Snow overperformance

 

As of 6Z, a heavy snowband has set over central New Jersey, sending moderate to heavy snow our way. At 5Z, I measured .6 inches in South Plainfield, NJ and there is likely near an inch at this point. The main culprit is 700mb frontogenesis.frontogenesis.gif

We have a few more hours of this band, and as moisture moves in from the south, we will receive even more snow before the precipitation shield finally moves offshore. Final snowfall forecast for central New Jersey: 1.5 to 2″. Meanwhile, south Jersey will not sufficiently recover from the dry air in place and lack of significant uplift. Therefore, revising their forecast down to C-1″.

First call forecast for Friday Snow

Good morning,

GFS 12Z and NAM12Z are in with a relative accumulation consensus between 1 and 2 inches for Central New Jersey. The set-up for this storm is as follows.

We start off with two pieces to this storm, one moving in from the west and one to our south moving up the coast. These areas of precipitation are associated with 500mb vorticity (to the west) and a surface low pressure system (to the south).NAMMA_prec_prec_039.png

The temperature background can be stated succinctly as this: cold enough for snow. The onset of snow will occur in the overnight hours, so temperatures will be on a downward trend from radiational cooling, and any further cooling will help to enhance snow ratios. Winds are out of the S/SW which may warm temperatures in central New Jersey to 32F, but I don’t see warming past freezing. At worst, we will deal with wet slushy snow early Friday morning. By 18Z friday as warm air surges from the south and the sun becomes a problem is when the probability of temperatures breaching freezing becomes most likely. However, most snow will be done falling by this time.

NAMMA_sfc_temp_039.png

The thermal differences between the NAM and GFS are subtle and negligent. That is, if you live in central and north Jersey. Differences between the NAM 12Z and GFS12Z for south jersey are significant and have precipitation type implications. GFS comes in warmer, even above freezing. There is an overstimation of the southern surge of warm air here and an underestimation of the difficulty of moving cold air out. Will settle for 32F in South Jersey as opposed to the 30F the NAM is selling and the 37F the GFS is selling. Hard to settle for above freezing but will not rule out a wintry mix in southern New Jersey early Friday morning.

Investigating this further, the GFS is showing serious errors in its surface wet bulb temperature. A wet bulb of almost 50F over southern New Jersey indicates model error. Not too sure what kind of model error, but this definitely doesn’t seem legitimate. GFSMA_sfc_wetblb_045.png

So throughout the course of early morning Friday, the western energy meets up with the coastal energy and together their precipitation shields expand over the northeast. Heavy snow is most likely to start  between 2AM and 4AM on January 6th.

NAMMA_prec_prec_045.png

The sounding during the onset of snowfall indicates the possibility for heavier snowfall in isolated bands. Total precipitation will range between .1 and .2, which will translate to 1 to 2.5 inches with a 12:1 ratio likely. The GFS and NAM total snow accumulations look like this:

GFSMA_prec_kuchsnow_057.pngNAMMA_prec_kuchsnow_045.png

An average 50/50 blend between the NAM and the GFS in the north and central parts of New Jersey are my going forecast. 90% of the NAM’s accumulations for southern New Jersey is my adjustment to these model simulations. Ultimately, accumulations will come down to where the heaviest snowbands set up that morning, and whether the position of the coastal low moves further west or east as it moves up the coast. Any changes in the position of the low west will increase totals in north and central Jersey, while lowering totals immediately along the coast. Any changes in the low to the east will lower totals everywhere except in southern New Jersey and along the coast, where totals will remain about the same.

Coupe

 

January 3rd, 2017 Weather

Current observations

anim_nerc.gif

With temperatures at 43F and light rain falling, it’s another wet and dreary January day across the northeast. New Jersey is just upstream of the base of a weak negatively tilted trough. A vorticity maxima at 500mb is clearly present to our SW, and vorticity advection is allowing for enhanced uplift in the Maryland/Virginia area. West of this shortwave there exists mostly zonal flow across the entire southern United States. Even the trough associated with a strong vorticity maxima based in Minnesota is very flat.vadv_sf.gif

At the jet level, we see a very broad, but strong feature overlaying a zonally oriented flow.  A jet streak exists over Colorado at the base of the deamplified trough to the north. A secondary jet streak to the east of the northern trough is also present. The left exit region of the southern jet and the right entrance region of the northern jet come together over parts of Iowa and Wisconsin, indicating additional uplift support from the upper levels of the atmosphere here. However, with dewpoints of 10F and precipitable water <0.2, the atmosphere is bone dry and no precipitation is expected over this area. 300mb_sf.gif

A potent cold front is present at the surface, enhanced by the upper level features previously mentioned. A cyclone north of Minnesota can be seen forcing cold air southward across the Great Plains while creating a warm sector just north of the Great Lakes. tadv_sf.gif

The main center of low pressure at the surface is northwest of Minnesota while a secondary low pressure has formed just south of Lake Erie. A tight pressure gradient between the cold, high pressure in the mountain west and the areas of low pressure moving to the east is allowing for very strong winds across the northern great plains into the midwest.pmsl.gif

Forecast

To understand the next few days, a gif of 500mb vorticity is most relevant. This is the 12Z NAM initialized on 1/3/17 showing the next 84 hours. The shortwave producing today’s rain passes through, which is followed by a great amount of energy from the deamplified trough that was north of Minnesota. The trough digs slightly into the Great Lakes region, looping as far south as the Mason Dixon Line before being propelled north again. Ridging in the western Atlantic prevents this trough from digging deep into the eastern United States and promoting cyclogenesis. Additionally, moisture is very limited with this air. Associated with this energy is an Arctic front which will drop temperatures on Thursday 1/4/17. As this front moves through, precipitable water across the northeast will drop below .2 in.12Z-20170103_NAMUS_500_avort.gif

850 mb temperatures over the course of the next few days tell the whole temperature story. Cold air moves south with a more or less zonal orientation, meaning the line of coldest temperatures is more or less west to east. With a tight temperature gradient along the east coast, the chance of cyclogenesis increases from 0% to at least 15%. Clearly within the NAM’s scope of forecast, the temperature gradient remains along the east coast for some time, with the possibility of a shortwave moving in and introducing energy to promote development. In the last frame of the NAM 500mb map, you can see an area of energy moving through the south. This is where the hype for a southern states blizzard comes from. As of now, it is mostly hype as to the specifics of who gets what. However, the set up of this baroclinic zone will promote the development of a strong cyclone with access to not just cold air, but some cold air damming in southern Appalachia.12Z-20170103_NAMUS_850_temp.gif

A summary of temperatures over the next few days at Rutgers  is easily captured with the model’s raw output, as there is a consensus over the next few days of a passing cold front with cooler temperatures. The cold front moves through between Wednesday 1PM and 7PM, which prevents Thursday’s high from getting above 35F.

tempgraph.png

Short term, 1/3/17-1/4/17

Rain will become lighter by 4PM on 1/3/17 as an area of low pressure develops just off the NJ coast, rearranging precipitation around the NW and E of the center of low pressure. Scattered showers are possible again after 10PM on and off through 4AM. The 12Z NAM is depicting the heaviest rainfall moving through around 3-4PM as the low pressure that forms restructures its precipitation shield. The next timestep shows rain quickly moving out.

1zna.png

The moisture sticks around for Wednesday, keeping temperatures above 40, possibly reaching 50 as our warm sector receives additional heat and moisture from the south. Our warmest conditions will likely be just before the front moves in. Wednesday appears mostly dry in terms of precipitation as subsidence occurs from upper level mass convergence.

 

Conclusion

It is still far too early to mention specifics about any coastal storms that develop on the eastern United States. The GFS is including a rapidly developing storm that impacts eastern New England but there is no run to  run consistency in this solution. As the energy associated with the potentially blockbuster storms moves onto the west coast of the United States, model consensus will likely become more apparent. At the very least, we will be able to come to an agreement about what is NOT possible.

Coupe