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Even I was a little concerned when I saw the ECMWF, then ETA, GFS and GGEM come in very close to one another, and actually the 0z GFS and 12z ECMWF in some ways were strikingly similar. There are some signs that a few of the models may be trying to hold back some energy, by that, were talking about one piece going out and then the other staying back behind, The details however a pretty sketchy, to say the least. As of this writing (135 AM EST), the 0z Sunday UKMET is not in.
First before I talk about the system, review tonight’s models and give you my thoughts on the crazy situation, I want to review with everyone what is needed synoptically speaking for a major east coast snowstorm to occur. There are three major things which come into play here.
First, you need to have a closed 50/50 low (Low pressure Located near 50 degrees north latitude and 50 degrees west longitude), this is probably overall the most important factor of all three. The 50/50 low helps to hold in areas of high pressure across either the great lakes, or Quebec, which in almost all situations is needed for a complete snow event in the I-95 corridor and at the coast. The 50/50 low also has a close relationship with the NAO, and a lot of times can directly affect its behavior, the same was the NAO can directly affect the 50/50 low. In these cases, the 50/50 low abruptly shortens the wavelengths in the northern branch of the jet stream that then sends the NAO negative if it was neutral and strongly negative if it’s already negative.
In the case of a Miller Type “A” Major east coast snowstorm or major east coast low, the appearance of a 50/50 low prevents the southern stream s/w from tracking inland, or if were talking about a Miller Type “B” Major east coast snowstorm, the 50/50 low causes the suppression of the height field across the eastern part of the country, which then directs the digging Polar jet s/w energy to go around it, on a more southeasterly track. It also delays the phasing of the Northern and Southern streams in a Miller Type B situation which prevents a system from tracking inland, in addition to forcing an initial inland running low pressure system transfer energy to a coastal low.
Secondly, the NAO has to be negative. Of course, like I just talked about, the 50/50 low can shorten the wavelengths and send the NAO negative; the same as the blocking associated with the negative NAO can result in a weaker system moving toward the Canadian Maritimes, Price Edward’s Island, Nova Scotia, or Newfoundland to slow down, and intensify (or close off), becoming the new 50/50 low. The blocking associated with a negative NAO may be found in three primary areas, first and probably most preferred would be right across Greenland, which we all know better as the classic Greenland Block. The second position is over Baffin Island, Labrador, The Davis Strait, and Northeastern Quebec, this however is a pretty extreme position to have the main above mean height center located, associated with the Negative Phase of the NAO. The third position is Near Ireland, Scotland, or England.
The last primary feature is the Polar Vortex. If the polar vortex is very strong and either, one, displaced well south of its climatological position, or located near Newfoundland, the strong jet develops in the confluent flow underneath the vortex causes shortwaves either in the polar or Arctic branch to be shunted quickly east instead of digging and potentially phasing with a Southern Stream entity. If the Polar Vortex is in climatological position and intensity, shortwaves would be encouraged to dig more, and as a result, have a better chance of phasing with southern branch energy.
Without Blocking, or a 50/50 low, high pressure systems will slide off the east coast ahead of a system, which then normally causes the flow to turn into the southeast along the east coast, turning precipitation type over to rain along the immediate coastal plain and the I-95 corridor. An amplified PNA ridge is also preferred. Please understand that having all of these factors present at the same time does not guarantee that a major east coast snowstorm is going to occur. You still need some sort of Northern and Southern branch energy phasing, or digging northern branch energy (Like an Manitoba Mauler, Saskatchewan Screamer, or Alberta Clipper) in order for these factors previously discussed in conjunction with either the digging or phasing (or both) in order to get something big. If there’s no shortwave(s), you won’t get any big storm.
This relates to our current situation in several ways, for one, we will have the 50/50 low, but whether or not it is closed off, and allows the jet to push the Polar jet s/w further south, causing it to phase with the energy coming out of the southwest remains to be seen. The Polar vortex is pretty far to the North (north or a climatological position, and a bit weaker than climatological intensity), but if the 50/50 low is sufficiently strong, it really may not matter. I want also point out to you that this situation is a lot different from the one which we had last week, in which the NAO was mostly positive, and there wasn’t any 50/50 low whatsoever.
This time around, we will have the 50/50 low in some capacity, and the blocking located in close to the perfect position, but the Polar vortex is displaced north of its climatological position, which as we know, isn’t favorable.
Ok, on to the models, we’ll talk about the ECMWF and GFS mostly, as I still haven’t had time to break down the rest of the data as much as what I would like to, but I’ll also give you a feel for what’s going on according to them (0z GGEM, 0z ETA).
Tonight’s ECMWF was heartbreaking for those in the Mid Atlantic and Northeast, but the thing that made it probably that much worse was the fact that the 0z Sunday GFS run looked strikingly similar. Here’s the 72 hour ECMWF valid 12z Tuesday.
http://web.wright-weather.com/wxp-model ... rt_h72.gif
Looking at the synoptic set-up the ECMWF has the Polar vortex located to the west of Baffin Island, which is good, the strong and clearly discernable blocking across the north Atlantic, and looks as if it’s trying to develop a closed 50/50 low. However, even with that in mind, the Polar jet energy is moving rapidly across the lakes, while the closed 500mb low is still located over Western Texas.
The GFS (shown above) valid at the same time has a ragged looking southern branch shortwave, which is weaker than the ECMWF and not closed off. The Vortex is located in pretty much the same position as where the ECMWF has it, the locking is there, and the 50/50 low is closed off at 528dm.
96 hour ECMWF valid at 12z Wednesday.
http://web.wright-weather.com/wxp-model ... rt_h96.gif
The ECMWF at this point, no longer has any hint of the closed 50/50 low; however the Polar vortex is still in the same position; west of Baffin Island, and the blocking is in position. But, by this time, the Polar Jet s/w energy is already almost clearing the east coast, while the closed 500mb low and positively tiled trough are well back to the west across Texas.
The GFS is very similar synoptically; we have the vortex in position but exiting to the northwest, no closed 50/50 low, and the blocking still there. The GFS forces the Polar jet energy quickly off to the east, while the southern stream low is well back to the west in relatively the same position as where the ECMWF has it, over Texas, at 552dm.
120 hour ECMWF valid 12z Thursday
http://web.wright-weather.com/wxp-model ... t_h120.gif
http://web.wright-weather.com/wxp-model ... 20_sfc.gif
By Thursday, the Polar get energy is well off to the east, and absorbed, the 50/50 low remains disorganized, the vortex is exiting out off to the northwest of Baffin Island, toward the Arctic, but what I do find interesting is the s/w nearing the Arrowhead of Minnesota, which may perhaps play a role, but what if any is unclear. Of course I could be making something out of nothing. Anyway, the closed low opens up across the southeast, and the surface low is analyzed off the northeast coast of Florida. If that track is indeed correct, this event would have little effect on anyone, with the exception of maybe South Carolina and Northeast Georgia, if enough cold air damming is in place supplied by 1036 high to the north.
The GFS pretty much is the same. So much so that there really isn’t much else to discuss as far as differences go, everything was pretty much covered above.
GFS 1000-500mb Thicknesses does indicate precipitation type problems across northern Georgia, and Northwestern South Carolina. But this is assuming that the GFS and ECMWF are correct, and besides, it’s a little too early to talk about that.
The placements of the Surface features are pretty similar also, weak surface low pressure off the coast of Florida, and slightly weaker 1028mb High pressure centered over Southern Quebec.
The 0z ETA is slightly more phased; however, the GGEM has now shifted its track also to a more suppressed one also, bringing it into line with the GFS, ECMWF, and previous 12z UKMET. By later in the morning we’ll probably have a better idea of where the GFS and GGEM ensembles stand and where the UKMET is at.
There is still time for things to change once again, but, the window of opportunity is closing pretty quickly.
The two major problems here are the lack of the closed 50/50 low, and the slow eastward progression of the Subtropical jet energy. If it was progressing out quicker, but we still had the northern stream s/w digging in ahead of it, we sill might have been able to get a handoff of energy from the southern stream to the northern branch, but even still, I’d like to have phasing. Remember, a in order for phasing to occur, in most cases the southern branch energy has to come out ahead of the Polar Jet energy, but if the two are relatively close, a handoff of energy sometimes can happen, much like we had in a situation this past January following the clipper. That event was not well forecasted by the models at all, and it was the ETA, which in the end picked up on it.
I'm not giving up here on the system just yet, eventhough, things may not look great. If by 0z This Evening the data (specifically the ECMWF), doesn't show any signs of changes, I'll give up on it, but right now, given that we are still at least 5 days away from it, I see no reason to get caught up in the model differences.
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