mark only the 4th time we've had more than 2" of snow this late in the season.

By the way, this snow doesn't give us any indication of what the rest of spring and summer will be like. More on the summer outlook in the weeks ahead.