1145 EST 15 JAN
The FIRST issue we have to deal wth is in the short term and wave of Low pressure which is going to develop on the cold front on the 17th and 18th as it moves through the Midwest and towards the East coast. Although this is going to be primarily a rain event for the Ohio valley and all of the Deep South… from Virginia and northward into the big cities of I 95 –there is some uncertainty as to the precipitation type and how long frozen precipitation is going to last before changes over to rain.
All the models agree that at 60 hours — the afternoon of the 17th –there going to be two areas of Low pressure over the middle portion of the country. One will be the Great Lakes and the other over the Delta. Originally it looked like the southern Low was going to track up the Appalachians or just west of it ….which would ensure that most of the precipitation (even into southeastern New England ) would fall as rain or snow rapidly changing over to rain. However the new model data is showing the southern Low developing a bit stronger and tracking much further to the east. The Oz GFS the 6z GFS and the 0z EURO a fairly strongly with the coastal low taking over by the inning of the 18th .
Complicating this even further it is the arrival the fresh cold area of High pressure on Sunday and Monday across the Great Lakes and into New England. If the cold HIGH was to stay locked in over the Northeast ….then this event could be a lot more snow and sleet then rain for anybody from Virginia to Maine but that is not going to happen.
There is no blocking feature in the jet stream over Eastern Canada and / or Greenland and there is no Low either at the surface or in the upper levels over southeastern Canada. This means that the cold High IS going to slide off the New England coast so winds will NOT stay NE but turn to a East direction. This in turn means the cold air over the coastal Plains of the NE will get eaten away.
For the Great lakes and the northern portions of the Ohio Valley and for the interior portions of the Northeast …such as western and central PA and NY this will be primarily a snow going over to sleet event and significant accumulations are likely .
However for the NE quadrant of the nation — Maine to Virginia –the key is going to be the timing and arrival of the precipitation over the Northeast. IF the precipitation begins early enough that it will start as snow or sleet over western VA and MD. It MIGHT begin as frozen precipitation over central and eastern VA and eastern MD but it should quickly change over to rain there. But over WVA western 1/3 of VA western third of MD significant snow & ice is a real possibility especially if the Cold High manges to keep the WEDGE of cold air in place over the VA Piedmont.
For the big cities of I95 – DCA to BOS… There is little doubt that the southern portion of the big cities – DCA BWI PHl cities will change over to sleet then rain. However over NYC CT and BOS more than half of the total precipitation may be either snow or sleet with additional accumulations possible and the precipitation and being as rain .
Down the road the pattern shows more promise if you like cold weather and winter precipitation. So far this winter three have been distinct blocking intervals or episodes in the atmosphere over the western hemisphere. The Blocking has been the development of a bubble or block over Greenland which has retrograded — moved west and set of east– into Eastern Canada and then eventually into North Central Canada and then into Alaska.
It is the repeating re-development of this block which has caused the pattern to become cold and stormy. In the last two episodes of the blocking we saw two very distinct major East coast winter storms which occurred as the blocking episodes were weakening or falling apart. The first coastal storm was the December 25 – 26 nor’easter… which is coming at the end of the very strong 2 week blocking episode which is falling apart over North Central Canada. The second event was the January 10-12 coastal storm which was a major event from Alabama to Boston — except for Central and western Virginia — which also a occurred as a intense blocking episode over Eastern Canada was coming to an end.
After the January 18 event the models all show a strong cold front which is going to drive deep into the Plains and into the Deep South. The European model on Friday the January 14 develop significant low pressure on the front…. as cold HIGH pressure moved into Montreal and Vermont. You can see what the model was showing here.
If the European model is correct it would be a major winter storm…. bringing possibly significant ice into Northern Georgia northwest SC much of NC and snow over much of VA into MD southern WVA DE and possibly into southern PA and southern NJ. The 0z SATURDAY EURO continues to show this event for JAN 21-22.
The 12z GFS and GFS ensemble from yesterday did not support this solution at all . Those Models show just large cold arctic High dominating the weather east of the Rockies and especially Eastern Mississippi River. And the 0z SATURDAY and 6z GFS continue to show no such event of any kind around January 21-22. Not surprisingly the 0z European and European ensembles continue to show a significant event .
Because this is a southern stream feature –that is to say the Low pressure area is a piece of energy in the southern jet stream which will be coming out of the Gulf coast or Delta region – it is likely that the GFS Models which do not handle southern features well at all ….will continue to not see the system until about 72 HRS before the event .
Instead the 0z GFS has a major coastal event developing around January 25. The model does this because it takes the blocking which develops east of Greenland and pulls it back towards Greenland and then Northeast Canada.
Longer term the European model yesterday showed a the return of a massive blocking feature over Greenland. This would be in the fourth major episode of strong Blocking over Greenland ( called a -NAO Iin the weather biz) and it’s not even February 1 yet.
The data this morning however is not quite as impressive with this potential blocking feature. The European model shows the the strong block developing but has it east of Greenland closer towards Iceland…. and this is supported by the GFS and GFS ensemble.
When the blocking develops east of Grenland — is called EAST BASED – NAO. When the blocking is over Greenland or northeastern Canada it is referred to in the weather biz as a WEST BASED -NAO. Got it?
If you like big East coast snowstorms then you want a good strong -NAO feature to help set up the overall winter pattern in the jet stream. However there is a difference as to the favorability of a EAST BASED -NAO vs WEST BASED -NAO. The western -NAO there is the entire East coast (see DEC 25-26 and JAN 11-12) whereas as a eastern based -NAO favors NYC to BOS.
At this Point I believe that even if we do end up seeing a east BASED -NAO initially did well retrograted back in court Greenland and northeastern Canada before the end of the month which will set up another stormy episode for the eastern third of the Conus.