Tuesday, September 20, 2011

This and That.

Starting Thursday, we will be in a prolonged period of wet weather.  The GFS and Euro agree that it will be wet. However, they disagree on the amount of rain we will be getting.  The GFS is showing rainfall amounts that are less than the Euro. The cut off low will have a Southerly flow that will be streaming up moisture into the area. we will have two main periods of rainfall. the first will be Wed night into Thur; the rain doesn't look like it will be all that bad. The 2nd event looks to be Fri Night. We look to see rainfall amounts that could  be as high as 1.5 - 2.0 inches. Saturday thru Tuesday will see off and on rain that will add to the totals.

                          Here is the GFS Accumulated precipitation forecast for Saturday

The Tropics
Still watching invest 98L in the central Atlantic. The system has become fairly well orginized. but it needs the  broad scale circulation to tighten up a bit now before it can close off fully and be declared a tropical depression. it is almost to that stage now, so it should become a named system by tomorrow.  The environment supports some strengthening until about 55W. at the point wind shear increases. and it will be sheared by the  upper-level westerlies. This shear will likely remain around the northeast Caribbean for the next week, making it difficult for 98L to strengthen much beyond a moderate tropical storm, It will be like Maria in the regard that a hurricane seems unlikely.  The track of 98L is fairly straight forward. A WNW track towards the leeward Antilles to the south of the subtropical ridge should be the rule for the next few days, with a more NW turn occurring west of 65W, probably taking 98L into Puerto Rico and Hispaniola.
There are signs that the  Caribbean might become active in 10-15 days, high pressure over eastern North America will stimulate surface convergence in the western Caribbean and allow a storm to try to form.

My Initial winter 2011-2012 thoughts.
With the feel of fall in the air our thoughts ineptly drift to winter and what it will bring.  The current pattern we're starting to experience is a very typical fall pattern. Now while it is too early for making a winter outlook/forecast. It's not too early to start looking at the way the pattern is setting up.  By the middle to end of November the winter pattern will be more or less locked in. The winter pattern starts with a strengthening jet as it makes it's migration south. Something we're just starting to see.  How the jet acts and sets up effects how the troughs will act and move during the winter.  Most agree that the winter of 2011-2012 will see the return of a moderate La Nada. The long range models are supporting this idea, more or less. In fact, looking at the sea surface temps show the La Nina is starting to strengthen. If this is the case, then the key to our upcoming winter will be the return of some strong high pressure blocking over northeastern Canada. The good news is the Euro long-range does not show much if any high pressure setting up over NE Canada. The Bad news is Last year's Euro long range showed some blocking but nowhere near as strong as what actually setup .  Last year was a La Nana and we all know how that turned out. Now if the Euro is right we won't have a block setup this year. This would mean just to our north, in places like Ontario and southern Quebec they would see tons of snow; while we had a warmer than normal winter with more or less normal snowfall. 
There are many such ways people try to use in forecasting long range weather events.  
There is a interesting theory called Lezak's recurring Cycle (LRC), many people don't but much stock in it, But I feel it does have things of interest. So first what the heck is the LRC. Well basically  he believes each year a unique weather pattern will set up between October 1st and November 10th. Lezak believes  once the pattern becomes established it cycles, repeats, and continues through winter, spring and into summer It isn’t just one long-wave trough, storm system, or ridge. It is a sequence of troughs and ridges that are cycling across the Northern Hemisphere within the Prevailing Westerly’s. I've looked back at past winters and feel some of what he is saying has merit. I have seen how it tracked “the storm” in last year's pattern, I have seen how it was responsible for how one area was affected by an event and another wasn’t. But it is still  just a theory about large scale upper air patterns using longwave positions to track 500mb vortices paths. Nothing in this theory talks about surface impact.
There's also a technique used with  Hovmoller diagrams that people try to use in forecasting long range weather events.  This gets very complicated, but it uses Hovmoller Diagrams for Long Range Forecasting of Significant Weather Events . Long range forecasters study the 500 mb height anomalies where they look for atmospheric signals and long wave anchors around the hemisphere. When viewed through wave theory principles, and in conjunction with Fast Fourier Transform applications, a forecaster can theoretically predict Arctic Outbreaks, strong frontal passages, and even severe weather events.

I just thought I would bring this to your attention......I do find them interesting from a forecasting standpoint. Anyway, back to the Jet stream and troughs.
Most of the time you can get an idea of how winter is going to shape up starting now and thru October,  Therefore, I always try to get a feel for the long term pattern around this time. what I'm starting to see is that the trough axis will be such that the Appalachians and into the  NEUS could see quite a bit of snow. The trough axis is the average axis of the troughs that will be  developing during the winter. It acts as the steering mechanism for inland and coastal storms.


At this time, this is how I see the trough axis setting up.  Remember, this is not my official outlook / forecast;  I will issue that in about 6 weeks. The axis will end-up looking different due to the effect of such things as the amplitude of the flow, but I do think, it will be close to what I show in the above chart. A trough axis like this would allow a few inland and coastal bombs to move into the NEUS. I will keep watching the pattern over the next 5-6 weeks And make changes as necessary, before I come to a final long range consensus.

Rebecca Ladd

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