Wednesday, September 21, 2016

What is Snowfall in Cleveland like AFTER Summers with Many 90 Degree Days?

Many ask me if there is a connection between summers with many 90 degree days and snowfall in the winter ahead.  According to this chart, maybe there is something to this.

I caution anyone who uses JUST ONE piece of data in drawing a conclusion about any upcoming season as there are MANY components in determining seasonal outlooks.

Friday, August 12, 2016

What Are Shelf Clouds?

Thursday, August 11, 2016 several strong thunderstorms passed over the Cleveland suburbs. Many viewers submitted photos of stranger cloud formations with some speculating that there tornadoes. What are these clouds?  Are they a rare phenomena?  Not really. These are called shelf clouds or Arcus Clouds. They are fairly common around thunderstorms even in northern Ohio. I blogged about shelf clouds over 10 years ago!

What are shelf clouds? The National Weather Service has a great description.
Shelf clouds are typically seen at the leading edge of a thunderstorm or squall line of thunderstorms. Remember, shelf clouds are not tornadoes or wall clouds. These are formed when rain-chilled air descends in a thunderstorm's downdraft, then spreads laterally when reaching Earth's surface. Warmer, more moist air is lifted at the leading edge, or gust front, of this rain-cooled air. When this warm, moist air condenses, you see the shelf cloud. 
Normally, you will feel a burst of cooler wind followed by rain and maybe hail. The higher gusts occur on the back edge which can cause downed trees and power outages. So when the next storm develops, look for the Arcus Cloud. Remember that tornadoes normally don't accompany these cloud formations just gusty winds, rain/hail then the highest winds toward the back end.

Monday, August 01, 2016

A Brief History of Drought in Northeastern Ohio

Since June 1st, we continue to accumulate a rainfall deficit across northern Ohio and many parts of New England. The overall pattern has featured storm clusters to travel northwest to southeast through the corn belt.  Yet much of northern Ohio, parts of Michigan and New England has missed out on frequent rainfall this summer.

As with many meteorological events, people on social media are comparing this dry period to other droughts of the past. For me, the big droughts of 1988, 1991 and 2002 come to mind. 1988 always appears on the top of my list because of the intense heat that summer. I didn't mow a lawn for 3 months!

Is there a way of comparing past periods of drought accurately? The Palmer Drought Severity Index is a great tool in comparing historical periods of above or below normal dryness or wetness of an area.

Per NOAA: "Palmer Drought Severity Index: attempts to measure the duration and intensity of the long-term drought...long-term drought is cumulative, so the intensity of drought during the current month is dependent on the current weather patterns plus the cumulative patterns of previous months".

Ohio has 10 climate divisions. I downloaded the historical PDSI monthly numbers for the northeastern Ohio climate division #3 and plotted them in roughly 30 year time periods. Green indicates wetter than normal, yellow shows drier than normal. THE SCALE ON THE LEFT CHANGES ON EACH GRAPH SO BE CAREFUL IN YOUR COMPARISONS

A few things to note based on these observations:

*  July 2016 PDSI is probably closer to -3.5. Montly numbers are not available as of this writing.

*  The 1991-92 drought was longer and more severe than any drought since the mid 1960s even beating the hot summer of 1998!

*  Frequency of wet periods were much higher than dry periods since 2000

*  The drought of 1962 to 1966 is comparable in duration to the drought of the early 1930s. These           drought events mark the only two instances where the PDSI dropped below -6

*  Many periods of drought from the 1910s to the 1930s with very little long term recovery

*  Three major droughts between 1895 and 1910

These graphs are great but they are annual monthly plots.  How about summer droughts? I singled out the summers (May through September) where PDSI levels stayed below -1. (NOTE: I CHANGED THE SIGN OF THE PDSI NUMBERS TO POSITIVE TO BETTER REFLECT THEIR SIGNIFICANCE GRAPHICALLY)

Some years to note:

* The summer droughts of 1991 and 1999 started off earlier and lasted into September. 1988 was tame in comparison.

*  During the summers between 1930 to 1934, fifteen of the twenty-five months had drought levels below -3.  During the 1960s' summer droughts, only six of those twenty months saw levels that dry.

* Yes, our soil moisture is significantly dry. But we have a long way to go before this drought becomes historic

Thursday, July 21, 2016

2016 Drought Conditions vs 2012

The dry conditions in northern Ohio are getting worse as the daytime temperatures reach the lower 90s coupled with higher humidity levels--heat index between 100 and 105--this weekend.  Many people are comparing summer to 2012 both in temperature and in degree of dryness. Is it a valid comparison? How do our dry conditions compare to other years in mid July?  When was the last time we had conditions this dry in mid July in northern Ohio?

The index that's used in determining the degree of dryness or wetness historically is the Palmer Drought Severity Index. It gives us a good barometer in comparing drought events of the past.

According to the National Drought Mitigation Center:  "The PDSI is calculated based on precipitation and temperature data, as well as the local available water content (AWC) of the soil. (Link here) From the inputs, all the basic terms of the water balance equation can be determined, including evapotranspiration, soil recharge, runoff, and moisture loss from the surface layer." 

The more negative the number, the more severe the drought.  Whereas higher numbers indicate wetter conditions. Each week the Climate Prediction Center updates the drought conditions nationwide for each climate division. I circled Ohio for reference.

Based on the PDSI, this summer shows little similarities to the summer of 2012 nationally. The PDSI is falling to 2012 levels in some spots in northern Ohio but the overall degree of dryness in 2012 was far more severe. You could argue that the summer of 2007 is a closer match to 2016. I threw in the Super El Nino summer of 1998 at the end since we are at the end of the Super El Nino of 2015-16.




Friday, July 15, 2016

Preliminary WINTER 2016-17 Outlook

My HIGHLY Preliminary WINTER 2016-17 outlook showing the average temperatures for DECEMBER THROUGH FEBRUARY.  Yes it's early and no, its not too late to gather the pieces. This is will be revised later this summer and again in the fall.

It is looking more likely that a weak La Nina (this post back in early June describes La Nina) will be the driver from the tropics this upcoming winter. Last winter, we had a very strong El Nino.

Take a close look at the snowfall numbers vs the 30 year average for these LA NINA years. I put this graphic together in early June.  HINT...HINT!

Again, all of this is HIGHLY PRELIMINARY and will need to be updated in the fall. This is why no specifics are indicated just general thoughts.

Snowfall departures below are snowfall amounts vs the 30 year average in past La Nina winters

Wednesday, June 22, 2016

Severe Event Likely Tonight. How Do I Convey The Message?

A significant severe weather event is likely across the Ohio Valley tonight. The Storm Prediction Center has western Ohio under a moderate risk, a slight risk for the center of northern Ohio overnight. We are only under a moderate risk a few times a year.  So far, no tornado warnings have been issued for any county in northern Ohio, a rarity this late into June. This is a situation that we need to take seriously.

Radar shows the first of two storm clusters passing just south of northern Ohio. Notice the movement: Northwest to Southeast on the eastern edge of the central US ridge.

At a speaking engagement recently, I surveyed the group of around a hundred people what word they think of when I say the words severe when referring to the weather. The majority of them said tornado. Yet statistically, roughly 10% of severe storms produce a tornado. This is why you will rarely hear me use the word severe unless the situation absolutely warrants it. The word severe is very powerful and conjures up powerful imagery and perceptions. Weather situations like the one tonight (June 23, 2016) reminds me of the psychology behind our weather forecasts.

I'd like to say that I make a forecast with a cold, rational eye but I don't. I take into account how people with react to EACH WORD knowing that most people will react with their preconceived weather notions they've developed over time. Viewers hear the word severe and they think tornado. They panic and fear the worse even if the cold hard facts say otherwise. Its hard to reverse that mindset. I learned that real quick after my first major lake effect event twenty years ago.

If I could make a poster with bullet points for meteorologists, it would list these five at the top

*  Public perception is very powerful

*  We need to be better communicators of information. Quality of the information is better than clicks or social media engagement

*  Choice of words is of the utmost importance in conveying severity of any weather situation

*  For the public, risk is personal and evokes powerful imagery.  Mass media is for the masses.  Yet the masses in this era of smartphone weather apps want personal forecasts. Huge conundrum.

*  Too much emphasis on uncertainty breeds confusion and inaction. (I am hugely guilty of this as a technical weather geek) We need to find a delicate balance between voicing uncertainty and sticking to a forecast without blowing the event out of proportion.

Friday, June 10, 2016

Developing La Nina Is Old News!

Many meteorologists including myself have written about the state of the winter El Nino and the strong probability that ENSO would transition to an infant La Nina in spring/summer of 2017 for a while now.  Main news sources give the impression at this transition out of El Nino as something new.  I tweeted a preliminary La Nina outlook based on CPC analogs BACK IN NOVEMBER!

Recently, NOAA stated in their newest bulletin, very accurately, that El Nino was finished as of June 9th. These transitions don't occur instantly. The transition away from El Nino toward La Nina has been ongoing for months.

The region used in determining the state of the equatorial Pacific is the ENSO 3.4 region.

All Nino regions (especially the key Nino 3.4 region) temperatures have been falling since the start of the year.

This animation showing the ocean temperatures vs normal values show this perfectly. See the cooler water on the right side (east).

A larger spherical look at the ocean temperatures show the transition even better starting in January. The last image is what the mature La Nina looked like in January of 1999.

According Bob Hensen at Weather Underground, a recent study found that about a 1/3 of first year La Nina events returned of persisted for a second year. This behavior seems to be more frequent over the last 150 years.  It is possible that La Nina could linger into 2018.

It takes months for the effects of any ENSO state (El Nino, neutral or La Nina) to be reflected in the atmosphere. So its very difficult to predict at this time what the winter will be like for specific locations. But we can perform some basic albeit general statistical comparisons between snowfall and La Nina.

Using the ERSSTv4 ocean temperature dataset, a list of La Nina strengths can be determined. Hat tip to Eric Webb.

Based on these years and rankings, I matched up our Cleveland snowfall for these La Nina years. Here is what I found.  The majority of these years had ABOVE NORMAL SNOWFALL in Cleveland!

This is no guarantee of above normal snowfall during the winter of 2016-17 as there are other factors yet to be determined. 

Last year, I posted my thoughts on the upcoming winter (2015-16) around Labor Day. Expect some more detailed thoughts on the effects of La Nina on the upcoming winter of 2016-17 around the same time this year.  Until then, let's enjoy summer!

Thursday, June 02, 2016

Is It Accurate to Say "It's Cleveland" When Talking About Our Weather?

Good morning everyone. This is a pet peeve of mine so bare with me:  

It's highly inaccurate to say "It's Cleveland" when making a GENERIC reference to our overall NE Ohio weather. I know I've upset many by saying this. We've been indoctrinated with this for decades and generations myself included. This phrase really only applies to winter conditions such as lake effect snow events or a strong lake breeze (especially in spring) which don't happen often. Most times (see image below showing the 6 week changes since early May) the changes are felt over a multi-state area! These regional changes don't originate here in northern Ohio nor are they religated to just northern Ohio. Again, the only exceptions that are strictly local in nature are Lake Effect snow events and lake breezes.

Tuesday, May 24, 2016

Memorial Day Temperatures Doing A Complete 180!

Back on May 10th, I posted this long range outlook showing that our confidence of warm finish to the month of May was very high. This was my thinking at the time.

The first 23 days of May were cool not only in Cleveland and northern Ohio but across 85% of the US.

The final 8 days will feel summer like across a 15 to 20 state area.

Who says realistic long range outlooks aren't possible?

Friday, May 20, 2016

The Weather Cast

Some days weather casts flow with metronomic ease. Each segment evolves with seemless precision incorporating sprinkles of down-to-earth science, flawless grammar resulting into an easy to understand message. It permeates the air with the richness of a chocolate cake. Other days it's like driving a dump truck through a nitroglycerin factory with no chance of rescue.  I've blown up a bunch of factories.