Mid Week Storm System What Is In Store?

This is the question that is burning up the internet right now as to what is going to happen with the mid week storm system. Will this be a snowstorm or will this be a cold rain storm or will this be a snow changing to rain storm. Well..we are going to attempt to answer this question with many maps from the guidance tonight from the GFS to the GGEM to the UKMET to the ECM and even the Nogaps..We are even going to look at the teleconections and see what these suggest as well.

So we will take a look at the teleonnections first..

Now the first thing we notice is that the Arctic Oscillation is positive.  Now many people may not understand what a positive or a negative AO means so here is the definition explained..

“In the negative phase, the polar low pressure system (also known as the polar vortex) over the Arctic is weaker, which results in weaker upper level winds (the westerlies). The result of the weaker westerlies is that cold, Arctic air is able to push farther south into the U.S., while the storm track also remains farther south. The opposite is true when the AO is positive: the polar circulation is stronger which forces cold air and storms to remain farther north. “

So according to the definition above a positive AO indicates a further north storm track and cold air is also locked further to the north and not able to dive as far south..

Now this is the North Atlantic Oscillation and what you can see by the above is that the NAO is positive. What exactly does this mean?

“

During a positive NAO there is a strengthening of the Icelandic low and Azores high. This strengthening results in an increased pressure gradient over the North Atlantic, which cause the westerlies to increase in strength. The increased westerlies allow cold air to drain off the North American continent rather than letting it build up and move south.

• Above average geopotential heights  are observed over the eastern U.S., which correlates to above average temperatures

• The eastern U.S. often sees a wetter pattern with stronger storms during the winter season in this phase due to increased upper level winds”

Well..what we see here is that there is no mechanism to keep colder air in place and that it leads to above average heights which correlate to above average temperatures. We also see that it also leads to stronger storms during the winter season.

So pretty much so far we are seeing two teleconnections that are against a snowstorm.

The PNA you can see is on the declining slide into negative territory. What does this mean?

“The negative phase of the PNA pattern features below average geopotential heights over the western U.S., and above average geopotential heights across the eastern U.S. This results in deep troughing over the western U.S., which allows cold air from western Canada to drain southward into this region. In the eastern U.S., warm, moist air from the Gulf of Mexico and the Atlantic Ocean is able to travel northward, often resulting in above normal temperatures “

This generally means that the colder air will be situated across the west and warmer then average temperatures will be across the east. In other words the exact opposite of a + PNA which would put the trough in the east and ridging into the west. Ridging into the west would result in stronger amplification of the pattern.

So we have a + NAO & a + AO along with a PNA going into the negative state. All this points to milder conditions in the east…a  lack of a mechanism to lock in any colder air (blocking) and the pattern to be progressive but with the coldest air into the west or Pacific Northwest region.

So the teleconnections themselves suggest a further north storm track with lack of cold air having the staying power…

So lets look at the guidance and see what it is suggesting and we are going to look at 90-120 hours on the guidance.

First up the GFS..

Now, what we see here is a primary that is heading towards the Great Lakes. This never bodes well for east coast snowstorms..Why? When you have a low cutting to the west and becoming vertically stacked such as is you have a warm southerly flow going out ahead of the main system. And we see this happening on the GFS with the only area at 90 hrs. cold enough for winter precipitation would be NE PA into Northern New Jersey and of course north of that area. (Remember + AO and + NAO where it provides the colder air and the storm track?)

However what happens is by 96 hrs. that 850 line goes north and we have a change over to rain in those locations.

By 108 hrs. we have a secondary develop from the primary but it develops to far north( + AO + NAO)  to have any major effect on PA.. So we have a wintry precipitation change to rain and end up with mainly a rain event in the PA/NJ area…

Now this is the link to the GGEM precipitation images and it covers thru 120 hours. (click here)

What we notice here is that it is along the same line of thinking with beginning as snow/ice across the same regions but then changes to rain and then rain along the coast in places like NYC..

We see one difference here in that the GGEM does not really develop a secondary but more or less moves a weak batch of moisture thru and this weak batch of moisture is mainly rain along the coast in places like NYC that could end as some flurries or sleet… Of course further north of those regions we are talking a more winter type event. Again remember the effects of the teleconnections in place.

UKMET we see is along the same lines as the GFS for the most part with the primary to the west at 96 hrs. with ridging into the east and it develops the secondary and is pretty far north at 120 hours out.

Even the progressive biased NOGAPS is in agreement with the above first part of the system and for the second half it ends up more or less closer to the GGEM with just w weaker batch of moisture moving across the region..

Finally this brings us to the ECM..

Well… from looking at this image we see the ECM as well brings warmer southerly flow into the region and it also begins off as snow in generally the same areas prior to this time frame but with the 850s this warm at 96 hrs. it would indicate a change over in the PA NJ regions..but now we see where the ECM becomes different at 120 hours..

Now the ECM is further south with the secondary then the rest of the guidance. Many people look at this model as the most accurate model ..however..the model is alone in being this far south and furthermore ..this southern solution for the secondary ..does not fit with the telconnections that are in place. Furthermore interestingly enough is when you turn to the ensemble means..

We are looking at a further NE position of that low and more progressive which is more fitting of the pattern.

So in summary..with the teleconnections in place and the southerly flow out ahead of the system and the lack of any locking mechanism for the colder air to stay in place..the best case scenario for winter weather lovers is a snow or snow/ice mix changing over to rain and the most prone areas for this to occur would be Northeast PA into Northern New Jersey..Of course north of that region has the best potential for a winter storm.

This is based on the guidance above along with the teleconnections & pattern that is in place. Speaking of pattern..this is what CPC put out earlier in the day yesterday..

This storm is probably winter last hurrah comparable to Custards last stand.

Later tonight we will put out a scenario map ! Stay tuned!