Monday, January 14, 2013

Modeling Struggles

With this morning's front sliding south through the region, there's still a good bit of uncertainty over precipitation type with the two waves of energy pushing northeast along the front.  Wave one pushes through tonight, with the second wave pushing in tomorrow night and early Wednesday morning.  Both of these waves are generally pretty weak and are sliding northeast along a frontal boundary that will slowly nose south through the region, drawing colder air into the region.

Wave one, which had been modeled to perhaps bring some sleet or snow coatings to parts of the region, looks to be capping its northern precipitation extent across the northern burbs if you believe the NAM.  The Euro and GFS nudge the northern extent of tonight's shower (and/or sleet and snow) shield a bit farther north...and it's possible a brief period of light snow or sleet could fall above Reading and Allentown tonight but odds of anything significant (more than a coating) are small.  However, all of the models send the steadiest precipitation across Delaware and South Jersey...and it will be rain for you guys down to our south.

Wave two is late Tuesday night into Wednesday morning...and the models are waffling all over the place with the handling of this second wave.  Earlier modeling was suppressing this system across South Jersey and Delaware with light snow and rain but last night's models have re-nudged that wave a bit farther north.  This second wave, since it would work into a slightly colder airmass than tonight's, may have a better chance of producing some light snow for parts of the region.  Again, there's a general lack of consistency but the main models all produced this northward nudge overnight.  The model nudge to the north would paint an inch to two inches of snow, if the models are right, across the far northern burbs.  The timing of this wave would suggest a precipitation start before the morning rush on Wednesday but would suggest that the Wednesday morning commute in the far northern burbs would be a bit sluggish.  Turnpike and south on the GFS and Euro would be rain while rain falls generally south of the city on the NAM with wave two.  The NAM waffles the city back and forth between rain and light snow.

The wave of low pressure isn't necessarily stronger as much as the models are struggling handling the strength of the ridge of high pressure to the southeast of the frontal zone, the same ridge that brought us our warm (albeit foggy overnight) start to the day.

Neither of these systems really amount to much in terms of strength -- they are both modest and weak, enough to provide some precipitation and drear but not enough to make you make a bread and milk run to the store. That said, the second system on Wednesday may be the slightly better storm for the snowstarved to get at least a coating, perhaps an inch or two, of snow on Wednesday morning.