WGN Weather Center Blog

Snow to follow 60s, hardly the weather most favored for spring's Saturday open

2010-03-19T04:33:11Z

When most Chicagoans think of the start of spring, warm temperatures, flowers in bloom and the chance to shed winter coats come to mind. But the reality of March's often quirky weather is that these idealized images occur far less often than most here care to think. Instead, in their place Saturday will be substantially lower temperatures, blustery northeast winds and precipitation which has transitioned from liquid to crystaline form. Snow is likely to have been falling a number of hours by the time spring 2010 gets underway as the sun's most direct rays cross the equator far to Chicago's south at 12:32 p.m. Saturday. That's the moment astronomers refer to as the "vernal equinox"---or astronomical start of spring.

A storm system of Saturday's predicted intensity would have been expected to produce 5 to 10-inch accumulations only a few months back. But, the abnormally mild temperatures of recent weeks---March is running more than 5-degrees above normal and 2010 is 2-degrees ahead of the same period a year ago---have helped warmed the ground while, at the same time, boosting Lake Michigan water temperatures off of which Saturday's gusty north to northeast winds are to blow. Shoreline water temperatures are running 3-degrees higher than this time last year---42-degrees versus 39 degrees. Factors such as these play a decisive role in determining how much of any late-season snow which falls is able to stick.

An average of the 43 most recent computer snowfall projections for the upcoming weekend works out to about 5 inches---though individual predictions range all the way from 0 to 9.3-inches. It's not wise to read too much into these stats just yet. It's likely far less than these amounts will actually end up sticking---but, if snow were to fall heavily amounts in the upper end of such a range couldn't be ruled out. It appears at this distance that the potential for some slushy accumulations on colder outdoor surfaces is possible in this system especially inland---away from the warmth of Lake Michigan Saturday and Saturday night.

Winter storm prompts warnings across 10 states; could send some Oklahoma seasonal snow tallies to all-time records

Concerns over the developing storm system prompted the issuance of winter storm watches and warnings across sections of 10 states to Chicago's west and southwest late Thursday. Early indications suggest sections of Oklahoma, Kansas and western Missouri may bear the brunt of the storm's snowfall with accumulations possibly totaling 6 to 10 inches. Were such an accumulation occur in Oklahoma City, it would push the current season tally of 20.7 inches to a new high---possibly breaking its all-time seasonal snow record of 25.2 inches set in 1947-48.

Sections of Florida shiver shiver through chilliest winter on the books

New all time records for the chilliest winter temperatures are about to be set across sections of Florida. Readings since Dec. 21---spanning the so-called "astronomical winter" period--- have averaged 55.8-degrees at Orlando, falling below the previous all-time low of 56.9-degrees. Orlando weather records span 65 years. Other Florida all-time low winter temperature averages include 56.6-degrees at Melborne and 57.6-degrees in Vero Beach.

Predicting snow tallies on warm ground dicey; more snow for Oklahoma

2010-03-19T03:53:09Z

How does the lack of subzero weather this season in Chicago compare with past years?

2010-03-19T02:59:15Z

Dear Tom,
How does the lack of subzero weather this season compare with past years?
--Greg Pracz, Westchester
Dear Greg,
So far this season, Chicago has recorded one subzero day, a low temperature of 1 degree below zero on Jan. 3, and with March 22 as the date of the city's latest ever subzero reading on the horizon, it appears that lone day will represent the season's final count. Since late 1870, the city's long-term average for subzero days is around eight, so this winter is definitely on the low-end of the spectrum. There have been only 12 cold seasons that failed to produce a single subzero day, the last one being the winter of 1982-83.
The opening decade of the 21st century has produced only 49 subzero days in Chicago, the lowest decadal total since the 1930s, which produced only 46. The 1980s take the honors for the most subzero days with 119.

Weather word: Inversion

2010-03-19T02:35:12Z

A beautiful Thursday evening in Chicago

2010-03-19T02:30:20Z

Former WGN Wether Center intern Monika Thorpe sent us this great shot of Chicago's skyline Thursday evening. Thanks Monika!

Photo courtesy of Monika Thorpe

Tim's Weather World: Quiet Start To Severe Season So Far...

2010-03-18T13:56:10Z

We made it through the first couple of weeks of March without one single report of severe weather in Illinois. There are signs our weather pattern is becoming a bit more "progressive" or volatile in the coming weeks and that will increase the chances for severe weather.

In the meantime, while we wait for more active weather, we can prepare. Chicago's National Weather Service office is offering severe weather spotter training over the coming weeks. Check out their schedule to find training near you.

If you can't make it out to the training, you can train online. Skywarn has provided some online severe weather training guides.

You can also print out a preparedness guide offered by NOAA and the Red Cross.

Last but not least, the Storm Prediction Center is on the front lines when it comes to preparing for severe weather. They issue "convective outlooks" every day that outlines areas with potential risk for severe weather.

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Jarring shift from 70-degrees to possible wet snow ahead

2010-03-18T03:23:27Z

March is to put on quite a meteorological show in coming days, strutting the weather of two distinctly different seasons before Chicagoans over a span of just days. Unseasonable warmth Thursday and Friday---including the year's highest daytime readings to date---is to yield to a wintry temperature downturn this weekend which may well set the area up for wet snow. It's sure to be a jarring change for many in the Chicago area with the wintry tone of the weather shift in conflict---at least in spirit---with spring's 12:32 p.m. Saturday arrival.

The year's mildest temperatures are due first---including a possible 70 degree high Thursday. It's a development which would propel this month into the ranks of the 70 percent of Marches over the past 140 years which have produced a 70-degree temperature. Not since a 73-degree high on Nov. 8 has the mercury warmed to that level here. The production of such warmth this early in the season always depends on the perfect alignment of a host of factors. West winds must overcome the tendency for the 2,000 ft. deep dome of cold, dense air, which hugs the chilly lake surface this time of year, to surge inland. And clouds must not seriously screen out sunlight which is especially critical in producing early season warmth.

It appears both conditions will be met Thursday---though the wild card will be high clouds expected to move across area skies as the day proceeds. Air sinking on a broad scale beneath a band of powerful jet stream winds is expected to produce enough warming to offset at least some of the impact of these clouds.

A 70-degree temperature would come one week earlier than the most recent 50 year average date of March 24 and nearly a year to the day of last year's first 70, which occurred last St. Patrick's Day.

Set-up behind Chicago's Thursday warm-up produced high winds, record-breaking temps in Montana

Sinking air beneath the same pocket of powerhouse jet stream winds expected to traverse Chicago airspace Thursday and Thursday night, helped produce record highs and powerful downsloping winds in Montana Wednesday. Record highs resulted at Billings (73-degrees) and Miles City (71).

March 2010 more the 5-degrees above normal

Chicago's March temperatures are running more than 5-degrees above normal to date and more than 3-degrees ahead of the same period a year ago. That's warm enough to place its opening 17 days among the warmest 13 percent of comparable periods since 1871.

Models hint at sticking weekend snow here or nearby---but stay tuned

Computer models suggest sticking snow may accompany this weekend's temperature crash over at least portions of the Chicago area. A suite of 29 different model forecasts put average snowfall Saturday afternoon and night around 4 inches. But it's a forecast which is hardly carved in stone. Predicting accumulations in late season snow systems, particularly when they follow air masses as mild as the one in place Thursday and Friday, is extremely challenging.

109 of the past 125 years---that's 87 percent of them---have hosted accumulating snow beyond March 18. It's a sign winter isn't over yet.

Weekend snow could stick; most years have snow beyond March 18

2010-03-18T03:10:37Z

What is the earliest date for the last measurable snowfall of a season in Chicago?

2010-03-18T03:00:35Z

Dear Tom,
What is the earliest date for the last measurable snowfall of a season in Chicago?
--Arleen Hambach

Dear Arleen,
It seems hard to believe, but Chicago's earliest last measurable snow has twice occurred in February. The earliest finish to a snow season was Feb. 27, 1997, when 0.5 inches of snow was measured. Beyond that only traces were recorded in March and April with the season's last flakes on April 13. Close behind was the winter of 1993-94 when the 0.8 inches that fell Feb. 28 was the season's last measurable snow. That year the final flurries were observed April 30. Despite the early end to those snow seasons, the seasonal totals were close to the city's average of about 40 inches. The winter of 1996-97 produced 40.6 inches while the winter of 1993-94 racked up 41.8 inches.

Area headed for 2010's warmest temps yet; first 70 in 4 months possible

2010-03-17T05:30:25Z

Bountiful St. Patrick's Day sunshine isn't to be the last in coming days. There's more great weather on deck---though there are also signs Chicago's weekend weather could become dicey with rain and even the threat of wet snow. Storms must be monitored closely this time of year. Their varied temperatures can take rain to snow despite a period of warmth. This storm's impact on the Chicago area is still days away and will depend on a variety of factors including its future track.

Snow is to be the last thing on people's minds Wednesday. Temperatures surged past 60-degrees Tuesday-- topping out at 61 at O'Hare and as warm as 69 at Elgin, 68 Itasca and 67 in Oswego and 66 at Blue Island. These readings are 18 or more degrees above normal---and Wednesday looks even warmer. The 65 predicted at O'Hare Wednesday afternoon would immediately become 2010's warmest to date and would arrive nearly a year to the day of last year's first 70-degree reading---a 74-degree high which occurred on today's date in 2009.

But it's Thursday which stands a good chance of becoming the warmest of the current mild spell. That's when the city's official high is predicted to move to within striking distance of 70-degrees. Large scale subsidence of air beneath the incoming nose of a powerful jet stream is to combine forces with Thursday's generous sunshine and strong west winds capable of overcome lake cooling to produce the first 70-degree reading of 2010 nearly 4 months after the Chicago area's last 70 on Nov. 8.

Warm weather isn't surprising this time of year nor is it mis-timed. In the past decade, March 22 has been the average first date for a 70 here---and March 24 has been the average over the past half century of readings at O'Hare.

Tuesday becomes one of only 10 days in the past 140 years with relative humidities in the teens

Remarkably low relative humidities (RH) across the metro area played a role in producing Tuesday's warm highs. Dry air heats expeditiously. A plunge in RH readings observed just after noon Tuesday coincided with rapid warming. The appearance of low humidities occurred as winds helped mix exceptionally dry air, which had hovered just above the surface since Monday, down to ground-level.

Chicago recorded 90 percent of its possible sunshine Tuesday bringing the March average to 43 percent---52 is considered "normal" here in March.

Windy Seattle storm could head toward the Midwest

The storm system which may impact the Midwest this swept hit Seattle and Pacific Northwest with 60+ mph winds Tuesday, forcing bridge closures and producing power outages. It produced wind gusts of up to 69 mph at Tatoosh Island WA and 46 mph gusts in Seattle proper. At least 6,000 were reported without power in the region.

Despite the unseasonably mild weather predicted in Chicago over coming days, the weekend storm is to bring rain to the area which could mix with or change to wet snow Sunday. March in Chicago has never closed without at least a trace (0.1 inch or less) of snow.

Clash of seasons could see 70 degrees and snow inside next 5 days

2010-03-17T03:15:07Z

How often has it been 60 degrees or higher on that day?

2010-03-17T02:34:55Z

Dear Tom,
It seems that it is usually cold on St. Patrick's Day. How often has it been 60 degrees or higher on that day?
--Nick Recchia, River Grove
Dear Nick,
Typically St. Patrick's Day brings highs in the middle or upper 40s, but there have been some stunningly warm exceptions. Just last year the mercury soared to 74 degrees, tying the record high for the day first logged in 1894. There have been two other St. Patrick's Days when the mercury topped 70 degrees -- in 1966 and 1973 when the high reached 73. The warmth in 1966 was a payback for a cold and snowy March 17 the year before when 3.7 inches of snow whitened the city. Seven other St. Patrick's Days have recorded highs in the 60s. There also have been some really cold Irish celebrations, including in 1941 when the high reached only 11 degrees and in 1900 when the early morning low was 1 degree below zero.

Weather Word: Pressure

2010-03-17T02:00:53Z

Tim's Weather World: So Long Cold Winter

2010-03-16T13:47:47Z

We are thawing out this week after a cold winter. Highs should soar to near 70 by Thursday. It's about time.

The numbers are in and it is official. This past winter was colder than normal. Not just here but across the United States. It was the 18th coldest winter on record for the country. It was the 9th coldest winter on record for Illinois. February was particularly frigid for most of the country. February's average temperature for the U.S. was 32.4 degrees, down 2.2 degrees from average. The southeast was especially cold with Florida having its fifth coldest February on record.

Precipitation was above average for most of the country. We officially had 52.4" during meteorological winter (December-February). That is more than two feet above average.

The cold U.S. winter may have been the exception to an otherwise warm season globally. According to the National Climatic Data Center, globally, this was a warm winter. The combined global land and ocean average surface temperature for December through February was the fifth warmest on record for the season.

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Sun's return to help temperatures to take off in coming days

2010-03-16T04:19:19Z

Temperatures across the Chicago could reach new 2010 highs later this week---a warm-up which may include 70-degrees (or a reading awfully close) Thursday and possibly Friday. It's a development which, by historical standards, is close to being on schedule. A 70 Thursday would come almost a year to the date of last year's first 70 on St. Patrick's Day (74 degrees on March 17) and only a week earlier than the March 24 average date of Chicago's first official 70 since readings began at O'Hare Field in 1959.

March sunshine plays a big role in sending temperatures higher this time of year. It arrives more than two and a half times stronger than December sunlight. Longer days and a daily trek across the sky more directly overhead are behind the strengthening.

While Monday's high stalled out at 48-degree under a heavy overcast, Tuesday's increased sunshine is to propel readings to the mid 50s---even a bit higher in warmer inland locations. Northeast winds will limit shoreline warming by delivering those areas lake-cooled air faster than the day's sunshine can warm it. From Chicago's lakefront north to Zion, Waukegan, Kenosha and Racine, that means highs may struggle to get close to 50 degrees.

Temperatures surged across the Midwest Monday in sun-drenched areas. While cloudy Chicago managed its 48-degree high, Madison Wis., where sunshine emerged during the afternoon, hit 58-degrees. Duluth Minn. and Sault Ste Marie, Mich.---saw record highs of 60 and 63-degrees respectively under mostly sunny skies

The "real warmth" is due here Thursday and Friday.

Thursday's atmospheric set-up which offers the most compelling case for warming. Not only is sunshine likely to be bountiful and will well-developed west to southwest winds will override lake cooling, but Chicago is to sit beneath the nose of powerful jet stream winds. It's a region of the atmosphere in which air sinks, compresses and warms on a large scale. This setup has been known to boost surface temperatures.

Record rains drench Boston a second day; March tallies there top 10 inches

The latest storm to lash sections of the Northeast has produced some extraordinary rainfalls since Friday, whipping the area with hurricane-force gusts. The system comes just two weeks after the region was pummeled by a gargantuan snowstorm. Monday saw another 2.86 inches of rain fall at the American Meteorological Society's headquarters in Boston, Massachusetts. The WeatherBug site there has tallied 10.90 inches since March began---more than six times the historical average.

Cold air's on the move this weekend; storm potential being monitored

A warm-up, including temperatures close to 70-degrees in coming days, may be only one in a series of big weather swings which lie ahead. By this weekend, a system lifting northeast from Texas and running along a sharp temperature contrast zone, is the basis for the rain being predicted here Saturday. The system increases prospects colder air could sweep in to the area Sunday and could change precipitation in portions of the Midwest to snow.