Tag Archives: Secondary Low


This potential storm for Philadelphia for Tuesday through Wednesday evening has been on the metaphorical radar for almost a week.  The binary nature of the storm and the inherent complexity in modeling such a complex system has pushed the models beyond their limits.

I’ve been ending each of my posts with “expect changes”.  I’ve been doing this for a reason–

There has been tremendous variations in the deterministic model forecast over the past few days.   The main system was expected  on Tuesday, then this system was expected to be suppressed to our south and the Wednesday system further suppressed eastward.

The statistical (Ensemble-based ) models have maintained a strong signal of a storm from Tuesday through Wednesday and have never stopped showing this.

This afternoon’s NAM model has just becoming available.  It shows the Tuesday storm to be relatively minimal, but energy and intensification and phasing of the jet streams now occurs with the second storm on Wednesday. This second system appears to  intensify and hug the coastline!

NAM Forecast for Wednesday morning

So we’re not out of the woods yet! Indeed, if the NAM is correct, we’ll have a major nor’easter for Wednesday.   Due to Daylight Saving Time, the major models will become available very late.

I’ll be traveling this entire week so updates will not be anywhere as frequent as in past storms!  (I must confess, this past Friday, I moved my airline reservations  to Monday instead of  Wednesday to avoid weather-related travel problems.  This morning, I thought I had made a mistake; but maybe not! ) 


Last night’s GFS model continued with the scenario that a low pressure system was going to develop off the coast, but miss us.  However, the recent trends have been to place this system closer to the coast with greater intensification.

This morning’s NAM has suddenly jumped on this scenario, with low pressure in a similar position, but somewhat more intensified, allowing some snow to move in on the western side and into the PHL area late Monday into Monday evening.

[su_note note_color=”#ebf2d9″]With the system evolving, the timing and QPF values and timing are likely to change.  Current QPF is a very light 0.16 inches water.  Currently not much of a ‘storm’, but driving could be slippery on Tuesday morning rush hour as cold air will be in place.[/su_note]

As mentioned in last night’s post, the GFS has been hinting at something happening off the coast.  This weak signal has been strengthened; some winter precip is looking more likely for late Monday.

NAM prediction for Monday evening
Saturday Morning NAM prediction for Monday evening

Expect details and timing to change.