Archive for December, 2010

The Nor’easter and Regional Snow Totals
December 27, 2010

The weekend nor’easter is pulling away from the coast today (Monday, Dec 27).

The midday satellite image shows the “eye” of the storm centered off the tip of Cape Cod. It closely resembles a hurricane.

The heaviest snows skirted south and east of Baltimore. A close-up visible satellite image actually shows the snow on the ground.

The Susquehanna River is evident cutting through the snow field north of the Chesapeake Bay. The heaviest snows were in southeast Virginia, southern Maryland, the DELMARVA Peninsula, eastern Pennsylvania, New Jersey and on up into New England.

The following list is a summary of snow reports turned into National Weather Service offices around the region.

John Collins

 


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Preliminary Snow Totals…Dec 26, 2010
December 27, 2010

Source: National Weather Service

John Collins

Storm May Drift Farther West!
December 25, 2010

Just as computer solutions seemed to settle on a more eastward track for the upcoming coastal storm, a switch to the idea of a more westward track is back in the picture.

The early Saturday afternoon NASA satellite image shows the developing storm center over the north-central Gulf coast. The newest storm track forecast takest the low center a little closer to the Mid Atlantic coast by late Sunday.

As we have been saying all week long, the closer to the coast this storm is, the greater the potential for a significant snow inland.

The National Weather Service forecast map for Sunday evening shows the storm position off, and relatively close to, the New Jersey coast line. At this point the heaviest snows would already have fallen over the Chesapeake Bay region.

How much?

Our in house computer model from WSI has boosted snow totals east of Frederick, MD and Washington, DC. Around Baltimore up to around six 8 inches is possible with more (8-10 inches close to a foot) in the northeast corner of Maryland. Parts of the Eastern Shore could receive more than a foot of snow based on this particular model. Other models and forecasts are a bit more conservative and I use these figures with a bit of caution because the ultimate track could modify these numbers significantly one way or the other.

The National Weather Service has issued a winter Storm Watch Warning for the eastern half portion of Maryland around the Bay and on the Eastern Shore because of the increased threat of a significant snowfall. Areas roughly west of the I-95 corridor are under a Winter Weather Advisory.

 

The Watch Warning will be in effect from Sunday morning through Monday morning and it is calling for 6-10 inches of snow in that time period.

Some fine tuning will still be necessary as the storm approaches so, stay tuned.

John Collins

Holiday Greetings
December 25, 2010

Christmas Weekend Snow Update
December 24, 2010

The storm we have been talking about all week long is taking shape in the Southern Plaines.

The track of the storm over the next couple of days is expected to be far enough east that the storm’s impact over most of Maryland will be relatively minor.

The National Weather Service Track Forecast Map shows the most likely path in black. The colored dots scattered along the path show “low center” positions forecast by various ensemble model forecasts and indicate that some possible margin of error still exists.

Tony’s forecast for the weekend indicates a low-moderate chance for what would be considered light snow over the area. The forecast map below is from one computer model we use in house.

The color coding indicates that most of Maryland has the potential to receive around an inch if snow or maybe a bit more. The blue shaded areas in western Maryland and on the DELMARVA Peninsula could receive two to four inches with areas close to the beaches a bit more than that.

Keep in mind that the storm is still more than 24 hours away and a slight change in the track, one way or the other, could have a huge impact on snowfall so keep checking in  to WBAL-TV and wbaltv.com.

John Collins

Wednesday Afternoon Weekend Snow Update
December 22, 2010

Computer models remain quite uncertain on the details of the storm that will likely be in the vicinity of the Mid Atlantic region over Christmas. About the only agreement among the models is that the storm will arrive a little later in the period, most likely Sunday into Monday.

I have annotated the late afternoon visible satellite image showing the position of the storm coming on to the west coast and the estimated track across the U.S. over the next few days. Note that the storm will likely dip to the Gulf coast as it moves eastward, picking up moisture before it moves up the East Coast.

The key is that move up the East Coast and how close the track will be to the coast. This is where the various computer models fall into two general camps. One, some distance from the coast with less snow and, the other, close to the coast with more snow.

The two forecast maps below show that difference, showing estimated storm positions during the pre dawn hours on Monday.

Both of these forecasts are from the Wednesday morning model runs. The top map is the GFS model(American) and shows the storm to be farther off shore than the bottom map (ECMWF-European).

The GFS MOS “numbers” show how an easterly track reduces the snow potential.

The yellow outline highlights the Saturday night through Monday morning timeframe. The blue outline highlights the precipitation probabilities at 6 and 24 hour intervals (less than 50%) with the “1” indicating less than a tenth of an inch of liquid equivalent precipitation. The red outline indicates that the type of precipitation would be all snow and the “1” indicates that up to two inches would be possible. Several days ago this very same MOS product projected up to and perhaps more than six inches of snow.

The European “operational” model has been consistent in developing a powerful storm close to the coast which would result in significant snowfall over the area. An ensemble of various ECMWF interpretations position the storm farther east however with somewhat lesser impact. So, even within a particular model there is no firm consensus.

The bottom line is that there is too much conflicting information on what the storm’s impact will be on the area once it gets here. A National Weather Service discussion on that very subject puts it best:

We will just have to sit tight and wait for more information.

Stay tuned,

John Collins

Sandra: Storm Moving At ‘Deliberate Pace’
December 22, 2010

A Baltimore White Christmas??
December 21, 2010

The prospect for a Christmas snow is still on the table! However…the latest computer model guidance is showing me that the whole storm system is slowing down. In other words, we might get some light snow on Christmas, but the main event could hold off until Sunday or even Monday. There are still a few models that have the whole thing missing us to the south. The two models I trust the most are actually split on the solution…the JMA model is the one with the miss…the ECMWF has a big slam snow storm for us! I am not aware of a public link for the JMA, but you can see the ECMWF here: http://meteocentre.com/models/models.php?mod=ecmwf&map=na&run=00&lang=en

Stay Tuned!

Tony Pann

Christmas Storm Potential Update
December 21, 2010

There has been no substantial change in the outlook for some snow on Christmas. Details on a possible storm track and snow amount are very much up in the air at this early stage but most computer models agree that some snowfall on Christmas is likely.

The Tuesday afternoon satellite picture shows a new storm coming on to the Pacific coast and this will likely be the one that will start the ball rolling on the next storm to move toward the East Coast.

The current thought is that the storm will move in Christmas Day with snow possibly continuing into Sunday. This is a little slower than earlier forecasts. It appears that temperatures would be cold enough for all snow.

The forecast map above is for Sunday morning with the storm off Cape Hatteras and beginning to turn up the coast. The map below is for Monday morning showing the storm center approaching Cape Cod as a nor’easter.

The key for the Mid Atlantic Region is how close the storm will be to the coast line and that is a question that can not be answered at this early stage. The storm’s proximity to the coast will influence the amount of snow the area receives. Two model runs in the past 24 hours have pegged a snow total range anywhere from a trace to as much as ten inches with the latest forecasting on the low side with up to four inches. As you can see, much fine tuning is needed before a definitive forecast can be issued.

John Collins

More On A Christmas Storm Potential
December 20, 2010

Tom’s previous blog points to some features in the computer models that have caught the attention of East Coast meteorologists … the potential for Christmas Day cyclogenesis, better known as storm development.

Those models continue to come together on a forecast that would point to the possible development of a significant coastal storm on Christmas Day.

The chart below is the forecast for late Christmas Day from the European Center for Medium-Range Forecasts.

This forecast map shows a strengthening storm off the mouth of the Chesapeake Bay. In the scenario the storm had spent the previous w24 hours moving eastward out of Tennessee and across North Carolina, generating snow in Maryland. Two National Weather Service surface forecast maps show the progress.

There is a slight difference in the position of the storm center between the National Weather Service maps and the European Center maps due to computer model interpretations. These differences are what make forecasting difficult beyond a couple of days.

The Model Output Statistics (MOS) for one global model generated by the National Weather Service Sunday morning (December 19) gives a rough numerical sketch for the week ahead, including Christmas Day.

The columns outlined in red are Christmas Eve and Day.

The dark blue outline highlights the precipitation probabilities the computer model has assigned for those two days for 12 and 24 hour periods.

The green outline highlights the quantitative precipitation forecast (liquid) for the 12 and 24 hour periods. The “4” in the 24 hour row indicates half to one inches of liquid precipitation is possible. At a ten to one ratio, this would yield 10 inches of snow. The high temperature for the day in this model is pegged at 37 degrees and all snow or a rain/snow mix is possible.

The light blue outline highlights the type of precipitation expected in that time frame. “S” indicates snow. The line immediately below the light blue box indicate the snowfall amount forecast. In this case the “6” indicates a 6-8 inch snowfall range is possible.

A comparison of the snow and liquid numbers in this particular computer run would seem to indicate a somewhat wet snow with a possibility of a rain/snow mix somewhere nearby. These numbers came from the 7am Sunday computer model run. The 1pm Sunday computer model run comes up with a slightly different storm track and lends some support to the 7am model’s hint at a rain/snow mix by bringing the storm center and warmer air farther north.

The forecast map above shows the storm center over the Baltimore/Washington area at 1pm Christmas Day. The blue line through the center of the storm is the freezing line at 5,000 feet. South and east of that line, temperatures at that altitude are above freezing and precipitation at that altitude would be rain. Temperatures at the surface south and east of that line would determine weather rain, freezing rain or sleet is falling. North and west of that line, snow would be the most likely type of precipitation.

The bottom line … we are 5-6 days away from Christmas and computer models are indicating some sort of storm development. Every 6 to 12 hours those model come out with slightly different ideas as to how the storm will behave. The models will continue to swing back and forth over the next few days with different solutions for Christmas Day weather. At this time, the final outcome is far from a sure thing. Stay tuned.

Check out Tom’s latest blog entry for a look at the setup for the week’s weather developments.

John Collins