01/23/16 Storm Update #4 - A Tough 1st Call

00z guidance last night and 12z guidance today were really good for the area. The models began the north trend last night and continued it this morning. However, there are some disconcerting trends showing up again. Yesterday we talked about how the confluence could prevent heights from rising up the coast, which could keep the storm too far south. Today, there are a couple of new negative trends to worry about if you're looking for big snow accumulations. The first one is a strong s/w in the eastern PAC crashing into the west coast and flattening / propagating the ridge east. The second is a sharp cut-off of snow amounts for areas N&W of NYC, including NW NJ and NEPA, is beginning to show on models.



Here are the difference in 500mb heights between the 06z and 12z GFS model valid 10pm Saturday. Notice on the west side of the 500mb low how heights are higher. This indicates the west coast ridge may be trending to collapse sooner than originally expected. If true, the 500mb trough will have a tough time transitioning from a neutral to negative tilt. As a result, heights along the EC would remain flatter and the storm will track more east than north. Also, notice in northern New England how heights are lower. While the confluence is not strong (and I think an H5 low that closes off quick enough can combat the confluence) it's still a negative trend worth mentioning. Between the collapsing western ridge and confluence this storm has a couple obstacles to overcome.



The 12z EURO showed a very nice storm for majority of the coverage area. The trough is slightly negative and the H5 low itself is strong and compact. The reason why the H5 low does not track any further north than what you see above is because of the flow turning fast over the mid-section of the country. The H5 low takes a track east-northeast instead of north-northeast and this is one of the reasons why a cut-off is showing up for northern areas.



The 18z GFS shows an H5 low slightly north of the EURO for the same time stamp, but notice the trough is a bit more broad and height contours are pointing more east than north. Again, the ridge out west is not helping matters and the H5 low is unable to gain latitude because of it. From this point, it takes a similar track to what the EURO shows and that is more east than north. On top of that, it begins to weaken / shear out because the H5 low closed off almost a full 24 hours before this time stamp.





700mb vertical velocity does a nice job of showing where the best frontogenesis, or lift, will be. Those under high VV's experience enhanced snow rates. Notice on the 12z GFS (top) the VV's extend from D.C. - Philly - NYC but on the 18z GFS (bottom) they are off the coast and no one really gets into the heavier snow bands. The H7 low on the 18z GFS is further east, another indicator models may be trying to hint at an east trend because of the collapsing ridge.



Here is a better look at 500mb heights using the anomalies. Even though heights are amplified into NJ, the H5 low only makes it as far north as VA/NC boarder because the top of the ridge is almost acting as a "downstream" block. Also notice the upper energy entering the west coast and forcing the ridge to track east. Additionally, heights are flat over New England whereas prior runs were shown to be more amplified.

Bottom Line:

Clearly this storm has not finished trending. The timing between when the PAC energy enters the west coast and when H5 closes off will go a long way in determining the final track of the H5 low. If the H5 low closes off and track north-northeast BEFORE the ridge begins propagating east than we'll see a storm track closer to the coast because most likely the 500mb trough will be negatively tilted. If the 500mb trough is neutral, that mean the surface low is likely to take more of an east-southeast track. I am NOT too concerned about the confluence because I think this storm will be strong enough to overcome that weak energy.



This is a very tough 1st call. Models have consistently been showing the DC area getting into the higher snowfall amounts. On top of that, since the H5 low pulls away around there latitude and the trough is negative, an inverted trough / norlun feature is showing up that enhances snow bands over that area.

I think this storm can go either way from anyone north-northeast of Philadelphia. There is a chance the 12"+ amounts reach NYC Metro if the H5 low can track further north, or the jet dynamics turn more favorable to put the CCB over the area for a longer period of time. If NYC Metro gets into the higher snow amounts, naturally those N&W of the city will also see more snow than what this map shows. I think the key over the next 24 hours is to monitor the exact track of the H5 low and where the upper level energy decides to setup. Since the start time of this storm has been pushed back to Saturday morning - between 7-9am - we still have 2 full days of model runs for additional trends. This is huge!

I would be surprised if my 2nd call map still looks like this. We'll see what happens.

Please be sure to join the chat tonight at 10pm. It is located the bottom of the home page. We will analyze the 00z models as they come in starting with the 00z GFS around 10:30pm.

Best,

Frank

Gr8 write up and I was try post on thst jma map that was 20 to 30 for nyc metro and just a scrap north msybe unto bx and msybe my by. But that's a nuts map imo. But would live it.

SoulSingMG wrote:Can we discuss that JMA??

The 18z NAVGEM and JMA are very nice for the area. 12"+

devsman wrote:

snow247 wrote:The fact that we still have a little more than 2 days left to trend makes me feel slightly better about this.

Or worse?

Yes - it could get worse. No denying that. But this storm is so large it would take really dramatic trends for it to get much worse than the 18z GFS IMO.

jimv45 wrote:frank what do you think the chances of this thing giving us valley peeps more snow?

It is very hard to say at this point. The gradient is incredibly tight. I personally think the cut-off is too dramatic. There is a big relative humidity field with this storm. The air should be saturated enough to get snow bands into northern areas. We have to see how far north the frontogenesis gets.

By the way - I will have the specifics around wind and coastal flooding tomorrow.

Errr did anyone see the 00z Euro para it came out finally, its south of the OP and the cutoff is into lower hudson vally and barely gives nyc 6 inches.