12/18/25 Thursday 3 am
Here at DWG HQ I am still finishing up MJO Part 2, but I’ve been getting a ton of questions about Christmas week, and I know that takes priority over the educational stuff right now. So, I’m hitting ‘pause’ on the MJO series for a moment to talk about the holiday. First off, I want to explain what the heck is going on with the models, because they are acting a bit strange lately and I have not done a great job helping you understand why.
Why the Christmas Forecast is Hitting a Wall
Forecasting for the holidays is proving to be a challenge because our weather models are currently hitting a major wall. The main culprit is the European model (ECMWF). While it is usually the ‘gold standard’ for active, stormy patterns, it has a well-known weakness: it tends to get stuck in a ‘dry loop’ when forecasting for the Western U.S. Once the model convinces itself that the ground is dry, it struggles to see a way out, often ignoring potential storms that could break the pattern.
The “Dry Loop” Problem🔄🌵
Imagine the weather model is like a person who is already thirsty. Because they are thirsty, they don’t sweat. Because they don’t sweat, they get even hotter. This is exactly what happens with the weather model in the West.
-
Dry Ground = Warmer Air: When the model starts with very dry soil, there is no moisture to evaporate. Normally, evaporation helps cool the ground. Without it, the sun’s energy goes straight into heating the air as I have said dozens of times, dry like to stay dry.
-
The “Rain-Eater” Layer: This extra heat creates a thick layer of very dry, warmer air near the surface. If a small storm tries to move in, this dry layer acts like a sponge and “eats” the rain before it can even hit the ground.
-
The Feedback Loop: Because it doesn’t rain, the soil stays dry. The model sees this dry soil and forecasts more heat for the next day, which creates more dry air, and the cycle repeats.
Why the European Model Struggles
The ECMWF is incredibly smart, but it has a few specific “personality traits” that cause this:
-
RRR (Ridiculously Resilient Ridges): It tends to build “high-pressure ridges” (areas of clear, dry weather) that are very strong and stable. Once it builds one, it’s hard for the model to “knock it down” in the forecast.
-
Soil Memory: The model relies heavily on its initial data. If it thinks the soil is dry at the start, it struggles to imagine a scenario where it gets wet again, essentially getting “stuck” in its own dry math. Also known as bad data in, bad data out. I have mentioned this many times in the past when I refer to”poor initialization”.
-
Small Details Get Lost: Sometimes small local storms or mountain effects could break the dry spell, but the model occasionally “smooths” these out in favor of the larger, dry pattern.
What Breaks the Loop? 🔄🔨
So, what does it take to finally smash this feedback loop? The Euro model won’t just “budge” on its own; it needs a major atmospheric shove. Usually, that comes in one of three ways:
-
The “Drought Buster” (Atmospheric Rivers): These are long, narrow plumes of deep tropical moisture. They act like a fire hose, dumping so much water (and heavy snow at high elevations) that the ground has no choice but to get saturated, instantly killing that “thirsty ground” feedback loop.
-
The Ridgeline Runner: Instead of storms staying off the coast, these systems dive down the “inside” of the Rockies. For those of you waiting on a powder day, these can be a bit of a tease—they often bring more wind and bitter cold than actual accumulation, but if they are deep enough, they can drag in just enough moisture to reset the model’s math.
-
The Cut-Off Low: This is when a storm gets separated from the main jet stream and just “parks” itself over the Southwest. These are the wildcards that the Euro often misses until the last minute. They are famous for dumping massive amounts of snow right when the models say it should be dry—the kind of surprise that turns a “dust on crust” day into an epic, unplanned powder morning.
The DWG Bottom Line
Speaking of those Atmospheric Rivers, take a look at the graphic below for Christmas morning. It shows that massive ‘fire hose’ of moisture I mentioned earlier—the deep green and blue plume aimed directly at the West Coast.
Christmas Eve 11 pm
Now, we have to be realistic: sometimes by the time these storms reach us in Southwest Colorado, we’re just catching the ‘leftovers’ and they aren’t quite as impressive as they looked out over the Pacific. But after weeks of this dry loop, seeing a major ‘circuit breaker’ like this on the map is a huge step in the right direction. I’ll be monitoring the track to see if it stays aimed at us or if it’s just a holiday tease. Stay tuned.
Venmo: @Jeff-Givens-11
OR
Cash App users: $JGDWG
Prefer ZELLE or send a check? Click below, and I will give you instructions.
The Two Key States
Global Impact and Significance