New York City Metro Weather

October kicks off with a major change in weather

By: NYCvort, 8:08 PM GMT on September 30, 2011

A look at this morning’s upper level chart reveals a highly amplified pattern, one that includes anomaly positions which are highly in favor of a deep trough developing in the eastern US.

A potent piece of jet energy dropping southward through the midwest will help to spawn an upper low near the Ohio Valley as the main jet stream begins to lift out.

This sub -3 standard deviation low will then continue to circulate near the mid-Atlantic region through early next week.

With the low remaining positioned just to our west for an extended time, a prolonged period of southerly flow in the upper levels will keep the cold air from filtering in too quickly. Thus, we will see a gradual drop in temperatures, with warm highs this afternoon followed by a cooling trend. The real core of the cold air mass doesn’t move in until tomorrow night and Sunday. Temperatures may not make it out of the 50s on Sunday.

Forecasting rain chances will be tricky. A weak surface low is expected to develop just off the coast tonight and act as a focus for warm advection showers.

The NAM is a bit more robust with this feature than the GFS. Then we look to get dry slotted for a short time followed by another chance for showers as dynamic lifting from energy associated with the upper low itself will lead to increasing instability.

The upper low will lift out through the middle of next week, but temperatures will still remain on the cool side as plenty of cold air aloft remains in place. In addition, northwest flow behind the Pacific disturbance that will be responsible for picking up our low will help to deliver another round of cool Canadian air Tuesday night. The GFS also shows strong high pressure building down through the end of next week.

The GFS translates a ridge into the region rather quickly late next week. On the other hand, the ECMWF keeps troughing over the area and doesn’t allow the ridge to really build in until late Columbus Weekend.

So while the GFS would suggest a strong Canadian high coming down late next week, the ECMWF would hold it off until next weekend.

The MJO has recently strengthened and is currently entering into phase 6. It is then expected to orbit into phases 7 and 8 starting later next week.

Here is the MJO composite for an MJO in phases 6, 7, and 8 during this time of year.

We can see that phase 6 is often associated with below normal temperatures along the eastern seaboard this time of year, just like what we are expecting for the next several days. As the MJO continues to orbit into phases 7 and 8, based on our chart this would suggest a significant warming trend with a strong ridge building in the east.

Heights will be rising aloft with drier weather; however, the strong 1032+ surface high, regardless of when it comes down, will significantly limit mixing and moderate the warming a great deal. As a result, temperatures don’t look to get much more than slightly above normal.

So while we will see an upper ridge build in, we will not fully feel the effects of it due to the strong surface high.

-NYCvorttumblr page counter

Updated: 4:34 PM GMT on October 01, 2011


New York City Metro Weather

About NYCvort

I am a meteorologist from New York who has been studying and forecasting the local weather for years. I especially enjoy tracking winter storms.