With yesterdays low pressure and associated cold front clearing the majority of the central/eastern US, high pressure has built in, providing cool but mainly dry conditions east of the Rockies. This won’t last long however, as a series of systems is expected to move out of the western US and affect the central and eastern US starting this weekend.
A current look at the weather pattern at 18,000 feet up reveals that the much anticipated blocking ridges of high pressure are developing over central Canada and also over Greenland, forcing the deep upper low over southeastern Canada to remain in place, forcing well below temperatures south into much of the US east of the Rockies. Note also how there is a very active Pacific jet, with one storm sitting off the west coast and another near Alaska, with very tightly packed height lines indicating a strong jet. This Pacific jet is what will increase precipitation chances for parts of the central/eastern US starting this weekend.
A look at the European model (ECMWF) forecast for Saturday morning shows the first piece of energy ejecting out of the Rockies into the Plains. Note how the model shows a bit of a buckle in the flow at 500mb (18,000 feet up) along with some vorticity (which results in large scale lift) moving into the Plains in the upper left panel. Also note how there is some mid level moisture (bottom panels) moving into the Plains, some of it in air cold enough for snow (850mb or 5000ft temperatures in bottom right, solid black line is freezing line at this level). The combination of some modest upper level lift in combination with moisture in the cold air will result in a swath of accumulating snow.
Note how by Sunday morning the European model shows the first piece of energy already moving off the southeast coast. However, note how there is some moisture in the colder air over the Mid Atlantic. This makes it reasonable to assume a swath of accumulating snow will occur from the high Plains east through the upper Mississippi Valley, Ohio Valley and lower Mid Atlantic. Right now it looks like parts of South Dakota, Nebraska, northern Missouri, southern 2/3rds of Iowa, northern 2/3rds of IL, southern IN, southern OH, WV, northern 2/3rds of VA, parts of MD, and possibly into southern PA, NJ and most of DE will be the areas that have the best shot at accumulating snow. Right now I think accumulations will range from 4-8” in a narrow band over the Plains, diminishing to 2-4” by the Ohio Valley, and then continuing east with possibly higher amounts over the mountains of WV and VA.
The reasoning for this forecast is that as the system moves east it will be fast moving, meaning only a short period of precipitation at any one location. Notice how the storm moves from the Plains to the east coast in 24 hours. In addition, note how the 500mb height lines (upper left panels in the model images) are tightly packed over the Great Lakes and northeast due to the large upper low near those locations. This is called “confluence” and will make it hard for the storm to track much farther north. In fact, it may cause the storm to weaken slightly as it moves east from the Plains. The Hydrometeorlogical Prediction Center picks up on this snow threat well, with a thin slight to moderate risk for heavy (4”+) of snow for Saturday and Sunday from the Plains east:
Note how cities like Baltimore and Washington appear to have a decent shot at a late season accumulating snow with this system.
As we move forward, the models have continued to suppress the storm that they were previously showing for the Monday-Wednesday timeframe. Let’s look at why:
Today’s run of the European model, valid Monday morning, shows the energy that was originally progged to possibly be a major storm moving out into the Plains. Initially, the models were moving this out a little faster, Sunday evening as opposed to Monday morning. In addition, note how the Euro, shown above, has the lobe of energy that was originally shown dropping into the Plains and phasing with the energy moving out of the west, dropping down farther east and sooner than what was originally forecasted.
What this does is allow cold, dry air and high pressure to spill well south ahead of the energy moving out of the western US, which essentially causes the energy moving out of the west to hit a brick wall, move farther south and remain weak.
Note how by Wednesday morning the European model shows what’s left of the energy moving through the eastern US. However, with a strong surface high pressure in place low level moisture has a hard time moving north. In addition, there is virtually no surface reflection with the energy as it moves east, meaning at best the European model would produce some light rain/snow mainly south of I-70 Tuesday-Wednesday as it brings the energy east.
The Canadian model (GGEM) agrees with the European model, showing no real storm over the east and mainly light precipitation. The Canadian keeps the vast majority of the precipitation south in the warmer air, as well.
The GFS model on the other hand shows no storm with the energy that moves east Monday-Wednesday, but instead ejects the next piece of energy much faster than the other models as shows a storm cutting into the Great lakes on Wednesday:
Right now there is very little support for the GFS solution. The reason being that NO other model shows as much ridging on the western US coast as the GFS, meaning they are all slower in amplifying the next piece of energy and ejecting it east.
As we look ahead a little at the large scale pattern for next Wednesday morning, note how the European ensembles, as discussed yesterday, break down the blocking high over Greenland (called a –NAO) and begin lifting the upper low from southeastern Canada northeastward towards Greenland. This allows heights to slowly rise over the east and allows temperatures to slowly warm.
The European ensembles also show the next piece of energy that will move out of the west late next week. The European ensembles, along with every other model not called the GFS are much slower in bringing this energy out.
This next piece of energy will likely stand the best chance out of all these pieces of energy of strengthening and developing into a strong storm east of the Rockies late next week. The reasoning being that the upper low will lift away from the northeastern US which will allow the confluence discussed earlier to weaken, which will give storms more room to intensify and move north, without getting suppressed or sheared out by a strong upper low.
Where this next storm goes is still a question, however with the –NAO block gone it is likely it may cut inland, somewhere, so the big cities may see a rainy solution. More on this in the coming days.
A note on the warm up starting late next week discussed yesterday. It still appears the –NAO will break down by mid next week and the Pacific will dominate the pattern by late next week. This will flood most of the nation, excluding the northwest, with milder air. Note how the European ensembles go from showing a large area of temperatures 5 to 10 degrees Celsius below normal from Friday-Tuesday to showing a smaller area of temperatures only 1 to 3 Celsius degrees below normal next Wednesday-Sunday, showing the warm up I mentioned yesterday: