The winter of 2009-10 continues to move up the ranks as one of the snowiest winters on record for a large geographical area, from Texas/southern plains, eastward through the deep South, and northeastward through the Mid atlantic states. The northern extent of the highly anomalous snow totals reaches central NJ and much of Long Island, just southeast of NYC itself. Central Park is sitting at a little over 30" of snow for the season, which qualifies as above average, but I can guarantee that total will not be final. The overall pattern regime is impressive in that we have historic blocking over the pole (AO values this winter are record territory - very negative), a strong sub tropical jet stream induced by the moderate to strong intensity El Nino, and ridging over the Western US (+PNA/-EPO), aiding in the transport of polar air into the Eastern US. Two major stratospheric warming events this winter -- one in mid November and the other in mid January, largely initiated the downward propagation of warmth below the tropopause and thus severe blocking across the northern latitudes resulted.
Note the AO GFS ensemble forecast for the near future; the AO will rise dramatically from standard deviations of -4/-5 to neutral by early March. This is a very strong Archambault signal for hvy precipitation events on the east coast. When one sees these AO sharp rises, it suggests pressure falls in the Eastern US are likely.
Below is the 00z ECMWF depiction of this system I'm referrencing -- valid Sunday at 00z:
If we take a look at the pattern over the next couple weeks, we have a short wave that will be causing problems for northwestern zones tomorrow (snow to sleet/freezing rain) and another more complex wave which will probably phase offshore and veer northward into New England by Friday. This second storm could end up as a major to historic blizzard for much of interior New England; wrap-arond snows may impact the NYC metro area if the low center retrogrades far enough west. However, at this point I don't believe the late week system will produce significant or major snows across the majority of our area. The potential threat I have my eye on comes about 7-8 days from now, in the beginning of March. Fairly impressive model consensus on a powerful short wave ejecting from the southern stream late week, in the SW US by this weekend, and moving cross-country by March 1st, then northeastward to the mid atlantic coast by March 2nd/3rd. Below I'm going to explain some crucial signals which argue in favor of this storm being potentially significant for us.
Note the AO GFS ensemble forecast for the near future; the AO will rise dramatically from standard deviations of -4/-5 to neutral by early March. This is a very strong Archambault signal for hvy precipitation events on the east coast. When one sees these AO sharp rises, it suggests pressure falls in the Eastern US are likely.
Below is the 00z ECMWF depiction of this system I'm referrencing -- valid Sunday at 00z:
By the time we reach the middle of next week, the low is vertically stacked with a couple closed contours at 500mb, and the surface reflection has a powerful nor'easter bombing along the mid atlantic coast.
Meanwhile tropical forcing provides more support for this potential threat; MJO will be bouncing around phase 8 for the beginning of March, which is a favorable octet for east coast storminess. In fact, all of the KU events of this winter occurred in phases 7-8 of the MJO. Classic mod-strong el nino trend.
If the early March system does not end up producing a snow event for our area, there should be more threats until the middle of March before we see a pattern breakdown. After all, blocking of this magnitude can only persist for so long. There is evidence in analogs and pattern progression that the neg NAO and pos PNA will remain intact for another 2-3 weeks at least. Thus I have a hard time seeing any sustained spring weather in our area until mid/late March at the earliest.
Bottom lines:
- 1) Northwestern zones - wintry mix of precipitation for storm #1 - not a significant snow maker for virtually everyone in the NYC area.
- 2) Storm #2 will phase offshore, veer northward into New England, and slow/stall or even retrograde southwest for 24hours. Major to historic snow producer for much of interior New England, possibly as far south as the Catskills. NYC area may receive wrap-around snows tht don't amount to much.
- 3) Storm #3 - will eject eastward from the southern stream this weekend and may reach our area as early as March 2nd/3rd (Tuesday/Wednesday of next week). This one as the most potential in my eyes; we'll see what transpires.
- 4) Favorable pattern for snow continues until mid March. No sustained spring in sight. Nino analogs to this year indicate a colder than normal March (and snowier than normal).
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