TIM’S WEATHER WORLD

December, January and February are the three coldest months of the year here so March 1st marks the beginning of meteorological spring.  We will start "spring" with a light snow at times today, tonight and into early tomorrow.  Marginal conditions are present for some lake effect snow so we don't expect big accumulations.  It is possible some areas near the lake shore could see between .5" to 1" total by Saturday afternoon.  Our .2" of snow yesterday means we have now just barely surpassed last year's snowfall through this point of the season (see image above).

A more significant snow could be on the way for early next week.   There are model differences in the timing and track of this next system but it appears there will be an accumulating snowfall for the Midwest sometime Monday into Tuesday.  Both the European model (top image below) and the GFS model keep the heaviest snowfall south of us.  Subtract about 1/2" of snow from the totals forecast for O'Hare for the lake effect today through tomorrow. That leaves us with somewhere between .5" and 1" of fresh snow with this upcoming system.  Stay tuned though since a slight northward change in the track could be the difference between an inch or two and several inches.

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Seven states saw record snowfall yesterday from Texas to Illinois.  Records were set for snowfall at both O'Hare and Midway on Tuesday.  3.6" of snow fell at Midway, a new record for February 26th.  O'Hare's 4.8" was also a record for the date.

So far this month we have seen 14.9" of snow at O'Hare or 81% of our entire snowfall for the season. The weather pattern has been more active this month and now there are indications it could remain active into March.  The North Atlantic Oscillation Index is one of the forecast indicators that we look at to give us a hint of what is to come.  The index forecasts the fluctuations in pressure fields between the Icelandic Low and the Azores High.  Bottom line is a positive index caused by greater pressure differences tends to result in relatively milder and dry conditions here.  A negative index means a weaker Icelandic Low and Azores High which allows for more frequent intrusions of colder air and a more active storm track.

The image below shows a forecast for a negative index forecast for the next 10 days leading me to believe we can expect colder than average temperatures and a greater frequency of storms compared to average.

The Climate Prediction Center's 6 to 10 day outlook seems to support the colder than average part of the forecast.  We have a 50% or greater probability of seeing below average temperatures for the forecast period of March 4th through March 8th (see graphic below).

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Most computer models are hinting a major winter storm could impact the midwest toward the end of next week.  Heavy snowfall is possible from the plains through the Chicago area with most of the snow falling late Thursday into early Friday.  It is still a long way off meteorologically speaking but in a season with so little snow (10.7" at O'hare or 42% of average) it's hard not to get at least a little excited.

The images below show the forecast for total accumulated snowfall between now and next Friday night.  Most of the snowfall projected should come form the late week storm.  The GFS model (above) is slightly more aggressive with its forecast of  7.9" compared to the European model's forecast of 5.3".

Both models are forecasting gusty winds with the storm that could lead to some blowing and drifting.

Stay tuned.....

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BRIAN SNYDER, REUTERS / February 9, 2013

Many in the northeast were still recovering from superstorm Sandy when they got hit by a blizzard over the weekend.  Now new reports on both storms review and assess their impacts.

The blizzard that produced record setting snowfall in New England rated 3 out 5 on the Regional Snowfall Index or RSI scale.  The National Climatic Data Center's RSI evaluates significant snowstorms that impact the eastern two thirds of the US.  The index ranks a storm's impact on a scale of 1 to 5 similar to the Saffir-Simpson scale that ranks hurricanes.  Storms on the low end of the scale with an index of 1 are considered "notable" while storms ranking a 5 on the high end are considered "extreme".  The recent blizzard registered a 3 on the index, considered a "major" storm.

According to the NCDC-

"While the area impacted by this storm was less than many other major storms, the heaviest snowfall landed in more densely populated areas, making it a “major “storm in the RSI categories. Over 49,000 people across 192 square miles saw 30 inches of snow or more as a result of this storm."

In a lengthy, detailed report on superstorm Sandy, NOAA concluded that Sandy was not a hurricane went it made landfall along the Jersey shore on October 29th, 2012.  Sandy's losing its hurricane classification as it moved onshore posed problems for forecasters.  The storm was technically a "post-tropical cyclone" at that point but advisories and warnings that accompany that type of storm may not carry the same sense of urgency (at least in the public's mind) as hurricane advisories and warnings.  Local National Weather Service offices began issuing advisories and warnings after the storm was downgraded and the National Hurricane Center no longer issued statements on the storm. The National Hurricane Center may “continue issuing formal advisories on post-tropical cyclones as long as those systems pose a significant threat to life and property” in the future for storms like Sandy according to proposed changes suggested in the report.

Other hi-lights from the report:

• Hurricane Sandy was the second costliest ($50 billion) in US history
• 72 deaths were attributed to Sandy, most for east coast storm since Hurricane Agnes killed 122 in 1972
• 8.5 million people lost power as result of the storm
• at least 650,000 houses were either damaged or destroyed
• highest storm surge in New York was more than 12½ feet at Kings Point on the west end of Long Island Sound

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It will be seasonably cold the next couple of days with a warm up Wednesday before temps come crashing down just in time for the weekend.  Temperatures will tumble on Valentine's day as a cold front sweeps through the area but despite the arrival of colder air, there is little measurable snow in the forecast for the foreseeable future.  There will be several chances for light snow or flurries over the next seven days but little in the way of accumulation expected.

The 7 day total accumulated snowfall forecast from the ECMWF (European model) squeezes out just a little over an inch between now and next Monday (top image).  The GFS model forecasts just under a third of an inch.  We have seen less than half the average snowfall to date at O'Hare.  So far we have picked up a total of 10.7" or 13.2" below average.

Hang in there snow lovers.  There is still plenty of winter left.  We typically see another foot of snow or nearly 34% of our seasonal snow before spring settles in.

Snow cover seems to be expanding all around us. As of Friday, 34.1% of the contiguous US had snow cover.  After the weekend blizzards in the northeast and the plains, now just under 45% of the contiguous US is reporting snow cover.

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Forecasting snowfall amounts is one of the most difficult challenges for meteorologists.  Yesterday's storm certainly confirms that statement.  Snowfall amounts varied from nearly a foot in Lake County (10" in Beach Park) to just 1.4" officially at O'Hare.  The graphic below from the National Weather Service office in Romeoville shows the wide snowfall gradient across the area.

The difficulty with a storm like the one we saw Thursday is determining when the change from rain to snow will occur.  The "Ping Project" can help.  Ping stands for positive identification near the ground.  The NOAA National  Severe Storms Laboratory has partnered with the University of Oklahoma to launch a free "Ping" app that allows users to report precipitation.  The app is availabe for both Iphones and Android mobile devices.   The Ping Project website is another way to report precipitation. Ping users began to report snow late yesterday morning in Lake and McHenry counties indicating the change from rain to snow was occurring there first.   That early transition to snow helped in part to produce the heavier snow totals there.   The graphic below shows how the ping reports helped identify the rain/snow line.

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We still have a snow deficit even though we had measurable snow for five straight days ending yesterday.  At least we have put a dent in our snowfall this season this February.  We picked up just under 6" of snow so far this month or roughly 62% of all the snow we have seen so far this winter.  Still, we are more than a foot behind where we should be in terms of average snowfall at this point.  We are not alone.  Most of the Midwest has seen less snow than normal with one glaring exception.

•                               Snowfall So Far               Above/Below Average
• Minneapolis                26.4"                                   -9.1"
• Rockford                    12.9"                                   -12.0"
• Chicago                       9.2"                                   -13.0"
• Milwaukee                  29.9"                                   -14.2"
• South Bend                31.7"                                   -14.6"
• Marquette                   95.4"                                   -27.8"
• Green Bay                  40.4"                                    +8.2"

So aside from Green Bay, most of these Midwest/Great Lake cities are a foot or more below average.

Prospects for snow during the next 7 day are highest north of Chicago.  Below are the 7 day total accumulated snowfall forecasts from two computer models.

So there is some hope for snow lovers over the next 7 days with the European model (above) and GFS model forecasting anywhere between just over 2" of snow to just over 5".

Speaking of snow....

Snow cover nationally has shrunk this month to 39.6% of the contiguous US, down from over 60% last month.

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