Bluish tinted snow

Dear Tom,
I noticed that the snow Monday and Tuesday in Arlington Heights had a distinct bluish cast. It reminded me of the color of glacial ice in Alaska. What would cause that?

Dale Hugo, Harper College, Palatine

Dear Dale,
It’s due to the physics of light reflection and absorption. Normal light (such as sunlight) consists of a blend of all colors of the spectrum, and our eyes interpret that “blended” light as white. The color of any given object is determined by the color of the light that it reflects. For example, a red sweater appears red because its cloth absorbs all colors of the spectrum except red light, which it reflects. Snow is white because it uniformly reflects the full spectrum of colors. However, most of the spectral range of colors is absorbed when light penetrates into snow or ice, but blue light is absorbed somewhat less. Any light that emerges will therefore have a slight bluish tint.

Snowy Cub fan in Texas

Brandon Kilgore from Grand Prairie Texas sent us this picture of the snow in Texas. He tells us:

“I watch you on WGN America and through you might be interested to see these snow men on a record setting day here in the Dallas Fort Worth Metroplex. There is about 6-7 inches on the ground here at my home in the Dallas suburb of Grand Prairie Texas.”

Thanks for the great shot Brandon!

Photo courtesy Brandon Kilgore, Grand Prairie, Texas

Snow records continue to fall across the U.S.

Tuesday it was Chicago.     Wednesday,  New York, Washington and Baltimore.      Now snow records are being broken in Dallas.

As of 3PM this Thursday afternoon, 6.2 inches of snow has fallen as the Dallas-Ft. Worth Airport (DFW), and it is still snowing.  

This breaks the daily snowfall record of 1.4″ for February 11th and is the heaviest snowfall at DFW since 1978.

The 2009-2010 winter season is now the sixth snowiest on record in Dallas. 

The snow may not let up until midnight, so more records may fall before the day is over. 

Final storm totals from February 8-9 Chicago snowstorm

Beach Park 14.0
Melrose Park 14.0
Northbrook 13.2
O’Hare 12.9
Park Ridge 1NNE 12.9
Gurnee 2W 12.5
La Grange 11.6
Chicago Botanic Gardens 11.0
Frankfort 11.0
Paxton 11.0
Willowbrook 11.0
Monee 10.8
Valparaiso 5NNE, IN 10.2
Oak Brook 10.1
Elk Grove Village 10.0
Midway 3SW 9.8
Mundelein 9.4
Highland, IN 9.0
Lake Zurich 9.0
Spring Grove 9.0
Wauconda 9.0
McHenry 8.3
Barrington 3SW 8.0
Naperville 8.0
Oregon 8.0
Wanatah, IN 8.0
Winfield 8.0
Streamwood 7.8
Lowell, IN 7.5
NWS Office  Romeoville 7.2
Peotone 7.2
Rockford 4NNW 7.0
RFD 6.9
St. Charles 7NW 6.8
Elgin 6.7
Paw Paw 6.5
Rensselaer, IN 6.2
Streator 6.0
Morris 5.7
Woodstock 5.5
DeKalb 5.4
Peru 5.3
Park Forest 5.2
Dwight 5.0
Joliet Lock/Dam 5.0
Marengo 5.0
Mendota 5.0
Ottawa 4SW 5.0
Plainfield 5.0
Coal City 4NNW 4.9
Marseilles 4.9
Batavia 4.8
Yorkville 2SE 4.8
Lake Village, IN 4.7
Remington, IN 4.6
Roscoe 4.5
Steward 4.5
Woodstock 5NW 4.5
Plano 4.3
Milford 5NW 4.2
Newark 2SSE 4.2
Bourbonnais 4.1
Kankakee 4.0
Rochelle 4.0
St. Anne 4.0
Herscher 3.7
Fairbury 3.6
Chatsworth 3.0
Watseka 3.0

map courtesy of the Chicago National Weather Service Office in Romeoville

Thursday's chill a long way from the area's earliest 70-degree reading 11 years ago

It seems almost unfathomable in Thursday morning’s chill that Chicago’s earliest 70-degree temperature occurred 11 years ago—on Feb. 11, 1999. That warm spell, brief as it was,couldn’t have come at a better time for winter-weary area residents. Only 5 weeks earlier, the city had been hit hard by a snowstorm which produced the 2nd heaviest snow since records began in the 1884-85 season.  (That January 1999 storm, replete with 50+ mph wind gusts, smothered the area beneath 18.6 inches of snow.) The city’s first 70-degree reading of the year has occurred on average on or about March 24.

Temperatures at that level are the last thing on the minds of many across the Chicago area Thursday morning. Clearing skies and diminishing overnight winds have allowed temperatures to dive into the single digits and teens—a temperature plunge spurred in part by the presence of the season’s deepest snow pack.

Chicago’s 2009-10 seasonal snow tally has reached 45.1 inches in the wake of Tuesday’s record snow—a total which ranks 9th snowiest of the 125 on the books to date. It’s nearly twice the 24.9 inches which has typically occurred by now.

Tuesday’s 12.6 inches of snow at O’Hare over becomes the city’s single heaviest calendar day February snow on record. The tally also qualifies as the 7th heaviest calendar day snowstorm in over 125 years of observations. 

Think snow’s bad here? Mid-Atlantic reeling in midst of snowiest season on record!
The Nation’s Capital, where schools, businesses and even a parts of the Federal government shut down in blizzard conditions Wednesday, is now home to a deeper snowpack—28 inches of it—than in either Anchorage Alaska (20 inches) or Marquette Mich. (27 inches). The latest snowstorm to hit the Mid-Atlantic generated 10.5 new inches of snow in Washington, D.C. 19.5 inches Baltimore, 14.4 Philadelphia and 12.5 in New York’s Bronx Wednesday.

Seasonal snow tallies in the region are stunning.  In Washington, where 15 inches falls on average during an entire season, 55.6 inches is now on the books—making this the snowiest season on record. The nearly 20 inches of snow which fell Wednesday on Baltimore in the midst of howling, blizzard-strength winds sent that city’s seasonal snow total soaring past 72 inches. Seasonal snow tallies have also reached new all-time highs in Philadelphia, Wilmington DE, and Atlantic City, N.J.

It’s now the third consecutive snowier than normal season
Some light snow reaches Chicago again Friday evening and night.  But, a new system Sunday night and Monday will have to be monitored for possibly more substantial snows. All of the snow of late has pushed Chicago’s seasonal snow above normal for a third consecutive winter. 

How weather visibility is determined

Dear Tom,
Can you explain how visibility is determined?

John A. Wilson, Sycamore
Dear John,
Prior to automation, visibility was determined by weather observers who noted the most distant object visible at a known distance, such as a building, water tower or geographical landmark. After dark, the observer relied on unfocused lights as darkness made most daytime objects unusable. In recent years automated weather observing systems have been implemented and complex algorithms compute the visibility using data obtained by bouncing a laser beam back and forth between a transmitter and a receiver. Observers can still augment the computer visibility value during rapidly changing conditions or when the computer measurements seem inaccurate. Ten miles is the maximum visibility reported by the automated system, a value considered ample for aviation safety.