SUMMARY:  The 12z FRIDAY  operational GFS still shows a  significant  event developing for the   eastern portions of the Upper Plains and Midwest  11/23-11/24.    The  GFS  has done a flip  flop... again... and  now shows a  colder  pattern   for the central and eastern US in the 1st  week of  DEC.   

There is not much to change in the short range or medium-range forecast based upon the midday models. It still looks like a significant Low is going to form over the eastern portions of the Upper Plains and the Midwest on the 23rd and 24th. In this system should bring additional significant rains ( 70% coverage of 0.25 to 1.25) to the eastern Dakotas and the northern WCB into the western Great Lakes.... with lesser rains over the lower WCB and ECB (50% coverage of 0.10 to 0.65) .

However the model is looking colder as we go into the 6-10 day and 11-15 . The Model takes a new piece of energy that drops out of Central Canada and tries to develop a northeast coastal storm November 26 -- 27. This system was up in the southeastern Canada helps alter the entire pattern so now the model is showing a significantly colder patter developing across central and eastern US by day 9 and 10. The model shows a large sprawling area of a fairly cold HIGH coming out of Western Canada and dominating much of the central and eastern US as we move into early December.

This is another model flip-flop.

One of the features which is driving the pattern is the MJO. Without getting too technical MJO weather phenomena which exists along the equatorial Pacific moving from Indonesia along the equator towards Peru.    As it moves from west to east ... it causes certain things to happen in the atmosphere. Meteorologists have divided the movement of the MJO into certain phases.... 8 of them to be exact.  Studies show that when the MJO    is strong   --like it is now ---and it moves into  phase 3 and 4 correlates to specific patterns developing over North America especially during the cold season months.

Over the last two months the MJO has been stuck in phase 2 3 and 4 which correlates to a fairly mild pattern for a good portion of the central and eastern US. Some of the MJO forecast models are showing that this repeating pattern is going to end next week. They move the MJO into phases 5 6 and 7. If this is correct... and not all the forecast models agree upon this... that would support a shift in the pattern in early December that could set up several cold days across the Plains and Midwest and the Northeast during the first week of December .

This may be what the midday GFS is catching on to a wide model has turned colder. However I need to point out that this is not at all certain and given the fact we have a moderate El Niño... the MJO could die and fall apart . This has been the trends as I said for October and November so it is something to keep in mind. If the MJO does fall apart then the cold pattern in early December were also fall apart.