NY NJ PA Weather Forecasts

Cold, Wintery, And Very Difficult Forecast Period

Making this forecast has been and will continue to be very difficult.  I want to touch on some important themes with the pattern as a whole and the state of the model guidance before diving into the actual forecast.

I believe we are about to enter a significant cold, and stormy pattern for much of the eastern two-thirds of the nation and this week will be a step down into that pattern.  I’ve been discussing the evolution of this period for the past two weeks, even though the models have been all over the place.  

First, about the models.  I hope we all learned an important lesson about the state of medium range model guidance so far this season.  Do not trust the details, trust your knowledge and what you know is needed for a snow event.  The GFS, ECMWF, and even the ensembles have all been guilty of advertising extremes.  Extreme cold, extreme warmth, extreme storms.  We’ve seen coastal solutions with snow down to Philadelphia and DC for tomorrow’s storm.  Why all the problems?  The problems stem from the fact that the model guidance has a poor handle on the evolution of the Pacific pattern and the higher latitude blocking due to a lack of a true ENSO state.  As such, if you see an extreme solution being advertised, beware of jumping on board, at least completely.  Remember when guidance showed a very strong negative NAO for this up coming period?  I stated that I wouldn’t believe the intensity, but I like the idea.  Well, the idea of a negative NAO is still there, just not the extreme intensity.  

Given all that, the best way to forecast for this period is to look at the model guidance and combine all the thoughts.  A forecaster in this type of pattern must compare, contrast, and use all guidance to best come up with a forecast.  This year I can promise that the GFS and the ECMWF will have some pretty big busts this winter, but if you follow the rule of moderation, you should be fine in the long run.  

Now with that laid out, let’s discuss this upcoming week.  There is little doubt now that the Arctic air will be on the move.  Again, not extreme cold, but certainly below normal temperatures and the chance for wintery weather will return to the forecast area.  

A strong cold front with Arctic air origins will move towards the Ohio Valley on Tuesday.  The forecast area will be under the influence of high pressure with moderating temperatures towards slightly above normal levels.  Partly cloudy conditions can be expected over the forecast area. 

The difference in the model guidance between the GFS and ECMWF, is the speed of the arctic cold front and the secondary cold fronts to follow.  I went with a blend of the guidance.

On Wednesday, clouds will increase with the cold front reaching the eastern Great Lakes by Wednesday evening.  High pressure will continue to slide east of the forecast area, producing a strengthening southwesterly wind ahead of the cold front.  A few scattered showers will enter the forecast area by Wednesday evening over northeastern Pennsylvania and the central Hudson Valley.

Thursday is the day where the temperatures crash.  Again, the GFS is much faster here in driving the cold front well off the coast by Thursday.  The difference here is the position of the 500 MB low and the upper level winds.  I think the GFS is too fast, but the ECMWF is way too slow here given the model’s upper level position of the jet stream.  I have the cold front moving through, likely in the morning hours, with scattered showers and temperatures falling through the afternoon.  The highs will likely be in the morning with the temperatures falling into the 30’s over much of the forecast area.

The pattern then becomes favorable for some wintery weather for next weekend.  The cold front on all guidance stalls from the North Carolina coast to the Oklahoma Panhandle.  A series of disturbances from the southern branch of the Polar Jet stream will begin to interact with this boundary and set up an environment for wide spread isentropic lifting induced cloud cover and precipitation.  The details are hazy this far out, but there are some key ingredients shown on all the model guidance that is key.

1.  Convergence and confluence at 500 MB from the northern Plains to the eastern Great Lakes.  This convergence and confluence is an important clue that COLD high pressure will be present to the north and west of low pressure develop along this cold front.

2.  The strong upper low setting up over eastern Canada will support a track to the south of the forecast area.  In other words, a track to the north and west of the forecast area is unlikely.  No lake cutters here.  Not in this pattern.  The upper low also appears to set up in such a manner to not suppress the storms too far to the south.  

3. A ridge off the Southeast coast.  A southeast ridge can be very scary to snow lovers, but in this case the ridge will support the evolution of isentropic lifting and thus a mechanism for moisture transportation.  

This low that develops will be a Miller A storm.  Precipitation from this storm likely will not be seen until next Saturday night.  I don’t want to get into details like rain/snow lines and accumulation amounts.  However, I will say that next weekend, especially the Sunday/Monday period will have one of the best potentials since last February for accumulating snowfall for the forecast area.  There is also a risk for mixed precipitation.  There will likely be periods of lulls in the precipitation, so there will be a question as whether to forecast this event as a whole storm or a series of separate disturbances, however the overall idea of cold air pressing south and then the warm air fight back is solid.

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