Our tranquil weather pattern will continue to finish out the week. But then across much of the nation the weather starts becoming much more active with a series of fast moving systems sweeping across a good chunk of the country every 2-4 days or so including some Miller As and Bs or hybrids as the Pacific Jet Stream is full of systems both North branch and sometimes the South branch. The first systems are likely to be Pan Handle Hook A or B types along with the “Millers.”
It looks like that more active pattern will continue for the most part the rest of the month along with yo-yo temperatures in our region biased a little below-normal on average.
When looking for future trends in the 6-10 day 10-15 day, 15-30 day and beyond forecasters often look to remote points on the globe for signals or teleconnections in places far far away from the local area. Some of these are “flare guns” that tell us to look for significant jet stream pattern changes that follow some number of days or weeks later in our part of the world. The North Pole, Alaska, North Pacific-Aleutian Islands, Greenland, Asia-Australia to name just a few.
And many of these teleconnections are measured by an index which we follow to get an early “heads up” of large-scale big picture changes to come across the Northern hemisphere.
JETHRO TULL, “Something’s on the move”:
I’ve discussed these dozens of times in my blogs over the years. Many tell us if there will be “blocking” in high latitudes like Russia and Greenland (and Polar or even Arctic regions) which will send the Jet Stream from North to South, or lock-in a weather pattern for weeks at a time. They go by abbreviations like: AO, NAO, PNA, WPO, EPO, MJO etc. These let us know about things BEFORE computer models show them!
Likewise we look way up high in the atmosphere at the STRATOSPHERE at things like the QBO and for signs of a split in the Stratospheric Polar Vortex due to a Sudden Stratospheric Warming SSW.
What is most interesting is that at this juncture the past few winters we have NOT seen anything like this, suggesting that we COULD be in for an atypical La Nina Winter or at least a period of time when the “window” will eventually open to give us a chance of something other than rain. It will happen first of course in the Great Plains and Midwest into the Upper South, New England, Mid-Atlantic and Southern Appalachians.
Even though it could turn out to be a false alarm, or cold air just doesn’t make it as far South as Atlanta. BUT AT LEAST we are seeing signs we forecasters have NOT seen two winters in a row that were mild and uneventful.
Models suggesting a SSW may help form a vortex split in the mid stratosphere:
Blocking high pressure 500 mb building over the Russian Urals/Arctic, strong high pressure in Northern latitudes in winter suggest heavy dense cold air may get blocked South:
At this time most of the signals support a build up of cold air in Canada over the next few weeks with some intrusion into the U.S. mostly down to or above I-40. However, the +EPO and -PNA are not supportive or less supportive of this scenario at least initially.
All this is to say that the pattern change is one that is supportive of some stormier and cooler weather for the Central and Eastern U.S. GRADUALLY EVOLVING the rest of this month into January. Long-range computer guidance temps will probably end up too warm. It’s a tantalizing potential for a White Christmas for the Central U.S. to New England.
NOTE the discrepancies between model forecast mean temperatures:
The main problem of course with these signals is the timing from signal to impact is not precise, i.e. it’s not always a perfect X number of days or weeks for the impact. So we just have to watch to see how it evolves.
It’s too early to determine exact timing and effects on local weather. The long and short of it is that after the present unseasonably warm spell ends, winter weather prospects are going to need baby-sitting for the rest of the year and into 2021 even here in the South.
For daily weather bits follow me on Twitter @MellishMeterWSB.