Level 1 Alert For the Mid Atlantic Into Southern New England

Level 1 Alert : On Guard. This means conditions look favorable for a significant winter event across the region

Alright the first thing we are going to talk about is the pattern that is in place. We have strong Greenland blocking along with a –NAO and a –AO. The one teleconnector that we are missing at this point and time is a positive PNA.

Why is this pattern important? Well this pattern is important because there is a potential storm on the horizon.

History of this particular system on the models has been a little frustrating because we have gone from Major East Coast Snowstorm to nothing. European computer model had a MECS for 4 runs in a row & then after that the following run sent the system out to sea off Hatteras.

The GFS for the longest time was not showing the system & then corrected itself and has its last 3 out of 4 runs shown a major east coast snowstorm. It too had one run where it lost the system.

So lets look at the surface maps of the GFS of the last 3 of the 4 runs.

As you can see from looking at the surface maps the GFS has been showing a decent Major East Coast Storm from anywhere from 6 inches to as much as 2 feet depending on where you reside.

Keep in mind the 12 Z lost the system but I am going to explain why .

This is the 500 mb chart off the 18 Z gfs. As you can see i have a S/W circled in red. This S/W is important as the 18 Z model, 00z Model and 6 Z model all had this S/W stronger and diving down into the backside of the trough which causes it to amplify and go negative tilt and you see the results in the system at the surface in the images above. If you look at these images you will see the same thing..

Now lets look at the 12 Z GFS.. Here you see that same S/W ..however you notice that out ahead of it is some ridging and this ridging prevents the S/W from diving down the backside of the trough which does not allow the trough to go negative tilt which does not allow the system to phase and hence it slides off the SE coast and does not effect the NE.

Lets look at the other models from today…

12 Z ECM today is basically a swing and a miss due to the phase occurring to late so it allows the system to slide off the east coast around Hatteras. However..compared to its 00z run the night before it was more amplified. So a step back in the right direction for those who would like to see a snowstorm out of this. Keep in mind that the ECM was the first model to sniff out and show a SECS or MECS for this period before backing off.

Now lets look at the means of the ECM

First is last nights 00z ECM means and we are going to only look at one image here.

As you can see that was pretty far off to the NE and out over the open waters of the Atlantic. Now lets look at the 12 Z ECM means

The means have actually come Southwest and are close to the benchmark which almost all the Significant Snowstorms end up tracking too.

Now lets look at the UKMET from last night and also from 12 Z.

As you can see the UKMET stands out once again to the ECM as a Red Flag and would actually be very similar to what the GFS has been showing minus 12 Z. The first image is 00z and with that high pressure off the coast there would be no way for the low to escape off to the east much like the ECM was showing. Today the UKMET is tucked in much closer to the coast and potentially could cause precipitation issues along the coast.

When looking at the modeling today ..and looking at the ensemble means of the models we are seeing more amplification in the means and more amplification in the operational models as well..Minus the 12 Z GFS. The same can even be said for the GGEM despite my not showing it here..

The ECM means have come SW and i find that interesting considering that the UKMET is showing the positioning of the low pressure where it is.

Perhaps another Red Flag to the ECM is the NOGAPS model..

Now normally when it comes to coastal storms the NOGAPS is the most suppressed model because that is the models bias. However..as you can see the model is not as suppressed as what the GFS at 12 Z was. Usually this is another good indicator if you see the NOGAPS and it is more NW then the other models you can generally expect the other models to move more towards the NW.

So with all the above happening and occurring ..Models starting to come back more amplified..means coming back more amplified..Strong greenland blocking…negative NAO..negative AO ..we have decided to issue a Level 1 Alert which means conditions look favorable for a Significant Winter Weather Event across the region. but this does not guarantee that it will happen.
Things to keep an eye on :

1. S/W over the PNW and whether it dives down into the backside of the trough.

2. Does the block retrograde?

3. Split flow causing the vortex to split? One piece remaining east for the cold confluence perspective and the other west for the amplification process?

These are the things to keep an eye on when looking at tonights models and we will continue to monitor the situation!

Stay tuned for more information on this developing storm!