Wednesday, November 30, 2011

Were the last 3 Decembers All that Similar?

Since early November when our winter weather outlook came out, we emphasized how variable this winter would be. We really didn't see this winter having long stretches of arctic cold like the last 2 or 3 winters.  The variables for this winter just didn't match up like the winter of 2010-11 or 2009-10 or even 2008-09.  Similarities do exist for sure but the differences can't be ignored which I believe will be significant players.

What are those differences?  The three that top our list are the PNA INDEX (Pacific-North American Index), the AO (Arctic Oscillation), the NAO (North Atlantic Oscillation) and La Nina or El Nino.  Don't fret over the technical specifics of each index.  Just realize that each one originating from different locations (Arctic, North Atlantic and the Pacific) has the capability of influencing storm tracks and intensity over northern Ohio.  Long term trends are great but can we see day-to-day details within these indices?

Look at the daily plots for the AO, NAO and PNA for each of the last 3 Decembers: First 2008, 2009 then finally 2010. Notice the fluidity of each of the last December's daily index levels.

What about the ever-popular El Nino/La Nina which gets all of the publicity?  The daily changes are significant when you look at the changes in the pressure patterns over the tropical Pacific (the SOI Index). Never mind the geeky "SOI", just know that it changed a great deal from December to December. Each pressure variation alters the jet stream over North America and the Great Lakes. Even the La Nina of 2008 and 2010 were very different.  This year's La Nina is also very different.

How did this relate to high temperatures? Below is the daily high temperature graph for December 2008, 09 and 10. Last year was consistently cold yet 2009 and 2008 had a lot of ups and downs with only limited cold shots.

What about December snows?  Not much in the last 3 winters.

So the variability of the Arctic, North Atlantic and Pacific/La Nina/El Nino can have effects on our Cleveland weather day to day. Comparing last December to this December or 2009 to 2011 isn't as easy as it seems when you look at the how these elements change on a daily basis. Some of these elements one year can produce more snow and cold in Cuyahoga county and in other years, the frequency of cold is far less in Akron and Mansfield. A look back to the previous year doesn't always work in giving us insight on the current forecast.

Will this December be as changeable as year's past.  Will we have a December like 2010 with continuous cold?  Will this December feature cold shots with some milder breaks?  I will address that in the next post.

Meanwhile, I'll be cutting down my Christmas tree in the mud followed by stringing lights on my house in shorts!

Wednesday, November 23, 2011

Comparing NOV/EARLY DEC 2009 vs 2010 vs 2011

Comparisons are always tricky. Go ahead and pick the data and sure enough, you can find some correlation or causal relationship to the current weather situation.  The operative word here is "CAUSAL". Is the information or data giving you an accurate snapshot of what is driving the current weather? In other words, is there a direct cause and effect relationship?

The index we look at as a direct measure of the strength of the arctic air to the north is the ARCTIC OSCILLATION.  Pressure differences over the arctic and temperatures high in the atmosphere can make the arctic air more or less changeable for us living around the Great Lakes. If the AO index is negative, the arctic air becomes unstable and has a tendency to drive southward. If its positive, its stays locked up in the higher latitudes of the arctic.

Look at 2009 from the fall into early December.  Notice how the AO was strongly negative into late November and early December.  We had 20 of the 31 days in December with highs in the 20s and 30s!!!
Now look at 2010, same ultra-low negative AO index reading. We had 28 of 31 days in December with highs in the 20s and 30s!!!

Look at the early December snow from last year:

Why is this year so different? Check out the AO index recently.  Its been strongly POSITIVE with no big signals that it will drop sharply negative. While this isn't the ONLY measure of a potential cold air shifts into Northern Ohio, it is a strong one.  So if you are going out to any one of the many Christmas farms in Medina County to cut down your tree, the chances of their being a prolonged snowfall are much less than in the last 2 winters. 

Monday, November 21, 2011

Colder Air Still Coming after Thanksgiving? You Bet!

I love the science of weather and the patterns that govern it. While some of my posts can get a bit scientifically technical, my aim is to describe in the most simplistic terms what we look at in formulating our forecasts both in the short and long term. Knowing the forecast is one thing.  Yet developing a basic understanding in how and why we come up with our forecasts is quite another beast. That's why I like to describe elements of the weather on the air. Its fun for me and hopefully informative for you. I liken it to a great meal: Eating the savory food is great. Being able to understand the recipe and recreate it later is even better!  Remember that I not only give you the meat and potatoes, I give you the recipe too!

Which brings me to the pattern changes in the upcoming week. Last Wednesday, I hinted at some colder air and snow for the Sunday after Thanksgiving. Here's what I said.

It still seems like that is a good possibility. But the colder pattern is slowing in its evolution. In other words, the low doesn't seem to want to establish itself over the Great Lakes as fast as it did last week. Here is Sunday evening...the following map is Monday

The squeezing of the LOW from the west and the east has me concerned that it might either, weaken or hold off longer until Tuesday. Either way, this is the ingredient for cold air and waves of either rain and/or snow!!!

That was the "meat and potatoes". Now the recipe:  Why the change in the overall pattern?

Normally we would look to the Arctic's behavior to see potential cold air outbreaks. In this early winter season (2011-12), the arctic shows no signs of heading into what we call "negative territory".  So we have to find another driver of this pattern shift.  That driver might be the highly variable Pacific Ocean/Northern Hemisphere pressure patterns. The area we look at is here:
 When this area is "negative", the snow and cold stay out west and the eastern US stays milder and snow free. When it turns "positive", the cold and snow shift east and the milder air shifts west as seen below.
The pattern has been strongly "negative" which has driven the milder air northward into northern Ohio. Temps in Westlake made it close to 70 a week ago. Norwalk hit a high of 65. Even in Akron, temps were well into the upper 60s. My kids were outside in t-shirts!  It happens in November.

It look like this pattern might shift "positive" in early December. Does this mean lots of cold air? Does this mean more snow? I think a little of both. IF this pattern gets "locked in" for a week or two, we can surely expect a handful of lake effect snow events and perhaps a general snow with temps below normal.

We are still holding on to the notion that this winter will have breaks in any cold period perhaps more than in the last several years. So when it gets cold, we don't anticipate it lasting weeks on end!

Hopefully for skiers, Brandywine will open before Christmas and the hills at Virginia Kendall Park in the Cuyahoga Valley will be primed for sledding.

Wednesday, November 16, 2011

2011 Thanksgiving Weekend Snowstorm?

We have often compared this upcoming winter to the winters of the early 1950s.  Those were La Nina winters. See my post from a few weeks ago. That this, the factors (Atlantic & Pacific Ocean temperature trends/temperatures) that were present then are somewhat present today among other factors too technical to mention.

The years that we found to match up well are 1950, 1954, 1955, 2008, 2010.  Aside from some differences in the Atlantic Ocean temps in the 60s and 70s, you can throw 1964 and 1976 in there too mainly due to the strong influences of the arctic in those years especially in the mid 1970s. If you recall the Blizzard of 1978, BOTH OF THEM, you know what I mean!

Heading into Thanksgiving week, my dad reminds me of the Great Snowstorm of 1950.  One of the most memorable snowstorms in Northeastern Ohio history. He was 5 years old at the time but he remembers it like it was yesterday growing up near St. Stevens Church in Cleveland's west side. Downtown Cleveland and Akron got hit with 25 inches of snow. Geneva 33 inches! Temps dropped from 38 at midnight to 14 in less than 12hours on Friday the 24th.

The classic Ohio State-Michigan football game was scheduled for that Saturday afternoon in Columbus, Temps that morning were in the single digits; winds were 40 mph.  The final score: 9 to 3.  Only 27 total yards!

I bring all of this up now because I noticed something "scary" on the maps for Thanksgiving weekend.  Here is the map for Friday the 25th. Not much to show.  Fairly quiet pattern.

Now look at Saturday the 26th. Notice the low developing just to the west.

Now look at Sunday the 27th.  WOW!  A monster storm over the Great Lakes and Cleveland!  Again, its more than a week away but scary nonetheless. What is even scarier is when we compare the 1950 snowstorm to next week's map:

Look at 2 days before the storm in 1950. Very quiet...

Now look at the day before the storm developed over the Great Lakes. Looks eerily like the map for next Saturday.

Now for the main storm day in 1950, Saturday during the Ohio State Michigan game in Columbus.

Looks almost exactly like the map for Thanksgiving weekend of this year!

Yeah, yeah, I know its more than week out and alot can change. But given the years (1950, 54, 55, etc) which we used in our comparison for this year's winter outlook, it bares watching. So if you are flying out Sunday the 27th, keep an eye on the 8day forecast. If this maps continue to show this storm early next week, it could paralyze air traffic from Cincinnati to New York!

Tuesday, November 15, 2011

Are November High Temperature Swings More Sharp Recently?

After a severe weather event like last night, the images and sounds become embedded in every one's mind much faster. The inevitable conclusion is that severe weather and wild temperature swings in November are unusual. After all, we associated colder temperatures with November not tornado watches and temperatures near 70!

While the disconnect between huge changes in temperature and tornadoes seem to be vast at first glance, the first often plays a big role in the latter. 

The first question: Have high temperature swings become more drastic in recent years in November?

Look at the last 20 Novembers (Since 1991). The first number is the # of times where daytime highs
varied more than 20 degrees over 24 hours. Specific instances are in parentheses. The second set are the highest high and lowest high for each November.

The 2000s certainly had more days with high temps changing more than 20 degrees! One so far this month.

2011     1 (43 to 61)
2010     0                                     69  34
2009     0                                     71  40
2008     0                                     72  28
2007     0                                     66  33
2006     1  (62 to 42)                    66  37
2005     4  (57 TO 70 TO 48)      70  29

                 67 TO 29; 58 TO 35)
2004     0                                     64  40
2003     2  (69 to 39; 71 TO 51)  79  45   TORNADOES
2002     1  (45 TO 65)                 67  30    TORNADOES
2001     1  (69 TO 48)                 69  42

2000     0                                     66  28
1999     1  (64 to 37)                    73  35
1998     1  (49 to 70)                    71  40
1997     0                                     60  31
1996     1  (70 to 45)                    70  30
1995     0                                      71  33
1994     0                                      72  39
1993     0                                      63  33
1992     3 (56 TO 36; 61 TO 39   65  33   TORNADOES
                63 TO 41)
1991     0                                      69  29

Normally with huge swings in high temperatures, a cold front lies in the middle which is often the firing line for severe storms and sometimes tornadoes. The maps of November tornadoes in Ohio is below. Notices the cluster of tornadoes in northeastern Ohio in 2002 and 2003. Then check above at the list of huge high temp swings. 2003 has 2 instances of  high temps changing more than 20 degrees. One was 30 degrees in 24 hours!

November is a month of wild weather for sure. This decade seems to have had more instances than in the 1990s.  

We are still waiting for the pattern to switch. The snow is falling out west. Denver was hit hard earlier this week. Its just a matter of time. Once it does, lake effect snow will begin and the mild stretches for us hiking in the Metroparks will be over!

In case you were wondering, here are the overall temperature averages through November over the last 5 years:

2011  +3.4         1 time below 32
2010  +1.4       16 times below 32
2009  +5.9         6 times below 32
2008   -1.6       15 times below 32
2007   -0.5       14 times below 32
2006   +3.1        7 times below 32

Will we make up for it in December? More on this coming up in my next post!!!

Thursday, November 10, 2011

The Many Faces of Lake Effect Snow

Cleveland weather is very unique due to its proximity to Lake Erie.  Weather patterns in Northeastern Ohio from November to March can vary greatly from location to location. Chardon could be receiving 3 inches of snow per hour with 15 inches on the ground while Westlake is snow free with mostly sunny skies!  This is exactly what happened from November 9th through the 15th in 1996 when Chardon received 69", Mayfield Heights had 37" yet Medina only had 3"! Watch the video taken in Mentor back in 1996.

It might seem that with all of our lake effect history and hundreds of lake effect events, predicting lake effect snow amounts should be easier.  Yet the lake continues to fool us just when we think we have the whole lake effect snow machine figured out. Why can one lake effect snow event produce tons more snow even if they have very similar conditions? 

First, all of these ingredients must be present for lake effect to occur:

1. Wind off of the lake - (over at least 60 miles of water)
2. Wind direction - North or Northwest preferably here in Cleveland
3. Wind speed - Between 10 and 40 mph
4. The wind direction from the ground up into the atmosphere has to be the same (less than 30 degree direction difference from the ground to roughly 10,000 feet.  If not, the changing winds sheer apart the lake effect snow bands which might spread the snow over a larger area.

5. Temperature difference between lake and cold air aloft (5000 feet) has to be at least 13 degrees C.  For example, If the lake is 52 degrees, the air aloft (around 5000 feet) has to be at least colder than 26 degrees.  The greater the temperature difference, the better.

6.    Abundant moisture at the surface.

7.  The cold air at the surface should be deep.  The deeper the cold air right above the lake, the more room for clouds to develop to trigger snow growth and the greater the chance for more significant snow amounts

8.  Higher terrain inland (Geauga, Lake and Ashtabula County at elevations of more than 1200 feet compared to 700 feet along the shorline) also helps in enhancing lake effect snow. The greater the elevation difference from the lake to the "hilltop" the greater the elevation effect. If any one of the ingredients changes even slightly, the snow amounts can change greatly! 

Today, we'll concentrate on one of the bigger component: COLD AIR OVER THE LAKE

For comparison sake, let's keep the lake water temperature consistent (52-54 degrees as it is now 11/10) and examine similar lake effect events in the past keeping all other variables as equal as possible given the lack of data from the 1960s and 1970s.  Look at how these four separate lake effect events change as we change the temperature of the cold air moving over the lake. 

November 12-13, 1968: 

Air temp aloft (5000 feet) in Celsius:  -7

Wind Direction: NW, gusts to 40
18,000 feet temp (indicator of thunder snow):  -28
Surface Temp:  low of 27, high of 40

Snow Amounts: Chardon: 1/2", Clear skies in Lake County

November 11, 1977: 

Air temp aloft (5000 feet) :  -8 to -9 degrees early then down to -10 to -12

Wind Direction: NW, gusty
18,000 feet temp (indicator of thunder snow):  -28
Surface Temp: low of 34, high of 43

Snow amounts: Painesville: 12", Chardon: 10", Southern Cuyahoga Co & Akron 3-6"

November 9-16, 1996:

Air temp aloft (5000 feet): -8, drop to -14

Wind Direction: W to WNW , gusts to 25 mph
18,000 feet temp (indicator of thunder snow):  -38
Surface Temp: 25-30

Snow amounts: Chardon 69", Geneva 38" , Hopkins 19", Hudson 15", Akron 2"

November 2-3, 2006:

Air temp aloft (5000 feet): -9 to -12

Wind Direction: NW 15-25 mph
18,000 feet temp (indicator of thunder snow):  -38
Surface temp:  38,  Dew Points: 19-23 (very dry)

Snow Amounts: Ashtabula 6", Cleveland 1/2", Eastside: 4"+

All other factors being close to equal, the difference between air over the lake at 19 degrees and 9 degrees can make the difference between 3" and 15 to 20" of snow!

Be sure to watch how cold the air gets later this month and into December.  The incoming cold air over the lake will no doubt be the main factor as to how much and how quickly we get our first BIG SNOW in Cleveland, Pepper Pike, Solon, Chardon, Painesville, Thompson and Ravenna.

Tuesday, November 08, 2011

Are 60 and 70 Degree Days in November Increasing?

November stands out in my experience as one of the most changeable weather months. The Polar Jet Stream is getting stronger and pushing south while the leftover pockets of summer warmth still remain across the country.  Cold fronts become more defined due to the sharp temperature differences along them. Wild swings of nearly 40 degrees in the span of 24 hours in not unheard of.  For example, back in 2005, the high on November 16th was 67 degrees. The high the following day was.....29!

All of that said, are these 60+ degree days in November become more common?

Let's split up the month into two halves. The chart below shows the 60+ degree days from November 1st to the 15th since 1980. The average per year is 4.4 days.

The 60+ degree days for the last half of November is obviously much lower. A third of the time we don't even have temps above 60!

If we split up the time showing the average since 1995 vs 1995 back to 1980 from November 1st thru the 15th, we show a decrease...

If we split up the time showing the average since 1995 vs 1995 back to 1980 from November 15th thru the 30th, we show the average remains fairly steady...

So are 60+ degree days in November increasing? Based on these numbers, no discernible trend upward over the last 30+ years is noticeable.  So goes our up and down November weather patterns in Cleveland!

Friday, November 04, 2011

Could We Receive 15" of Snow By Christmas?

"Another La Nina Winter" has been the catch-phrase among meteorologists as they unveil their Winter Weather Outlooks. Scour the internet and you'll find La Nina as the focal point of every outlook from California to the Carolinas.  La Nina--and to the other extreme--El Nino are terms that describe the changing ocean temperatures in the Pacific.  El Nino is warmer ocean temps and La Nina is colder.

While La Nina/El Nino describes the ocean temps, it doesn't paint a good picture of how the colder or warmer ocean temps are affecting the atmosphere ABOVE the ocean. Luckily, there is one index or number that describes the many elements of the La Ninas and El Ninos that ultimately effect our weather in the US and here in Ohio. This index is called the MULTIVARIATE INDEX or MEI.

The variables are combined to form the MEI:  Sea-level pressure, all directional components of the surface wind, sea surface temperature, surface air temperature and total cloudiness fraction of the sky.

Basically, its a great tool to describe the "NINAS" of all shapes and sizes. Below is the plot of the MEI numbers since 1950. La Nina years--like the one we are entering--are below zero while El Nino years are above zero.  Notice last year's La Nina in the lower right.

What does this have to do with whether or not we see snow in Cleveland before Christmas? Take a look at the list of strongest La Nina Novembers and Decembers since 1950 according to the MEI and the snow totals for each and the average over those years by the end of December.  (The blue years are closer matches to this year than the others)

        NOV/DEC  SEASON TOTALS                                
1955     18.5"            54.2"         
1973     17.1"            58.5"             
1975     18.7"            54.4"            
2010     12.7"            59.8"          
1988     19.6"            54.8"           
1950     34.0"            77.2"   (Thanksgiving Storm) 
1970     11.2"            51.4"             
1999     11.9"            60.1"          
2007     10.7"            77.2"   (March 8th Blizzard: 15-20"+) 
1954     11.8"            49.3"    

 AVG:    16.6"

The November and December snow totals since 1950 in years like this year are fairly consistent. Here are the totals plotted on the MEI graph. The numbers below the zero line are La Nina years.

For comparison, below is the strongest El Nino Novembers and Decembers per the MEI with snow totals. Notice the relatively weak snow years (the one outlier is 2002)


1982      8.5"             38.0"
1997    19.3"             34.0"
1972    13.3"             68.5"
1991    12.9"             65.7"
1987    17.4"             71.3"
1965      4.4"             37.3"
1957    10.0"             31.1"
1994      1.0"             43.6"
1986      4.2"             55.8"
2002    28.5"             95.7" (Christmas Day Snow)

AVG    11.9"
What does this tell about this year's early winter from now until after Christmas?

1.  We typically get more November/December snows during strong La Ninas than during strong El Ninos. 
 The difference is noticeable. Look at 1994!

2.  If the LA NINA factor stays prominent, expect around
16 inches of snow by New Years Eve!!!

Tuesday, November 01, 2011

Why this QUIET early November pattern scares me

Early November "milder" periods like the one we are entering in today are not that unusual. Over the last 5 Novembers, only in 2008 have we received more than 2 inches of snow during the month so "milder" or "not so cold" November periods happen and happen quite frequently.

That said, it is these stretches of 50 and 60 degree days with the lack of strong storms across Ohio that have me on guard for what is to come. Let me illustrate why by looking at the long range computer projections for next week.

 This first map is for this upcoming Saturday.  Notice the "L" or LOW out west and the "bubble" or ridge over Ohio. For us, this means temps above normal with little rain or snow. This also signifies a deepening "trough" out west which allows these "LOWS" to grow and strengthen. All signs of the changing season from late fall to early winter. The trough out west are much DEEPER and STRONGER than what they were in September.

By Tuesday of next week, watch that "L" out west.Its gets "gobbled up" as it hits the Great Lakes only to be replaced by the next one which slides into Arizona. Yet here in Ohio, we stay somewhat dry with above normal temps. More importantly, notice that none of these "Ls" are close to Ohio. The eastern "ridge" of dry air stays strong.

By next week the 10th, the eastern ridge stays mostly intact while the lows out west spin themselves out before reaching Ohio. If this projection verifies, the chances of seeing any lake effect snow will be very slim.

By the the 13th through the 15th, the ridge breaks down, the "LOWS" track across the Great Lakes and Ohio which should allow our first lake effect snow event.  This is the Sunday (Nov 13th) projection...
...Now the 15th of November. 

Now look at last year at this time. The "L" was right over Ohio producing our first round of early November snow.

The bottom line is that this "dry and somewhat milder" pattern scares me because the stronger the troughs out west, the stronger the colder air behind them.  The trough will eventually drift east being our first lake effect snow of the season by Thanksgiving!