March: A return to real winter

With our last snow event, Keene is now above its seasonal average snowfall. However, the pattern of the last 5 weeks have been far from wintry. With a generally positive or east based NAO, along with a continued raging La Nina, zonal flow across the nation has been above average with below normal heights in the west, and above normal heights over the southeast. So even when we get a strong cold front from Canada to bring below normal temperatures to the region, it never sticks around long enough for the next storm. A strong Pacific Jet whisks away the cold air, a ridge develops over the southeast, and the next southern jet storm system ends up being pushed north into the Great Lakes region. This results in a snow changing to ice or rain senario, similar to the last number of storms we've had.

Our next storm on the horizon is Sunday into Monday. Once again, it is a lakes cutter. A cold air mass moving in tonight and lasting a grand total of 36 hours will allow for precipitation to begin as light snow Sunday afternoon. This will change to rain, freezing rain, and sleet Sunday Night as warm air floods the mid levels, and some of the antecendent cold holds on. No strong high pressure to the north will allow this cold air to be scoured out quickly meaning a quick change to plain rain by Monday morning, with temperatures soaring to the upper 40's.

Behind this storm, normal temperatures will move back into place on Tuesday. The AO has been projected to rise rapidly to near +3SD by the 21st. The NAO is projected to rise to around +1SD, with the PNA positive but falling. However, with a clipper moving through the region on Wednesday with some light snow showers, cold will be reinforced a little while longer. This will be enough to allow for a partial snow event for a couple of storm potentials next weekend and into early next week.

Temperatures will likely be mild through the 27th of February, with a predominant +NAO. The status of the PNA and the AO will dictate exact departures, which could provide a few below normal days between now and then.

At this point, the stratospheric warming that I mentioned will come into play. The initial record rise in 10mb temperatures was a warning shot to the real propogating warming. A second warming occurred 5 days later, and now we are on the verge of this warming event propogating downward. The ECMWF projects warming to begin at least to the 100mb level by next Monday (25). Negative zonal wind anomalies will develop in the artic. This all results in the polar vortex weakening and be displaced southward. In addition, La Nina will begin to weaken. The beginnings of a -NAO should begin by March 1st. The -NAO with strong cold anomalies in the east will support what I think will be two significant snow storms between the 1st and the 15th. The current target time for the first storm is March 2 to 5, and the second storm March 7 to 12. Considering ENSO and the SSW event, analogs include March 2001, and January 1996.