ECMWF screaming MAJOR overrunning event (CAD) on Day 7

[donsutherland1]

Over the next several days, the storm that will bring heavy rain to parts of the eastern U.S. will move into eastern Canada and very slowly northeastward from there. Afterward, high pressure will likely build from the upper Midwest to upstate New York/northern New England and slowly east-northeastward from there. It will probably have a central pressure of 1035 mb to 1040 mb, perhaps a little stronger.

In the meantime, a weak ridge of high pressure should build into Spain, though by the weekend it should be centered over eastern Spain. Consequently, one can look for a weak ridge out over the Atlantic Ocean. In its position, it should:

1) ensure that the storm does not escape out to sea (suppressed track) as shown on the 12/10 0Z run of the GFS
2) ensure that the storm turns northward.

Given high pressure over upstate New York or northern New England by Sunday, along with what the ensembles show will likely be a neutral to somewhat negative NAO, I do not believe that this system will cut to the west of the Appalachians.

Rather, one center will probably move northeastward along the Appalachians sparking secondary cyclogenesis east of Cape Hatteras. This secondary system will eventually become the primary system as it tracks east-northeastward offshore but not far from the Coast (perhaps by the time it reaches the Delmarva?).

I do not believe that the high pressure over eastern Canada will race off to the northeast as quickly as depicted on the latest 12Z run of the ECMWF. Rather, I expect a slower drift of the high. Thus, the exit of cold air should be delayed sufficiently to afford the big cities at least a period of accumulating snow. How much? That remains the question.

At this time, I believe that interior sections of the Mid-Atlantic and Northeast i.e. Harrisburg, Albany, etc., have a real possibility of being plastered by a heavy wet snowfall. Local amounts could exceed a foot. The big cities from Philadelphia to Boston will probably start with accumulating snow changing to rain and then end with more snow possibly with some additional accumulation. All said, these cities will probably see at least a few inches of snow and possibly more especially if the high largely holds in place.

Finally, since 12/4, there have been several days in which the above normal height anomalies have linked up across North America. Such a linking-up, especially when it is sustained, has sometimes been a precursor of significant Arctic outbreaks in the past. With some signs that the pool of coldest air may be starting to expand to our side of the North Pole, this is a situation that will bear watching, especially as there are also hints that a strong low could take residence near the Aleutian Islands in the near-term.

Should such an Arctic outbreak occur--and it's not yet a certainty--it appears that it could begin to overspread the eastern U.S. sometime between 12/19-23 perhaps preceded by an important storm (between 12/18 and 22?) that could lead to the Ohio Valley, northern Mid-Atlantic and Northeast enjoying snowcover for Christmas.

[donsutherland1]

RNS,

I agree with you. The ECMWF appears to be doing a poor job with regard to the 12/15 system. BTW, as you make the comparison with the Christmas Day nor'easter, if I recall correctly, the Euro also had difficulty handling that system.

[RNS]

RNS,

I agree with you. The ECMWF appears to be doing a poor job with regard to the 12/15 system. BTW, as you make the comparison with the Christmas Day nor'easter, if I recall correctly, the Euro also had difficulty handling that system.

personally...all the model output aside...if one looks at the evolution of the pattern the system looks alot like Xmas 02 or the early jan noreaster...but the only difference is the high to the north which leads me to think that the system (though running up along or west of the mountains initially)...will transfer energy to the coast further south than xmas or jan 03 (due to the supressive high) and will be a rapid deepener. (I.E... bomb cyclogenesis.) So right now i see this as an ice problem for DC and BWI...perhaps PHL (though prob biased more toward snow there as well as in NYC and BOX).

in these situations you cant take the model output seriously...this is where an understanding of the trend of the pattern becomes HIGHLY important. So if one can find a mean between the EC and GFS...IMO thats your storm.

[RNS]

New 0z GGEM:

I want folks to notice something here...and it aruges strongly against the EC...



Notice that while we have ridging over spain at 108 hours...the flow is still somewhat split across the central ATL w/ neg tilted H5 trough...this would help to pump the ridge to the north of it and strengthen the blocking in eastern greenland (notice the height rises taking place along the easten shore). this would help to hold the trough over quebec and newfoundland. therefore the high would be forced to move slower...and the teleconnection between the ridge over spain will be mitigated enough so that the system is not an inland runner...but the effect of the teleconnection is still indirectly present (helping to turn the system up instead of shearing it out).



as we can see here...the canadian has aclassic miller B scenario...w/ the reack of low pressure from the outerbanks to just southeast of nova scotia.

[JCT777]

RNS & donsutherland - Great posts, and I am anxious to see how the models trend over the next few days.

[donsutherland1]

RNS,

Your comparison to the XMAS 2002 nor'easter with colder air is a good one. I expect the modeling to begin to trend in that direction over the next day or two. The mean you suggest between the GFS and ECMWF looks like as good an idea as is possible at this time.

[Stephanie]

So far the forecast for Sunday is a mixture of rain/snow/ice. Rob Guarino from Fox Philadelphia is still suggesting another winter storm but later next week? Actually, up until yesterday, Sunday was supposed to be nice.

[CaptinCrunch]

All of our local news channels for Dallas/Ft Worth are calling for the chance of snow mix with sleet friday night thru saturday afternon, lets hope they are right.....

[Suncat]

The NWS as of Wednesday morning is only calling for a 30 percent chance of rain on Sunday for central NC. No mention of frozen precip.

[jpp5862]

Here in Charlotte they have a 50% chance of freezing rain or rain, with temperatures in the lower 40's. There is clearly a huge degree of uncertainty in their forecast. The Duke Power meteorologists indicate precip amounts here will be light, so if we get any frozen precip it won't be a major event.

Still a long ways out though, anything can happen. They have lowered temps significantly, almost 15 degrees since Monday. We'll see.

[verycoolnin]

Rain is predicted here for Sunday