Weather or Not

To the chagrin of the region’s snow-lovers, that weekend storm is looking wetter and wetter.

This morning, the computer models evidently are coming into agreement that the storm will take a path that will draw in warm air.

Any snow or sleet in Philadelphia, the National Weather Service says, is going to quickly turn into a cold, cruel rain.

Ken Reeves, the head of forecast operations at Accu-Weather, predicted that by Sunday morning the snow will have disappeared without a trace.

Also, the models have backed off the cold foreseen for early next week. The forecast now calls for highs closer to 40 than 30.

As we learned this week, December stories can be messy, and that was the case on this date in 1951.

A total of 5.3 inches was measured at Philadelphia International Airport on a day when the total precipitation was over an inch, meaning that only about half of it was in the form of snow.

It also rained the next day.

As it turned out, it was the heftiest snow accumulation of the meteorological winter – Dec. 1 to Feb. 28 – but 6 inches did fall on March 1. The early 1950s represented an amazingly snow-less period.

North and west of the city temperatures are below freezing this morning, and fog is frozen on car windows.

Also, watch out for the dreaded “black ice” from the frozen remnants of yesterday’s mess.

As expected, the National Weather Service is bumping down its snow forecast, but it is upping the ice.

Temperatures have inched above freezing at Philadelphia International Airport, and were right at freezing to the north and west.

Light rain was falling at Philadelphia, Mount Holly, Millville and Wilmington, and freezing rain at Pottstown.

Given that it has been warm, the streets should be toasty enough to prevent significant icing from any freezing rain on the roads in the immediate Philadelphia area, says Tony Gigi, a meteorologist at the National Weather Service office in Mount Holly.

The official forecast for Philadelphia now just calls for periods of rain, but sleet remains a threat to the north and west. It is sleeting as far north as Allentown, with heavy snow to the north of the ice line.

It is still possible that an inch or so of sleet could accumulate in Philadelphia’s adjacent suburbs.

Around here, the precipitation could stop for a time, however another batch of sleet is moving in from the west. Here is the latest radar image.

Ice is starting to accumulate on trees and colder surfaces north and west of Philadelphia, with a combination of sleet and freezing rain and temperatures near freezing.

The temperature has nudged above 32 at International airport, and liquid rain was reported there and in Wilmington.

The radar image shows a so-called "dry slot" moving eastward, suggesting that the precipitation could stop for awhile, but it is expected to pick up again.

The early returns indicate that the snow-sleet accumulation estimates are overdone, but the freezing-rain threat might have been underestimated.

Weather enthusiasts in the Midatlantic region are posting their observations here. For the latest, go to the last page.

Rain has overspread Philadelphia and most of Chester and Delaware Counties, with some sleet to the north of a line through northern Chester County.

Here is the latest radar image, which shows a pulse of frozen stuff moving west to east. The snow is well to the north, above Reading.

Given that the precipitation was expected to start in frozen form before changing to rain, odds are that areas from Philadelphia south and east aren’t going to see much in the way of accumulation.

And don’t be surprised if the 1-3 estimates to the north and west also get adjusted downward before lunchtime.

Temperatures are falling as the precipitation starts. It was 32 at Pottstown, and at Philadelphia International Airport, it’s down to 33; at 6 a.m., it was 36.

http://www.intellicast.com/National/Radar/Current.aspx?location=USDC0001&animate=true&enlarge=true

For most of the region’s snow-lovers, it looks like a good day to scroll ahead to the weekend.

Winter is still better than a week away but we are about to experience the most-eventful winter weather since March with storms today and perhaps a bigger one on the weekend.

A storm from the Southwest is colliding with a cold dome of air over the Northeast and Midatlantic, and that is going to set off some significant precipitation today.

The forecast calls for snow and sleet to creep into the region, thankfully right after the peak commuting period this morning.

It looks like it will change to rain everywhere south and east of the city but the frozen varieties might last longer to the north and west.

At this late date the discriminating reader will find plenty of hedging in the National Weather Service forecast discussion.

The official forecast calls for 1 to 3 inches in the Pennsylvania suburbs. The Accu-Weather map has the 1 to 3 line drawn just north of Philadelphia.

Elsewhere, it looks like a cold and heavy rain will dominate.

As for the weekend, the models have been consistent in blowing up a storm off the East Coast.

Once again, the I-95 corridor will be in the battleground zone between warmer and colder air, and some mixing and possibly a complete changeover is possible in Philadelphia.

Reading between the lines, the total precipitation amount from that storm is expected to be about an inch. That’s the water equivalent of about a foot of snow, but mixing would suppress the accumulations.

If the computer models are accurate, this one would be a nasty nor’easter, with powerful onshore winds stirring beach-eroding waves and heavy snows in the interior Northeast.

You can track the latest thinking and rumors among the professionals and snow enthusiasts here.

With the entire region encased in a heavy snow cover and schools still closed from the storm of Dec. 11-12, on this date in 1960 the Philadelphia temperature fell to a record low of 8.

Over 14 inches of snow had fallen, and the whiteness clearly had an effect on temperature.

Snow repels sunlight during the day and radiates heat back into space at night when the skies are clear and winds are light.

On the 13th and 14th, the lows were 10 and 7, respectively.

It continues to look almost certain that some ice and snow will fall in the region tomorrow.

And as usual, the questions you really care about – how much, and when will it start – have not yet been answered.

The latest thinking is that snow and/or ice could show up in time for the morning commute, with temperatures hovering around freezing.

Eventually, the precipitation is expected to be primarily rain from Philadelphia south and east, with a mix in varying concentrations on north and west.

The National Weather Service sees a potential for 1-2 inches in the city, with perhaps a few inches more in the northern and western suburbs before it all ends tomorrow night.

The weather-service has a winter-storm warning posted for Berks County with a forecast of 4 to 8 inches.

Looking ahead to the weekend, it is looking more likely that a major winter storm will affect the region Saturday into Sunday.

Here is the weather service discussion covering both storms.

Naturally, the Eastern weather chat board is abuzz with the possibilities.

As expected, the details remain elusive, but it’s now all but certain that a significant winter mess is coming to a neighborhood near you tomorrow.

The timing remains uncertain, however the best guess is that whatever shows up will hold off until just after the morning commute.

Areas to the north and west of Philadelphia could see some accumulating snow, and the National Weather Service says there a 10 percent chance that 2 inches could land at Philadelphia International Airport.

The forecast right now calls for mostly rain south and east of the city, with at least some ice and snow on the menu to the north and west. Winter storm watches are posted as nearby as Lancaster County.

The model-output suggests that about a half-inch of precipitation will fall, or the water equivalent of 5 or 6 inches of snow.

Here is the latest weather service discussion.

As we mentioned (see “White Christmas” below), we are still well shy of the peak snow season in the Midatlantic, but December has produced some memorable snows.

On this date 25 years ago, a surprise snowstorm left 6.8 inches officially at Philadelphia International Airport.

The snow began Saturday night as a fine fall, and then built to a steady, heavy snow that continued through Sunday morning.

It remains to be seen whether a similar storm is in the offing for the weekend.

The overwhelming consensus is that the winter ahead will be a gentle one, however the next several days may be adventurous in the Midatlantic and Northeast, climaxing with a major nor'easter.

We will get the inconsequential leftovers of the Midwest ice storm tonight in the form of rain and rising temperatures. Some ice is possible up in the mountains, but nothing around here.

Then, after a warm start tomorrow, it will turn colder tomorrow night, and perhaps cold enough for snow and/or ice when the next batch of precipitation arrives on Thursday.

The main event, however, might occur this weekend as computer models show the potential for a significant coastal storm Saturday into Sunday.

Right now, the precipitation type is up in the air, so to speak, and we foresee a 100 percent of model meteorological waffling between now and the appearance of the first flakes or raindrops.

If you want to follow the storm buzz, check out the Eastern weather chat board.

The Midwest ice storms that began during the weekend are being blamed for at least 23 deaths and zapping power to a million homes and businesses.

A state of emergency has been declared in Oklahoma, and today the ice is bedeviling parts of Iowa as the storm progress eastward.

Today the ice is bedeviling parts of Iowa, and schools were shut down in Des Moines. Here is the latest storm roundup from the Associated Press.

In addition, Reuters reports that ice has shut down operations at a key Oklahoma oil-delivery hub and that oil prices have jumped 2.6 percent to over $90 a barrel. Here is that article.

By the time the storm gets here, its effects should be benign. In fact it is forecast to take a path to our north and west, meaning we’ll be on the warm side and should get by with just some liquid rain.

Then things get interesting.

This one won’t leave much of a legacy, but the 15th named storm of the 2007 hurricane season has made landfall in the Dominican Republic.

The track forecast calls for Olga to follow the well-worn path of predecessors and proceed to the far-western Caribbean before making a second landfall, perhaps near Belize.

Here is the latest discussion from the National Hurricane Center.

Winds are topping out at 45 m.p.h. – just 6 m.p.h. above the minimum requirement for getting a name – and it is expected to weaken.

While named storms are unusual after Nov. 30, the official end of the hurricane season, they are by no means unprecedented.

Consider it a gift if it happens, because the climatological odds are against any measureable snow being around Philadelphia on Christmas Day.

It has happened, just not very often. In 1966, over a foot fell on Christmas Eve, and snow continued into the early-morning hours.

Five years ago, a slushy 1.1 inches was recorded at the airport on Christmas Day , with substantially more in some suburban areas as rain turned to snow.

By the solstice, it may be getting colder, but the peak snow season is still about a month away.

In December, the ocean surface is warm enough to work against big snowstorms in the I-95 corridor. Coastal storms generate powerful winds from the east, and that can draw in enough warmth to turn snow to cold rain.

Here is the Christmas snow list for the period in which official measurements have been taken at Philadelphia International Airport.

On Sunday morning on this date in 1960, the official forecast called for snow changing to rain.

The rain never came, but the snow kept coming. It snowed from late morning until around daybreak on the 12th.

By the time it stopped, 14.5 inches had fallen officially in Philadelphia, the most ever before the winter solistice.

The storm was followed by extreme cold, and two other 10-plus snowfalls later in the winter.

Anyone who was around here during the winter of 1994-94 would have empathy for the icy nastiness that is encasing parts of the Midwest.

The icy rains that began during the weekend have been blamed for traffic accidents that have caused at least 15 deaths in Oklahoma.

Now the ice plague is spreading eastward as cold air at the surface holds its ground against warmer air aloft. Here is a roundup from the Associated Press.

The problem is freezing rain, which is rain that freezes on contact. That allows the ice to accumulate until it becomes a hazardous enameled layer that is all put impossible to drive upon.

The weight of the ice drags down tree limbs and power lines. It is estimated that about one-third of Oklahomans lost power. Here are a few photos.

In January and February of 1994, we had a sequence of ice storms around here. Icing on Jan. 7 caused more than 600,000 power outages.

December, when the remnants of fall haven’t quite been routed and winter is poised for a takeover, can be a wildly variable month.

On this date in 1966, the high temperature in Philadelphia reached 71, it was a record for the date and the second consecutive day the high had hit 70.

Three days later, it snowed, with about 2 inches measured at the airport.

On Dec. 24,more than a foot of snow made fell upon the region, making it one of the whitest Christmases ever.

Didn't the hurricane season just end, you may rightfully ask yourself.

It did, on Nov. 30, but today the Colorado State University forecast team issued its 2008 outlook, and they say it is highly unlikely to be as kind to U.S. taxpayers as the 2007 season.

For the season that begins June 1, 2008 and ends Nov. 30, they foresee a total of 13 named storms, or one fewer than this season’s. To get a name, a storm has to have winds of 39 m.p.h. or better.

The forecasters, Philip Klotzbach and William M. Gray, warn of a high likelihood that at least one major hurricane, with winds of 111 m.p.h. or better, will make U.S. landfall -- something that did not happen this year.

Loyal readers (see "Hurricane Season, Post Mortem" below) may recall that the 2007 season left an early Christmas present for U.S. taxpayers. Not a single major disaster was declared for a hurricane this fiscal year, according to Ashley Small, spokeswoman for the Federal Emergency Management Agency.

Scroll back to 2005, the year of Katrina, and FEMA committed $37.8 billion to clean up for hurricane disasters.

If you watched the movie, “The Day After Tomorrow,” you saw the cartoon version of what would happen if the circulation of the North Atlantic suddenly slowed or stopped.

The movie was built on the hypothesis that if the ocean were to cease transporting warm water from the tropics toward the Poles, all form of hell – and ice – would break loose. In the movie, it was not a particularly good time to be in Manhattan.

While the movie should not be taken seriously, the Greenland ice core record does show evidence of an abrupt climate shift roughly 8,200 years ago during a period of glacial melt.

A paper published this week in the journal “Sciencexpress” suggests that a major change in the North Atlantic circulation was behind the dramatic and sudden onset of the cold spell.

The paper appears to support some earlier research holding that the cold spell was tied to a massive influx of freshwater from a melting glacial lake in North America, just south of Hudson Bay, known as Lake Agassiz.

The rapid injection of such a colossal quantity of water into the North Atlantic might have been sufficient to interrupt the Atlantic heat-transport system.

Lead author Helga Flesche Kleivin, of the University of Bergen, Norway, and her colleagues noted that this was a case in which large-scale changes in the natural world matched computer simulations.

The findings are of import, they say, given all the concerns over how warming will affect the Greenland ice sheet .