Sunday, February 15, 2004


- Blue Swede, from the soundtrack of Reservoir Dogs

This forecast discussion is for the I-95 corridor. Central PA is still going to watch the fun from a distance.

The arctic express has arrived, and you'll notice throughout today that despite the bright sunshine, temperatures will continue to drop as the wind picks up. This cold blast will hang tough into Monday, and you all know that cold air is denser and heavier than warm air, so it will take longer to "scour out." As the high slowly departs on Tuesday, computer projections show the classic cold air damming signature behind.

That means cold air will continue to filter down the east side of the Appalachians, and the way all the systems are lined up, the incoming warm air is not coming from the southwest and south like previous storms. Thus there is no over-running warm air over cold air, which caused the sleet and freezing rain situation earlier this month. And there are a whole host of other little details that on the first glance are not that serious, but when combined with the cold air produces a significant snow event.



The westward leaning models bring the storm closer to the coast, forming off S. Carolina Monday night-Tuesday and then north on Tuesday. The onset of snow would be from southwest to northeast... starting Tuesday night in DC and Baltimore, early Wednesday morning in Philly, and Wednesday late morning to noon in New York. The commute Wednesday morning will be a disaster from DC on north since the snow will become steadier and heavier throughout the day. It will end late Wednesday with some clearing, and temps below freezing Wed night. Although your NWS forecasts on the left links make it look like we will get buried from Tuesday through Wednesday, in theory they are only calling for a 30-40% chance of snow, which is to say: "It's probably gonna snow, we just don't know how much right now."

The eastward leaning models have the storm forming off S. Carolina, and bring the snow along the Del-Mar-Va, but then take it out to sea from there. The best you would see is clouds and flurries... a busted storm forecast and everyone goes to school Wednesday with a light dusting on the ground. I have a real problem with this projection. My reasoning is that the US-generated "GFS" (Global Forecast System) model, often preferred by the NWS, has been very inconsistent for several days on the storm. This model projects the arctic high over our area now to be shoved off the Maine coast before the storm moves up the coast. This would allow the storm to move out under the high, thereby taking it out to sea. Baltimore-Philly is then grazed with flurries only. However, this was part of the problem with the forecasts for the blizzard last year. Once the snow started falling last February 16, do you remember how the TV stations kept upping the accumulation amounts? The reason for that was the forecasters underestimated the speed of the cold high moving out. Because it ended up "getting stuck" and nosed out into the Atlantic instead of moving off the coast, the moisture loaded low had nowhere to go. The combined easterly flow of the high and low brought in more moisture right into the cold air, and whamo.. you had a crippling snowstorm.

You'll notice the Philly area weather service has come out of the gate with a special weather statement that basically puts it all on the table. Baltimore is calling for snow, but being reserved about it. The difference is in the computer models. One shows a raging snowstorm from DC to Boston Tuesday night into Thursday morning. The other shows a glancing blow with more snow in Del-Mar-Va and nothing in New England. So the best they can do right now is a compromise. The other reason they are holding back is the infamous March 2001 superbust. It was the first week of March 2001, of the 12 or more computer models, 11 were calling for the storm of the century. Massively heavy snow from Richmond to Boston... 2-3 feet, gale force wind, bitterly cold... a winter's Armaggedon. What actually happened? 2-3 inches followed by partly cloudy.

So the weather service sees that we are between a President's Day 1979 major miss and a March 2001 major hit. I have to tell you that as the title for today reads, I'm hooked on a feeling that there are too many atmospheric rules in play that this storm, once it formed, cannot be denied. I think you are going to see gradual uptick in the snowfall forecast from the NWS and the TV stations as we progress through the next 48 hours. My rules for why are listed below.

This storm is demonstrating the factors necessary to deliver a Fabulous February. Consider:

1. A low moving north to northeast is going to bring in moist air from the Atlantic ahead of it due to counter-clockwise flow.

2. A high moving east will also bring in moist air from the Atlantic due to clock-wise flow.

3. Combined these two forces and run that moisture into solidly parked cold air along the coast, and you have a raging snowstorm.

4. The big kahuna is if the high slows down or noses into the Atlantic, you'll have a slowing low that cannot penetrate the wall of cold air in front of it.

The result? What was going to be a 4 inch+ storm, turns into a 8-12 or more. So stay tuned and check back often. The next update will be late this afternoon after the computer models make another run.

To conclude, we go on to Tip # 5 on how to beat winter-weather stress:

5. When forecasters say: "We're tracking the storm," it means they don't know what is going to happen.


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