Monday, July 31, 2017

Are Days With Oppressively High Dew Points More Common Now?

In June, days with dew points higher than 70 were more common in the 1950s and the 1990s/early 2000s than in the last 15 years.


In July (two graphics above) 12 years since the late 1940s had at least 15 days with 70 degree dew points. The peak in the data period was over a 25 year period from the late 1970s through the early 2000s. We have trended below normal since the early 2000s in August.

In August, spikes of 70 degree dew points in August in the 1980s through the early 2000s. Small peaks in the late 1950s, 1980s and late 1990s in September with a small peak in the last 7 years.

How about 80 degree dew points?

Its only happened three times since the late 1940s. Twice in 1995 and once in 1998

Monday, July 10, 2017

Are Summer Temperatures in Northern Ohio Getting Warmer?

Many people have asked if summer temperatures are getting warmer in northern Ohio over the years. Answering this question isn't easy because there are so many automated observation stations that yield different answers depending where you are across our 20+ county area. Cleveland Hopkins isn't an accurate representation of Geauga County.  Akron or Canton isn't good in representing Sandusky. See the problem?

Luckily, Ohio is broken down into ten climate divisions to make our quest easier.

Using the NCEI (National Center for Environmental Information) "Climate at a Glance site, it was easy to plot the average temperature for the divisions that encompass northern Ohio.

(I also used the Southern Regional Climate Center site to show 5 year averages (blue and red bottom graphic) for each division. I used divisions two, three, six and seven to best reflect all northeastern Ohio counties).  These graphs above give us a pretty good idea on long term trends dating back to the 1890s. 





A few points to consider when interpreting these temperature graphs:

1)   Interestingly and surprisingly, these northern Ohio climate divisions show very little long term temperature variations during the summer months (June, July and August).  We see general above normal warmth from the 1930s through the 1950s, a cooler trend from the 1960s through the mid 1980s and a warmer trend since the 1990s. Will this warmer trend continue? That's the big question

2)   Its very important to note that these graphs don't necessarily reflect any temperature trend on a larger scale nationally or globally. What occurs on the local level like northern Ohio can be very different from global trends. So using this data or any local data to dispel Climate Change ideas would be inaccurate.

NWS Cleveland ASOS
So how were these divisional temperatures calculated?

Were main reporting stations that we use on the air like Cleveland, Akron, Mansfield, etc the only ones used?  In searching for the answer, I remembered my discussion with Derek Arndt, Chief, Climate Monitoring Branch at the National Climate Data Center (NCDC) back in 2012 and my recent follow up in which he outlined the procedure:

"For our month-to-month reports, the climate divisional averages are constructed from all available stations (NWS) within the division at the time. We only use stations that are in the GHCN-Daily network of stations with a service record long enough to establish some kind of "normal". These are your familier NWS ASOS/AFOS/AWOS stations, NWS-commissioned COOPerative observers. .This preliminary makeup won't change dramatically from month to month. The major airport stations you mentioned will almost always be there, unless there are problems at the station. The more obscure cooperative observer stations may be a little less reliable and may drop in / drop out from month to month..."
"...After a few months the "paper based" records roll in (the ones that are literally recorded on paper and old-school mailed to the weather service). At that time, we'll recalculate the divisional averages, and call these our "final" values.  The preliminary average isn't a straight average. There are some mild gymnastics involved to account for missing stations; this has little impact on the outcome especially for temperatures."
That's probably more than you needed to know.  As a scientist, it's essential to ask these questions so that you can have some working knowledge of the process. Asking WHY or HOW is often times more important than the result.

Thursday, May 04, 2017

Why The Abrupt Cooler Pattern in the Northeast?

After the warmest April on record in places like Cleveland, Ohio and across much of the Ohio Valley and much of the eastern US, the pattern has not only reverted back to spring, it took several steps back resembling elements of winter. Throughout April, this high pressure ridge stayed east which allowed the ridge across the eastern US to build allowing above normal temperatures. Many were fooled into thinking that summer was here and we were in the clear to plant gardens. Not so fast!

Look at April temperatures versus the 30 year average:

Now look at the first week or so of May per the American model (GFS).

Why the sudden flip?  In this case, we have to look over Greenland for the answer.

Remember that across the mid-latitudes, troughs and ridges (valleys and peaks in the upper levels of the atmosphere) travel like a fluid through the atmosphere. When one location is lucky enough to be blanketed by a ridge, fair weather typically is the result. Once the succession of trough and ridges is changed by an interruption in the wave pattern, the weather will change at the surface. These changes (too much to go into here. See Southern Oscillation Index) often originate over the Pacific Ocean and propagate east. Currently, these changes are reflected over the northern Atlantic and Greenland.

Notice the red (high pressure) at the top inching west blocking/stalling the blue (low pressure systems) over the NE
We can quantify the strength of this ridge using the NAO of the North Atlantic Oscillation.  The more negative the index goes, the stronger the Greenland ridge. The NAO has been forecasted to drop close to -300. Historically this has only happened once in the month of May since record keeping began.  That was back in 1993.

NAO drops to -300 soon

But be warned, historically, this pattern over Greenland in May doesn't always produce a cold and rainy May. Look at the high temperatures in Cleveland during these years of record low May NAO:

Look at the resultant upper level pattern across the US in each of these years. All but 1948 and 2008 show dominant warmth.







The NAO this low (or any other index) isn't always a great predictor of temperature and the overall pattern. 

Unfortunately, unlike any of the previous instances of strongly negative NAO in May, this cold is locked in for at least another week.  So get ready for rain, scattered frost and perhaps some light snow!

Friday, April 21, 2017

Don't Plant Tomato Plants Just Yet

This happens every year we enjoy a very warm period in early spring.  People prematurely want to plant their garden. Don't do least not now. (as of this writing April 21)

Below are the top 15 warmest April years in Cleveland.  Interestingly, the majority of these years featured overnight lows in the lower 30s in May.

Thursday, March 16, 2017

Do The Defensive Trends Shed Light on NBA Offensive Increase?

The previous post looked at the dramatic increase in 3-point field goals and other offensive statistics over the last 30 seasons. Do the rate of steals, turnovers and personal fouls per game shed any light on this?

* Turnovers per game started dropping from 1989 through 2000 with a leveling off over the last 10 seasons.

* Steals per game started dropping in the late 1990s with some leveling off for brief period over the last 15 seasons.

* Personal fouls feature some ups and downs with a steady decline since 2006

Monday, March 06, 2017

Morning Severe Storm Event of March 1st

Lightning damage in Dorset, Ohio

We just experienced our first severe weather event during the morning show in almost 3 years.  Given the volatile history of the storm system which was responsible for baseball size hail and one fatality from a tornado in central Illinois, we knew this event had pretty high potential for severe storms and a tornado warning or two.  We mentioned the increased likelihood of strong/severe storms more than 24 hours before the event.

If you familiar with my weather casts, you know that I rarely use the word "severe" to describe storms unless the situation warrants it.  The reason why is simple: When most people hear the word "severe" when describing storms, they immediately think "tornadoes".  The last thing I want to do is invoke the idea of tornadoes when in most severe storm cases (less than 10%) the chances of a tornado occurring are small.

Tuesday morning--24 hours before--was one of those instances where I used the word "severe" multiple times to describe the next day's outbreak. The possibility of northern Ohio going under a severe thunderstorm watch was high enough to be included in the forecast. All high resolution projections showed two distinct severe storm clusters tracking across Ohio between 12am and 8am. It was the second one that had us concerned not only because of it's elevated severe weather potential but because it was developing overnight when most people are sleeping. This animation below was generated at 1am Tuesday more than 24 hours before the event:

The two severe storm clusters projected location at 1am Wednesday.

By Wednesday morning, the second storm line above had already produced a strong tornado in central Illinois and one fatality.  That same storm produced baseball size hail.

Ottawa, Illinois

The Storm Prediction Center had issued this discussion specifically for the second line of storms BEFORE the severe thunderstorm watch was issued at 3:25am. See the strong wording below.

Mesoscale Discussion 0233
   NWS Storm Prediction Center Norman OK
   1244 AM CST Wed Mar 01 2017

   Areas affected...Portions of southern Lower
   Michigan...northeastern/central Indiana...and northwestern Ohio

   Concerning...Severe Thunderstorm Watch 45...49...

   Valid 010644Z - 010745Z

   The severe weather threat for Severe Thunderstorm Watch 45, 49

   SUMMARY...A squall line will continue advancing east across the
   discussion area early this morning. An attendant threat for damaging
   winds will persist as these storms track east.

   DISCUSSION...With broader large-scale ascent (e.g., coupled upper
   jet structure) spreading across the Great Lakes region, rejuvenation
   of an ongoing squall line over southern Lower Michigan/northern
   Indiana has occurred. Despite some surface-based convective
   inhibition/weak low-level stability, the upscale organization of the
   line, combined with 1-km flow around 50 kts, will maintain a threat
   for occasional damaging wind gusts, especially in any bowing
   segments. Additionally, considering the magnitude of the low-level
   shear, a brief tornado remains possible.

The severe thunderstorm watch was issued a few hours later for ALL of northern Ohio. Remember, on FOX8News This Morning the day before, we mentioned the strong possibility of a watch being issued.

Several tornado warnings were issued for portions of CUYAHOGA, GEAUGA, SUMMIT. MEDINA AND PORTAGE counties between 6 and 6:30am Wednesday morning by the National Weather Service due to rotation being detected by Doppler Radar. By 7am, the line was east of northern Ohio. The Severe Thunderstorm watch was discontinued from west to east.


Yet even after a potentially dangerous situation like this, there continues to be individuals especially on social media who question how we covered the event. For the record, I always grade myself after events like this. Did I do everything right?  Did I convey the seriousness of the event without blowing it out of proportion?  I can honestly can that I wouldn't have done anything different.

In the weeks ahead, we'll talk about the advancements of severe weather prediction and communication.