Saturday 1:45 PM

Two storms are about to affect the Northeast. The first one will spread mostly light snow sleet and rain from northern Virginia and Maryland late tonight through Philadelphia and New York City tomorrow morning. With temperatures borderline and liquid equivalent precipitation amounts generally less than a tenth of an inch, no major accumulatons are likely. However, motorists and pedestrians will need to watch for slippery areas.

The main storm forms along the north Florida and Georgia coasts tomorrow, and then treks northeast to be off Cape Cod Monday afternoon. The NMM-WRF continues its lonesome stance of predicting that significant accumulaitons stay just east of the major cities. I say "lonely" because the GFS, the Navy NOGAPS and Japanese models all bring more substantial precipitation to the Washington to New York corridor and then to Boston. If this is right, the major cities will have an old fashioned cold-wind snowstorm. I say old fashioned based solely on a scientific study of recent emails from people in these areas saying that we don't get snowstorms like they did back then (like a few times earlier this century and in 1996). The amounts are still uncertain. Last night's 7PM run and this morning's 7AM run of the GFS each suggested that the area from our nation's capital to New York City should get at least 6 inches of snow. The NWS office serving the Philadedphia area places the chance of at least 4 inches at 80% and of at least 6 inches at 60%. The GFS run from 1AM last night had the heavier snow east of the major cities but still suggested enough snow should fall to make things slippery tomorrow night and for the morning commute on Monday. This morning's GFS has the added attraction of a second batch of snow on the back side of the storm later Monday, covering northeast Maryland, eastern Pennsylvania and parts of New Jersey. The model also predicts a major snowstorm for Providence, Boston and Portland.

As with many storms, the area with heavy snow may be rather narrow. Areas to the northwest get less snow because there is less moisture, and areas farther southeast get enough warming to get a change to rain or sleet. This will have to watched along the New England Coast.

At this point you may get the impression I feel certain that this storm is coming to the places I have described. After all, we see a potent upper air trough coming through the Midwest, a strong frontal zone off the East Coast and a cold high pressure that stays to the north. But I have been at this too long to be brazen about this. I can get ready to cross the street and notice a big truck coming right down the street in the correct lane. If the driver stays alert and follows the road, I can stand right where I am and will not get hit. But you know what... I will keep an eye on that truck until it is past me just in case! As the second storm's precipitation area becomes organized tomorrow morning and we see how the jet stream, the moisture, and all the surface features are set up, confidence in whatever forecast we make at that time will increase dramatically. Until then...

Saturday 6:55 AM

Two low pressure areas will affect the Eastern Seaboard in the next three days. The first will spread precipitation northeastward along the I95 corridor tonight and tomorrow morning. It appears temperatures will be borderline between favoring a mix of rain sleet and snow vs mostly snow. Since it was mild the last few days, there will be a tendency for precipitation to melt on the streets. However, the precipitation is likely to fall during what is typically the coldest part of the day, and if there is enough sleet at any given point, it can quickly cover the ground and make things slippery (as well as conditioning the surface to allow more of whatever snow there is to stick more easily)

The second storm is going to be the bigger of the two, and will affect the Washinton to New York City area tomorrow night into Monday. However, the question remains where the heaviest precipitation will be concentrated. When the 00z (7PM EST) run of the GFS came in last night and agreed with the European model (ECMWF), you could almost hear the cheering from frustrated snow lovers. There it was: the big one, with areas between Philaldelphia and eastern New England getting at least 5 to10 inches of snow along with blowing and drifting. Then, to throw more ice on the igloo, the National Weather Service issued winter storm watches for most of the these same areas for the Sunday night to Monday storm. Watches need to be issued far enough in advance that people can make preparations for a possible storm

I suspect fewer people were up when the 6Z (1AM) GFS results started flowing between 4 and 5 AM EST. I was looking at maps around 5:15 and discussed the situation with one of our bright and insightful (yes Mark, I am talking about you) snow warning service meteorologists. The 6Z run, and the NMM-WRF run both suggested the heaviest precipitation would fall offshore and that the Philadlelphia to New York City area might get as little as 1 to 3 inches out of the storm that looked so impressive on the earlier run. I typically trust the 00z rin more than the later product, but both have scored their victories.

At this point, we can draw two main conclusions: the first event late tonight and tomorrrow morning does not look like a big snow or ice producer, but it could make things slippery tomorrow morning. The second storm will be much bigger, but in a northwest to southeast slice across the storm's precipitation shield, there could be anywhere from nothing to more than a foot with that difference showing up in a linear distance of less than 150 miles. From the vantage point of these comments made 36 to 48 hours in advance, I know better than to claim anyone can reliably and consistently hit such a forecast perfectly. I know some of our readers who make their own predictions will nail this one right away, but I would remind everyone that even the best home run hitters strike out more than they want.

This video shows more about the situation. When I watched it before posting it (sometimes I wish I could spend much more time reviewing and re-doing these creations), I noticed that at one point I was talking about the second storm offering more snow potential than the first, but I actually said first storm instead. Keep that in mind when you get to that point.

Posted by Elliot Abrams on Saturday, February 28, 2009 1:39 PM
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