Predicting Winter Weather Patterns in Baja
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The winter weather in Baja is more active and since there are more visitors to Baja in the winter, can affect more people. Sweeping in from the north, Baja winter weather is still was nice as summer in other places and why Baja is such a popular tourist destination.
Over the last 9 years I have written hundreds of articles about our summer weather here in Baja. But I have spent just as much time observing and learning the winter weather patterns. In fact, the Baja California peninsula gets more ‘weather’ from the north than we do from the south.
The weather on the peninsula is influenced from the north beginning in late November through early April. Our summer weather influences come in the form of Tropical Cyclones from late July through mid October. In between; October to November and May through July, are neutral periods of the most stable weather Baja has to offer.
Baja entered the winter phase, where our influences come from the north, rather early this year. Coastal areas of Baja California had rain in October and our first norther came to the Sea of Cortez the first week of November. Cold fronts have swept across the entire peninsula and brought rain to the whole peninsula when combining with the moisture from Hurricane Kenneth, well to our southwest.
Early winter weather is the favorite of kiters and windsurfers. The northern hemisphere cools north of Baja faster than the more southern peninsula and Sea of Cortez and Eastern Pacific. Colder air is heavier than warm air, creating a pressure difference between the western United States and Canada verses Baja and the Sea of Cortez. Lows develop south of Baja, increasing the gradient difference. When you look at a surface chart during high winds the gradient isobars are very compressed. So, with just a pressure difference we almost have a constant base level breeze every day from the NNW. In late summer our base barometer reading is around 1012Mb, while high pressure sets in over the western US at around 1018Mb.
The more constant temperature air over the Sea of Cortez is between two land masses which have both altitude and daytime convection. This creates a trough that is also fairly constant running the length of the Sea of Cortez. It shifts to the east and west a bit, but think of it as a canyon in the atmosphere that channels the pressure generated winds down into the Sea.
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Precipitation in the Winter
The northern most reaches of the Baja peninsula, along the coast and right along the border are the first to be affected by winter storms moving southeast. These storms originate in the warm western Pacific, move north past Japan and merge with cold artic air as they pass south of the Bearing Sea. As these Lows slam into British Columbia, Washington and Oregon the pressures can be as low as a Category 2 hurricane and with winds just as ferocious. These storms work south southeast until they run into more tropical air. This meeting point migrates south as the season progresses and by early December these storms can easily sweep southeast across all of Baja.
This season Baja Sur received more rain in November than we had received previously this year. The rain showers were both artic and tropical in origin and the reason why November is a potentially rainy month in Baja Sur. Category 4 Hurricane Kenneth was well southwest of Baja. But spin-off moisture from the storm was working its way across Baja Sur. At the same time a cold front from a winter storms worked all the way to the southern most portions of the peninsula, bringing a little rain with it. When the cold air met the moist tropical air the water literally fell out of the clouds.
The northern deserts are often green in the spring time, following winter rains that sweep SE from our northern influences. Southern deserts are most likely to be found in greenery in late fall, following a tropical cyclone or spin-off. But it is not uncommon for a winter storm to work across the entire peninsula from late January to early February delivering a few inches of rain sometimes.
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North Winds in the Sea
Northers are the bane of mariners and the god-send to wind surfers and kiters. As stated earlier, the pressure difference between the continental US and the Eastern Pacific provides an engine for winds from the north. When the winds really get cranking is when a series of High pressure systems move across the 4 Corners Region of the US.
Cold air weighs more. It falls from clear skies with high radiational cooling like a rock toward the earth. As it falls the Coriolis Effect forces it to spin clockwise, the exact opposite of the formation of a tropical Low or cyclone, therefore it is referred to as an ‘anti-cyclone’.
15th Weather Adage |
The 15th of the month seems to be significant in forecasting Baja Sur WeatherJan 15 – Winter begins |
When these strong Highs, greater than about 1035Mb, pass over the 4 Corners they are lined up perfectly to pump cold Canadian air south into the Sea of Cortez, and at quite a velocity aided by the pressure difference. The barometric pressure will trend upward just in advance of a norther, usually the temperatures will fall precipitously, and often we have cloudy skies in Baja Sur. Conversely, the coastal areas of Baja California can have some of their nicest weather in the early fall when the Santa Ana winds are formed by the same mechanism and pushed warm dry air into the coastal areas from the east.
The cycle of Highs and passing Lows begins in November and continues through March. But the winds are the best for windsurfing through February. As the spring comes the difference between northern pressures and temperatures is moderated against through to our south and the winds become less dramatic. The length of the norther blows peaks in December and January where winds can blow for 5 to 7 days straight as a parade of Highs moves across the US. By early spring the blows are less fierce and only blow a day or two.
For those new to sailing the Sea of Cortez, particularly those who have sailed blue water, sailing in 20-25kt winds would seem to be a particularly expeditious way to cross the Sea of Cortez. From experience, you might want to rethink that assumption.
I grew up sailing on Lake Champlain, between Vermont and New York in the few months that it didn’t have ice floating in it. Winds could blow up very quickly and deliver 6’ waves on a very short period making navigation more difficult that I have experienced on the high seas. The Sea is very much like a lake, with waves of very short period being generated and making for a very rough ride which is hard to make way against. Nine foot waves in the southern Sea on a crossing to the mainland hit you at about a 30° angle and will kick the s@^t out of you for 30 hours or more of your crossing.
The Nice Days
In between the fronts and the Northers exists the weather that our snowbirds come to Baja during the winter to enjoy. Baja Sur can have 80°F days until about New Years and we’re often back into shirt sleeves if Carnaval arrives in late February. In Baja California, particularly in the coastal areas the weather is much like San Diego. January and February can mean a lot of gray skies and drizzle, daytime highs are pleasant, in the mid to upper 60’s and the nights get crisp, nearing freezing. This is what makes the region a good wine producing area. The nice days run in stretches too, going for 10 days or more sometimes. By mid to late March the weather begins to stabilize, the nice days go for longer stretches and it becomes obvious why it is one of the most popular travel times of the year for all of Baja.
Just as a side note for visitors – we ‘locals’ find the Sea winter cold now and wouldn’t go out of our way to get in the water like we do in August. But as cold as the Sea gets, it is always warmer than the warmest the Pacific gets off the coast of Southern California. Come on down and go for a swim, anytime!
Tomas