Saturday, April 20, 2013

Snow in April? Has this Happened Before?

Its April 20th and we had snow showers earlier in the morning. I could hear the collective "Where is spring? Its not supposed to snow this late into April!" In most years, you and the rest of northern Ohio would be correct. 

Cleveland Heights
South Euclid
How many times have we seen only a tenth (0.1") of snow AFTER APRIL 20TH? Believe it or not, its happened 24 TIMES SINCE 1895 here in Cleveland.

Here are the years and the days this has occurred. The first numbers are the temps leading up to the day of snow. Notice that this year is the first time we've had an 80+ day followed by measurable snow  36 hours AFTER the 80+ degree high.

2013 - 84, 71, 44 (0.1" - 20th)
2005 - 12.4" over 3 days (23-25th)  
2004 - 70, 62, 49 (0.1" snow late on 27th)
1996 - 60, 73, 58 (0.1" overnight)1993 - 73, 40 (0.1" on 21st)
1978 - 50, 42 (0.2" on 21st)
1971 - 60, 52 (0.1" overnight on 21st)
1968 - 51, 29 (0.2" on 25th)

1967 - 49, 39 (0.1" on 24th)
1963 - 65, 59 (0.3" overnight on 30th)
1953 - 34, 57 over 2 days (1.6" & 0.1" on 20-21st)
1934 - 42 (0.7" on 21st)
1922 - 39 (0.2" on 21st)1920 - 59, 48 (0.1" on 28th)
1908 - 41 (1.4" on 30th)
1907 - 59, 42 (0.2" on 26th)

1906 - 41 (0.2" on 23rd)
1904 - 31 (0.3" on 20th)

1903 - 41 (0.1" on 22nd)
1901 - 35, 40 (2.8" & 1.8" on 20-21st)

Incidentally, how often have we seen measurable snowfall in May? 11 TIMES

1902 - 0.6" on 10th
1906 - 0.1" on 9th
1907 - 0.5" & 0.2" on 4th & 10th
1908 - 0.1" on 2nd
1909 - 0.1" & 0.3" on 1st & 2nd
1963 - 0.1" on 1st
1973 - 0.6" on 4th
1974 - 2.0" & 0.1" on 6th & 7th

Friday, April 19, 2013

Friday's HUGE changes...

Temps continue to fall behind the front...rain moving out.

Thursday, April 18, 2013

Today/Tonight's Severe Weather Threat


The radar looks fairly uniform this morning. Well defined line of rain and storms in the middle of the country. .
A WATCH might have to be issued for Indiana later this morning. No showers/storms on radar over northern Ohio as of 9AM.

For Ohio, we will see three elements evolve today before the storms arrive: First the strong winds. The pressure gradient is strong along the front as is the temperature gradient. Temps early this morning were in the upper 70s in St. Louis; 45 in Kansas City. The pressure gradient and the low level winds will translate down to the surface reaching 40-45 late today as we reach prime heating. Dew points are also climbing.

The second element is the temperatures. In April, we need a strong southerly wind to reach 80. That should not be a problem later. the only inhibiting factor will be some cloud cover. History tells us that the winds should mix out the cloud deck. Expect a fair amount of sunshine. Morning temperatures ahead of the front already in the 70s!

The third component (the toughest to nail down) is the energy ahead of the main front. Will this energy kick up some spotty storms later today/evening? Once again, history dictates that the chances are pretty good. The HRRR model shows the random, pre-frontal storms very well. The Storm Prediction Center has western Ohio in a slight risk later today for severe storms

Then we await the arrival of the winds ahead of the front. Storms will pass through the area at the right time of day (late evening/overnight) so as to diminish the severe weather threat. A few storms will reach severe limits tonight but it should not be widespread.

Expect rain early Friday, temps will remain in the 60s early. The models continue to push this front through FAST. So look for the rain to move into Pennsylvania by noon Friday. Temperatures will drop quickly into the lower 50s by afternoon. Some sunny breaks behind the front.

Tuesday, April 16, 2013

Just How BIG have this April's "Ups and Downs" been so far?...

Cleveland Skyline
The dramatic "ups and downs" in recent weeks have caused many to draw the conclusion that this pattern must be something very unique even for spring. Andre has a great blog on his website about how our memory is very selective. We tend to put more weight on recent events or events that are important to us without taking a look at the "big picture" and the data. I've also written extensively about our cognitive biases in how they shape how we perceive the weather (behavioral meteorology) HERE and the human condition pertaining to weather HERE. Our cognitive dissonance couldn't be more apparent in how we view this recent 14 days weather pattern, i.e. One day at 80 then 30s with drizzle and sleet, etc

So how does this April so far compare to the last few years comparing day-to-day HIGH temperatures drops and rises compared to the normal high of the day?  Here are the largest "drops and rises" compared to the daily normal over the 25 Aprils through the first two weeks. For example, if the high was 80 (normal for that date was 60 for a +20 degree difference) and the next day, the high was 45 (normal was 61 for a -16 degree difference), the final difference over the 24 hour period was -36 degrees! These are the numbers I used in the graph below.

Don't be intimidated by this chart. There a lot of numbers here. First, I BOLDFACED the instances of day-to-day positive change (WARMER) of more than 10 degrees. Second, I underlined instances where the temperature change was more than 10 degrees for back-to-back days.  Frankly, I couldn't figure out a good way of illustrating this so the raw data will have to do for now.

Here are some of my notable conclusions:

Recently, 2011 had some VERY big "ups and downs". During one stretch in 2011, temperatures dropped 31 degrees in 24 hours then rose 13 degrees the following day!

April 2010 had an instance where temperatures dropped 20 degrees and then rose 22 degrees the following day.

April 2007 had a 12 degree jump then a 17 degree drop followed by ANOTHER 35 degree drop.

April 1995 from a Sunday to Friday saw a 20 degree jump, a 17 degree drop, a 12 degree drop, 22 degree jump then finally a 19 degree drop!


The bottom line is that historically, April is known for wild swings in temperature and weather. We just don't want to believe it because what's happening NOW is usually perceived as more significant than what happened in the past.