Weather Models: Looking For The Elusive Pattern Change
Overnight model runs seem to be indicating more of the same. As we pointed out a few days ago the primary problem is that the polar vortex is located well to the west of Canada and is sitting primarily North of Alaska and Eastern Russia. This prevents any kind of truly cold air from coming into Canada and into the Untied States. Thanks to Tropical Tidbits for the use of the the wonderful model website and for the great maps!
What can change all this. Well it is probably going to take a monumental event in the atmosphere somewhere to create a pattern breakdown and a formation of something different from this. The Atlantic Oscillation and the North Atlantic Oscillation indicators are about as positive as you will ever see which continues to favor warm weather and a ridge position in the east. It also means dry weather continues as weather systems moving from west to east crash into that mean ridge in the east and just fall apart.
Looking at the ensemble weather models there are indications that this positive state of NAO and the AO are going to change in the middle of this month. The last 4 ensemble runs have showed this and they showed this again last night.
Both oscillations are forecast to peak next week and the drop back to neutral or slightly negative by the middle of this month. Now I want to caution everyone that this could at least open the door to a stormier period later this month but it doesn’t necessarily mean a colder period. As long as the polar vortex is well west and north as it is now it will keep cold air cut off. The negative trends to the oscillations might however allow weather systems to move across and at least remain intact, giving us the opportunity for a few rain events for the second half of the month. Naturally we will be eyeing models closely for any changes in the flow across the Arctic. Perhaps the negative trend, if it occurs might create a mechanism to being a gradual shift of the polar vortex to the east and south. This is not something that happens overnight. It is a process that can take weeks to occur sometimes. Until that happens the overall warmer dry pattern continues with occasional intrusions of cooler air that bring temperatures down to near normal for a few days followed by more warm ups. At least we are enjoying some of the nicest fall weather you can possibly get in the Autumn