QUICK START TO WINTER...
The JMA (Japanese Meteorological Agency) climate model has come out with its winter outlook. I consider the JMA one of the better long range forecasting tools so I pay attention, especially with the winter season not all that far away. Here's what it shows at 500mb for the month of December.
There's a lot of blocking at northern latitudes and a ridge off the west coast. The broad interpretation of those factors from me is that it would be a favorable pattern for a quick start to winter. Such a set-up implies access to cold air and a close enough proximity to the storm track to perhaps get a couple of December snows. We have not had a December like that for some time. It's important to remember this is by no means a forecast so don't confuse what I am saying as such. This is just one models output and my interpretation of what it's indicating. However, as a man who likes winter (especially in the month of December) this is a heartening trend.
Below you can see the 500mb forecast for the winter period December through February. Overall the look is similar to what is shown for December. The broad brush take away... if the JMA is on the mark, the winter ahead has a chance to get off to a fast start and stay wintry for longer periods than what we've seen in recent years. Other models are yet to come in and of course their interpretation could be significantly different. Stay tuned.
In the short term, there's nothing wintry about our forecast as the alignment of the upper level pattern is favorable for a prolonged period of above normal temperatures. Here's the 500mb jet next week. If you follow the heights you can see the SW flow at all levels of the atmosphere enabling the warmth.
Proof positive are the temperature anomalies that result in a massive area of above normal temperatures in the central U.S. the first half of next week.
Here's the EURO meteogram showing the potential of a 90 degree day next Tuesday or Wednesday. Those get hard to come by in the last 10 days of September.
The GFS is comparable in high temperature output but a day shorter in the warmth's duration.
The national model blend (NBM) is not as warm as either model but agrees with the shorter duration of the GFS.
All in all, there's good agreement we're going to stay nice and warm into at least next Wednesday. Why not?
Confidence is lower when it comes to precipitation, especially this weekend. As warmth increases and moisture deepens, models over the past 24 hours have trended higher with rain chances, especially with the SW flow sending spokes of energy northeast into the Midwest. Instability appears to be sufficient in today's data for scattered showers and thunderstorms both Saturday and Sunday. As you can see, moisture is ample with available water vapor pushing 1.80 inches come Sunday.
That generates the instability (measured in CAPE) necessary for scattered thunderstorms.
With the high moisture levels it is conceivable that some heavy downpours are possible in the stronger areas of convection. Mesoscale details which are impossible to ascertain at this distance will play a large roll in the eventual placement of the heavier rain bands. We'll know more on that later in the week. The most likely period for rain appears to be Saturday night and early Sunday. Meantime, here's what models are suggesting for rainfall Saturday through Sunday.
The NBM (national model blend)
The Weather Prediction Center