How Often Do Conditions Develop To Produce Lake Effect Snow?

One of the many variables to produce lake effect snow is a significant enough difference between the water temperature and the temperature 5000 feet off the ground. Typically you need a difference of at least 13 degrees Celsius. So if the water temperatures is say 50 degrees F (10 Celsius) and the air temperature at 5000 feet is 27 degrees (-3 Celsius) that would be the lowest difference to allow evaporation and eventually the condensation of water vapor to occur as the colder air moves over the warmer lake.  The greater the difference, the faster the air rises and the more unstable the lake effect snow becomes.

This satellite image shows the uniform bands of lake effect cloud cover off every Great Lakes with a strong northwest wind. Notice the lack of cloud cover on the windward (western) side of each lake. The condensation of the water vapor occurs more than 20 miles offshore as the warm water vapor rises into the colder air aloft. 

How often does a difference of 13 degrees Celsius occur in northern Ohio in the prime lake effect snow time of the year?

I cross referenced the Lake Erie water temperature and the temperature at 5000 feet for five straight winters (Nov 2014 through January 2019). Each instance where the difference meets of exceeds 13 degrees Celsius I shaded that day in blue.

We average about four instances where the Lake Erie/5000 foot temperature difference exceeded 13 degrees (high enough for lake effect snow) each winter between 2014 and 2019.  How many of these produced significant snow?  More on that later.

What Happened to the "Warm" Lake Erie?

It was only a little over 3 weeks ago (November 18) when Lake Erie was the warmest ever at this point in November. Satellite water temperatures go back to the mid 1990s. This was undoubtedly in response to the very warm early November.

The warmth started in October across the central US and Great Lakes.

When you look at just the first 3 weeks of November the warmest expanded and intensified.

November 14 through the 19th warmth continued to move into the Midwest.

Once we moved past Thanksgiving, the overall pattern became dominantly colder across areas that were breaking record high temperatures. Here is the progression of the cold from central Canada starting in late November. Each image is a 10 day period. First image starts November 19th.

The first half of December has been below normal overall across much of the Great Lakes even after the core of the cold retreated back north.

The graph below illustrates the Lake Erie water temperature each year (1995 through 2024) starting on November 28 and ending December 17. Notice how this year was the warmest 3 weeks ago. Look how the Lake Erie water temperatures responded to the below normal temperatures. Compared to the last 30 years, the water temperature now is near average. A huge drop of roughly 10 degrees in almost 3 weeks!

Given the 2-3 day period of cold this weekend then the warmer pattern between Christmas and New Years, the water temperature drop will probably slow.  Look at the new Canadian long range model output for early January. Ridge development near Greenland, Gulf of Alaska/Aleutian island low shifts west. Ridge/warmth over the central US shifts west. Trough/cold settles into the Great Lakes/eastern US the first week of January. (This setup was highlighted on the the FOX 8 Morning Newscast December 9). If this verifies, Lake Erie water temperature will continue to drop. Good bet we will have some ice coverage by the second week of January.

First San Francisco Tornado Warning Ever!

Tornadoes in California are a rarity but not unprecedented. 

 Here is the short list of tornado warnings issued by the NWS office in San Francisco since 1989:

Composite map showing all 9 tornado warnings since 1986.

Each tornado warning and the radar composite for each event:

December 14, 2024

The warning went out before 6am Saturday and ended at 6:15am. Damage assessments from the NWS said the tornado had peak winds of 90 mph

A team from the National Weather Service San Francisco Bay Area conducted a storm survey in Scotts Valley. The team identified a swath of tornadic damage that began near the intersection of Mount Hermon Rd and Lockewood Ln and continued southeast along Mount Hermon Rd until just short of Kings Village Rd. A wide range of damage was observed including: downed trees, downed power poles, trees stripped of branches, numerous overturned vehicles, and damaged street signs. Based on these damage indicators the survey team assessed a maximum wind speed of 90 mph, which is a weak EF1 tornado.

March 2, 2024

March 18, 2011

January 20, 2010

January 23, 2010

September 18, 1989

FINAL snow totals from Thanksgiving Weekend Lake Effect Event

 

Ashtabula County...

  1 NNE Saybrook         63.2"

  1 NNE Geneva           50.5" 

  2 ESE Monroe Center    45.2"    

  Edgewood               42.3"    

  2 S Ashtabula          40.0"   

  3 E South Madison      37.8"  

  3 S Kingsville         34.0"   

  4 SE Harpersfield      26.3"   

  3 ENE Trumbull         25.0"   

  3 NNE Andover           9.0"   

  1 E Orwell              7.4"   

  2 NNW Cherry Valley     4.0"

Cuyahoga County...

  2 NE Euclid             9.0"   

  1 SSE Mayfield          5.0"   

  1 NNE Richmond Heigh    2.6"   

  1 ENE Lyndhurst         2.6"   

  Pepper Pike             1.1"   

  1 WSW Shaker Heights    0.7"   

  2 SW Cleveland Heigh    0.1"   

  Middleburg Heights        T   

Geauga County...

  4 S Madison            33.0"   

  2 ESE South Thompson   22.6"   

  1 S Montville          14.7"   

  Chardon                 9.5"   

  3 SW Chardon            9.4"   

  2 ENE Russell Center    3.8"   

  3 WSW Auburn Corners    2.6"   

Hancock County...

  1 SSW Findlay           0.5"   

Lake County...

  North Madison          45.0"   

  3 W South Madison      40.0"   

  2 WSW North Madison    36.1"   

  2 WNW Concord          34.1"   

  1 SSE Mentor           29.2"   

  2 ESE Perry            27.8"   

  Mentor-on-the-Lake     25.3"   

  3 N Willoughby         24.0"   

  2 SSW Mentor-On-the-Lake   24.0"   

  2 S Waite Hill         20.8"      

  1 W Eastlake           15.9"    

  Willoughby             13.0"   

Lorain County...

  3 SE Elyria               T   

Lucas County...

  3 N Holland             0.1"   

  1 ESE Neapolis            T   

Mahoning County...

  2 ESE Austintown        0.9"  

  Canfield                0.7"   

Morrow County...

  Mount Gilead              T   

Portage County...

  Hiram                   2.0"   

  2 W Ravenna             0.5"   

Richland County...

  1 W Mansfield           0.2"   

Seneca County...

  4 S Old Fort              T   

Stark County...

  2 ENE Canton            0.5"   

Summit County...

  1 W Barberton           3.0"   

  1 NW Tallmadge          0.7"   

  3 N Portage Lakes         T   

Trumbull County...

  Cortland                2.7"   

  1 WNW Newton Falls      1.2"   

Wayne County...

  2 ESE Doylestown        0.2"   

Wood County...

   2 NW Tontogany         0.6"   

Photos Courtesy NWS Cleveland:

Winter Weather Outlook 2024-25

 Full Video here.  Email with any questions:  scott.sabol@fox8.com

Rainfall Rates, Atmospheric Moisture & Humidity - Part IV

In the previous three posts, I examined WHY it was so dry and warm, the temperatures during and prior and the lack of rain mid month. This post looks at the influence the Rex Block had on the amount of moisture in the atmosphere and the rainfall rates as systems approached from the west and the two tropical system from the south as well as the overall moisture in the atmosphere.

Precipitable Water (PW) is a measurement of the amount of moisture in the atmosphere at a specific location. Roughly, anything under 1" is considered a low amount. Above 1" and especially 1.5 to 2" is considered moderate to high. We use PW to determine whether or not the precipitation event will be significant . The high the PW number, the stronger the downpours.

Here is the animation of PW from September 6 to September 21. Cool colors are very low PW values and warmer colors are high PW values. Focus on the Ohio Valley. See how the ridge (Rex Block) suppressed higher atmospheric moisture movement from the south even as the remains of Francine moved inland. 

A close up of the rainfall rates told a similar story. Warm colors indicate low rainfall rates. Cool colors indicate above normal rainfall rates. Watch the two tropical system head north and either get deflected west and/or fall apart. It was around the 21st when the ridge started to weaken allowing a front to pass from the west. (See purple colors)

Rainfall amounts were only in areas where the Rex Block did not have a pronounced effect.

Humidity levels across northern Ohio were relatively low compared to the overall temperatures especially when compared to other long stretches of 80 degree days in September.

Cloud cover across northern Ohio was well below normal during this time.

What's interesting about this is that the frequency of clear skies with temperatures 80+ is barely 20% in September?

Last year's cloud cover (September)

2022 September cloud cover

2021 September cloud cover

2020 September cloud cover

Why Was It So Dry and Warm? Part III

The answer has many elements. We'll work from the more direct and near-by causes to the antecedent ones.

The pattern across North America was dominated by a "Rex Block" named after Meteorologist Daniel Rex in 1950 who discovered it. You can read about it HERE.

The configuration resembles a backward "S" with high pressure north of low pressure.  These are more common in the western US then over the Great Lakes. The result was a dominant easterly/SE flow which kept the temperatures well above normal not only across Ohio but much of the Great Lakes and Midwest with little rainfall. READ PART I HERE and  READ PART II HERE

Why did this Rex Block form?  I believe the answer lies first in the changing Equatorial Pacific. We have been teetering with a La Nina since last winter/spring.  Most of the summer has been in neutral territory. In the last month, the upwelling of cooler water to the surface is lowing sea surface temperatures especially west.

The pressure changes between Darwin station and Tahiti have been quick.

SOI changes have gone from positive to negative in recent weeks.

Further north in the higher latitudes, the North Atlantic Oscillation also went through changes at roughly the same time. Notice how the jet stream across North America and Europe was strong. Follow the black line across the US, northern Atlantic and Europe.

HUGE low pressure north of the Arctic circle and northern Atlantic with high pressure over Canada and eastern Europe.

As the NAO went negative, the jet stream shifted into southern US and Mexico and east into northern Africa. Little jet stream influence across Canada and the northern Atlantic.

HUGE high pressure ridge developed in eastern Canada north into the Arctic. This extended into the northern Atlantic and into northern Europe.

These changes in the tropics as well as the pattern shift in the higher latitudes among others all contributed to the changes across North America in early/mid September.

What about other years that had similar long stretches of 80+ degree warmth?

Here were the patterns across the US/Canada in east instance: Notice in most instances, the configuration is very similar.