October has been a kind month, especially when it comes to temperatures. Here in Cedar Rapids we are running 7 degrees above normal per day. 12 of the first 20 days have seen a high of 70 or above. So far the sting of the coming winter is yet to be felt. Here's the monthly departures showing the widespread warmth.
The MJO (Madden Julien Oscillation) is now going through phase 6 which is known to produce mild Midwest temperatures in October.
Phase 6 should see to it that temperatures remain above normal through Monday. After that the MJO suggests a pass through 7, 8, and 1 which is likely to result in significant cooling. Follow the dotted green lines which represent the daily progression. Now note the temperature correlation associated with each phase.
The operational models have really jumped on this trend today and we should get our first good taste of cold air late next weekend. This Tuesday will also be chilly but that's just a sampling of the deeper cold to come. Just look at this trough the GFS displays next Friday at 500mb!
The associated temperature departure looks like this. In F. readings would be 20-25 degrees below normal.
These are the highs the GFS shows Friday the 27th.
This trend was well supported by the EURO earlier Friday but now the night run has pulled the trough further west. This slows the arrival of the cold air and keeps the bulk of the snow further west. Here's the EURO temperature departure Saturday the 28th. That's a big change from the GFS but one that probably wins out in the end.
The EURO also has this for snowfall next weekend.
The 0z GFS does not see evolution in a similar way as it spins a different wave up over the upper Midwest much further east. Look at what it shows for 10 day snowfall. Most of this next weekend.
While I have high confidence on the cold at some point next weekend (typhoon rule applied) snow is far from a certainty. I would not bet on that. However, the cold is sufficient to produce snowflakes if and where it comes. It's just too far away to pinpoint a wave, its amplitude or track. Just based on October climatology I prefer the EURO's handling of the pattern. I will say, based on the amount of cold air that digs into the Midwest late next weekend, it could be sufficient for flurries or snow showers even without a wave (just based on pure instability). If the trends continue in coming runs, flakes may fly in parts of the Midwest within a week and you know I'll greet them with open arms, even if they are off to the west or north. Stay tuned and roll weather...TS