After the MJO/tropical weakened during the last week of February, the pacific pattern changed to -PNA pattern. The west ridge retrograded into NE Pacific. However, this also kept the EPO negative and support for a cross-polar flow into US. So the first five days features wintry threats. Including one that gave many parts of the 4″ to 8″ of snow on Thursday, March 5th. We have now finally much warmer temperatures today and for much of this week.Well, enjoy it, because it now looks the MJO will be picking up later this month.. Model forecasts are for the MJO to progress and become very strong into between phases 7 and 8. If we reach phases 8, this support a cooler and stormier pattern to return around or after March 20th:
The +PDO still looks favorable for more -EPO/+PNA pattern to continue to reload into early Spring. The -QBO continues to fall as the February value was -28.62. This could lead to more planetary waves impacting the the polar vortex. So even if MJO or tropical forcing doesn’t last long, the +PNA (west coast ridge) will likely return and there are some signs of the NAO may go negative for period as well. As we get later in March, climatology favors less snow for the coastal plain. However, the potential for anomalous pattern to show up again, we can’t rule out entirely another moderate or significant snowfall threat for even the coast. Stay tuned
The 12z GEFS today showing +PNA pattern evolving around March 20th
After historic cold air for February, a moderating trend appears to be in store as we go into March. However the threat more winter storms will continue longer. Today most of region misses out on significant snowstorm to our south. Southern New Jersey saw several inches of snow today. While the rest of the area are saw just snow showers or flurries with very little accumulation. The -PNA (negative Pacific North American Oscillation) will support a storm track further north over the Central and Eastern US for the first week of March.
Currently model guidance shows an upper-level shortwave trough and weak surface low pressure moving through late Sunday afternoon and Sunday night. Model thermal profiles support mainly snow from this system from Central New Jersey . Some light to moderate snowfall accumulations are possible here. This will be fast mover and not a big storm. But light to moderate snowfall accumulations will be possible. This could make for Monday morning commute to work or school hazardous. Again this event just a possibility. We will have to monitor future models for more consistency and details. A small change in the track or strength of this system could result in less precipitation or more of a wintry mix for parts of the area.
18z NAM today model showing snow from CNJ north on Monday morning.
Model guidance is also showing a much larger storm system coming out of the Central Plains, Tuesday afternoon into Wednesday for the Northeast and Mid-Atlantic regions. Some very cold will be already in place on Tuesday morning in the Tri-state area. But the model consensus today is for this storm to to track to over to our west over the Ohio Valley and Great Lakes. Which brings low-level and mid-level warming for any snow and ice to change to rain by late Tuesday night or early Wednesday morning. At this time, the pattern shown on the models would support this solution. There is a deep trough over West Coast and strong ridge over the Southeast US. There is also upper-level low over Western Canada and the could pull this storm further north. The polar vortex is also lifting out SE Canada quickly, without enough high-latitude blocking. However, there is still plenty of time for details to change. For example, if Sunday night system is stronger and phasing with the polar vortex over Southeast Canada, this could cause more confluence and cold high pressure over Northeast. That would force a secondary low off too form off the East coast and at least slow down the warm air intrusion. This would result in heavier snowfall totals or more significant icing. It is possible, the models may not catch on to a solution like this until Monday. I will continue to monitor this system through early next week for any significant changes
18z GFS showing the Wednesday’s storm taking a track into Great Lakes. A deep trough is present over West Coast and big ridge over the East Coast.
Over the last few weeks, we’ve been in a pattern that has feature more extreme arctic intrusion that with the low temperatures that we have for NYC in many years. Record lows where shattered on Friday morning over the Tri-State area. What is amazing is that we seen the Artic Oscillation and North Atlantic Oscillation remain positive. The arctic air is from a combination -EPO and +PNA. The question is how long does this pattern continue. Well the models and ensembles show -EPO/+PNA gradually retrograding into Central Pacific, over next two weeks. Some support for this pattern change is the MJO looking become neutral to unfavorable the next few weeks. As tropical forcing at 200mb and 850mb diminishes in Western Hemisphere and reemerges over the Indian Ocean and Indonesia, during the 2-3 weeks.
200mb anomalies forecast to shifting over Indian Ocean and Indonesia 850mb OLR and Wind Anomalies shifting the MJO/tropical convection into Indian Ocean and Indonesia over the next 2 weeks
However, the Pacfic SSTs continue to show a strong +PDO and weak, west-based +ENSO. If there’s no change here, this could support a reload of -EPO/+PNA again sometime in March, provided we see the forcing mechanism for it again.
Sea-Surface Temperature Anomalies still warm over Eastern Pacific
The ECMWF shows more perturbations with the stratospheric vortex over next 10 days. However, these perturbations appear to be related to changes in troposphere or 200mb-500mb level. There is no significant warming or decrease in westerly winds occurring at 10mb and 60N. Despite more significant warming episodes previously, the stratospheric vortex has remained intact for most part this winter, particularly at 50mb. So I think the AO and NAO will continue remain largely on the positive side going into March Some weak or transient -AO/-NAO episodes are possible from time to time with each polar vortex perturbation.
ECMWF model forecasting little change with stratosphere wind,fluxes and temperatures at between 60-90N
For sensible weather in the Tri-state area, I expect very cold air intrusions to continue this week. Then a gradual moderating trend with temperatures during the first ten days of March. Temperatures will still likely average below normal. But should come out of the deep freeze that we’ve seen the past couple weeks. The southern stream remains active enough, to keep potential going for more wintry threats in this pattern. However, with the lack of high-latitude blocking and a sustained West Coast ridge, don’t expect anything major or historic for the Tri-State area. Chances are flow will wind being too fast over the area, for any cold high pressure to remain to our north or the trough to take extreme negative tilt and close off at 500mb. Parts of Northern and Central New England, which has seen historic snowfall this year, may a different story. But even there the pattern may be to progressive. When any threat on the models appears to be legit, I will discuss more in the wintry wx section.
Miguel Pierre Weather 