Friday, November 18, 2016

Historically Does US Warmth In Fall Connect to Higher Eurasian Snow Cover?

Eurasian Snow Cover - November 12 (2015 vs 2016)
The snow cover across northern Asia is now 3rd highest since record keeping began in the mid 1960s for early November.

The northern Pacific jet has been very strong and stable with little "waviness" until the last few days. The low over the Aleutian Islands is locked in place as the strong northern Pacific jet undercuts the low pumping up the ridge across North America locking in abnormally warm temperatures.

November temperatures vs normal
Is the high snow cover across Asia influencing the strong jet stream?  Is there a history of this in early November in very high/very low Eurasian snow cover years?

I examined the 500 mb vector wind, sea surface temperature anomaly and US surface temperature anomalies (Oct 15 through Nov 15) for the years (top 10) with greatest Eurasian snow cover in week 44 (early November): These are: 1976, 72, 2016, 1969, 2015, 2012, 1973, 2009, 2014 and 1966.

While this year's cool pool in the northern Pacific has expanded recently, three of the top four years had significantly larger and colder cool pools (reanalysis is in Kelvin). Interestingly, widespread US warmth from mid October to mid November only occurred in 2016, 2015, 2014, 2012 and 2009.










What about the years with very low Eurasian snow cover (bottom 10) since 1966? 10th lowest to all-time lowest? The 500 mB jet seems consistently stronger in years with lower Eurasian snow cover. The northern Pacific water temperatures seem cooler overall. Only 1975, 83 and 2007 has widespread above normal temperatures in late October and early November.









Comparing high and low Eurasian snow cover to the ENSO state shows a blend to either side--cool and warm. 8 of the 20 years occurred during a strong ENSO state. Overall, there doesn't seem to be an overall trend which suggests that other factors are at play aside from ENSO.



Thursday, November 10, 2016

How Do Current Lake Erie Water Temperatures Compare to Other Warm Years? More Snow?

Lake Erie ice cover from 2011

After the warmest period from June 1st to October 31st on record at the official NWS reporting station at Hopkins Airport, the Lake Erie water temperature is above any of the most recent years with the exception of 2005. 

Average Lake Erie water temperature on November 1, 2005 was 15° Celsius. 
This year: 14.8°C. As of this writing (November 10), the average water temperature is still well above normal at 14.5°C or about 58 degrees F.

This is 5 degrees warmer than the closest years--2007 and 2005!

Each year regardless of the air temperature, the water temperatures dropped significantly to between 0°C and 5°C.

How will this affect lake effect snow?  If a decent shot of arctic air slides across the lake before the water temperatures fall around the first of the year, any lake effect snowfall could be significant.

I wrote several post a FEW YEARS AGO about the subject of Lake Effect snow.

Here are the ingredients for Lake Effect:

1. Temperature difference between the lake and the air aloft (5000 feet) has to be at least 13 degrees celsius. The more, the better.

2. Abundant atmospheric moisture independent of the lake

3. Wind speed

4. Wind direction

5. Fetch Length (How far does the wind blow over the lake)

6. Instability and instability depth (Usually driven by a cold front/trough and/or the lake temperature difference) Deeper the instability, the deeper the snow growth

7. Orographic lift (elevation differences between Cleveland and the snowbelt. 1200 feet in portions of Geauga county)

Even if #1, 3, 4, 5 and 6 are present (the most common variables), subtract any one of these variables especially 2 and 5--sometimes 7 if the wind direction shifts) and snowfall forecasts can turn out much different than anticipated. 

Will we see one of these 3 "flavors" of lake effect snow dominate this winter?  More on this next month.

Tuesday, October 11, 2016

If Hurricane Matthew Rain Was Snow, How Much Snow Would You Have?

13.6 trillion gallons of water fell on the 5 state region (Florida, Georgia, North/South Carolina and Virginia) from Hurricane Matthew. This amounts to only 1% of the total rainfall across the continental United States this year. Hat tip: Ryan Maue

Rainfall through early October
It's very hard to wrap our minds around what a trillion gallons of anything looks like. But what if this water was lake effect snow?  How much would it amount to?  How much snow would cover the entire state of Ohio?

Here is how you would calculate this:

Ohio covers 44,852 square miles. This is roughly 1,250,400,000,000 square feet

Convert 14 trillion gallons of water to cubic feet gives us 1,818,055,555,556 cubic feet

Divide the two and convert to inches yields roughly 17 inches of water over the entire state of Ohio.

In order to convert the water to snowfall, we need the snow ratio.  That is the amount of snow per one inch of liquid. The problem is lake effect snow can have a ratio from 20 to 1 to almost 40 to 1 depending a variety of factors.  So let's take the lower conservative end:  20 to 1.

This gives us......drum roll please...

28 feet of lake effect snow over the the entire state of Ohio

Thursday, October 06, 2016

Hurricane Matthew: VERY Strong Statement from the NWS

I haven't seen a National Weather Service discussion with language this strong since Hurricane Katrina 11 years ago:

Statement from the National Weather Service office in New Orleans before Hurricane Katrina:

Tuesday, October 04, 2016

PART II - Northern Ohio Summer Recap

Summer Recap - PART II

Summer of 2016-17 was the warmest on record in Cleveland and at many recording stations across northern Ohio.

Graphic Courtesy NWS Cleveland

Regarding how you define summer (see Part I in previous post), it was the warmest ever!
Summer temperatures versus average over the last 10 years. 2010 and 2012 were the closest to this past summer.

The top 10 warmest summers for historical perspective show five of the top ten warmest summers have occurred since 2000.

We typically remember past weather for its extremes not averages. Although we didn't break many daily records, the warmth was steady both day and night.

 Second most number of days at or above 85 degrees ever!

Very warm overnight lows.

Humidity levels measured by dew point wasn't as high as most thought. 2010 and 2011 featured more higher humidity days.

Relative cooler days were few and far between...

Our rainfall was well below normal for the first time since 2012, driest since 2002. Four of the last six summers have had above normal rainfall.

Many use the drought year of 1988 as the standard for which we measure very dry summers. Interestingly, this summer's rainfall was nearly identically to 1988.  Yet 2016 and 1988 didn't crack the top 10 driest.

Summer rainfall varied from place to place. Only Mansfield made it into the top ten driest on record. Cleveland 26th and Akron 35th.

The storm track took the majority of the rain and storms through the heart of the corn belt.

Purple colors indicate above normal rainfall

We forget that 2002 and 1991 were consistently drier than 1988 and 2016 even into the fall. This year, the rainfall deficit has improved with recent late September rainfall.

In my next post, I'll talk about how the above average Lake Erie water temperatures this summer compare to warm summers of the recent past and how that might impact lake effect snowfall.