Today’s video:
PDF report (click link to the right to open in HD): 12-13-19 Long-range analysis
Key Points:
- Data has begun to converge on a solution for Sunday/Monday with increasing likelihood of accumulating snow in the Missouri and Ohio Valley regions.
- A poleward shift of the jet is favored in week 2 which favors more mild Pacific air into the CONUS. However, we expect this signal and the +EPO to weaken later in week 2. The EPS hangs onto that signal so it is likely too warm. We are suspect of warmer overnight data runs.
- However, increasing –AO/-NAO signals are counteracting the Pacific warm signal for the east coast. The Polar Vortex orientation will favor cooler shots of air in the northeast.
- Sub-tropical jet will be main storm driver in week 2 with weaker Northern stream leading to wet risks south/east and drier risks in the Central US.
Weeks 1/2 temperature outlooks:
Week 1:
- Overall, colder than normal conditions persist in the Northern Plains.
- Ahead of the storm systems East Coast will get warm and average slightly above normal.
- Snowpack could help keep some areas cooler following the storm early next week. This looks to be from Kansas to near St. Louis then along and north of I-70.
Week 2:
- The +EPO signal is going to help the Central US be warmer than normal in week 2. This signal often leads to more warmth into the eastern US, however, given the –AO/-NAO signals we think the Eastern third of the US can stay cooler than normal.
- The warmer overnight model runs are a bit suspect given the blocking signal. We also think the EPS is too strong with the jet given –EAMT in week 2 which is why it is much warmer.
- Model performance has been extremely poor as of late, so we are not going to make any major adjustments to our forecast.
Weeks 1/2 precipitation outlooks:
Week 1:
- Increasing likelihood of accumulating snow in the Ohio Valley on Sunday/Monday.
- However, the 5-10 day period is looking like a drier period with a brief time of a lack of storm dates/sub-tropical jet influence.
- Northern stream is overall weaker than it has been so wintry chances in the Northern Plains will be light.
- Major systems stay in the Eastern third of the US.
Week 2:
- A strong Pacific jet will flood moisture on the West Coast, however, the stronger jet in week 2 looks to be the sub-tropical jet for the CONUS.
- This will lead to wetter risks in the TN Valley to East Coast.
- With a –AO state possible at times, snow chances are not off the table.
- Given a lack of storm dates to start this period – we can’t rule out some drier days for much of the CONUS, but activity should pick up towards Christmas.
Weeks 3/4 updated outlooks:
Discussion:
- It’s no secret the forecast models are likely causing some significant stress for all of us. We cannot keep chasing these run to run changes as models beyond day 10 right now have a skill of around 10%. I’m not going to make any major changes to the forecast generally and just mention my thoughts going forward. At the end of the day we must put something on paper and just run with it. The evolution and orientation of the polar vortex is responsible for the blocking that’s currently developing (-AO/-NAO) and regardless of what models say this will keep the eastern 3rd below normal. The wild card is the EPO but with what we see in research for this to flip negative its not a matter of if but when. When the EPO finally flips negative and can have some staying power there will be drastic model adjustments and the conus will likely be flooded with true arctic air. As of this morning I’m not interested in what the models say as this forecast is just more so on what we know and what we’ve been researching for the last several weeks. Right or wrong this is our call and see no reason to back off or wave white flag.
Updated pattern drivers into late December:
Updated winter patter drivers:
