December 25, 2000
First, a Merry Christmas to all!! It is at least partially white outside, so it definitely feels like Christmas time. It is also quite cold outside. Although the current temperature is in the low 20s across the region, the wind is making it feel like 0 to -5 degrees. The winds will increase to 25-35 mph and wind chills will approach dangerous levels well below zero. The remainder of Christmas Day will be mostly sunny and unseasonably cold with the high in the low to mid 20s. Winds will subside slightly by afternoon. There will also be a partial solar eclipse at 12:45PM which we will be able to view. Tuesday will be mostly sunny and continued cold with the high in the upper 20s. Wednesday will be partly to mostly cloudy with the chance of a show flurry or snow shower in the afternoon. The high will be near freezing. Thursday will be partly cloudy with the high around 30.
Once again, things get pretty complicated in the medium/long range towards the end of the week, but surprisingly, many of the models are in good agreement with important upper level features. There are just some questions as to timing and phasing (which will likely happen between 2, *possibly* 3 jet streams). Now the details. A bend of the AVN/EC/GGEM at 72 hours (or early Wednesday) shows a cutoff low anchored over southern New Mexico while a vortmax (we'll call this vortmax #1 for discussion purposes) is barreling through the Great Lakes region towards Cape Cod. BTW, this is the system associated with our chance of a flurry or snow shower Wednesday afternoon. Meanwhile, the potential troublemaker is just entering the Pacific Northwest (we'll call this vortmax #2). By Thursday, vortmax #1 is heading off the New England coast, the large cutoff low in the southwest is moving into Texas while gradually opening up, and vortmax #2 is near North Dakota. Some of the models are bit slower and weaker with second vortmax, allowing the cutoff to advance ahead of it. By Friday, vortmax #1 should be east of Nova Scotia, so no problems with that. At the same time, what was once our cutoff low has opened up and began ejecting eastward towards SE Louisiana. Vortmax #2 is digging towards Wisconsin and trying to catch up to the energy over Louisiana. At the surface, low pressure will be in the northern Gulf of Mexico. By Saturday, the energy over Louisiana has begun to round the base of the 500mb trough and is approaching the SE coast. Vortmax #2 is vigorously digging into the Tennessee Valley and is phasing with the energy off the coast. At the surface, low pressure is on the east coast of northern Florida. By the looks of the potency of vortmax #2 by the models coupled with a Greenland Block, this could spell trouble for the East Coast come later on Saturday. By Sunday, both systems phase and the trough goes negative. Low pressure is just off the New England coast. Needless to say, this would spell a major coastal storm.
As stated above, went with a blend of the AVN/EC/GGEM for this forecast. Why? The AVN upper air to surface comparison is reasonable. Also, it fits well with the EC, the most consistent model. The EC has shown this scenario for three straight runs. It is also supposed to be our most reliable medium range model. As for the GGEM, it's not far behind the two with it's upper air features, perhaps a bit faster with vortmax #2 which may allow the systems to phase sooner spelling a slightly farther west track. The GGEM at 96 hours is downright scary as it has two closed 500mb lows virtually stacked one above the other from north to south, one at 533mb over southern Minnesota, and another at 564mb over southern Texas. This would spell a MAJOR storm for parts of the east.
Now the different possibilities that may play out. First, confidence in this forecast is medium. Timing of the second s/w and the ejecting cutoff is critical. If the cutoff ejects out ahead of vortmax #2 too quickly, the vortmax will act as a kicker to boot the potential storm off the SE coast and out to sea (model trends say no on this scenario). If the cutoff doesn't eject and vortmax #2 passes east prior, that means no storm (no model predicts this). If the cutoff ejects just slightly ahead of the second piece of energy, it will likely catch up to it in time to phase as it hits the Atlantic coast spelling a major storm for the East (this scenario is shown the most by guidance). If the systems phase too late, a storm will develop, but will be out to sea (this is a possibility as trends are showing the cutoff moving a bit quicker). And finally, if both pieces of energy are synchronized with each other pressing east, they will phase sooner meaning a storm right along or just west of the coast. With the Greenland Block forecast to be as strong as it is, this scenario too seems unlikely. Alot of 'ifs' eh? That's what happens when guidance is onto to something potentially major past 4 days.
With that said, see two possible solutions at this time based on guidance. Number 1, the systems phase off the FL coast sending a major storm up the eastern seaboard. Number 2, the systems phase too late sending the system out to sea off the SE coast. Looks like all or nothing at this point, but this may change as the week progresses. Just keep in the back of your head that something potentially major could be coming later in the week.
Forecast . . . too early to nail down at this time. Trends among guidance are starting to line up, but trends could also push this thing out sea with any minor change. Alot of timing issues in the upper levels. This discussion is very detailed for a system potentially 5 days down the road, so be forewarned that it will likely change. Just a heads up as to what may *possibly* transpire later in the week. The upper air pattern has ramifications similar to a standoff...something's gotta give sooner or later. Stay tuned.
