Teleconnections (2130 1/16)
Consensus to a significant drop of the AO, including a drop to neutral or negative by all models by the 23rd.
The NAO also now has a consensus of neutral to negative by the 23rd plus a significant fall by at least 50%.
The PNA forecast still remains neutral although a slow positive rise.
We have for the first time since October a projection for a true greenland block setting up. As I have repeated over and over, our blocking periods have had the set up too far east. With a negative AO projected, we have a shot at blocking developing closer to 30W.
This entire set of forecast data is a new sight for the 06-07 winter season, and a welcome sight indeed.
Essentially, the 19th storm is going to reinforce cold air across the region and encourage an already falling AO. With the AO out of the extreme positives, and especially with one dropping to neutral/negative, block potential closer the Greenland will kill the southeast ridge and allow for an east coast trough to form. This will set the stage for the event that I have spoken so frequently about: The 23rd.
UPDATE (710): Front has passed the area, and temperatures have started dropping off quickly. At the airport, temperatures have fallen from 34 at 6:15am to 27 degrees at 6:55am. A drop of 7 degrees in 40 minutes. At 1000ft (my house) temperatures have fallen from 31.1 at 6:15am to 22.5 currently; a fall of 8.6 degrees in 55 minutes. Winds have become gusty and scattered flurries and snow showers have moved in. Be careful on the roads this morning with icy conditions plus possible down branches and power lines.
Before I launch into impending pattern change, I would like to announce with lots of enthusiam that SAU29 HAS A TWO HOUR DELAY! So at least something good happened with this storm. A storm summary will be posted in the winter weather outlook page later this morning.
...Moving on...
Temperatures are the big story this morning, and will continue to by so through tomorrow night. The cold front associated with yesterday's storm has passed the area, however warmth out ahead of a secondary front will mean temperatures wont start falling until 8am or so. There is a sharp temperature difference between SW NH and Southen VT right now with Keene sitting at 36 and Springfield at 21. Those temperatures will be arriving here shortly. Philadelphia, PA and Trenton, NJ both have wild tales of temperatures to tell this morning as a surge of warmth ahead of the front brought temperatures into the low 60's! Trenton and Philly both tied their record highs for today... at midnight! The front has now passed on to the west, and temperatures have started their plunge. Anyone along the east coast that woke up to balmy conditions this morning, will be in for a suprise as temperatures fall a solid 20 to 30 degrees by this evening. Tonight, temperatures will just keep going, down below zero possibly for the first time this season. Tomorrow will mark the peak of the cold, with highs barely making the teens! Tomorrow night will have another shot at sub zero temperatures. Through all this, winds gusting up to 25mph to 30mph behind the front will continue on into Wednesday. The combination of the winds and cold will produce a windchill of around 20 below zero. Windchill advisories may be issued later today. Take precaution when going outside tonight. In windchills of -20, frostbite occurs on exposed skin in 30 minutes.
Warmer air will return to the region (although still below average by a few degrees) on Thursday, as a southerly flow develops out ahead of a storm system approaching from the west. This is our first potential event. The GFS and NAM continue to indicate secondary development along the front. The problem being now, that the primary low may be moving too fast for phasing to occur. Even if phasing does occur, the latest projections indicate we will likely have track issues to contend with. Whatever the case will be, additional moisture flow will allow for at least moderate accumulations of snow on Friday. One thing that I am glad about though, is that with this storm, cold air will not be an issue for once, as it will be in place to start with.
Behind the storm, a reinforcement of cold air will overspread the region, along with high pressure bringing dry conditions to New England. The weekend looks beautiful right now, if you dont mind the cold. Highs will reach the low 20's, and lows will fall into the single digits.
The second storm to watch is the 23rd event which I have talked about for three weeks now. This storm has had support from the GFS for many runs now. Obviously, variables such as track and temperature have been fluctuating significantly in some of the runs, but the low itself has stayed.
In the case of temperatures, while cold air will be in place over New England, a southeast ridge, which refuses to break down (even with this latest surge of cold) might complicate the forecast.
The ridge shown by the 06z ECMWF:
Track wise, the GFS has been far off the coast for a few runs now, enough to make me a little nervous. If the NAO can go negative behind the Friday storm, then we have a shot with some blocking developing to the east. Without it, the 23rd will just be another cold dry day.
Another arctic surge will bring temperatures back into the teens and 20's by mid week, then another storm threat appears late week. This one has had some minimal discussion, but will mention it nonetheless. The GFS does take this one well east of the region, but this storm will stronger than the our first two events. If nothing else, this will likely be a significant marine hazard.
|posted by Sam Lillo @ 1/16/2007 05:44:00 AM
